internal/pkg: optional dependency graph size limit

This provides a quick check against cyclic dependencies without hurting cure performance.

Signed-off-by: Ophestra <cat@gensokyo.uk>

.gitea/workflows/test.yml

@@ -72,6 +72,23 @@ jobs:
           path: result/*
           retention-days: 1
 
+  sharefs:
+    name: ShareFS
+    runs-on: nix
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Run NixOS test
+        run: nix build --out-link "result" --print-out-paths --print-build-logs .#checks.x86_64-linux.sharefs
+
+      - name: Upload test output
+        uses: actions/upload-artifact@v3
+        with:
+          name: "sharefs-vm-output"
+          path: result/*
+          retention-days: 1
+
   hpkg:
     name: Hpkg
     runs-on: nix
@@ -96,6 +113,7 @@ jobs:
       - race
       - sandbox
       - sandbox-race
+      - sharefs
       - hpkg
     runs-on: nix
     steps:

.gitignore

@@ -27,6 +27,7 @@ go.work.sum
 
 # go generate
 /cmd/hakurei/LICENSE
+/internal/pkg/testdata/testtool
 
 # release
 /dist/hakurei-*

cmd/sharefs/fuse-operations.c

@@ -0,0 +1,282 @@
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE /* O_DIRECT */
+#endif
+
+#include <dirent.h>
+#include <errno.h>
+#include <unistd.h>
+
+/* TODO(ophestra): remove after 05ce67fea99ca09cd4b6625cff7aec9cc222dd5a reaches a release */
+#include <sys/syscall.h>
+
+#include "fuse-operations.h"
+
+/* MUST_TRANSLATE_PATHNAME translates a userspace pathname to a relative pathname;
+ * the resulting address points to a constant string or part of pathname, it is never heap allocated. */
+#define MUST_TRANSLATE_PATHNAME(pathname) \
+    do {                                  \
+        if (pathname == NULL)             \
+            return -EINVAL;               \
+        while (*pathname == '/')          \
+            pathname++;                   \
+        if (*pathname == '\0')            \
+            pathname = ".";               \
+    } while (0)
+
+/* GET_CONTEXT_PRIV obtains fuse context and private data for the calling thread. */
+#define GET_CONTEXT_PRIV(ctx, priv) \
+    do {                            \
+        ctx = fuse_get_context();   \
+        priv = ctx->private_data;   \
+    } while (0)
+
+/* impl_getattr modifies a struct stat from the kernel to present to userspace;
+ * impl_getattr returns a negative errno style error code. */
+static int impl_getattr(struct fuse_context *ctx, struct stat *statbuf) {
+    /* allowlist of permitted types */
+    if (!S_ISDIR(statbuf->st_mode) && !S_ISREG(statbuf->st_mode) && !S_ISLNK(statbuf->st_mode)) {
+        return -ENOTRECOVERABLE; /* returning an errno causes all operations on the file to return EIO */
+    }
+
+#define OVERRIDE_PERM(v) (statbuf->st_mode & ~0777) | (v & 0777)
+    if (S_ISDIR(statbuf->st_mode))
+        statbuf->st_mode = OVERRIDE_PERM(SHAREFS_PERM_DIR);
+    else if (S_ISREG(statbuf->st_mode))
+        statbuf->st_mode = OVERRIDE_PERM(SHAREFS_PERM_REG);
+    else
+        statbuf->st_mode = 0; /* should always be symlink in this case */
+
+    statbuf->st_uid = ctx->uid;
+    statbuf->st_gid = SHAREFS_MEDIA_RW_ID;
+    statbuf->st_ctim = statbuf->st_mtim;
+    statbuf->st_nlink = 1;
+    return 0;
+}
+
+/* fuse_operations implementation */
+
+int sharefs_getattr(const char *pathname, struct stat *statbuf, struct fuse_file_info *fi) {
+    struct fuse_context *ctx;
+    struct sharefs_private *priv;
+    GET_CONTEXT_PRIV(ctx, priv);
+    MUST_TRANSLATE_PATHNAME(pathname);
+
+    (void)fi;
+
+    if (fstatat(priv->dirfd, pathname, statbuf, AT_SYMLINK_NOFOLLOW) == -1)
+        return -errno;
+    return impl_getattr(ctx, statbuf);
+}
+
+int sharefs_readdir(const char *pathname, void *buf, fuse_fill_dir_t filler, off_t offset, struct fuse_file_info *fi, enum fuse_readdir_flags flags) {
+    int fd;
+    DIR *dp;
+    struct stat st;
+    int ret = 0;
+    struct dirent *de;
+
+    struct fuse_context *ctx;
+    struct sharefs_private *priv;
+    GET_CONTEXT_PRIV(ctx, priv);
+    MUST_TRANSLATE_PATHNAME(pathname);
+
+    (void)offset;
+    (void)fi;
+
+    if ((fd = openat(priv->dirfd, pathname, O_RDONLY | O_DIRECTORY | O_CLOEXEC)) == -1)
+        return -errno;
+    if ((dp = fdopendir(fd)) == NULL) {
+        close(fd);
+        return -errno;
+    }
+
+    errno = 0; /* for the next readdir call */
+    while ((de = readdir(dp)) != NULL) {
+        if (flags & FUSE_READDIR_PLUS) {
+            if (fstatat(dirfd(dp), de->d_name, &st, AT_SYMLINK_NOFOLLOW) == -1) {
+                ret = -errno;
+                break;
+            }
+
+            if ((ret = impl_getattr(ctx, &st)) < 0)
+                break;
+
+            errno = 0;
+            ret = filler(buf, de->d_name, &st, 0, FUSE_FILL_DIR_PLUS);
+        } else
+            ret = filler(buf, de->d_name, NULL, 0, 0);
+
+        if (ret != 0) {
+            ret = errno != 0 ? -errno : -EIO; /* filler */
+            break;
+        }
+
+        errno = 0; /* for the next readdir call */
+    }
+    if (ret == 0 && errno != 0)
+        ret = -errno; /* readdir */
+
+    closedir(dp);
+    return ret;
+}
+
+int sharefs_mkdir(const char *pathname, mode_t mode) {
+    struct fuse_context *ctx;
+    struct sharefs_private *priv;
+    GET_CONTEXT_PRIV(ctx, priv);
+    MUST_TRANSLATE_PATHNAME(pathname);
+
+    (void)mode;
+
+    if (mkdirat(priv->dirfd, pathname, SHAREFS_PERM_DIR) == -1)
+        return -errno;
+    return 0;
+}
+
+int sharefs_unlink(const char *pathname) {
+    struct fuse_context *ctx;
+    struct sharefs_private *priv;
+    GET_CONTEXT_PRIV(ctx, priv);
+    MUST_TRANSLATE_PATHNAME(pathname);
+
+    if (unlinkat(priv->dirfd, pathname, 0) == -1)
+        return -errno;
+    return 0;
+}
+
+int sharefs_rmdir(const char *pathname) {
+    struct fuse_context *ctx;
+    struct sharefs_private *priv;
+    GET_CONTEXT_PRIV(ctx, priv);
+    MUST_TRANSLATE_PATHNAME(pathname);
+
+    if (unlinkat(priv->dirfd, pathname, AT_REMOVEDIR) == -1)
+        return -errno;
+    return 0;
+}
+
+int sharefs_rename(const char *oldpath, const char *newpath, unsigned int flags) {
+    struct fuse_context *ctx;
+    struct sharefs_private *priv;
+    GET_CONTEXT_PRIV(ctx, priv);
+    MUST_TRANSLATE_PATHNAME(oldpath);
+    MUST_TRANSLATE_PATHNAME(newpath);
+
+    /* TODO(ophestra): replace with wrapper after 05ce67fea99ca09cd4b6625cff7aec9cc222dd5a reaches a release */
+    if (syscall(__NR_renameat2, priv->dirfd, oldpath, priv->dirfd, newpath, flags) == -1)
+        return -errno;
+    return 0;
+}
+
+int sharefs_truncate(const char *pathname, off_t length, struct fuse_file_info *fi) {
+    int fd;
+    int ret;
+
+    struct fuse_context *ctx;
+    struct sharefs_private *priv;
+    GET_CONTEXT_PRIV(ctx, priv);
+    MUST_TRANSLATE_PATHNAME(pathname);
+
+    (void)fi;
+
+    if ((fd = openat(priv->dirfd, pathname, O_WRONLY | O_CLOEXEC)) == -1)
+        return -errno;
+    if ((ret = ftruncate(fd, length)) == -1)
+        ret = -errno;
+    close(fd);
+    return ret;
+}
+
+int sharefs_utimens(const char *pathname, const struct timespec times[2], struct fuse_file_info *fi) {
+    struct fuse_context *ctx;
+    struct sharefs_private *priv;
+    GET_CONTEXT_PRIV(ctx, priv);
+    MUST_TRANSLATE_PATHNAME(pathname);
+
+    (void)fi;
+
+    if (utimensat(priv->dirfd, pathname, times, AT_SYMLINK_NOFOLLOW) == -1)
+        return -errno;
+    return 0;
+}
+
+int sharefs_create(const char *pathname, mode_t mode, struct fuse_file_info *fi) {
+    int fd;
+
+    struct fuse_context *ctx;
+    struct sharefs_private *priv;
+    GET_CONTEXT_PRIV(ctx, priv);
+    MUST_TRANSLATE_PATHNAME(pathname);
+
+    (void)mode;
+
+    if ((fd = openat(priv->dirfd, pathname, fi->flags & ~SHAREFS_FORBIDDEN_FLAGS, SHAREFS_PERM_REG)) == -1)
+        return -errno;
+    fi->fh = fd;
+    return 0;
+}
+
+int sharefs_open(const char *pathname, struct fuse_file_info *fi) {
+    int fd;
+
+    struct fuse_context *ctx;
+    struct sharefs_private *priv;
+    GET_CONTEXT_PRIV(ctx, priv);
+    MUST_TRANSLATE_PATHNAME(pathname);
+
+    if ((fd = openat(priv->dirfd, pathname, fi->flags & ~SHAREFS_FORBIDDEN_FLAGS)) == -1)
+        return -errno;
+    fi->fh = fd;
+    return 0;
+}
+
+int sharefs_read(const char *pathname, char *buf, size_t count, off_t offset, struct fuse_file_info *fi) {
+    int ret;
+
+    (void)pathname;
+
+    if ((ret = pread(fi->fh, buf, count, offset)) == -1)
+        return -errno;
+    return ret;
+}
+
+int sharefs_write(const char *pathname, const char *buf, size_t count, off_t offset, struct fuse_file_info *fi) {
+    int ret;
+
+    (void)pathname;
+
+    if ((ret = pwrite(fi->fh, buf, count, offset)) == -1)
+        return -errno;
+    return ret;
+}
+
+int sharefs_statfs(const char *pathname, struct statvfs *statbuf) {
+    int fd;
+    int ret;
+
+    struct fuse_context *ctx;
+    struct sharefs_private *priv;
+    GET_CONTEXT_PRIV(ctx, priv);
+    MUST_TRANSLATE_PATHNAME(pathname);
+
+    if ((fd = openat(priv->dirfd, pathname, O_RDONLY | O_CLOEXEC)) == -1)
+        return -errno;
+    if ((ret = fstatvfs(fd, statbuf)) == -1)
+        ret = -errno;
+    close(fd);
+    return ret;
+}
+
+int sharefs_release(const char *pathname, struct fuse_file_info *fi) {
+    (void)pathname;
+
+    return close(fi->fh);
+}
+
+int sharefs_fsync(const char *pathname, int datasync, struct fuse_file_info *fi) {
+    (void)pathname;
+
+    if (datasync ? fdatasync(fi->fh) : fsync(fi->fh) == -1)
+        return -errno;
+    return 0;
+}

cmd/sharefs/fuse-operations.h

@@ -0,0 +1,34 @@
+#define FUSE_USE_VERSION FUSE_MAKE_VERSION(3, 12)
+#include <fuse.h>
+#include <fuse_lowlevel.h> /* for fuse_cmdline_help */
+
+#if (FUSE_VERSION < FUSE_MAKE_VERSION(3, 12))
+#error This package requires libfuse >= v3.12
+#endif
+
+#define SHAREFS_MEDIA_RW_ID (1 << 10) - 1 /* owning gid presented to userspace */
+#define SHAREFS_PERM_DIR 0700             /* permission bits for directories presented to userspace */
+#define SHAREFS_PERM_REG 0600             /* permission bits for regular files presented to userspace */
+#define SHAREFS_FORBIDDEN_FLAGS O_DIRECT  /* these open flags are cleared unconditionally */
+
+/* sharefs_private is populated by sharefs_init and contains process-wide context */
+struct sharefs_private {
+    int dirfd;       /* source dirfd opened during sharefs_init */
+    uintptr_t setup; /* cgo handle of opaque setup state */
+};
+
+int sharefs_getattr(const char *pathname, struct stat *statbuf, struct fuse_file_info *fi);
+int sharefs_readdir(const char *pathname, void *buf, fuse_fill_dir_t filler, off_t offset, struct fuse_file_info *fi, enum fuse_readdir_flags flags);
+int sharefs_mkdir(const char *pathname, mode_t mode);
+int sharefs_unlink(const char *pathname);
+int sharefs_rmdir(const char *pathname);
+int sharefs_rename(const char *oldpath, const char *newpath, unsigned int flags);
+int sharefs_truncate(const char *pathname, off_t length, struct fuse_file_info *fi);
+int sharefs_utimens(const char *pathname, const struct timespec times[2], struct fuse_file_info *fi);
+int sharefs_create(const char *pathname, mode_t mode, struct fuse_file_info *fi);
+int sharefs_open(const char *pathname, struct fuse_file_info *fi);
+int sharefs_read(const char *pathname, char *buf, size_t count, off_t offset, struct fuse_file_info *fi);
+int sharefs_write(const char *pathname, const char *buf, size_t count, off_t offset, struct fuse_file_info *fi);
+int sharefs_statfs(const char *pathname, struct statvfs *statbuf);
+int sharefs_release(const char *pathname, struct fuse_file_info *fi);
+int sharefs_fsync(const char *pathname, int datasync, struct fuse_file_info *fi);

cmd/sharefs/fuse.go

@@ -0,0 +1,556 @@
+package main
+
+/*
+#cgo pkg-config: --static fuse3
+
+#include "fuse-operations.h"
+#include <stdlib.h>
+#include <string.h>
+
+extern void *sharefs_init(struct fuse_conn_info *conn, struct fuse_config *cfg);
+extern void sharefs_destroy(void *private_data);
+
+typedef void (*closure)();
+static inline struct fuse_opt _FUSE_OPT_END() { return (struct fuse_opt)FUSE_OPT_END; };
+*/
+import "C"
+import (
+	"context"
+	"encoding/gob"
+	"errors"
+	"fmt"
+	"io"
+	"log"
+	"os"
+	"os/exec"
+	"os/signal"
+	"path"
+	"runtime"
+	"runtime/cgo"
+	"strconv"
+	"syscall"
+	"unsafe"
+
+	"hakurei.app/container"
+	"hakurei.app/container/check"
+	"hakurei.app/container/std"
+	"hakurei.app/hst"
+	"hakurei.app/internal/helper/proc"
+	"hakurei.app/internal/info"
+	"hakurei.app/message"
+)
+
+type (
+	// closure represents a C function pointer.
+	closure = C.closure
+
+	// fuseArgs represents the fuse_args structure.
+	fuseArgs = C.struct_fuse_args
+
+	// setupState holds state used for setup. Its cgo handle is included in
+	// sharefs_private and considered opaque to non-setup callbacks.
+	setupState struct {
+		// Whether sharefs_init failed.
+		initFailed bool
+
+		// Whether to create source directory as root.
+		mkdir bool
+
+		// Open file descriptor to fuse.
+		Fuse int
+
+		// Pathname to open for dirfd.
+		Source *check.Absolute
+		// New uid and gid to set by sharefs_init when starting as root.
+		Setuid, Setgid int
+	}
+)
+
+func init() { gob.Register(new(setupState)) }
+
+// destroySetup invalidates the setup [cgo.Handle] in a sharefs_private structure.
+func destroySetup(private_data unsafe.Pointer) (ok bool) {
+	if private_data == nil {
+		return false
+	}
+	priv := (*C.struct_sharefs_private)(private_data)
+
+	if h := cgo.Handle(priv.setup); h != 0 {
+		priv.setup = 0
+		h.Delete()
+		ok = true
+	}
+	return
+}
+
+//export sharefs_init
+func sharefs_init(_ *C.struct_fuse_conn_info, cfg *C.struct_fuse_config) unsafe.Pointer {
+	ctx := C.fuse_get_context()
+	priv := (*C.struct_sharefs_private)(ctx.private_data)
+	setup := cgo.Handle(priv.setup).Value().(*setupState)
+
+	if os.Geteuid() == 0 {
+		log.Println("filesystem daemon must not run as root")
+		goto fail
+	}
+
+	cfg.use_ino = C.true
+	cfg.direct_io = C.false
+	// getattr is context-dependent
+	cfg.attr_timeout = 0
+	cfg.entry_timeout = 0
+	cfg.negative_timeout = 0
+
+	// all future filesystem operations happen through this dirfd
+	if fd, err := syscall.Open(setup.Source.String(), syscall.O_DIRECTORY|syscall.O_RDONLY|syscall.O_CLOEXEC, 0); err != nil {
+		log.Printf("cannot open %q: %v", setup.Source, err)
+		goto fail
+	} else if err = syscall.Fchdir(fd); err != nil {
+		_ = syscall.Close(fd)
+		log.Printf("cannot enter %q: %s", setup.Source, err)
+		goto fail
+	} else {
+		priv.dirfd = C.int(fd)
+	}
+
+	return ctx.private_data
+
+fail:
+	setup.initFailed = true
+	C.fuse_exit(ctx.fuse)
+	return nil
+}
+
+//export sharefs_destroy
+func sharefs_destroy(private_data unsafe.Pointer) {
+	if private_data != nil {
+		destroySetup(private_data)
+		priv := (*C.struct_sharefs_private)(private_data)
+
+		if err := syscall.Close(int(priv.dirfd)); err != nil {
+			log.Printf("cannot close source directory: %v", err)
+		}
+	}
+}
+
+// showHelp prints the help message.
+func showHelp(args *fuseArgs) {
+	executableName := sharefsName
+	if args.argc > 0 {
+		executableName = path.Base(C.GoString(*args.argv))
+	} else if name, err := os.Executable(); err == nil {
+		executableName = path.Base(name)
+	}
+
+	fmt.Printf("usage: %s [options] <mountpoint>\n\n", executableName)
+
+	fmt.Println("Filesystem options:")
+	fmt.Println("    -o source=/data/media  source directory to be mounted")
+	fmt.Println("    -o setuid=1023         uid to run as when starting as root")
+	fmt.Println("    -o setgid=1023         gid to run as when starting as root")
+
+	fmt.Println("\nFUSE options:")
+	C.fuse_cmdline_help()
+	C.fuse_lib_help(args)
+}
+
+// parseOpts parses fuse options via fuse_opt_parse.
+func parseOpts(args *fuseArgs, setup *setupState, log *log.Logger) (ok bool) {
+	var unsafeOpts struct {
+		// Pathname to writable source directory.
+		source *C.char
+
+		// Whether to create source directory as root.
+		mkdir C.int
+
+		// Decimal string representation of uid to set when running as root.
+		setuid *C.char
+		// Decimal string representation of gid to set when running as root.
+		setgid *C.char
+
+		// Decimal string representation of open file descriptor to read setupState from.
+		// This is an internal detail for containerisation and must not be specified directly.
+		setup *C.char
+	}
+
+	if C.fuse_opt_parse(args, unsafe.Pointer(&unsafeOpts), &[]C.struct_fuse_opt{
+		{templ: C.CString("source=%s"), offset: C.ulong(unsafe.Offsetof(unsafeOpts.source)), value: 0},
+		{templ: C.CString("mkdir"), offset: C.ulong(unsafe.Offsetof(unsafeOpts.mkdir)), value: 1},
+		{templ: C.CString("setuid=%s"), offset: C.ulong(unsafe.Offsetof(unsafeOpts.setuid)), value: 0},
+		{templ: C.CString("setgid=%s"), offset: C.ulong(unsafe.Offsetof(unsafeOpts.setgid)), value: 0},
+
+		{templ: C.CString("setup=%s"), offset: C.ulong(unsafe.Offsetof(unsafeOpts.setup)), value: 0},
+
+		C._FUSE_OPT_END(),
+	}[0], nil) == -1 {
+		return false
+	}
+
+	if unsafeOpts.source != nil {
+		defer C.free(unsafe.Pointer(unsafeOpts.source))
+	}
+	if unsafeOpts.setuid != nil {
+		defer C.free(unsafe.Pointer(unsafeOpts.setuid))
+	}
+	if unsafeOpts.setgid != nil {
+		defer C.free(unsafe.Pointer(unsafeOpts.setgid))
+	}
+
+	if unsafeOpts.setup != nil {
+		defer C.free(unsafe.Pointer(unsafeOpts.setup))
+
+		if v, err := strconv.Atoi(C.GoString(unsafeOpts.setup)); err != nil || v < 3 {
+			log.Println("invalid value for option setup")
+			return false
+		} else {
+			r := os.NewFile(uintptr(v), "setup")
+			defer func() {
+				if err = r.Close(); err != nil {
+					log.Println(err)
+				}
+			}()
+			if err = gob.NewDecoder(r).Decode(setup); err != nil {
+				log.Println(err)
+				return false
+			}
+		}
+		if setup.Fuse < 3 {
+			log.Println("invalid file descriptor", setup.Fuse)
+			return false
+		}
+		return true
+	}
+
+	if unsafeOpts.source == nil {
+		showHelp(args)
+		return false
+	} else if a, err := check.NewAbs(C.GoString(unsafeOpts.source)); err != nil {
+		log.Println(err)
+		return false
+	} else {
+		setup.Source = a
+	}
+	setup.mkdir = unsafeOpts.mkdir != 0
+
+	if unsafeOpts.setuid == nil {
+		setup.Setuid = -1
+	} else if v, err := strconv.Atoi(C.GoString(unsafeOpts.setuid)); err != nil || v <= 0 {
+		log.Println("invalid value for option setuid")
+		return false
+	} else {
+		setup.Setuid = v
+	}
+	if unsafeOpts.setgid == nil {
+		setup.Setgid = -1
+	} else if v, err := strconv.Atoi(C.GoString(unsafeOpts.setgid)); err != nil || v <= 0 {
+		log.Println("invalid value for option setgid")
+		return false
+	} else {
+		setup.Setgid = v
+	}
+
+	return true
+}
+
+// copyArgs returns a heap allocated copy of an argument slice in fuse_args representation.
+func copyArgs(s ...string) fuseArgs {
+	if len(s) == 0 {
+		return fuseArgs{argc: 0, argv: nil, allocated: 0}
+	}
+	args := unsafe.Slice((**C.char)(C.malloc(C.size_t(uintptr(len(s))*unsafe.Sizeof(s[0])))), len(s))
+	for i, arg := range s {
+		args[i] = C.CString(arg)
+	}
+	return fuseArgs{argc: C.int(len(s)), argv: &args[0], allocated: 1}
+}
+
+// freeArgs frees the contents of argument list.
+func freeArgs(args *fuseArgs) { C.fuse_opt_free_args(args) }
+
+// unsafeAddArgument adds an argument to fuseArgs via fuse_opt_add_arg.
+// The last byte of arg must be 0.
+func unsafeAddArgument(args *fuseArgs, arg string) {
+	C.fuse_opt_add_arg(args, (*C.char)(unsafe.Pointer(unsafe.StringData(arg))))
+}
+
+func _main(s ...string) (exitCode int) {
+	msg := message.New(log.Default())
+	container.TryArgv0(msg)
+	runtime.LockOSThread()
+
+	// don't mask creation mode, kernel already did that
+	syscall.Umask(0)
+
+	var pinner runtime.Pinner
+	defer pinner.Unpin()
+
+	args := copyArgs(s...)
+	defer freeArgs(&args)
+
+	// this causes the kernel to enforce access control based on
+	// struct stat populated by sharefs_getattr
+	unsafeAddArgument(&args, "-odefault_permissions\x00")
+
+	var priv C.struct_sharefs_private
+	pinner.Pin(&priv)
+	var setup setupState
+	priv.setup = C.uintptr_t(cgo.NewHandle(&setup))
+	defer destroySetup(unsafe.Pointer(&priv))
+
+	var opts C.struct_fuse_cmdline_opts
+	if C.fuse_parse_cmdline(&args, &opts) != 0 {
+		return 1
+	}
+	if opts.mountpoint != nil {
+		defer C.free(unsafe.Pointer(opts.mountpoint))
+	}
+
+	if opts.show_version != 0 {
+		fmt.Println("hakurei version", info.Version())
+		fmt.Println("FUSE library version", C.GoString(C.fuse_pkgversion()))
+		C.fuse_lowlevel_version()
+		return 0
+	}
+
+	if opts.show_help != 0 {
+		showHelp(&args)
+		return 0
+	} else if opts.mountpoint == nil {
+		log.Println("no mountpoint specified")
+		return 2
+	} else {
+		// hack to keep fuse_parse_cmdline happy in the container
+		mountpoint := C.GoString(opts.mountpoint)
+		pathnameArg := -1
+		for i, arg := range s {
+			if arg == mountpoint {
+				pathnameArg = i
+				break
+			}
+		}
+		if pathnameArg < 0 {
+			log.Println("mountpoint must be absolute")
+			return 2
+		}
+		s[pathnameArg] = container.Nonexistent
+	}
+
+	if !parseOpts(&args, &setup, msg.GetLogger()) {
+		return 1
+	}
+	asRoot := os.Geteuid() == 0
+
+	if asRoot {
+		if setup.Setuid <= 0 || setup.Setgid <= 0 {
+			log.Println("setuid and setgid must not be 0")
+			return 1
+		}
+
+		if setup.Fuse >= 3 {
+			log.Println("filesystem daemon must not run as root")
+			return 1
+		}
+
+		if setup.mkdir {
+			if err := os.MkdirAll(setup.Source.String(), 0700); err != nil {
+				if !errors.Is(err, os.ErrExist) {
+					log.Println(err)
+					return 1
+				}
+				// skip setup for existing source directory
+			} else if err = os.Chown(setup.Source.String(), setup.Setuid, setup.Setgid); err != nil {
+				log.Println(err)
+				return 1
+			}
+		}
+	} else if setup.Fuse < 3 && (setup.Setuid > 0 || setup.Setgid > 0) {
+		log.Println("setuid and setgid has no effect when not starting as root")
+		return 1
+	} else if setup.mkdir {
+		log.Println("mkdir has no effect when not starting as root")
+		return 1
+	}
+
+	op := C.struct_fuse_operations{
+		init:    closure(C.sharefs_init),
+		destroy: closure(C.sharefs_destroy),
+
+		// implemented in fuse-helper.c
+		getattr:  closure(C.sharefs_getattr),
+		readdir:  closure(C.sharefs_readdir),
+		mkdir:    closure(C.sharefs_mkdir),
+		unlink:   closure(C.sharefs_unlink),
+		rmdir:    closure(C.sharefs_rmdir),
+		rename:   closure(C.sharefs_rename),
+		truncate: closure(C.sharefs_truncate),
+		utimens:  closure(C.sharefs_utimens),
+		create:   closure(C.sharefs_create),
+		open:     closure(C.sharefs_open),
+		read:     closure(C.sharefs_read),
+		write:    closure(C.sharefs_write),
+		statfs:   closure(C.sharefs_statfs),
+		release:  closure(C.sharefs_release),
+		fsync:    closure(C.sharefs_fsync),
+	}
+
+	fuse := C.fuse_new_fn(&args, &op, C.size_t(unsafe.Sizeof(op)), unsafe.Pointer(&priv))
+	if fuse == nil {
+		return 3
+	}
+	defer C.fuse_destroy(fuse)
+	se := C.fuse_get_session(fuse)
+
+	if setup.Fuse < 3 {
+		// unconfined, set up mount point and container
+		if C.fuse_mount(fuse, opts.mountpoint) != 0 {
+			return 4
+		}
+		// unmounted by initial process
+		defer func() {
+			if exitCode == 5 {
+				C.fuse_unmount(fuse)
+			}
+		}()
+
+		if asRoot {
+			if err := syscall.Setresgid(setup.Setgid, setup.Setgid, setup.Setgid); err != nil {
+				log.Printf("cannot set gid: %v", err)
+				return 5
+			}
+			if err := syscall.Setgroups(nil); err != nil {
+				log.Printf("cannot set supplementary groups: %v", err)
+				return 5
+			}
+			if err := syscall.Setresuid(setup.Setuid, setup.Setuid, setup.Setuid); err != nil {
+				log.Printf("cannot set uid: %v", err)
+				return 5
+			}
+		}
+
+		msg.SwapVerbose(opts.debug != 0)
+		ctx := context.Background()
+		if opts.foreground != 0 {
+			c, cancel := signal.NotifyContext(ctx, syscall.SIGINT, syscall.SIGTERM)
+			defer cancel()
+			ctx = c
+		}
+		z := container.New(ctx, msg)
+		z.AllowOrphan = opts.foreground == 0
+		z.Env = os.Environ()
+
+		// keep fuse_parse_cmdline happy in the container
+		z.Tmpfs(check.MustAbs(container.Nonexistent), 1<<10, 0755)
+
+		if a, err := check.NewAbs(container.MustExecutable(msg)); err != nil {
+			log.Println(err)
+			return 5
+		} else {
+			z.Path = a
+		}
+		z.Args = s
+		z.ForwardCancel = true
+		z.SeccompPresets |= std.PresetStrict
+		z.ParentPerm = 0700
+		z.Bind(setup.Source, setup.Source, std.BindWritable)
+		if !z.AllowOrphan {
+			z.WaitDelay = hst.WaitDelayMax
+			z.Stdin, z.Stdout, z.Stderr = os.Stdin, os.Stdout, os.Stderr
+		}
+		z.Bind(z.Path, z.Path, 0)
+		setup.Fuse = int(proc.ExtraFileSlice(&z.ExtraFiles, os.NewFile(uintptr(C.fuse_session_fd(se)), "fuse")))
+
+		var setupWriter io.WriteCloser
+		if fd, w, err := container.Setup(&z.ExtraFiles); err != nil {
+			log.Println(err)
+			return 5
+		} else {
+			z.Args = append(z.Args, "-osetup="+strconv.Itoa(fd))
+			setupWriter = w
+		}
+
+		if err := z.Start(); err != nil {
+			if m, ok := message.GetMessage(err); ok {
+				log.Println(m)
+			} else {
+				log.Println(err)
+			}
+			return 5
+		}
+		if err := z.Serve(); err != nil {
+			if m, ok := message.GetMessage(err); ok {
+				log.Println(m)
+			} else {
+				log.Println(err)
+			}
+			return 5
+		}
+
+		if err := gob.NewEncoder(setupWriter).Encode(&setup); err != nil {
+			log.Println(err)
+			return 5
+		} else if err = setupWriter.Close(); err != nil {
+			log.Println(err)
+		}
+
+		if !z.AllowOrphan {
+			if err := z.Wait(); err != nil {
+				var exitError *exec.ExitError
+				if !errors.As(err, &exitError) || exitError == nil {
+					log.Println(err)
+					return 5
+				}
+				switch code := exitError.ExitCode(); syscall.Signal(code & 0x7f) {
+				case syscall.SIGINT:
+				case syscall.SIGTERM:
+
+				default:
+					return code
+				}
+			}
+		}
+		return 0
+	} else { // confined
+		C.free(unsafe.Pointer(opts.mountpoint))
+		// must be heap allocated
+		opts.mountpoint = C.CString("/dev/fd/" + strconv.Itoa(setup.Fuse))
+
+		if err := os.Chdir("/"); err != nil {
+			log.Println(err)
+		}
+	}
+
+	if C.fuse_mount(fuse, opts.mountpoint) != 0 {
+		return 4
+	}
+	defer C.fuse_unmount(fuse)
+
+	if C.fuse_set_signal_handlers(se) != 0 {
+		return 6
+	}
+	defer C.fuse_remove_signal_handlers(se)
+
+	if opts.singlethread != 0 {
+		if C.fuse_loop(fuse) != 0 {
+			return 8
+		}
+	} else {
+		loopConfig := C.fuse_loop_cfg_create()
+		if loopConfig == nil {
+			return 7
+		}
+		defer C.fuse_loop_cfg_destroy(loopConfig)
+
+		C.fuse_loop_cfg_set_clone_fd(loopConfig, C.uint(opts.clone_fd))
+
+		C.fuse_loop_cfg_set_idle_threads(loopConfig, opts.max_idle_threads)
+		C.fuse_loop_cfg_set_max_threads(loopConfig, opts.max_threads)
+		if C.fuse_loop_mt(fuse, loopConfig) != 0 {
+			return 8
+		}
+	}
+
+	if setup.initFailed {
+		return 1
+	}
+	return 0
+}

cmd/sharefs/fuse_test.go

@@ -0,0 +1,113 @@
+package main
+
+import (
+	"bytes"
+	"log"
+	"reflect"
+	"testing"
+
+	"hakurei.app/container/check"
+)
+
+func TestParseOpts(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name    string
+		args    []string
+		want    setupState
+		wantLog string
+		wantOk  bool
+	}{
+		{"zero length", []string{}, setupState{}, "", false},
+
+		{"not absolute", []string{"sharefs",
+			"-o", "source=nonexistent",
+			"-o", "setuid=1023",
+			"-o", "setgid=1023",
+		}, setupState{}, "sharefs: path \"nonexistent\" is not absolute\n", false},
+
+		{"not specified", []string{"sharefs",
+			"-o", "setuid=1023",
+			"-o", "setgid=1023",
+		}, setupState{}, "", false},
+
+		{"invalid setuid", []string{"sharefs",
+			"-o", "source=/proc/nonexistent",
+			"-o", "setuid=ff",
+			"-o", "setgid=1023",
+		}, setupState{
+			Source: check.MustAbs("/proc/nonexistent"),
+		}, "sharefs: invalid value for option setuid\n", false},
+
+		{"invalid setgid", []string{"sharefs",
+			"-o", "source=/proc/nonexistent",
+			"-o", "setuid=1023",
+			"-o", "setgid=ff",
+		}, setupState{
+			Source: check.MustAbs("/proc/nonexistent"),
+			Setuid: 1023,
+		}, "sharefs: invalid value for option setgid\n", false},
+
+		{"simple", []string{"sharefs",
+			"-o", "source=/proc/nonexistent",
+		}, setupState{
+			Source: check.MustAbs("/proc/nonexistent"),
+			Setuid: -1,
+			Setgid: -1,
+		}, "", true},
+
+		{"root", []string{"sharefs",
+			"-o", "source=/proc/nonexistent",
+			"-o", "setuid=1023",
+			"-o", "setgid=1023",
+		}, setupState{
+			Source: check.MustAbs("/proc/nonexistent"),
+			Setuid: 1023,
+			Setgid: 1023,
+		}, "", true},
+
+		{"setuid", []string{"sharefs",
+			"-o", "source=/proc/nonexistent",
+			"-o", "setuid=1023",
+		}, setupState{
+			Source: check.MustAbs("/proc/nonexistent"),
+			Setuid: 1023,
+			Setgid: -1,
+		}, "", true},
+
+		{"setgid", []string{"sharefs",
+			"-o", "source=/proc/nonexistent",
+			"-o", "setgid=1023",
+		}, setupState{
+			Source: check.MustAbs("/proc/nonexistent"),
+			Setuid: -1,
+			Setgid: 1023,
+		}, "", true},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			var (
+				got setupState
+				buf bytes.Buffer
+			)
+			args := copyArgs(tc.args...)
+			defer freeArgs(&args)
+			unsafeAddArgument(&args, "-odefault_permissions\x00")
+
+			if ok := parseOpts(&args, &got, log.New(&buf, "sharefs: ", 0)); ok != tc.wantOk {
+				t.Errorf("parseOpts: ok = %v, want %v", ok, tc.wantOk)
+			}
+
+			if !reflect.DeepEqual(&got, &tc.want) {
+				t.Errorf("parseOpts: setup = %#v, want %#v", got, tc.want)
+			}
+
+			if buf.String() != tc.wantLog {
+				t.Errorf("parseOpts: log =\n%s\nwant\n%s", buf.String(), tc.wantLog)
+			}
+		})
+	}
+}

cmd/sharefs/main.go

@@ -0,0 +1,31 @@
+package main
+
+import (
+	"log"
+	"os"
+	"slices"
+)
+
+// sharefsName is the prefix used by log.std in the sharefs process.
+const sharefsName = "sharefs"
+
+// handleMountArgs returns an alternative, libfuse-compatible args slice for
+// args passed by mount -t fuse.sharefs [options] sharefs <mountpoint>.
+//
+// In this case, args always has a length of 5 with index 0 being what comes
+// after "fuse." in the filesystem type, 1 is the uninterpreted string passed
+// to mount (sharefsName is used as the magic string to enable this hack),
+// 2 is passed through to libfuse as mountpoint, and 3 is always "-o".
+func handleMountArgs(args []string) []string {
+	if len(args) == 5 && args[1] == sharefsName && args[3] == "-o" {
+		return []string{sharefsName, args[2], "-o", args[4]}
+	}
+	return slices.Clone(args)
+}
+
+func main() {
+	log.SetFlags(0)
+	log.SetPrefix(sharefsName + ": ")
+
+	os.Exit(_main(handleMountArgs(os.Args)...))
+}

cmd/sharefs/main_test.go

@@ -0,0 +1,29 @@
+package main
+
+import (
+	"slices"
+	"testing"
+)
+
+func TestHandleMountArgs(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name string
+		args []string
+		want []string
+	}{
+		{"nil", nil, nil},
+		{"passthrough", []string{"sharefs", "-V"}, []string{"sharefs", "-V"}},
+		{"replace", []string{"/sbin/sharefs", "sharefs", "/sdcard", "-o", "rw"}, []string{"sharefs", "/sdcard", "-o", "rw"}},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			if got := handleMountArgs(tc.args); !slices.Equal(got, tc.want) {
+				t.Errorf("handleMountArgs: %q, want %q", got, tc.want)
+			}
+		})
+	}
+}

cmd/sharefs/test/configuration.nix

@@ -0,0 +1,41 @@
+{ pkgs, ... }:
+{
+  users.users = {
+    alice = {
+      isNormalUser = true;
+      description = "Alice Foobar";
+      password = "foobar";
+      uid = 1000;
+    };
+  };
+
+  home-manager.users.alice.home.stateVersion = "24.11";
+
+  # Automatically login on tty1 as a normal user:
+  services.getty.autologinUser = "alice";
+
+  environment = {
+    # For benchmarking sharefs:
+    systemPackages = [ pkgs.fsmark ];
+  };
+
+  virtualisation = {
+    diskSize = 6 * 1024;
+
+    qemu.options = [
+      # Increase test performance:
+      "-smp 8"
+    ];
+  };
+
+  environment.hakurei = rec {
+    enable = true;
+    stateDir = "/var/lib/hakurei";
+    sharefs.source = "${stateDir}/sdcard";
+    users.alice = 0;
+
+    extraHomeConfig = {
+      home.stateVersion = "23.05";
+    };
+  };
+}

cmd/sharefs/test/default.nix

@@ -0,0 +1,44 @@
+{
+  testers,
+
+  system,
+  self,
+}:
+testers.nixosTest {
+  name = "sharefs";
+  nodes.machine =
+    { options, pkgs, ... }:
+    let
+      fhs =
+        let
+          hakurei = options.environment.hakurei.package.default;
+        in
+        pkgs.buildFHSEnv {
+          pname = "hakurei-fhs";
+          inherit (hakurei) version;
+          targetPkgs = _: hakurei.targetPkgs;
+          extraOutputsToInstall = [ "dev" ];
+          profile = ''
+            export PKG_CONFIG_PATH="/usr/share/pkgconfig:$PKG_CONFIG_PATH"
+          '';
+        };
+    in
+    {
+      environment.systemPackages = [
+        # For go tests:
+        (pkgs.writeShellScriptBin "sharefs-workload-hakurei-tests" ''
+          cp -r "${self.packages.${system}.hakurei.src}" "/sdcard/hakurei" && cd "/sdcard/hakurei"
+          ${fhs}/bin/hakurei-fhs -c 'CC="clang -O3 -Werror" go test ./...'
+        '')
+      ];
+
+      imports = [
+        ./configuration.nix
+
+        self.nixosModules.hakurei
+        self.inputs.home-manager.nixosModules.home-manager
+      ];
+    };
+
+  testScript = builtins.readFile ./test.py;
+}

cmd/sharefs/test/test.py

@@ -0,0 +1,60 @@
+start_all()
+machine.wait_for_unit("multi-user.target")
+
+# To check sharefs version:
+print(machine.succeed("sharefs -V"))
+
+# Make sure sharefs started:
+machine.wait_for_unit("sdcard.mount")
+
+machine.succeed("mkdir /mnt")
+def check_bad_opts_output(opts, want, source="/etc", privileged=False):
+    output = machine.fail(("" if privileged else "sudo -u alice -i ") + f"sharefs -f -o source={source},{opts} /mnt 2>&1")
+    if output != want:
+        raise Exception(f"unexpected output: {output}")
+
+# Malformed setuid/setgid representation:
+check_bad_opts_output("setuid=ff", "sharefs: invalid value for option setuid\n")
+check_bad_opts_output("setgid=ff", "sharefs: invalid value for option setgid\n")
+
+# Bounds check for setuid/setgid:
+check_bad_opts_output("setuid=0", "sharefs: invalid value for option setuid\n")
+check_bad_opts_output("setgid=0", "sharefs: invalid value for option setgid\n")
+check_bad_opts_output("setuid=-1", "sharefs: invalid value for option setuid\n")
+check_bad_opts_output("setgid=-1", "sharefs: invalid value for option setgid\n")
+
+# Non-root setuid/setgid:
+check_bad_opts_output("setuid=1023", "sharefs: setuid and setgid has no effect when not starting as root\n")
+check_bad_opts_output("setgid=1023", "sharefs: setuid and setgid has no effect when not starting as root\n")
+check_bad_opts_output("setuid=1023,setgid=1023", "sharefs: setuid and setgid has no effect when not starting as root\n")
+check_bad_opts_output("mkdir", "sharefs: mkdir has no effect when not starting as root\n")
+
+# Starting as root without setuid/setgid:
+check_bad_opts_output("allow_other", "sharefs: setuid and setgid must not be 0\n", privileged=True)
+check_bad_opts_output("setuid=1023", "sharefs: setuid and setgid must not be 0\n", privileged=True)
+check_bad_opts_output("setgid=1023", "sharefs: setuid and setgid must not be 0\n", privileged=True)
+
+# Make sure nothing actually got mounted:
+machine.fail("umount /mnt")
+machine.succeed("rmdir /mnt")
+
+# Unprivileged mount/unmount:
+machine.succeed("sudo -u alice -i mkdir /home/alice/{sdcard,persistent}")
+machine.succeed("sudo -u alice -i sharefs -o source=/home/alice/persistent /home/alice/sdcard")
+machine.succeed("sudo -u alice -i touch /home/alice/sdcard/check")
+machine.succeed("sudo -u alice -i umount /home/alice/sdcard")
+machine.succeed("sudo -u alice -i rm /home/alice/persistent/check")
+machine.succeed("sudo -u alice -i rmdir /home/alice/{sdcard,persistent}")
+
+# Benchmark sharefs:
+machine.succeed("fs_mark -v -d /sdcard/fs_mark -l /tmp/fs_log.txt")
+machine.copy_from_vm("/tmp/fs_log.txt", "")
+
+# Check permissions:
+machine.succeed("sudo -u sharefs touch /var/lib/hakurei/sdcard/fs_mark/.check")
+machine.succeed("sudo -u sharefs rm /var/lib/hakurei/sdcard/fs_mark/.check")
+machine.succeed("sudo -u alice rm -rf /sdcard/fs_mark")
+machine.fail("ls /var/lib/hakurei/sdcard/fs_mark")
+
+# Run hakurei tests on sharefs:
+machine.succeed("sudo -u alice -i sharefs-workload-hakurei-tests")

container/capability.go

@@ -14,6 +14,7 @@ const (
 
 	CAP_SYS_ADMIN    = 0x15
 	CAP_SETPCAP      = 0x8
+	CAP_NET_ADMIN    = 0xc
 	CAP_DAC_OVERRIDE = 0x1
 )
 

container/check/absolute.go

@@ -9,46 +9,60 @@ import (
 	"slices"
 	"strings"
 	"syscall"
+	"unique"
 )
 
 // AbsoluteError is returned by [NewAbs] and holds the invalid pathname.
-type AbsoluteError struct{ Pathname string }
+type AbsoluteError string
 
-func (e *AbsoluteError) Error() string { return fmt.Sprintf("path %q is not absolute", e.Pathname) }
+func (e AbsoluteError) Error() string {
-func (e *AbsoluteError) Is(target error) bool {
+	return fmt.Sprintf("path %q is not absolute", string(e))
-	var ce *AbsoluteError
+}
+
+func (e AbsoluteError) Is(target error) bool {
+	var ce AbsoluteError
 	if !errors.As(target, &ce) {
 		return errors.Is(target, syscall.EINVAL)
 	}
-	return *e == *ce
+	return e == ce
 }
 
 // Absolute holds a pathname checked to be absolute.
-type Absolute struct{ pathname string }
+type Absolute struct{ pathname unique.Handle[string] }
+
+// ok returns whether [Absolute] is not the zero value.
+func (a *Absolute) ok() bool { return a != nil && *a != (Absolute{}) }
 
 // unsafeAbs returns [check.Absolute] on any string value.
-func unsafeAbs(pathname string) *Absolute { return &Absolute{pathname} }
+func unsafeAbs(pathname string) *Absolute {
+	return &Absolute{unique.Make(pathname)}
+}
 
+// String returns the checked pathname.
 func (a *Absolute) String() string {
-	if a.pathname == "" {
+	if !a.ok() {
 		panic("attempted use of zero Absolute")
 	}
+	return a.pathname.Value()
+}
+
+// Handle returns the underlying [unique.Handle].
+func (a *Absolute) Handle() unique.Handle[string] {
 	return a.pathname
 }
 
+// Is efficiently compares the underlying pathname.
 func (a *Absolute) Is(v *Absolute) bool {
 	if a == nil && v == nil {
 		return true
 	}
-	return a != nil && v != nil &&
+	return a.ok() && v.ok() && a.pathname == v.pathname
-		a.pathname != "" && v.pathname != "" &&
-		a.pathname == v.pathname
 }
 
 // NewAbs checks pathname and returns a new [Absolute] if pathname is absolute.
 func NewAbs(pathname string) (*Absolute, error) {
 	if !path.IsAbs(pathname) {
-		return nil, &AbsoluteError{pathname}
+		return nil, AbsoluteError(pathname)
 	}
 	return unsafeAbs(pathname), nil
 }
@@ -70,35 +84,49 @@ func (a *Absolute) Append(elem ...string) *Absolute {
 // Dir calls [path.Dir] with [Absolute] as its argument.
 func (a *Absolute) Dir() *Absolute { return unsafeAbs(path.Dir(a.String())) }
 
-func (a *Absolute) GobEncode() ([]byte, error) { return []byte(a.String()), nil }
+// GobEncode returns the checked pathname.
+func (a *Absolute) GobEncode() ([]byte, error) {
+	return []byte(a.String()), nil
+}
+
+// GobDecode stores data if it represents an absolute pathname.
 func (a *Absolute) GobDecode(data []byte) error {
 	pathname := string(data)
 	if !path.IsAbs(pathname) {
-		return &AbsoluteError{pathname}
+		return AbsoluteError(pathname)
 	}
-	a.pathname = pathname
+	a.pathname = unique.Make(pathname)
 	return nil
 }
 
-func (a *Absolute) MarshalJSON() ([]byte, error) { return json.Marshal(a.String()) }
+// MarshalJSON returns a JSON representation of the checked pathname.
+func (a *Absolute) MarshalJSON() ([]byte, error) {
+	return json.Marshal(a.String())
+}
+
+// UnmarshalJSON stores data if it represents an absolute pathname.
 func (a *Absolute) UnmarshalJSON(data []byte) error {
 	var pathname string
 	if err := json.Unmarshal(data, &pathname); err != nil {
 		return err
 	}
 	if !path.IsAbs(pathname) {
-		return &AbsoluteError{pathname}
+		return AbsoluteError(pathname)
 	}
-	a.pathname = pathname
+	a.pathname = unique.Make(pathname)
 	return nil
 }
 
 // SortAbs calls [slices.SortFunc] for a slice of [Absolute].
 func SortAbs(x []*Absolute) {
-	slices.SortFunc(x, func(a, b *Absolute) int { return strings.Compare(a.String(), b.String()) })
+	slices.SortFunc(x, func(a, b *Absolute) int {
+		return strings.Compare(a.String(), b.String())
+	})
 }
 
 // CompactAbs calls [slices.CompactFunc] for a slice of [Absolute].
 func CompactAbs(s []*Absolute) []*Absolute {
-	return slices.CompactFunc(s, func(a *Absolute, b *Absolute) bool { return a.String() == b.String() })
+	return slices.CompactFunc(s, func(a *Absolute, b *Absolute) bool {
+		return a.Is(b)
+	})
 }

container/check/absolute_test.go

@@ -31,8 +31,8 @@ func TestAbsoluteError(t *testing.T) {
 	}{
 		{"EINVAL", new(AbsoluteError), syscall.EINVAL, true},
 		{"not EINVAL", new(AbsoluteError), syscall.EBADE, false},
-		{"ne val", new(AbsoluteError), &AbsoluteError{Pathname: "etc"}, false},
+		{"ne val", new(AbsoluteError), AbsoluteError("etc"), false},
-		{"equals", &AbsoluteError{Pathname: "etc"}, &AbsoluteError{Pathname: "etc"}, true},
+		{"equals", AbsoluteError("etc"), AbsoluteError("etc"), true},
 	}
 
 	for _, tc := range testCases {
@@ -45,7 +45,7 @@ func TestAbsoluteError(t *testing.T) {
 		t.Parallel()
 
 		want := `path "etc" is not absolute`
-		if got := (&AbsoluteError{Pathname: "etc"}).Error(); got != want {
+		if got := (AbsoluteError("etc")).Error(); got != want {
 			t.Errorf("Error: %q, want %q", got, want)
 		}
 	})
@@ -62,8 +62,8 @@ func TestNewAbs(t *testing.T) {
 		wantErr  error
 	}{
 		{"good", "/etc", MustAbs("/etc"), nil},
-		{"not absolute", "etc", nil, &AbsoluteError{Pathname: "etc"}},
+		{"not absolute", "etc", nil, AbsoluteError("etc")},
-		{"zero", "", nil, &AbsoluteError{Pathname: ""}},
+		{"zero", "", nil, AbsoluteError("")},
 	}
 
 	for _, tc := range testCases {
@@ -84,7 +84,7 @@ func TestNewAbs(t *testing.T) {
 		t.Parallel()
 
 		defer func() {
-			wantPanic := &AbsoluteError{Pathname: "etc"}
+			wantPanic := AbsoluteError("etc")
 
 			if r := recover(); !reflect.DeepEqual(r, wantPanic) {
 				t.Errorf("MustAbs: panic = %v; want %v", r, wantPanic)
@@ -175,7 +175,7 @@ func TestCodecAbsolute(t *testing.T) {
 
 			`"/etc"`, `{"val":"/etc","magic":3236757504}`},
 		{"not absolute", nil,
-			&AbsoluteError{Pathname: "etc"},
+			AbsoluteError("etc"),
 			"\t\x7f\x05\x01\x02\xff\x82\x00\x00\x00\a\xff\x80\x00\x03etc",
 			",\xff\x83\x03\x01\x01\x06sCheck\x01\xff\x84\x00\x01\x02\x01\bPathname\x01\xff\x80\x00\x01\x05Magic\x01\x06\x00\x00\x00\t\x7f\x05\x01\x02\xff\x82\x00\x00\x00\x0f\xff\x84\x01\x03etc\x01\xfb\x01\x81\xda\x00\x00\x00",
 

container/container.go

@@ -35,6 +35,8 @@ type (
 	// Container represents a container environment being prepared or run.
 	// None of [Container] methods are safe for concurrent use.
 	Container struct {
+		// Whether the container init should stay alive after its parent terminates.
+		AllowOrphan bool
 		// Cgroup fd, nil to disable.
 		Cgroup *int
 		// ExtraFiles passed through to initial process in the container,
@@ -252,8 +254,7 @@ func (p *Container) Start() error {
 	}
 	p.cmd.Dir = fhs.Root
 	p.cmd.SysProcAttr = &SysProcAttr{
-		Setsid:    !p.RetainSession,
+		Setsid: !p.RetainSession,
-		Pdeathsig: SIGKILL,
 		Cloneflags: CLONE_NEWUSER | CLONE_NEWPID | CLONE_NEWNS |
 			CLONE_NEWIPC | CLONE_NEWUTS | CLONE_NEWCGROUP,
 
@@ -262,12 +263,17 @@ func (p *Container) Start() error {
 			CAP_SYS_ADMIN,
 			// drop capabilities
 			CAP_SETPCAP,
+			// bring up loopback interface
+			CAP_NET_ADMIN,
 			// overlay access to upperdir and workdir
 			CAP_DAC_OVERRIDE,
 		},
 
 		UseCgroupFD: p.Cgroup != nil,
 	}
+	if !p.AllowOrphan {
+		p.cmd.SysProcAttr.Pdeathsig = SIGKILL
+	}
 	if p.cmd.SysProcAttr.UseCgroupFD {
 		p.cmd.SysProcAttr.CgroupFD = *p.Cgroup
 	}

container/dispatcher.go

@@ -61,6 +61,8 @@ type syscallDispatcher interface {
 	mountTmpfs(fsname, target string, flags uintptr, size int, perm os.FileMode) error
 	// ensureFile provides ensureFile.
 	ensureFile(name string, perm, pperm os.FileMode) error
+	// mustLoopback provides mustLoopback.
+	mustLoopback(msg message.Msg)
 
 	// seccompLoad provides [seccomp.Load].
 	seccompLoad(rules []std.NativeRule, flags seccomp.ExportFlag) error
@@ -164,6 +166,7 @@ func (k direct) mountTmpfs(fsname, target string, flags uintptr, size int, perm
 func (direct) ensureFile(name string, perm, pperm os.FileMode) error {
 	return ensureFile(name, perm, pperm)
 }
+func (direct) mustLoopback(msg message.Msg) { mustLoopback(msg) }
 
 func (direct) seccompLoad(rules []std.NativeRule, flags seccomp.ExportFlag) error {
 	return seccomp.Load(rules, flags)

container/dispatcher_test.go

@@ -465,6 +465,8 @@ func (k *kstub) ensureFile(name string, perm, pperm os.FileMode) error {
 		stub.CheckArg(k.Stub, "pperm", pperm, 2))
 }
 
+func (*kstub) mustLoopback(message.Msg) { /* noop */ }
+
 func (k *kstub) seccompLoad(rules []std.NativeRule, flags seccomp.ExportFlag) error {
 	k.Helper()
 	return k.Expects("seccompLoad").Error(

container/errors.go

@@ -18,7 +18,7 @@ func messageFromError(err error) (m string, ok bool) {
 	if m, ok = messagePrefixP[os.PathError]("cannot ", err); ok {
 		return
 	}
-	if m, ok = messagePrefixP[check.AbsoluteError](zeroString, err); ok {
+	if m, ok = messagePrefix[check.AbsoluteError](zeroString, err); ok {
 		return
 	}
 	if m, ok = messagePrefix[OpRepeatError](zeroString, err); ok {

container/errors_test.go

@@ -37,7 +37,7 @@ func TestMessageFromError(t *testing.T) {
 			Err:  stub.UniqueError(0xdeadbeef),
 		}, "cannot mount /sysroot: unique error 3735928559 injected by the test suite", true},
 
-		{"absolute", &check.AbsoluteError{Pathname: "etc/mtab"},
+		{"absolute", check.AbsoluteError("etc/mtab"),
 			`path "etc/mtab" is not absolute`, true},
 
 		{"repeat", OpRepeatError("autoetc"),

container/init.go

@@ -170,6 +170,10 @@ func initEntrypoint(k syscallDispatcher, msg message.Msg) {
 		offsetSetup = int(setupFd + 1)
 	}
 
+	if !params.HostNet {
+		k.mustLoopback(msg)
+	}
+
 	// write uid/gid map here so parent does not need to set dumpable
 	if err := k.setDumpable(SUID_DUMP_USER); err != nil {
 		k.fatalf(msg, "cannot set SUID_DUMP_USER: %v", err)

container/initoverlay_test.go

@@ -312,7 +312,10 @@ func TestMountOverlayOp(t *testing.T) {
 			},
 		}},
 
-		{"ephemeral", new(Ops).OverlayEphemeral(check.MustAbs("/nix/store"), check.MustAbs("/mnt-root/nix/.ro-store")), Ops{
+		{"ephemeral", new(Ops).OverlayEphemeral(
+			check.MustAbs("/nix/store"),
+			check.MustAbs("/mnt-root/nix/.ro-store"),
+		), Ops{
 			&MountOverlayOp{
 				Target: check.MustAbs("/nix/store"),
 				Lower:  []*check.Absolute{check.MustAbs("/mnt-root/nix/.ro-store")},
@@ -320,7 +323,10 @@ func TestMountOverlayOp(t *testing.T) {
 			},
 		}},
 
-		{"readonly", new(Ops).OverlayReadonly(check.MustAbs("/nix/store"), check.MustAbs("/mnt-root/nix/.ro-store")), Ops{
+		{"readonly", new(Ops).OverlayReadonly(
+			check.MustAbs("/nix/store"),
+			check.MustAbs("/mnt-root/nix/.ro-store"),
+		), Ops{
 			&MountOverlayOp{
 				Target: check.MustAbs("/nix/store"),
 				Lower:  []*check.Absolute{check.MustAbs("/mnt-root/nix/.ro-store")},

container/initsymlink.go

@@ -31,7 +31,7 @@ func (l *SymlinkOp) Valid() bool { return l != nil && l.Target != nil && l.LinkN
 func (l *SymlinkOp) early(_ *setupState, k syscallDispatcher) error {
 	if l.Dereference {
 		if !path.IsAbs(l.LinkName) {
-			return &check.AbsoluteError{Pathname: l.LinkName}
+			return check.AbsoluteError(l.LinkName)
 		}
 		if name, err := k.readlink(l.LinkName); err != nil {
 			return err

container/initsymlink_test.go

@@ -23,7 +23,7 @@ func TestSymlinkOp(t *testing.T) {
 			Target:      check.MustAbs("/etc/mtab"),
 			LinkName:    "etc/mtab",
 			Dereference: true,
-		}, nil, &check.AbsoluteError{Pathname: "etc/mtab"}, nil, nil},
+		}, nil, check.AbsoluteError("etc/mtab"), nil, nil},
 
 		{"readlink", &Params{ParentPerm: 0755}, &SymlinkOp{
 			Target:      check.MustAbs("/etc/mtab"),

container/netlink.go

@@ -0,0 +1,269 @@
+package container
+
+import (
+	"encoding/binary"
+	"errors"
+	"net"
+	"os"
+	. "syscall"
+	"unsafe"
+
+	"hakurei.app/container/std"
+	"hakurei.app/message"
+)
+
+// rtnetlink represents a NETLINK_ROUTE socket.
+type rtnetlink struct {
+	// Sent as part of rtnetlink messages.
+	pid uint32
+	// AF_NETLINK socket.
+	fd int
+	// Whether the socket is open.
+	ok bool
+	// Message sequence number.
+	seq uint32
+}
+
+// open creates the underlying NETLINK_ROUTE socket.
+func (s *rtnetlink) open() (err error) {
+	if s.ok || s.fd < 0 {
+		return os.ErrInvalid
+	}
+
+	s.pid = uint32(Getpid())
+	if s.fd, err = Socket(
+		AF_NETLINK,
+		SOCK_RAW|SOCK_CLOEXEC,
+		NETLINK_ROUTE,
+	); err != nil {
+		return os.NewSyscallError("socket", err)
+	} else if err = Bind(s.fd, &SockaddrNetlink{
+		Family: AF_NETLINK,
+		Pid:    s.pid,
+	}); err != nil {
+		_ = s.close()
+		return os.NewSyscallError("bind", err)
+	} else {
+		s.ok = true
+		return nil
+	}
+}
+
+// close closes the underlying NETLINK_ROUTE socket.
+func (s *rtnetlink) close() error {
+	if !s.ok {
+		return os.ErrInvalid
+	}
+
+	s.ok = false
+	err := Close(s.fd)
+	s.fd = -1
+	return err
+}
+
+// roundtrip sends a netlink message and handles the reply.
+func (s *rtnetlink) roundtrip(data []byte) error {
+	if !s.ok {
+		return os.ErrInvalid
+	}
+
+	defer func() { s.seq++ }()
+
+	if err := Sendto(s.fd, data, 0, &SockaddrNetlink{
+		Family: AF_NETLINK,
+	}); err != nil {
+		return os.NewSyscallError("sendto", err)
+	}
+	buf := make([]byte, Getpagesize())
+
+done:
+	for {
+		p := buf
+		if n, _, err := Recvfrom(s.fd, p, 0); err != nil {
+			return os.NewSyscallError("recvfrom", err)
+		} else if n < NLMSG_HDRLEN {
+			return errors.ErrUnsupported
+		} else {
+			p = p[:n]
+		}
+
+		if msgs, err := ParseNetlinkMessage(p); err != nil {
+			return err
+		} else {
+			for _, m := range msgs {
+				if m.Header.Seq != s.seq || m.Header.Pid != s.pid {
+					return errors.ErrUnsupported
+				}
+				if m.Header.Type == NLMSG_DONE {
+					break done
+				}
+				if m.Header.Type == NLMSG_ERROR {
+					if len(m.Data) >= 4 {
+						errno := Errno(-std.ScmpInt(binary.NativeEndian.Uint32(m.Data)))
+						if errno == 0 {
+							return nil
+						}
+						return errno
+					}
+					return errors.ErrUnsupported
+				}
+			}
+		}
+	}
+
+	return nil
+}
+
+// mustRoundtrip calls roundtrip and terminates via msg for a non-nil error.
+func (s *rtnetlink) mustRoundtrip(msg message.Msg, data []byte) {
+	err := s.roundtrip(data)
+	if err == nil {
+		return
+	}
+	if closeErr := Close(s.fd); closeErr != nil {
+		msg.Verbosef("cannot close: %v", err)
+	}
+
+	switch err.(type) {
+	case *os.SyscallError:
+		msg.GetLogger().Fatalf("cannot %v", err)
+
+	case Errno:
+		msg.GetLogger().Fatalf("RTNETLINK answers: %v", err)
+
+	default:
+		msg.GetLogger().Fatalln("RTNETLINK answers with unexpected message")
+	}
+}
+
+// newaddrLo represents a RTM_NEWADDR message with two addresses.
+type newaddrLo struct {
+	header NlMsghdr
+	data   IfAddrmsg
+
+	r0 RtAttr
+	a0 [4]byte // in_addr
+	r1 RtAttr
+	a1 [4]byte // in_addr
+}
+
+// sizeofNewaddrLo is the expected size of newaddrLo.
+const sizeofNewaddrLo = NLMSG_HDRLEN + SizeofIfAddrmsg + (SizeofRtAttr+4)*2
+
+// newaddrLo returns the address of a populated newaddrLo.
+func (s *rtnetlink) newaddrLo(lo int) *newaddrLo {
+	return &newaddrLo{NlMsghdr{
+		Len:   sizeofNewaddrLo,
+		Type:  RTM_NEWADDR,
+		Flags: NLM_F_REQUEST | NLM_F_ACK | NLM_F_CREATE | NLM_F_EXCL,
+		Seq:   s.seq,
+		Pid:   s.pid,
+	}, IfAddrmsg{
+		Family:    AF_INET,
+		Prefixlen: 8,
+		Flags:     IFA_F_PERMANENT,
+		Scope:     RT_SCOPE_HOST,
+		Index:     uint32(lo),
+	}, RtAttr{
+		Len:  uint16(SizeofRtAttr + len(newaddrLo{}.a0)),
+		Type: IFA_LOCAL,
+	}, [4]byte{127, 0, 0, 1}, RtAttr{
+		Len:  uint16(SizeofRtAttr + len(newaddrLo{}.a1)),
+		Type: IFA_ADDRESS,
+	}, [4]byte{127, 0, 0, 1}}
+}
+
+func (msg *newaddrLo) toWireFormat() []byte {
+	var buf [sizeofNewaddrLo]byte
+
+	*(*uint32)(unsafe.Pointer(&buf[0:4][0])) = msg.header.Len
+	*(*uint16)(unsafe.Pointer(&buf[4:6][0])) = msg.header.Type
+	*(*uint16)(unsafe.Pointer(&buf[6:8][0])) = msg.header.Flags
+	*(*uint32)(unsafe.Pointer(&buf[8:12][0])) = msg.header.Seq
+	*(*uint32)(unsafe.Pointer(&buf[12:16][0])) = msg.header.Pid
+
+	buf[16] = msg.data.Family
+	buf[17] = msg.data.Prefixlen
+	buf[18] = msg.data.Flags
+	buf[19] = msg.data.Scope
+	*(*uint32)(unsafe.Pointer(&buf[20:24][0])) = msg.data.Index
+
+	*(*uint16)(unsafe.Pointer(&buf[24:26][0])) = msg.r0.Len
+	*(*uint16)(unsafe.Pointer(&buf[26:28][0])) = msg.r0.Type
+	copy(buf[28:32], msg.a0[:])
+	*(*uint16)(unsafe.Pointer(&buf[32:34][0])) = msg.r1.Len
+	*(*uint16)(unsafe.Pointer(&buf[34:36][0])) = msg.r1.Type
+	copy(buf[36:40], msg.a1[:])
+
+	return buf[:]
+}
+
+// newlinkLo represents a RTM_NEWLINK message.
+type newlinkLo struct {
+	header NlMsghdr
+	data   IfInfomsg
+}
+
+// sizeofNewlinkLo is the expected size of newlinkLo.
+const sizeofNewlinkLo = NLMSG_HDRLEN + SizeofIfInfomsg
+
+// newlinkLo returns the address of a populated newlinkLo.
+func (s *rtnetlink) newlinkLo(lo int) *newlinkLo {
+	return &newlinkLo{NlMsghdr{
+		Len:   sizeofNewlinkLo,
+		Type:  RTM_NEWLINK,
+		Flags: NLM_F_REQUEST | NLM_F_ACK,
+		Seq:   s.seq,
+		Pid:   s.pid,
+	}, IfInfomsg{
+		Family: AF_UNSPEC,
+		Index:  int32(lo),
+		Flags:  IFF_UP,
+		Change: IFF_UP,
+	}}
+}
+
+func (msg *newlinkLo) toWireFormat() []byte {
+	var buf [sizeofNewlinkLo]byte
+
+	*(*uint32)(unsafe.Pointer(&buf[0:4][0])) = msg.header.Len
+	*(*uint16)(unsafe.Pointer(&buf[4:6][0])) = msg.header.Type
+	*(*uint16)(unsafe.Pointer(&buf[6:8][0])) = msg.header.Flags
+	*(*uint32)(unsafe.Pointer(&buf[8:12][0])) = msg.header.Seq
+	*(*uint32)(unsafe.Pointer(&buf[12:16][0])) = msg.header.Pid
+
+	buf[16] = msg.data.Family
+	*(*uint16)(unsafe.Pointer(&buf[18:20][0])) = msg.data.Type
+	*(*int32)(unsafe.Pointer(&buf[20:24][0])) = msg.data.Index
+	*(*uint32)(unsafe.Pointer(&buf[24:28][0])) = msg.data.Flags
+	*(*uint32)(unsafe.Pointer(&buf[28:32][0])) = msg.data.Change
+
+	return buf[:]
+}
+
+// mustLoopback creates the loopback address and brings the lo interface up.
+// mustLoopback calls a fatal method of the underlying [log.Logger] of m with a
+// user-facing error message if RTNETLINK behaves unexpectedly.
+func mustLoopback(msg message.Msg) {
+	log := msg.GetLogger()
+
+	var lo int
+	if ifi, err := net.InterfaceByName("lo"); err != nil {
+		log.Fatalln(err)
+	} else {
+		lo = ifi.Index
+	}
+
+	var s rtnetlink
+	if err := s.open(); err != nil {
+		log.Fatalln(err)
+	}
+	defer func() {
+		if err := s.close(); err != nil {
+			msg.Verbosef("cannot close netlink: %v", err)
+		}
+	}()
+
+	s.mustRoundtrip(msg, s.newaddrLo(lo).toWireFormat())
+	s.mustRoundtrip(msg, s.newlinkLo(lo).toWireFormat())
+}

container/netlink_test.go

@@ -0,0 +1,72 @@
+package container
+
+import (
+	"testing"
+	"unsafe"
+)
+
+func TestSizeof(t *testing.T) {
+	if got := unsafe.Sizeof(newaddrLo{}); got != sizeofNewaddrLo {
+		t.Fatalf("newaddrLo: sizeof = %#x, want %#x", got, sizeofNewaddrLo)
+	}
+
+	if got := unsafe.Sizeof(newlinkLo{}); got != sizeofNewlinkLo {
+		t.Fatalf("newlinkLo: sizeof = %#x, want %#x", got, sizeofNewlinkLo)
+	}
+}
+
+func TestRtnetlinkMessage(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name string
+		msg  interface{ toWireFormat() []byte }
+		want []byte
+	}{
+		{"newaddrLo", (&rtnetlink{pid: 1, seq: 0}).newaddrLo(1), []byte{
+			/* Len   */ 0x28, 0, 0, 0,
+			/* Type  */ 0x14, 0,
+			/* Flags */ 5, 6,
+			/* Seq   */ 0, 0, 0, 0,
+			/* Pid   */ 1, 0, 0, 0,
+
+			/* Family    */ 2,
+			/* Prefixlen */ 8,
+			/* Flags     */ 0x80,
+			/* Scope     */ 0xfe,
+			/* Index     */ 1, 0, 0, 0,
+
+			/* Len     */ 8, 0,
+			/* Type    */ 2, 0,
+			/* in_addr */ 127, 0, 0, 1,
+
+			/* Len     */ 8, 0,
+			/* Type    */ 1, 0,
+			/* in_addr */ 127, 0, 0, 1,
+		}},
+
+		{"newlinkLo", (&rtnetlink{pid: 1, seq: 1}).newlinkLo(1), []byte{
+			/* Len   */ 0x20, 0, 0, 0,
+			/* Type  */ 0x10, 0,
+			/* Flags */ 5, 0,
+			/* Seq   */ 1, 0, 0, 0,
+			/* Pid   */ 1, 0, 0, 0,
+
+			/* Family */ 0,
+			/* pad    */ 0,
+			/* Type   */ 0, 0,
+			/* Index  */ 1, 0, 0, 0,
+			/* Flags  */ 1, 0, 0, 0,
+			/* Change */ 1, 0, 0, 0,
+		}},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			if got := tc.msg.toWireFormat(); string(got) != string(tc.want) {
+				t.Fatalf("toWireFormat: %#v, want %#v", got, tc.want)
+			}
+		})
+	}
+}

dist/install.sh

@@ -2,7 +2,7 @@
 cd "$(dirname -- "$0")" || exit 1
 
 install -vDm0755 "bin/hakurei" "${HAKUREI_INSTALL_PREFIX}/usr/bin/hakurei"
-install -vDm0755 "bin/hpkg" "${HAKUREI_INSTALL_PREFIX}/usr/bin/hpkg"
+install -vDm0755 "bin/sharefs" "${HAKUREI_INSTALL_PREFIX}/usr/bin/sharefs"
 
 install -vDm4511 "bin/hsu" "${HAKUREI_INSTALL_PREFIX}/usr/bin/hsu"
 if [ ! -f "${HAKUREI_INSTALL_PREFIX}/etc/hsurc" ]; then

flake.nix

@@ -69,6 +69,8 @@
             withRace = true;
           };
 
+          sharefs = callPackage ./cmd/sharefs/test { inherit system self; };
+
           hpkg = callPackage ./cmd/hpkg/test { inherit system self; };
 
           formatting = runCommandLocal "check-formatting" { nativeBuildInputs = [ nixfmt-rfc-style ]; } ''
@@ -136,6 +138,10 @@
               ;
           };
           hsu = pkgs.callPackage ./cmd/hsu/package.nix { inherit (self.packages.${system}) hakurei; };
+          sharefs = pkgs.linkFarm "sharefs" {
+            "bin/sharefs" = "${hakurei}/libexec/sharefs";
+            "bin/mount.fuse.sharefs" = "${hakurei}/libexec/sharefs";
+          };
 
           dist = pkgs.runCommand "${hakurei.name}-dist" { buildInputs = hakurei.targetPkgs ++ [ pkgs.pkgsStatic.musl ]; } ''
             # go requires XDG_CACHE_HOME for the build cache
@@ -160,7 +166,10 @@
           pkgs = nixpkgsFor.${system};
         in
         {
-          default = pkgs.mkShell { buildInputs = hakurei.targetPkgs; };
+          default = pkgs.mkShell {
+            buildInputs = hakurei.targetPkgs;
+            hardeningDisable = [ "fortify" ];
+          };
           withPackage = pkgs.mkShell { buildInputs = [ hakurei ] ++ hakurei.targetPkgs; };
 
           vm =

go.mod

@@ -1,3 +1,3 @@
 module hakurei.app
 
-go 1.24
+go 1.25

internal/outcome/sppulse_test.go

@@ -108,7 +108,7 @@ func TestSpPulseOp(t *testing.T) {
 			call("lookupEnv", stub.ExpectArgs{"PULSE_COOKIE"}, "proc/nonexistent/cookie", nil),
 		}, nil, nil, &hst.AppError{
 			Step: "locate PulseAudio cookie",
-			Err:  &check.AbsoluteError{Pathname: "proc/nonexistent/cookie"},
+			Err:  check.AbsoluteError("proc/nonexistent/cookie"),
 		}, nil, nil, nil, nil, nil},
 
 		{"cookie loadFile", func(bool, bool) outcomeOp {
@@ -272,7 +272,7 @@ func TestDiscoverPulseCookie(t *testing.T) {
 			call("verbose", stub.ExpectArgs{[]any{(*check.Absolute)(nil)}}, nil, nil),
 		}}, &hst.AppError{
 			Step: "locate PulseAudio cookie",
-			Err:  &check.AbsoluteError{Pathname: "proc/nonexistent/pulse-cookie"},
+			Err:  check.AbsoluteError("proc/nonexistent/pulse-cookie"),
 		}},
 
 		{"success override", fCheckPathname, stub.Expect{Calls: []stub.Call{
@@ -286,7 +286,7 @@ func TestDiscoverPulseCookie(t *testing.T) {
 			call("verbose", stub.ExpectArgs{[]any{(*check.Absolute)(nil)}}, nil, nil),
 		}}, &hst.AppError{
 			Step: "locate PulseAudio cookie",
-			Err:  &check.AbsoluteError{Pathname: "proc/nonexistent/home"},
+			Err:  check.AbsoluteError("proc/nonexistent/home"),
 		}},
 
 		{"home stat", fCheckPathname, stub.Expect{Calls: []stub.Call{
@@ -321,7 +321,7 @@ func TestDiscoverPulseCookie(t *testing.T) {
 			call("verbose", stub.ExpectArgs{[]any{(*check.Absolute)(nil)}}, nil, nil),
 		}}, &hst.AppError{
 			Step: "locate PulseAudio cookie",
-			Err:  &check.AbsoluteError{Pathname: "proc/nonexistent/xdg"},
+			Err:  check.AbsoluteError("proc/nonexistent/xdg"),
 		}},
 
 		{"xdg stat", fCheckPathname, stub.Expect{Calls: []stub.Call{

internal/pipewire/core.go

@@ -514,7 +514,7 @@ var ErrNotDone = errors.New("did not receive a Core::Done event targeting previo
 const (
 	// syncTimeout is the maximum duration [Core.Sync] is allowed to take before
 	// receiving [CoreDone] or failing.
-	syncTimeout = 5 * time.Second
+	syncTimeout = 10 * time.Second
 )
 
 // Sync queues a [CoreSync] message for the PipeWire server and initiates a Roundtrip.

internal/pipewire/pipewire.go

@@ -19,7 +19,6 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"net"
 	"os"
 	"path"
 	"runtime"
@@ -27,10 +26,16 @@ import (
 	"strconv"
 	"strings"
 	"syscall"
+	"time"
 )
 
 // Conn is a low level unix socket interface used by [Context].
 type Conn interface {
+	// MightBlock informs the implementation that the next call to
+	// Recvmsg or Sendmsg might block. A zero or negative timeout
+	// cancels this behaviour.
+	MightBlock(timeout time.Duration)
+
 	// Recvmsg calls syscall.Recvmsg on the underlying socket.
 	Recvmsg(p, oob []byte, flags int) (n, oobn, recvflags int, err error)
 
@@ -138,45 +143,142 @@ func New(conn Conn, props SPADict) (*Context, error) {
 	return &ctx, nil
 }
 
-// A SyscallConnCloser is a [syscall.Conn] that implements [io.Closer].
+// unixConn is an implementation of the [Conn] interface for connections
-type SyscallConnCloser interface {
+// to Unix domain sockets.
-	syscall.Conn
+type unixConn struct {
-	io.Closer
+	fd int
+
+	// Whether creation of a new epoll instance was attempted.
+	epoll bool
+	// File descriptor referring to the new epoll instance.
+	// Valid if epoll is true and epollErr is nil.
+	epollFd int
+	// Error returned by syscall.EpollCreate1.
+	epollErr error
+	// Stores epoll events from the kernel.
+	epollBuf [32]syscall.EpollEvent
+
+	// If non-zero, next call is treated as a blocking call.
+	timeout time.Duration
 }
 
-// A SyscallConn is a [Conn] adapter for [syscall.Conn].
+// Dial connects to a Unix domain socket described by name.
-type SyscallConn struct{ SyscallConnCloser }
+func Dial(name string) (Conn, error) {
+	if fd, err := syscall.Socket(syscall.AF_UNIX, syscall.SOCK_STREAM|syscall.SOCK_CLOEXEC|syscall.SOCK_NONBLOCK, 0); err != nil {
+		return nil, os.NewSyscallError("socket", err)
+	} else if err = syscall.Connect(fd, &syscall.SockaddrUnix{Name: name}); err != nil {
+		_ = syscall.Close(fd)
+		return nil, os.NewSyscallError("connect", err)
+	} else {
+		return &unixConn{fd: fd}, nil
+	}
+}
 
-// Recvmsg implements [Conn.Recvmsg] via [syscall.Conn.SyscallConn].
+// MightBlock informs the implementation that the next call
-func (conn SyscallConn) Recvmsg(p, oob []byte, flags int) (n, oobn, recvflags int, err error) {
+// might block for a non-zero timeout.
-	var rc syscall.RawConn
+func (conn *unixConn) MightBlock(timeout time.Duration) {
-	if rc, err = conn.SyscallConn(); err != nil {
+	if timeout < 0 {
+		timeout = 0
+	}
+	conn.timeout = timeout
+}
+
+// wantsEpoll is called at the beginning of any method that might use epoll.
+func (conn *unixConn) wantsEpoll() error {
+	if !conn.epoll {
+		conn.epoll = true
+		conn.epollFd, conn.epollErr = syscall.EpollCreate1(syscall.EPOLL_CLOEXEC)
+		if conn.epollErr == nil {
+			if conn.epollErr = syscall.EpollCtl(conn.epollFd, syscall.EPOLL_CTL_ADD, conn.fd, &syscall.EpollEvent{
+				Events: syscall.EPOLLERR | syscall.EPOLLHUP,
+				Fd:     int32(conn.fd),
+			}); conn.epollErr != nil {
+				_ = syscall.Close(conn.epollFd)
+			}
+		}
+	}
+	return conn.epollErr
+}
+
+// wait waits for a specific I/O event on fd. Caller must arrange for wantsEpoll
+// to be called somewhere before wait is called.
+func (conn *unixConn) wait(event uint32) (err error) {
+	if conn.timeout == 0 {
+		return nil
+	}
+	deadline := time.Now().Add(conn.timeout)
+	conn.timeout = 0
+
+	if err = syscall.EpollCtl(conn.epollFd, syscall.EPOLL_CTL_MOD, conn.fd, &syscall.EpollEvent{
+		Events: event | syscall.EPOLLERR | syscall.EPOLLHUP,
+		Fd:     int32(conn.fd),
+	}); err != nil {
 		return
 	}
 
-	if controlErr := rc.Control(func(fd uintptr) {
+	for timeout := deadline.Sub(time.Now()); timeout > 0; timeout = deadline.Sub(time.Now()) {
-		n, oobn, recvflags, _, err = syscall.Recvmsg(int(fd), p, oob, flags)
+		var n int
-	}); controlErr != nil && err == nil {
+		if n, err = syscall.EpollWait(conn.epollFd, conn.epollBuf[:], int(timeout/time.Millisecond)); err != nil {
-		err = controlErr
+			return
+		}
+
+		switch n {
+		case 1: // only the socket fd is ever added
+			if conn.epollBuf[0].Fd != int32(conn.fd) { // unreachable
+				return syscall.ENOTRECOVERABLE
+			}
+			if conn.epollBuf[0].Events&event == event ||
+				conn.epollBuf[0].Events&syscall.EPOLLERR|syscall.EPOLLHUP != 0 {
+				return nil
+			}
+			err = syscall.ETIME
+			continue
+
+		case 0: // timeout
+			return syscall.ETIMEDOUT
+
+		default: // unreachable
+			return syscall.ENOTRECOVERABLE
+		}
 	}
 	return
 }
 
-// Sendmsg implements [Conn.Sendmsg] via [syscall.Conn.SyscallConn].
+// Recvmsg calls syscall.Recvmsg on the underlying socket.
-func (conn SyscallConn) Sendmsg(p, oob []byte, flags int) (n int, err error) {
+func (conn *unixConn) Recvmsg(p, oob []byte, flags int) (n, oobn, recvflags int, err error) {
-	var rc syscall.RawConn
+	if err = conn.wantsEpoll(); err != nil {
-	if rc, err = conn.SyscallConn(); err != nil {
+		return
+	} else if err = conn.wait(syscall.EPOLLIN); err != nil {
 		return
 	}
 
-	if controlErr := rc.Control(func(fd uintptr) {
+	n, oobn, recvflags, _, err = syscall.Recvmsg(conn.fd, p, oob, flags)
-		n, err = syscall.SendmsgN(int(fd), p, oob, nil, flags)
-	}); controlErr != nil && err == nil {
-		err = controlErr
-	}
 	return
 }
 
+// Sendmsg calls syscall.Sendmsg on the underlying socket.
+func (conn *unixConn) Sendmsg(p, oob []byte, flags int) (n int, err error) {
+	if err = conn.wantsEpoll(); err != nil {
+		return
+	} else if err = conn.wait(syscall.EPOLLOUT); err != nil {
+		return
+	}
+
+	n, err = syscall.SendmsgN(conn.fd, p, oob, nil, flags)
+	return
+}
+
+// Close closes the underlying socket and the epoll fd if populated.
+func (conn *unixConn) Close() (err error) {
+	if conn.epoll && conn.epollErr == nil {
+		conn.epollErr = syscall.Close(conn.epollFd)
+	}
+	if err = syscall.Close(conn.fd); err != nil {
+		return
+	}
+	return conn.epollErr
+}
+
 // MustNew calls [New](conn, props) and panics on error.
 // It is intended for use in tests with hard-coded strings.
 func MustNew(conn Conn, props SPADict) *Context {
@@ -310,7 +412,7 @@ func (ctx *Context) recvmsg(remaining []byte) (payload []byte, err error) {
 			}
 			if err != syscall.EAGAIN && err != syscall.EWOULDBLOCK {
 				ctx.closeReceivedFiles()
-				return nil, os.NewSyscallError("recvmsg", err)
+				return nil, &ProxyFatalError{Err: os.NewSyscallError("recvmsg", err), ProxyErrs: ctx.cloneAsProxyErrors()}
 			}
 		}
 
@@ -347,7 +449,7 @@ func (ctx *Context) sendmsg(p []byte, fds ...int) error {
 		}
 
 		if err != nil && err != syscall.EAGAIN && err != syscall.EWOULDBLOCK {
-			return os.NewSyscallError("sendmsg", err)
+			return &ProxyFatalError{Err: os.NewSyscallError("sendmsg", err), ProxyErrs: ctx.cloneAsProxyErrors()}
 		}
 		return err
 	}
@@ -598,8 +700,15 @@ func (ctx *Context) Roundtrip() (err error) {
 	return
 }
 
+const (
+	// roundtripTimeout is the maximum duration socket operations during
+	// Context.roundtrip is allowed to block for.
+	roundtripTimeout = 5 * time.Second
+)
+
 // roundtrip implements the Roundtrip method without checking proxyErrors.
 func (ctx *Context) roundtrip() (err error) {
+	ctx.conn.MightBlock(roundtripTimeout)
 	if err = ctx.sendmsg(ctx.buf, ctx.pendingFiles...); err != nil {
 		return
 	}
@@ -633,6 +742,7 @@ func (ctx *Context) roundtrip() (err error) {
 	}()
 
 	var remaining []byte
+	ctx.conn.MightBlock(roundtripTimeout)
 	for {
 		remaining, err = ctx.consume(remaining)
 		if err == nil {
@@ -857,14 +967,14 @@ const Remote = "PIPEWIRE_REMOTE"
 
 const DEFAULT_SYSTEM_RUNTIME_DIR = "/run/pipewire"
 
-// connectName connects to a PipeWire remote by name and returns the [net.UnixConn].
+// connectName connects to a PipeWire remote by name and returns the resulting [Conn].
-func connectName(name string, manager bool) (conn *net.UnixConn, err error) {
+func connectName(name string, manager bool) (conn Conn, err error) {
 	if manager && !strings.HasSuffix(name, "-manager") {
 		return connectName(name+"-manager", false)
 	}
 
 	if path.IsAbs(name) || (len(name) > 0 && name[0] == '@') {
-		return net.DialUnix("unix", nil, &net.UnixAddr{Name: name, Net: "unix"})
+		return Dial(name)
 	} else {
 		runtimeDir, ok := os.LookupEnv("PIPEWIRE_RUNTIME_DIR")
 		if !ok || !path.IsAbs(runtimeDir) {
@@ -879,7 +989,7 @@ func connectName(name string, manager bool) (conn *net.UnixConn, err error) {
 		if !ok || !path.IsAbs(runtimeDir) {
 			runtimeDir = DEFAULT_SYSTEM_RUNTIME_DIR
 		}
-		return net.DialUnix("unix", nil, &net.UnixAddr{Name: path.Join(runtimeDir, name), Net: "unix"})
+		return Dial(path.Join(runtimeDir, name))
 	}
 }
 
@@ -897,12 +1007,11 @@ func ConnectName(name string, manager bool, props SPADict) (ctx *Context, err er
 		}
 	}
 
-	var conn *net.UnixConn
+	var conn Conn
 	if conn, err = connectName(name, manager); err != nil {
 		return
 	}
-
+	if ctx, err = New(conn, props); err != nil {
-	if ctx, err = New(SyscallConn{conn}, props); err != nil {
 		ctx = nil
 		_ = conn.Close()
 	}

internal/pipewire/pipewire_test.go

@@ -6,6 +6,7 @@ import (
 	"strconv"
 	. "syscall"
 	"testing"
+	"time"
 
 	"hakurei.app/container/stub"
 	"hakurei.app/internal/pipewire"
@@ -715,6 +716,18 @@ type stubUnixConn struct {
 	current int
 }
 
+func (conn *stubUnixConn) MightBlock(timeout time.Duration) {
+	if timeout != 5*time.Second {
+		panic("unexpected timeout " + timeout.String())
+	}
+	if conn.current == 0 ||
+		(conn.samples[conn.current-1].nr == SYS_RECVMSG && conn.samples[conn.current-1].errno == EAGAIN && conn.samples[conn.current].nr == SYS_SENDMSG) ||
+		(conn.samples[conn.current-1].nr == SYS_SENDMSG && conn.samples[conn.current].nr == SYS_RECVMSG) {
+		return
+	}
+	panic("unexpected blocking hint before sample " + strconv.Itoa(conn.current))
+}
+
 // nextSample returns the current sample and increments the counter.
 func (conn *stubUnixConn) nextSample(nr uintptr) (sample *stubUnixConnSample, wantOOB []byte, err error) {
 	sample = &conn.samples[conn.current]

internal/pkg/dir.go

@@ -0,0 +1,210 @@
+package pkg
+
+import (
+	"crypto/sha512"
+	"encoding/binary"
+	"errors"
+	"io"
+	"io/fs"
+	"math"
+	"os"
+	"path/filepath"
+	"syscall"
+
+	"hakurei.app/container/check"
+)
+
+// FlatEntry is a directory entry to be encoded for [Flatten].
+type FlatEntry struct {
+	Mode fs.FileMode // file mode bits
+	Path string      // pathname of the file
+	Data []byte      // file content or symlink destination
+}
+
+/*
+| mode uint32 | path_sz uint32 |
+|        data_sz uint64        |
+|         path string          |
+|         data []byte          |
+*/
+
+// wordSize is the boundary which binary segments are always aligned to.
+const wordSize = 8
+
+// alignSize returns the padded size for aligning sz.
+func alignSize(sz int) int {
+	return sz + (wordSize-(sz)%wordSize)%wordSize
+}
+
+// Encode encodes the entry for transmission or hashing.
+func (ent *FlatEntry) Encode(w io.Writer) (n int, err error) {
+	pPathSize := alignSize(len(ent.Path))
+	if pPathSize > math.MaxUint32 {
+		return 0, syscall.E2BIG
+	}
+	pDataSize := alignSize(len(ent.Data))
+
+	payload := make([]byte, wordSize*2+pPathSize+pDataSize)
+	binary.LittleEndian.PutUint32(payload, uint32(ent.Mode))
+	binary.LittleEndian.PutUint32(payload[wordSize/2:], uint32(len(ent.Path)))
+	binary.LittleEndian.PutUint64(payload[wordSize:], uint64(len(ent.Data)))
+	copy(payload[wordSize*2:], ent.Path)
+	copy(payload[wordSize*2+pPathSize:], ent.Data)
+	return w.Write(payload)
+}
+
+// ErrInsecurePath is returned by [FlatEntry.Decode] if validation is requested
+// and a nonlocal path is encountered in the stream.
+var ErrInsecurePath = errors.New("insecure file path")
+
+// Decode decodes the entry from its representation produced by Encode.
+func (ent *FlatEntry) Decode(r io.Reader, validate bool) (n int, err error) {
+	var nr int
+
+	header := make([]byte, wordSize*2)
+	nr, err = r.Read(header)
+	n += nr
+	if err != nil {
+		if errors.Is(err, io.EOF) && n != 0 {
+			err = io.ErrUnexpectedEOF
+		}
+		return
+	}
+
+	ent.Mode = fs.FileMode(binary.LittleEndian.Uint32(header))
+	pathSize := int(binary.LittleEndian.Uint32(header[wordSize/2:]))
+	pPathSize := alignSize(pathSize)
+	dataSize := int(binary.LittleEndian.Uint64(header[wordSize:]))
+	pDataSize := alignSize(dataSize)
+
+	buf := make([]byte, pPathSize+pDataSize)
+	nr, err = r.Read(buf)
+	n += nr
+	if err != nil {
+		if errors.Is(err, io.EOF) {
+			if nr != len(buf) {
+				err = io.ErrUnexpectedEOF
+				return
+			}
+		} else {
+			return
+		}
+	}
+
+	ent.Path = string(buf[:pathSize])
+	if ent.Mode.IsDir() {
+		ent.Data = nil
+	} else {
+		ent.Data = buf[pPathSize : pPathSize+dataSize]
+	}
+
+	if validate && !filepath.IsLocal(ent.Path) {
+		err = ErrInsecurePath
+	}
+
+	return
+}
+
+// DirScanner provides an efficient interface for reading a stream of encoded
+// [FlatEntry]. Successive calls to the Scan method will step through the
+// entries in the stream.
+type DirScanner struct {
+	// Underlying reader to scan [FlatEntry] representations from.
+	r io.Reader
+
+	// First non-EOF I/O error, returned by the Err method.
+	err error
+
+	// Entry to store results in. Its address is returned by the Entry method
+	// and is updated on every call to Scan.
+	ent FlatEntry
+
+	// Validate pathnames during decoding.
+	validate bool
+}
+
+// NewDirScanner returns the address of a new instance of [DirScanner] reading
+// from r. The caller must no longer read from r after this function returns.
+func NewDirScanner(r io.Reader, validate bool) *DirScanner {
+	return &DirScanner{r: r, validate: validate}
+}
+
+// Err returns the first non-EOF I/O error.
+func (s *DirScanner) Err() error {
+	if errors.Is(s.err, io.EOF) {
+		return nil
+	}
+	return s.err
+}
+
+// Entry returns the address to the [FlatEntry] value storing the last result.
+func (s *DirScanner) Entry() *FlatEntry { return &s.ent }
+
+// Scan advances to the next [FlatEntry].
+func (s *DirScanner) Scan() bool {
+	if s.err != nil {
+		return false
+	}
+
+	var n int
+	n, s.err = s.ent.Decode(s.r, s.validate)
+	if errors.Is(s.err, io.EOF) {
+		return n != 0
+	}
+	return s.err == nil
+}
+
+// Flatten writes a deterministic representation of the contents of fsys to w.
+// The resulting data can be hashed to produce a deterministic checksum for the
+// directory.
+func Flatten(fsys fs.FS, root string, w io.Writer) (n int, err error) {
+	var nr int
+	err = fs.WalkDir(fsys, root, func(path string, d fs.DirEntry, err error) error {
+		if err != nil {
+			return err
+		}
+
+		var fi fs.FileInfo
+		fi, err = d.Info()
+		if err != nil {
+			return err
+		}
+
+		ent := FlatEntry{
+			Path: path,
+			Mode: fi.Mode(),
+		}
+		if ent.Mode.IsRegular() {
+			if ent.Data, err = fs.ReadFile(fsys, path); err != nil {
+				return err
+			}
+		} else if ent.Mode&fs.ModeSymlink != 0 {
+			var newpath string
+			if newpath, err = fs.ReadLink(fsys, path); err != nil {
+				return err
+			}
+			ent.Data = []byte(newpath)
+		} else if !ent.Mode.IsDir() {
+			return InvalidFileModeError(ent.Mode)
+		}
+
+		nr, err = ent.Encode(w)
+		n += nr
+		return err
+	})
+	return
+}
+
+// HashFS returns a checksum produced by hashing the result of [Flatten].
+func HashFS(fsys fs.FS, root string) (Checksum, error) {
+	h := sha512.New384()
+	if _, err := Flatten(fsys, root, h); err != nil {
+		return Checksum{}, err
+	}
+	return (Checksum)(h.Sum(nil)), nil
+}
+
+// HashDir returns a checksum produced by hashing the result of [Flatten].
+func HashDir(pathname *check.Absolute) (Checksum, error) {
+	return HashFS(os.DirFS(pathname.String()), ".")
+}

internal/pkg/dir_test.go

@@ -0,0 +1,537 @@
+package pkg_test
+
+import (
+	"bytes"
+	"io/fs"
+	"reflect"
+	"testing"
+	"testing/fstest"
+
+	"hakurei.app/internal/pkg"
+)
+
+func TestFlatten(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name    string
+		fsys    fs.FS
+		entries []pkg.FlatEntry
+		sum     pkg.Checksum
+		err     error
+	}{
+		{"bad type", fstest.MapFS{
+			".":       {Mode: fs.ModeDir | 0700},
+			"invalid": {Mode: fs.ModeCharDevice | 0400},
+		}, nil, pkg.Checksum{}, pkg.InvalidFileModeError(
+			fs.ModeCharDevice | 0400,
+		)},
+
+		{"empty", fstest.MapFS{
+			".":          {Mode: fs.ModeDir | 0700},
+			"checksum":   {Mode: fs.ModeDir | 0700},
+			"identifier": {Mode: fs.ModeDir | 0700},
+			"work":       {Mode: fs.ModeDir | 0700},
+		}, []pkg.FlatEntry{
+			{Mode: fs.ModeDir | 0700, Path: "."},
+			{Mode: fs.ModeDir | 0700, Path: "checksum"},
+			{Mode: fs.ModeDir | 0700, Path: "identifier"},
+			{Mode: fs.ModeDir | 0700, Path: "work"},
+		}, pkg.MustDecode("E4vEZKhCcL2gPZ2Tt59FS3lDng-d_2SKa2i5G_RbDfwGn6EemptFaGLPUDiOa94C"), nil},
+
+		{"sample cache file", fstest.MapFS{
+			".": {Mode: fs.ModeDir | 0700},
+
+			"checksum": {Mode: fs.ModeDir | 0700},
+			"checksum/vsAhtPNo4waRNOASwrQwcIPTqb3SBuJOXw2G4T1mNmVZM-wrQTRllmgXqcIIoRcX": {Mode: 0400, Data: []byte{0}},
+			"checksum/0bSFPu5Tnd-2Jj0Mv6co23PW2t3BmHc7eLFj9TgY3eIBg8zislo7xZYNBqovVLcq": {Mode: 0400, Data: []byte{0, 0, 0, 0, 0xad, 0xb, 0, 4, 0xfe, 0xfe, 0, 0, 0xfe, 0xca, 0, 0}},
+
+			"identifier": {Mode: fs.ModeDir | 0700},
+			"identifier/vsAhtPNo4waRNOASwrQwcIPTqb3SBuJOXw2G4T1mNmVZM-wrQTRllmgXqcIIoRcX": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/vsAhtPNo4waRNOASwrQwcIPTqb3SBuJOXw2G4T1mNmVZM-wrQTRllmgXqcIIoRcX")},
+			"identifier/0bSFPu5Tnd-2Jj0Mv6co23PW2t3BmHc7eLFj9TgY3eIBg8zislo7xZYNBqovVLcq": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/0bSFPu5Tnd-2Jj0Mv6co23PW2t3BmHc7eLFj9TgY3eIBg8zislo7xZYNBqovVLcq")},
+			"identifier/cafebabecafebabecafebabecafebabecafebabecafebabecafebabecafebabe": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/0bSFPu5Tnd-2Jj0Mv6co23PW2t3BmHc7eLFj9TgY3eIBg8zislo7xZYNBqovVLcq")},
+			"identifier/deadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeef": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/0bSFPu5Tnd-2Jj0Mv6co23PW2t3BmHc7eLFj9TgY3eIBg8zislo7xZYNBqovVLcq")},
+
+			"work": {Mode: fs.ModeDir | 0700},
+		}, []pkg.FlatEntry{
+			{Mode: fs.ModeDir | 0700, Path: "."},
+
+			{Mode: fs.ModeDir | 0700, Path: "checksum"},
+			{Mode: 0400, Path: "checksum/0bSFPu5Tnd-2Jj0Mv6co23PW2t3BmHc7eLFj9TgY3eIBg8zislo7xZYNBqovVLcq", Data: []byte{0, 0, 0, 0, 0xad, 0xb, 0, 4, 0xfe, 0xfe, 0, 0, 0xfe, 0xca, 0, 0}},
+			{Mode: 0400, Path: "checksum/vsAhtPNo4waRNOASwrQwcIPTqb3SBuJOXw2G4T1mNmVZM-wrQTRllmgXqcIIoRcX", Data: []byte{0}},
+
+			{Mode: fs.ModeDir | 0700, Path: "identifier"},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/0bSFPu5Tnd-2Jj0Mv6co23PW2t3BmHc7eLFj9TgY3eIBg8zislo7xZYNBqovVLcq", Data: []byte("../checksum/0bSFPu5Tnd-2Jj0Mv6co23PW2t3BmHc7eLFj9TgY3eIBg8zislo7xZYNBqovVLcq")},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/cafebabecafebabecafebabecafebabecafebabecafebabecafebabecafebabe", Data: []byte("../checksum/0bSFPu5Tnd-2Jj0Mv6co23PW2t3BmHc7eLFj9TgY3eIBg8zislo7xZYNBqovVLcq")},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/deadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeef", Data: []byte("../checksum/0bSFPu5Tnd-2Jj0Mv6co23PW2t3BmHc7eLFj9TgY3eIBg8zislo7xZYNBqovVLcq")},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/vsAhtPNo4waRNOASwrQwcIPTqb3SBuJOXw2G4T1mNmVZM-wrQTRllmgXqcIIoRcX", Data: []byte("../checksum/vsAhtPNo4waRNOASwrQwcIPTqb3SBuJOXw2G4T1mNmVZM-wrQTRllmgXqcIIoRcX")},
+
+			{Mode: fs.ModeDir | 0700, Path: "work"},
+		}, pkg.MustDecode("St9rlE-mGZ5gXwiv_hzQ_B8bZP-UUvSNmf4nHUZzCMOumb6hKnheZSe0dmnuc4Q2"), nil},
+
+		{"sample http get cure", fstest.MapFS{
+			".": {Mode: fs.ModeDir | 0700},
+
+			"checksum": {Mode: fs.ModeDir | 0700},
+			"checksum/fLYGIMHgN1louE-JzITJZJo2SDniPu-IHBXubtvQWFO-hXnDVKNuscV7-zlyr5fU": {Mode: 0400, Data: []byte("\x7f\xe1\x69\xa2\xdd\x63\x96\x26\x83\x79\x61\x8b\xf0\x3f\xd5\x16\x9a\x39\x3a\xdb\xcf\xb1\xbc\x8d\x33\xff\x75\xee\x62\x56\xa9\xf0\x27\xac\x13\x94\x69")},
+
+			"identifier": {Mode: fs.ModeDir | 0700},
+			"identifier/NqVORkT6L9HX6Za7kT2zcibY10qFqBaxEjPiYFrBQX-ZFr3yxCzJxbKOP0zVjeWb": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/fLYGIMHgN1louE-JzITJZJo2SDniPu-IHBXubtvQWFO-hXnDVKNuscV7-zlyr5fU")},
+
+			"work": {Mode: fs.ModeDir | 0700},
+		}, []pkg.FlatEntry{
+			{Mode: fs.ModeDir | 0700, Path: "."},
+
+			{Mode: fs.ModeDir | 0700, Path: "checksum"},
+			{Mode: 0400, Path: "checksum/fLYGIMHgN1louE-JzITJZJo2SDniPu-IHBXubtvQWFO-hXnDVKNuscV7-zlyr5fU", Data: []byte("\x7f\xe1\x69\xa2\xdd\x63\x96\x26\x83\x79\x61\x8b\xf0\x3f\xd5\x16\x9a\x39\x3a\xdb\xcf\xb1\xbc\x8d\x33\xff\x75\xee\x62\x56\xa9\xf0\x27\xac\x13\x94\x69")},
+
+			{Mode: fs.ModeDir | 0700, Path: "identifier"},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/NqVORkT6L9HX6Za7kT2zcibY10qFqBaxEjPiYFrBQX-ZFr3yxCzJxbKOP0zVjeWb", Data: []byte("../checksum/fLYGIMHgN1louE-JzITJZJo2SDniPu-IHBXubtvQWFO-hXnDVKNuscV7-zlyr5fU")},
+
+			{Mode: fs.ModeDir | 0700, Path: "work"},
+		}, pkg.MustDecode("bqtn69RkV5E7V7GhhgCFjcvbxmaqrO8DywamM4Tyjf10F6EJBHjXiIa_tFRtF4iN"), nil},
+
+		{"sample directory step simple", fstest.MapFS{
+			".": {Mode: fs.ModeDir | 0500},
+
+			"check": {Mode: 0400, Data: []byte{0, 0}},
+
+			"lib":            {Mode: fs.ModeDir | 0700},
+			"lib/libedac.so": {Mode: fs.ModeSymlink | 0777, Data: []byte("/proc/nonexistent/libedac.so")},
+
+			"lib/pkgconfig": {Mode: fs.ModeDir | 0700},
+		}, []pkg.FlatEntry{
+			{Mode: fs.ModeDir | 0500, Path: "."},
+
+			{Mode: 0400, Path: "check", Data: []byte{0, 0}},
+
+			{Mode: fs.ModeDir | 0700, Path: "lib"},
+			{Mode: fs.ModeSymlink | 0777, Path: "lib/libedac.so", Data: []byte("/proc/nonexistent/libedac.so")},
+
+			{Mode: fs.ModeDir | 0700, Path: "lib/pkgconfig"},
+		}, pkg.MustDecode("qRN6in76LndiiOZJheHkwyW8UT1N5-f-bXvHfDvwrMw2fSkOoZdh8pWE1qhLk65b"), nil},
+
+		{"sample directory step garbage", fstest.MapFS{
+			".": {Mode: fs.ModeDir | 0500},
+
+			"lib":       {Mode: fs.ModeDir | 0500},
+			"lib/check": {Mode: 0400, Data: []byte{}},
+
+			"lib/pkgconfig": {Mode: fs.ModeDir | 0500},
+		}, []pkg.FlatEntry{
+			{Mode: fs.ModeDir | 0500, Path: "."},
+
+			{Mode: fs.ModeDir | 0500, Path: "lib"},
+			{Mode: 0400, Path: "lib/check", Data: []byte{}},
+
+			{Mode: fs.ModeDir | 0500, Path: "lib/pkgconfig"},
+		}, pkg.MustDecode("CUx-3hSbTWPsbMfDhgalG4Ni_GmR9TnVX8F99tY_P5GtkYvczg9RrF5zO0jX9XYT"), nil},
+
+		{"sample directory", fstest.MapFS{
+			".": {Mode: fs.ModeDir | 0700},
+
+			"checksum": {Mode: fs.ModeDir | 0700},
+			"checksum/qRN6in76LndiiOZJheHkwyW8UT1N5-f-bXvHfDvwrMw2fSkOoZdh8pWE1qhLk65b":                {Mode: fs.ModeDir | 0500},
+			"checksum/qRN6in76LndiiOZJheHkwyW8UT1N5-f-bXvHfDvwrMw2fSkOoZdh8pWE1qhLk65b/check":          {Mode: 0400, Data: []byte{0, 0}},
+			"checksum/qRN6in76LndiiOZJheHkwyW8UT1N5-f-bXvHfDvwrMw2fSkOoZdh8pWE1qhLk65b/lib":            {Mode: fs.ModeDir | 0700},
+			"checksum/qRN6in76LndiiOZJheHkwyW8UT1N5-f-bXvHfDvwrMw2fSkOoZdh8pWE1qhLk65b/lib/pkgconfig":  {Mode: fs.ModeDir | 0700},
+			"checksum/qRN6in76LndiiOZJheHkwyW8UT1N5-f-bXvHfDvwrMw2fSkOoZdh8pWE1qhLk65b/lib/libedac.so": {Mode: fs.ModeSymlink | 0777, Data: []byte("/proc/nonexistent/libedac.so")},
+
+			"identifier": {Mode: fs.ModeDir | 0700},
+			"identifier/HnySzeLQvSBZuTUcvfmLEX_OmH4yJWWH788NxuLuv7kVn8_uPM6Ks4rqFWM2NZJY": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/qRN6in76LndiiOZJheHkwyW8UT1N5-f-bXvHfDvwrMw2fSkOoZdh8pWE1qhLk65b")},
+			"identifier/Zx5ZG9BAwegNT3zQwCySuI2ktCXxNgxirkGLFjW4FW06PtojYVaCdtEw8yuntPLa": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/qRN6in76LndiiOZJheHkwyW8UT1N5-f-bXvHfDvwrMw2fSkOoZdh8pWE1qhLk65b")},
+
+			"work": {Mode: fs.ModeDir | 0700},
+		}, []pkg.FlatEntry{
+			{Mode: fs.ModeDir | 0700, Path: "."},
+
+			{Mode: fs.ModeDir | 0700, Path: "checksum"},
+			{Mode: fs.ModeDir | 0500, Path: "checksum/qRN6in76LndiiOZJheHkwyW8UT1N5-f-bXvHfDvwrMw2fSkOoZdh8pWE1qhLk65b"},
+			{Mode: 0400, Path: "checksum/qRN6in76LndiiOZJheHkwyW8UT1N5-f-bXvHfDvwrMw2fSkOoZdh8pWE1qhLk65b/check", Data: []byte{0, 0}},
+			{Mode: fs.ModeDir | 0700, Path: "checksum/qRN6in76LndiiOZJheHkwyW8UT1N5-f-bXvHfDvwrMw2fSkOoZdh8pWE1qhLk65b/lib"},
+			{Mode: fs.ModeSymlink | 0777, Path: "checksum/qRN6in76LndiiOZJheHkwyW8UT1N5-f-bXvHfDvwrMw2fSkOoZdh8pWE1qhLk65b/lib/libedac.so", Data: []byte("/proc/nonexistent/libedac.so")},
+			{Mode: fs.ModeDir | 0700, Path: "checksum/qRN6in76LndiiOZJheHkwyW8UT1N5-f-bXvHfDvwrMw2fSkOoZdh8pWE1qhLk65b/lib/pkgconfig"},
+
+			{Mode: fs.ModeDir | 0700, Path: "identifier"},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/HnySzeLQvSBZuTUcvfmLEX_OmH4yJWWH788NxuLuv7kVn8_uPM6Ks4rqFWM2NZJY", Data: []byte("../checksum/qRN6in76LndiiOZJheHkwyW8UT1N5-f-bXvHfDvwrMw2fSkOoZdh8pWE1qhLk65b")},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/Zx5ZG9BAwegNT3zQwCySuI2ktCXxNgxirkGLFjW4FW06PtojYVaCdtEw8yuntPLa", Data: []byte("../checksum/qRN6in76LndiiOZJheHkwyW8UT1N5-f-bXvHfDvwrMw2fSkOoZdh8pWE1qhLk65b")},
+
+			{Mode: fs.ModeDir | 0700, Path: "work"},
+		}, pkg.MustDecode("WVpvsVqVKg9Nsh744x57h51AuWUoUR2nnh8Md-EYBQpk6ziyTuUn6PLtF2e0Eu_d"), nil},
+
+		{"sample tar step unpack", fstest.MapFS{
+			".": {Mode: fs.ModeDir | 0500},
+
+			"checksum": {Mode: fs.ModeDir | 0500},
+			"checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP":                {Mode: fs.ModeDir | 0500},
+			"checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP/check":          {Mode: 0400, Data: []byte{0, 0}},
+			"checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP/lib":            {Mode: fs.ModeDir | 0500},
+			"checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP/lib/pkgconfig":  {Mode: fs.ModeDir | 0500},
+			"checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP/lib/libedac.so": {Mode: fs.ModeSymlink | 0777, Data: []byte("/proc/nonexistent/libedac.so")},
+
+			"identifier": {Mode: fs.ModeDir | 0500},
+			"identifier/HnySzeLQvSBZuTUcvfmLEX_OmH4yJWWH788NxuLuv7kVn8_uPM6Ks4rqFWM2NZJY": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP")},
+			"identifier/Zx5ZG9BAwegNT3zQwCySuI2ktCXxNgxirkGLFjW4FW06PtojYVaCdtEw8yuntPLa": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP")},
+
+			"work": {Mode: fs.ModeDir | 0500},
+		}, []pkg.FlatEntry{
+			{Mode: fs.ModeDir | 0500, Path: "."},
+
+			{Mode: fs.ModeDir | 0500, Path: "checksum"},
+			{Mode: fs.ModeDir | 0500, Path: "checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP"},
+			{Mode: 0400, Path: "checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP/check", Data: []byte{0, 0}},
+			{Mode: fs.ModeDir | 0500, Path: "checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP/lib"},
+			{Mode: fs.ModeSymlink | 0777, Path: "checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP/lib/libedac.so", Data: []byte("/proc/nonexistent/libedac.so")},
+			{Mode: fs.ModeDir | 0500, Path: "checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP/lib/pkgconfig"},
+
+			{Mode: fs.ModeDir | 0500, Path: "identifier"},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/HnySzeLQvSBZuTUcvfmLEX_OmH4yJWWH788NxuLuv7kVn8_uPM6Ks4rqFWM2NZJY", Data: []byte("../checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP")},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/Zx5ZG9BAwegNT3zQwCySuI2ktCXxNgxirkGLFjW4FW06PtojYVaCdtEw8yuntPLa", Data: []byte("../checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP")},
+
+			{Mode: fs.ModeDir | 0500, Path: "work"},
+		}, pkg.MustDecode("cTw0h3AmYe7XudSoyEMByduYXqGi-N5ZkTZ0t9K5elsu3i_jNIVF5T08KR1roBFM"), nil},
+
+		{"sample tar", fstest.MapFS{
+			".": {Mode: fs.ModeDir | 0700},
+
+			"checksum": {Mode: fs.ModeDir | 0700},
+			"checksum/cTw0h3AmYe7XudSoyEMByduYXqGi-N5ZkTZ0t9K5elsu3i_jNIVF5T08KR1roBFM":                                                                                          {Mode: fs.ModeDir | 0500},
+			"checksum/cTw0h3AmYe7XudSoyEMByduYXqGi-N5ZkTZ0t9K5elsu3i_jNIVF5T08KR1roBFM/checksum":                                                                                 {Mode: fs.ModeDir | 0500},
+			"checksum/cTw0h3AmYe7XudSoyEMByduYXqGi-N5ZkTZ0t9K5elsu3i_jNIVF5T08KR1roBFM/checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP":                {Mode: fs.ModeDir | 0500},
+			"checksum/cTw0h3AmYe7XudSoyEMByduYXqGi-N5ZkTZ0t9K5elsu3i_jNIVF5T08KR1roBFM/checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP/check":          {Mode: 0400, Data: []byte{0, 0}},
+			"checksum/cTw0h3AmYe7XudSoyEMByduYXqGi-N5ZkTZ0t9K5elsu3i_jNIVF5T08KR1roBFM/checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP/lib":            {Mode: fs.ModeDir | 0500},
+			"checksum/cTw0h3AmYe7XudSoyEMByduYXqGi-N5ZkTZ0t9K5elsu3i_jNIVF5T08KR1roBFM/checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP/lib/libedac.so": {Mode: fs.ModeSymlink | 0777, Data: []byte("/proc/nonexistent/libedac.so")},
+			"checksum/cTw0h3AmYe7XudSoyEMByduYXqGi-N5ZkTZ0t9K5elsu3i_jNIVF5T08KR1roBFM/checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP/lib/pkgconfig":  {Mode: fs.ModeDir | 0500},
+			"checksum/cTw0h3AmYe7XudSoyEMByduYXqGi-N5ZkTZ0t9K5elsu3i_jNIVF5T08KR1roBFM/identifier":                                                                               {Mode: fs.ModeDir | 0500},
+			"checksum/cTw0h3AmYe7XudSoyEMByduYXqGi-N5ZkTZ0t9K5elsu3i_jNIVF5T08KR1roBFM/identifier/HnySzeLQvSBZuTUcvfmLEX_OmH4yJWWH788NxuLuv7kVn8_uPM6Ks4rqFWM2NZJY":              {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP")},
+			"checksum/cTw0h3AmYe7XudSoyEMByduYXqGi-N5ZkTZ0t9K5elsu3i_jNIVF5T08KR1roBFM/identifier/Zx5ZG9BAwegNT3zQwCySuI2ktCXxNgxirkGLFjW4FW06PtojYVaCdtEw8yuntPLa":              {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP")},
+			"checksum/cTw0h3AmYe7XudSoyEMByduYXqGi-N5ZkTZ0t9K5elsu3i_jNIVF5T08KR1roBFM/work":                                                                                     {Mode: fs.ModeDir | 0500},
+
+			"identifier": {Mode: fs.ModeDir | 0700},
+			"identifier/-P_1iw6yVq_letMHncqcExSE0bYcDhYI5OdY6b1wKASf-Corufvj__XTBUq2Qd2a": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/cTw0h3AmYe7XudSoyEMByduYXqGi-N5ZkTZ0t9K5elsu3i_jNIVF5T08KR1roBFM")},
+			"identifier/0_rRxIqbX9LK9L_KDbuafotFz6HFkonNgO9gXhK1asM_Y1Pxn0amg756vRTo6m74": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/cTw0h3AmYe7XudSoyEMByduYXqGi-N5ZkTZ0t9K5elsu3i_jNIVF5T08KR1roBFM")},
+
+			"temp": {Mode: fs.ModeDir | 0700},
+			"work": {Mode: fs.ModeDir | 0700},
+		}, []pkg.FlatEntry{
+			{Mode: fs.ModeDir | 0700, Path: "."},
+
+			{Mode: fs.ModeDir | 0700, Path: "checksum"},
+			{Mode: fs.ModeDir | 0500, Path: "checksum/cTw0h3AmYe7XudSoyEMByduYXqGi-N5ZkTZ0t9K5elsu3i_jNIVF5T08KR1roBFM"},
+			{Mode: fs.ModeDir | 0500, Path: "checksum/cTw0h3AmYe7XudSoyEMByduYXqGi-N5ZkTZ0t9K5elsu3i_jNIVF5T08KR1roBFM/checksum"},
+			{Mode: fs.ModeDir | 0500, Path: "checksum/cTw0h3AmYe7XudSoyEMByduYXqGi-N5ZkTZ0t9K5elsu3i_jNIVF5T08KR1roBFM/checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP"},
+			{Mode: 0400, Path: "checksum/cTw0h3AmYe7XudSoyEMByduYXqGi-N5ZkTZ0t9K5elsu3i_jNIVF5T08KR1roBFM/checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP/check", Data: []byte{0, 0}},
+			{Mode: fs.ModeDir | 0500, Path: "checksum/cTw0h3AmYe7XudSoyEMByduYXqGi-N5ZkTZ0t9K5elsu3i_jNIVF5T08KR1roBFM/checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP/lib"},
+			{Mode: fs.ModeSymlink | 0777, Path: "checksum/cTw0h3AmYe7XudSoyEMByduYXqGi-N5ZkTZ0t9K5elsu3i_jNIVF5T08KR1roBFM/checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP/lib/libedac.so", Data: []byte("/proc/nonexistent/libedac.so")},
+			{Mode: fs.ModeDir | 0500, Path: "checksum/cTw0h3AmYe7XudSoyEMByduYXqGi-N5ZkTZ0t9K5elsu3i_jNIVF5T08KR1roBFM/checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP/lib/pkgconfig"},
+			{Mode: fs.ModeDir | 0500, Path: "checksum/cTw0h3AmYe7XudSoyEMByduYXqGi-N5ZkTZ0t9K5elsu3i_jNIVF5T08KR1roBFM/identifier"},
+			{Mode: fs.ModeSymlink | 0777, Path: "checksum/cTw0h3AmYe7XudSoyEMByduYXqGi-N5ZkTZ0t9K5elsu3i_jNIVF5T08KR1roBFM/identifier/HnySzeLQvSBZuTUcvfmLEX_OmH4yJWWH788NxuLuv7kVn8_uPM6Ks4rqFWM2NZJY", Data: []byte("../checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP")},
+			{Mode: fs.ModeSymlink | 0777, Path: "checksum/cTw0h3AmYe7XudSoyEMByduYXqGi-N5ZkTZ0t9K5elsu3i_jNIVF5T08KR1roBFM/identifier/Zx5ZG9BAwegNT3zQwCySuI2ktCXxNgxirkGLFjW4FW06PtojYVaCdtEw8yuntPLa", Data: []byte("../checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP")},
+			{Mode: fs.ModeDir | 0500, Path: "checksum/cTw0h3AmYe7XudSoyEMByduYXqGi-N5ZkTZ0t9K5elsu3i_jNIVF5T08KR1roBFM/work"},
+
+			{Mode: fs.ModeDir | 0700, Path: "identifier"},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/-P_1iw6yVq_letMHncqcExSE0bYcDhYI5OdY6b1wKASf-Corufvj__XTBUq2Qd2a", Data: []byte("../checksum/cTw0h3AmYe7XudSoyEMByduYXqGi-N5ZkTZ0t9K5elsu3i_jNIVF5T08KR1roBFM")},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/0_rRxIqbX9LK9L_KDbuafotFz6HFkonNgO9gXhK1asM_Y1Pxn0amg756vRTo6m74", Data: []byte("../checksum/cTw0h3AmYe7XudSoyEMByduYXqGi-N5ZkTZ0t9K5elsu3i_jNIVF5T08KR1roBFM")},
+
+			{Mode: fs.ModeDir | 0700, Path: "temp"},
+			{Mode: fs.ModeDir | 0700, Path: "work"},
+		}, pkg.MustDecode("sxbgyX-bPoezbha214n2lbQhiVfTUBkhZ0EX6zI7mmkMdrCdwuMwhMBJphLQsy94"), nil},
+
+		{"sample tar expand step unpack", fstest.MapFS{
+			".": {Mode: fs.ModeDir | 0500},
+
+			"libedac.so": {Mode: fs.ModeSymlink | 0777, Data: []byte("/proc/nonexistent/libedac.so")},
+		}, []pkg.FlatEntry{
+			{Mode: fs.ModeDir | 0500, Path: "."},
+
+			{Mode: fs.ModeSymlink | 0777, Path: "libedac.so", Data: []byte("/proc/nonexistent/libedac.so")},
+		}, pkg.MustDecode("CH3AiUrCCcVOjOYLaMKKK1Da78989JtfHeIsxMzWOQFiN4mrCLDYpoDxLWqJWCUN"), nil},
+
+		{"sample tar expand", fstest.MapFS{
+			".": {Mode: fs.ModeDir | 0700},
+
+			"checksum": {Mode: fs.ModeDir | 0700},
+			"checksum/CH3AiUrCCcVOjOYLaMKKK1Da78989JtfHeIsxMzWOQFiN4mrCLDYpoDxLWqJWCUN":            {Mode: fs.ModeDir | 0500},
+			"checksum/CH3AiUrCCcVOjOYLaMKKK1Da78989JtfHeIsxMzWOQFiN4mrCLDYpoDxLWqJWCUN/libedac.so": {Mode: fs.ModeSymlink | 0777, Data: []byte("/proc/nonexistent/libedac.so")},
+
+			"identifier": {Mode: fs.ModeDir | 0700},
+			"identifier/-P_1iw6yVq_letMHncqcExSE0bYcDhYI5OdY6b1wKASf-Corufvj__XTBUq2Qd2a": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/CH3AiUrCCcVOjOYLaMKKK1Da78989JtfHeIsxMzWOQFiN4mrCLDYpoDxLWqJWCUN")},
+			"identifier/0_rRxIqbX9LK9L_KDbuafotFz6HFkonNgO9gXhK1asM_Y1Pxn0amg756vRTo6m74": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/CH3AiUrCCcVOjOYLaMKKK1Da78989JtfHeIsxMzWOQFiN4mrCLDYpoDxLWqJWCUN")},
+
+			"temp": {Mode: fs.ModeDir | 0700},
+			"work": {Mode: fs.ModeDir | 0700},
+		}, []pkg.FlatEntry{
+			{Mode: fs.ModeDir | 0700, Path: "."},
+
+			{Mode: fs.ModeDir | 0700, Path: "checksum"},
+			{Mode: fs.ModeDir | 0500, Path: "checksum/CH3AiUrCCcVOjOYLaMKKK1Da78989JtfHeIsxMzWOQFiN4mrCLDYpoDxLWqJWCUN"},
+			{Mode: fs.ModeSymlink | 0777, Path: "checksum/CH3AiUrCCcVOjOYLaMKKK1Da78989JtfHeIsxMzWOQFiN4mrCLDYpoDxLWqJWCUN/libedac.so", Data: []byte("/proc/nonexistent/libedac.so")},
+
+			{Mode: fs.ModeDir | 0700, Path: "identifier"},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/-P_1iw6yVq_letMHncqcExSE0bYcDhYI5OdY6b1wKASf-Corufvj__XTBUq2Qd2a", Data: []byte("../checksum/CH3AiUrCCcVOjOYLaMKKK1Da78989JtfHeIsxMzWOQFiN4mrCLDYpoDxLWqJWCUN")},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/0_rRxIqbX9LK9L_KDbuafotFz6HFkonNgO9gXhK1asM_Y1Pxn0amg756vRTo6m74", Data: []byte("../checksum/CH3AiUrCCcVOjOYLaMKKK1Da78989JtfHeIsxMzWOQFiN4mrCLDYpoDxLWqJWCUN")},
+
+			{Mode: fs.ModeDir | 0700, Path: "temp"},
+			{Mode: fs.ModeDir | 0700, Path: "work"},
+		}, pkg.MustDecode("4I8wx_h7NSJTlG5lbuz-GGEXrOg0GYC3M_503LYEBhv5XGWXfNIdIY9Q3eVSYldX"), nil},
+
+		{"testtool", fstest.MapFS{
+			".": {Mode: fs.ModeDir | 0500},
+
+			"check": {Mode: 0400, Data: []byte{0}},
+		}, []pkg.FlatEntry{
+			{Mode: fs.ModeDir | 0500, Path: "."},
+
+			{Mode: 0400, Path: "check", Data: []byte{0}},
+		}, pkg.MustDecode("GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9"), nil},
+
+		{"sample exec container", fstest.MapFS{
+			".": {Mode: fs.ModeDir | 0700},
+
+			"checksum": {Mode: fs.ModeDir | 0700},
+			"checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9":       {Mode: fs.ModeDir | 0500},
+			"checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9/check": {Mode: 0400, Data: []byte{0}},
+			"checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU":       {Mode: fs.ModeDir | 0500},
+			"checksum/OLBgp1GsljhM2TJ-sbHjaiH9txEUvgdDTAzHv2P24donTt6_529l-9Ua0vFImLlb":       {Mode: 0400, Data: []byte{}},
+
+			"identifier": {Mode: fs.ModeDir | 0700},
+			"identifier/U2cbgVgEtjfRuvHfE1cQnZ3t8yoexULQyo_VLgvxAVJSsobMcNaFIsuDWtmt7kzK": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9")},
+			"identifier/_gAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/OLBgp1GsljhM2TJ-sbHjaiH9txEUvgdDTAzHv2P24donTt6_529l-9Ua0vFImLlb")},
+			"identifier/nfeISfLeFDr1k-g3hpE1oZ440kTqDdfF8TDpoLdbTPqaMMIl95oiqcvqjRkMjubA": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU")},
+
+			"temp": {Mode: fs.ModeDir | 0700},
+			"work": {Mode: fs.ModeDir | 0700},
+		}, []pkg.FlatEntry{
+			{Mode: fs.ModeDir | 0700, Path: "."},
+
+			{Mode: fs.ModeDir | 0700, Path: "checksum"},
+			{Mode: fs.ModeDir | 0500, Path: "checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9"},
+			{Mode: 0400, Path: "checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9/check", Data: []byte{0}},
+			{Mode: fs.ModeDir | 0500, Path: "checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU"},
+			{Mode: 0400, Path: "checksum/OLBgp1GsljhM2TJ-sbHjaiH9txEUvgdDTAzHv2P24donTt6_529l-9Ua0vFImLlb", Data: []byte{}},
+
+			{Mode: fs.ModeDir | 0700, Path: "identifier"},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/U2cbgVgEtjfRuvHfE1cQnZ3t8yoexULQyo_VLgvxAVJSsobMcNaFIsuDWtmt7kzK", Data: []byte("../checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9")},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/_gAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA", Data: []byte("../checksum/OLBgp1GsljhM2TJ-sbHjaiH9txEUvgdDTAzHv2P24donTt6_529l-9Ua0vFImLlb")},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/nfeISfLeFDr1k-g3hpE1oZ440kTqDdfF8TDpoLdbTPqaMMIl95oiqcvqjRkMjubA", Data: []byte("../checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU")},
+
+			{Mode: fs.ModeDir | 0700, Path: "temp"},
+			{Mode: fs.ModeDir | 0700, Path: "work"},
+		}, pkg.MustDecode("UiV6kMz7KrTsc_yphiyQzFLqjRanHxUOwrBMtkKuWo4mOO6WgPFAcoUEeSp7eVIW"), nil},
+
+		{"testtool net", fstest.MapFS{
+			".": {Mode: fs.ModeDir | 0500},
+
+			"check": {Mode: 0400, Data: []byte("net")},
+		}, []pkg.FlatEntry{
+			{Mode: fs.ModeDir | 0500, Path: "."},
+
+			{Mode: 0400, Path: "check", Data: []byte("net")},
+		}, pkg.MustDecode("a1F_i9PVQI4qMcoHgTQkORuyWLkC1GLIxOhDt2JpU1NGAxWc5VJzdlfRK-PYBh3W"), nil},
+
+		{"sample exec net container", fstest.MapFS{
+			".": {Mode: fs.ModeDir | 0700},
+
+			"checksum": {Mode: fs.ModeDir | 0700},
+			"checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU":       {Mode: fs.ModeDir | 0500},
+			"checksum/OLBgp1GsljhM2TJ-sbHjaiH9txEUvgdDTAzHv2P24donTt6_529l-9Ua0vFImLlb":       {Mode: 0400, Data: []byte{}},
+			"checksum/a1F_i9PVQI4qMcoHgTQkORuyWLkC1GLIxOhDt2JpU1NGAxWc5VJzdlfRK-PYBh3W":       {Mode: fs.ModeDir | 0500},
+			"checksum/a1F_i9PVQI4qMcoHgTQkORuyWLkC1GLIxOhDt2JpU1NGAxWc5VJzdlfRK-PYBh3W/check": {Mode: 0400, Data: []byte("net")},
+
+			"identifier": {Mode: fs.ModeDir | 0700},
+			"identifier/_gAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/OLBgp1GsljhM2TJ-sbHjaiH9txEUvgdDTAzHv2P24donTt6_529l-9Ua0vFImLlb")},
+			"identifier/QdsJhGgnk5N2xdUNGcndXQxFKifxf1V_2t9X8CQ-pDcg24x6mGJC_BiLfGbs6Qml": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/a1F_i9PVQI4qMcoHgTQkORuyWLkC1GLIxOhDt2JpU1NGAxWc5VJzdlfRK-PYBh3W")},
+			"identifier/nfeISfLeFDr1k-g3hpE1oZ440kTqDdfF8TDpoLdbTPqaMMIl95oiqcvqjRkMjubA": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU")},
+
+			"temp": {Mode: fs.ModeDir | 0700},
+			"work": {Mode: fs.ModeDir | 0700},
+		}, []pkg.FlatEntry{
+			{Mode: fs.ModeDir | 0700, Path: "."},
+
+			{Mode: fs.ModeDir | 0700, Path: "checksum"},
+			{Mode: fs.ModeDir | 0500, Path: "checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU"},
+			{Mode: 0400, Path: "checksum/OLBgp1GsljhM2TJ-sbHjaiH9txEUvgdDTAzHv2P24donTt6_529l-9Ua0vFImLlb", Data: []byte{}},
+			{Mode: fs.ModeDir | 0500, Path: "checksum/a1F_i9PVQI4qMcoHgTQkORuyWLkC1GLIxOhDt2JpU1NGAxWc5VJzdlfRK-PYBh3W"},
+			{Mode: 0400, Path: "checksum/a1F_i9PVQI4qMcoHgTQkORuyWLkC1GLIxOhDt2JpU1NGAxWc5VJzdlfRK-PYBh3W/check", Data: []byte("net")},
+
+			{Mode: fs.ModeDir | 0700, Path: "identifier"},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/QdsJhGgnk5N2xdUNGcndXQxFKifxf1V_2t9X8CQ-pDcg24x6mGJC_BiLfGbs6Qml", Data: []byte("../checksum/a1F_i9PVQI4qMcoHgTQkORuyWLkC1GLIxOhDt2JpU1NGAxWc5VJzdlfRK-PYBh3W")},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/_gAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA", Data: []byte("../checksum/OLBgp1GsljhM2TJ-sbHjaiH9txEUvgdDTAzHv2P24donTt6_529l-9Ua0vFImLlb")},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/nfeISfLeFDr1k-g3hpE1oZ440kTqDdfF8TDpoLdbTPqaMMIl95oiqcvqjRkMjubA", Data: []byte("../checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU")},
+
+			{Mode: fs.ModeDir | 0700, Path: "temp"},
+			{Mode: fs.ModeDir | 0700, Path: "work"},
+		}, pkg.MustDecode("ek4K-0d4iRSArkY2TCs3WK34DbiYeOmhE_4vsJTSu_6roY4ZF3YG6eKRooal-i1o"), nil},
+
+		{"sample exec container overlay root", fstest.MapFS{
+			".": {Mode: fs.ModeDir | 0700},
+
+			"checksum": {Mode: fs.ModeDir | 0700},
+			"checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9":       {Mode: fs.ModeDir | 0500},
+			"checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9/check": {Mode: 0400, Data: []byte{0}},
+			"checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU":       {Mode: fs.ModeDir | 0500},
+
+			"identifier": {Mode: fs.ModeDir | 0700},
+			"identifier/5ey2wpmMpj483YYa7ZZQciYLA2cx3_l167JCqWW4Pd-5DVp81dj9EsBtVTwYptF6": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9")},
+			"identifier/nfeISfLeFDr1k-g3hpE1oZ440kTqDdfF8TDpoLdbTPqaMMIl95oiqcvqjRkMjubA": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU")},
+
+			"temp": {Mode: fs.ModeDir | 0700},
+			"work": {Mode: fs.ModeDir | 0700},
+		}, []pkg.FlatEntry{
+			{Mode: fs.ModeDir | 0700, Path: "."},
+
+			{Mode: fs.ModeDir | 0700, Path: "checksum"},
+			{Mode: fs.ModeDir | 0500, Path: "checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9"},
+			{Mode: 0400, Path: "checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9/check", Data: []byte{0}},
+			{Mode: fs.ModeDir | 0500, Path: "checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU"},
+
+			{Mode: fs.ModeDir | 0700, Path: "identifier"},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/5ey2wpmMpj483YYa7ZZQciYLA2cx3_l167JCqWW4Pd-5DVp81dj9EsBtVTwYptF6", Data: []byte("../checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9")},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/nfeISfLeFDr1k-g3hpE1oZ440kTqDdfF8TDpoLdbTPqaMMIl95oiqcvqjRkMjubA", Data: []byte("../checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU")},
+
+			{Mode: fs.ModeDir | 0700, Path: "temp"},
+			{Mode: fs.ModeDir | 0700, Path: "work"},
+		}, pkg.MustDecode("VIqqpf0ip9jcyw63i6E8lCMGUcLivQBe4Bevt3WusNac-1MSy5bzB647qGUBzl-W"), nil},
+
+		{"sample exec container overlay work", fstest.MapFS{
+			".": {Mode: fs.ModeDir | 0700},
+
+			"checksum": {Mode: fs.ModeDir | 0700},
+			"checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9":       {Mode: fs.ModeDir | 0500},
+			"checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9/check": {Mode: 0400, Data: []byte{0}},
+			"checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU":       {Mode: fs.ModeDir | 0500},
+
+			"identifier": {Mode: fs.ModeDir | 0700},
+			"identifier/acaDzHZv40dZaz4cGAXayqbRMgbEOuiuiUijZL8IgDQvyeCNMFE3onBMYfny-kXA": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9")},
+			"identifier/nfeISfLeFDr1k-g3hpE1oZ440kTqDdfF8TDpoLdbTPqaMMIl95oiqcvqjRkMjubA": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU")},
+
+			"temp": {Mode: fs.ModeDir | 0700},
+			"work": {Mode: fs.ModeDir | 0700},
+		}, []pkg.FlatEntry{
+			{Mode: fs.ModeDir | 0700, Path: "."},
+
+			{Mode: fs.ModeDir | 0700, Path: "checksum"},
+			{Mode: fs.ModeDir | 0500, Path: "checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9"},
+			{Mode: 0400, Path: "checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9/check", Data: []byte{0}},
+			{Mode: fs.ModeDir | 0500, Path: "checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU"},
+
+			{Mode: fs.ModeDir | 0700, Path: "identifier"},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/acaDzHZv40dZaz4cGAXayqbRMgbEOuiuiUijZL8IgDQvyeCNMFE3onBMYfny-kXA", Data: []byte("../checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9")},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/nfeISfLeFDr1k-g3hpE1oZ440kTqDdfF8TDpoLdbTPqaMMIl95oiqcvqjRkMjubA", Data: []byte("../checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU")},
+
+			{Mode: fs.ModeDir | 0700, Path: "temp"},
+			{Mode: fs.ModeDir | 0700, Path: "work"},
+		}, pkg.MustDecode("q8x2zQg4YZbKpPqKlEBj_uxXD9vOBaZ852qOuIsl9QdO73I_UMNpuUoPLtunxUYl"), nil},
+
+		{"sample exec container multiple layers", fstest.MapFS{
+			".": {Mode: fs.ModeDir | 0700},
+
+			"checksum": {Mode: fs.ModeDir | 0700},
+			"checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9":       {Mode: fs.ModeDir | 0500},
+			"checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9/check": {Mode: 0400, Data: []byte{0}},
+			"checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU":       {Mode: fs.ModeDir | 0500},
+			"checksum/OLBgp1GsljhM2TJ-sbHjaiH9txEUvgdDTAzHv2P24donTt6_529l-9Ua0vFImLlb":       {Mode: 0400, Data: []byte{}},
+			"checksum/nY_CUdiaUM1OL4cPr5TS92FCJ3rCRV7Hm5oVTzAvMXwC03_QnTRfQ5PPs7mOU9fK":       {Mode: fs.ModeDir | 0500},
+			"checksum/nY_CUdiaUM1OL4cPr5TS92FCJ3rCRV7Hm5oVTzAvMXwC03_QnTRfQ5PPs7mOU9fK/check": {Mode: 0400, Data: []byte("layers")},
+
+			"identifier": {Mode: fs.ModeDir | 0700},
+			"identifier/_gAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/OLBgp1GsljhM2TJ-sbHjaiH9txEUvgdDTAzHv2P24donTt6_529l-9Ua0vFImLlb")},
+			"identifier/nfeISfLeFDr1k-g3hpE1oZ440kTqDdfF8TDpoLdbTPqaMMIl95oiqcvqjRkMjubA": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU")},
+			"identifier/rXLKjjYfGSyoWmuvEJooHkvGJIZaC0IAWnKGvtPZkM15gBxAgW7mIXcxRVNOXAr4": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/nY_CUdiaUM1OL4cPr5TS92FCJ3rCRV7Hm5oVTzAvMXwC03_QnTRfQ5PPs7mOU9fK")},
+			"identifier/tfjrsVuBuFgzWgwz-yPppFtylYuC1VFWnKhyBiHbWTGkyz8lt7Ee9QXWaIHPXs4x": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9")},
+
+			"temp": {Mode: fs.ModeDir | 0700},
+			"work": {Mode: fs.ModeDir | 0700},
+		}, []pkg.FlatEntry{
+			{Mode: fs.ModeDir | 0700, Path: "."},
+
+			{Mode: fs.ModeDir | 0700, Path: "checksum"},
+			{Mode: fs.ModeDir | 0500, Path: "checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9"},
+			{Mode: 0400, Path: "checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9/check", Data: []byte{0}},
+			{Mode: fs.ModeDir | 0500, Path: "checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU"},
+			{Mode: 0400, Path: "checksum/OLBgp1GsljhM2TJ-sbHjaiH9txEUvgdDTAzHv2P24donTt6_529l-9Ua0vFImLlb", Data: []byte{}},
+			{Mode: fs.ModeDir | 0500, Path: "checksum/nY_CUdiaUM1OL4cPr5TS92FCJ3rCRV7Hm5oVTzAvMXwC03_QnTRfQ5PPs7mOU9fK"},
+			{Mode: 0400, Path: "checksum/nY_CUdiaUM1OL4cPr5TS92FCJ3rCRV7Hm5oVTzAvMXwC03_QnTRfQ5PPs7mOU9fK/check", Data: []byte("layers")},
+
+			{Mode: fs.ModeDir | 0700, Path: "identifier"},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/_gAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA", Data: []byte("../checksum/OLBgp1GsljhM2TJ-sbHjaiH9txEUvgdDTAzHv2P24donTt6_529l-9Ua0vFImLlb")},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/nfeISfLeFDr1k-g3hpE1oZ440kTqDdfF8TDpoLdbTPqaMMIl95oiqcvqjRkMjubA", Data: []byte("../checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU")},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/rXLKjjYfGSyoWmuvEJooHkvGJIZaC0IAWnKGvtPZkM15gBxAgW7mIXcxRVNOXAr4", Data: []byte("../checksum/nY_CUdiaUM1OL4cPr5TS92FCJ3rCRV7Hm5oVTzAvMXwC03_QnTRfQ5PPs7mOU9fK")},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/tfjrsVuBuFgzWgwz-yPppFtylYuC1VFWnKhyBiHbWTGkyz8lt7Ee9QXWaIHPXs4x", Data: []byte("../checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9")},
+
+			{Mode: fs.ModeDir | 0700, Path: "temp"},
+			{Mode: fs.ModeDir | 0700, Path: "work"},
+		}, pkg.MustDecode("SITnQ6PTV12PAQQjIuLUxkvsXQiC9Gq_HJQlcb4BPL5YnRHnx8lsW7PRM9YMLBsx"), nil},
+
+		{"sample file short", fstest.MapFS{
+			".": {Mode: fs.ModeDir | 0700},
+
+			"checksum": {Mode: fs.ModeDir | 0700},
+			"checksum/vsAhtPNo4waRNOASwrQwcIPTqb3SBuJOXw2G4T1mNmVZM-wrQTRllmgXqcIIoRcX": {Mode: 0400, Data: []byte{0}},
+
+			"identifier": {Mode: fs.ModeDir | 0700},
+			"identifier/lIx_W4M7tVOcQ8jh08EJOfXf4brRmkEEjvUa7c17vVUzlmtUxlhhrgqmc9aZhjbn": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/vsAhtPNo4waRNOASwrQwcIPTqb3SBuJOXw2G4T1mNmVZM-wrQTRllmgXqcIIoRcX")},
+
+			"work": {Mode: fs.ModeDir | 0700},
+		}, []pkg.FlatEntry{
+			{Mode: fs.ModeDir | 0700, Path: "."},
+			{Mode: fs.ModeDir | 0700, Path: "checksum"},
+			{Mode: 0400, Path: "checksum/vsAhtPNo4waRNOASwrQwcIPTqb3SBuJOXw2G4T1mNmVZM-wrQTRllmgXqcIIoRcX", Data: []byte{0}},
+
+			{Mode: fs.ModeDir | 0700, Path: "identifier"},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/lIx_W4M7tVOcQ8jh08EJOfXf4brRmkEEjvUa7c17vVUzlmtUxlhhrgqmc9aZhjbn", Data: []byte("../checksum/vsAhtPNo4waRNOASwrQwcIPTqb3SBuJOXw2G4T1mNmVZM-wrQTRllmgXqcIIoRcX")},
+
+			{Mode: fs.ModeDir | 0700, Path: "work"},
+		}, pkg.MustDecode("hnrfmJtivNKcgtETsKnU9gP_OwPgpNY3DSUJnmxnmeOODSO-YBvEBiTgieY4AAd7"), nil},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			t.Run("roundtrip", func(t *testing.T) {
+				t.Parallel()
+
+				var buf bytes.Buffer
+				if _, err := pkg.Flatten(
+					tc.fsys,
+					".",
+					&buf,
+				); !reflect.DeepEqual(err, tc.err) {
+					t.Fatalf("Flatten: error = %v, want %v", err, tc.err)
+				} else if tc.err != nil {
+					return
+				}
+
+				s := pkg.NewDirScanner(bytes.NewReader(buf.Bytes()), true)
+				var got []pkg.FlatEntry
+				for s.Scan() {
+					got = append(got, *s.Entry())
+				}
+				if err := s.Err(); err != nil {
+					t.Fatalf("Err: error = %v", err)
+				}
+
+				if !reflect.DeepEqual(got, tc.entries) {
+					t.Fatalf("Scan: %#v, want %#v", got, tc.entries)
+				}
+			})
+
+			if tc.err != nil {
+				return
+			}
+
+			t.Run("hash", func(t *testing.T) {
+				t.Parallel()
+
+				if got, err := pkg.HashFS(tc.fsys, "."); err != nil {
+					t.Fatalf("HashFS: error = %v", err)
+				} else if got != tc.sum {
+					t.Fatalf("HashFS: %v", &pkg.ChecksumMismatchError{
+						Got:  got,
+						Want: tc.sum,
+					})
+				}
+			})
+		})
+	}
+}

internal/pkg/exec.go

@@ -0,0 +1,378 @@
+package pkg
+
+import (
+	"bufio"
+	"bytes"
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"path"
+	"slices"
+	"strconv"
+	"syscall"
+	"time"
+
+	"hakurei.app/container"
+	"hakurei.app/container/check"
+	"hakurei.app/container/fhs"
+	"hakurei.app/container/std"
+	"hakurei.app/message"
+)
+
+// AbsWork is the container pathname [CureContext.GetWorkDir] is mounted on.
+var AbsWork = fhs.AbsRoot.Append("work/")
+
+// ExecPath is a slice of [Artifact] and the [check.Absolute] pathname to make
+// it available at under in the container.
+type ExecPath struct {
+	// Pathname in the container mount namespace.
+	P *check.Absolute
+	// Artifacts to mount on the pathname, must contain at least one [Artifact].
+	// If there are multiple entries or W is true, P is set up as an overlay
+	// mount, and entries of A must not implement [File].
+	A []Artifact
+	// Whether to make the mount point writable via the temp directory.
+	W bool
+}
+
+// Path returns a populated [ExecPath].
+func Path(pathname *check.Absolute, writable bool, a ...Artifact) ExecPath {
+	return ExecPath{pathname, a, writable}
+}
+
+// MustPath is like [Path], but takes a string pathname via [check.MustAbs].
+func MustPath(pathname string, writable bool, a ...Artifact) ExecPath {
+	return ExecPath{check.MustAbs(pathname), a, writable}
+}
+
+const (
+	// ExecTimeoutDefault replaces out of range [NewExec] timeout values.
+	ExecTimeoutDefault = 15 * time.Minute
+	// ExecTimeoutMax is the arbitrary upper bound of [NewExec] timeout.
+	ExecTimeoutMax = 48 * time.Hour
+)
+
+// An execArtifact is an [Artifact] that produces output by running a program
+// part of another [Artifact] in a [container] to produce its output.
+//
+// Methods of execArtifact does not modify any struct field or underlying arrays
+// referred to by slices.
+type execArtifact struct {
+	// Caller-supplied user-facing reporting name, guaranteed to be nonzero
+	// during initialisation.
+	name string
+	// Caller-supplied inner mount points.
+	paths []ExecPath
+
+	// Passed through to [container.Params].
+	dir *check.Absolute
+	// Passed through to [container.Params].
+	env []string
+	// Passed through to [container.Params].
+	path *check.Absolute
+	// Passed through to [container.Params].
+	args []string
+
+	// Duration the initial process is allowed to run. The zero value is
+	// equivalent to execTimeoutDefault. This value is never encoded in Params
+	// because it cannot affect outcome.
+	timeout time.Duration
+}
+
+var _ fmt.Stringer = new(execArtifact)
+
+// execNetArtifact is like execArtifact but implements [KnownChecksum] and has
+// its resulting container keep the host net namespace.
+type execNetArtifact struct {
+	checksum Checksum
+
+	execArtifact
+}
+
+var _ KnownChecksum = new(execNetArtifact)
+
+// Checksum returns the caller-supplied checksum.
+func (a *execNetArtifact) Checksum() Checksum { return a.checksum }
+
+// Kind returns the hardcoded [Kind] constant.
+func (a *execNetArtifact) Kind() Kind { return KindExecNet }
+
+// Params is [Checksum] concatenated with [KindExec] params.
+func (a *execNetArtifact) Params() []byte {
+	return slices.Concat(a.checksum[:], a.execArtifact.Params())
+}
+
+// Cure cures the [Artifact] in the container described by the caller. The
+// container retains host networking.
+func (a *execNetArtifact) Cure(f *FContext) error {
+	return a.cure(f, true)
+}
+
+// NewExec returns a new [Artifact] that executes the program path in a
+// container with specified paths bind mounted read-only in order. A private
+// instance of /proc and /dev is made available to the container.
+//
+// The working and temporary directories are both created and mounted writable
+// on [AbsWork] and [fhs.AbsTmp] respectively. If one or more paths target
+// [AbsWork], the final entry is set up as a writable overlay mount on /work for
+// which the upperdir is the host side work directory. In this configuration,
+// the W field is ignored, and the program must avoid causing whiteout files to
+// be created. Cure fails if upperdir ends up with entries other than directory,
+// regular or symlink.
+//
+// If checksum is non-nil, the resulting [Artifact] implements [KnownChecksum]
+// and its container runs in the host net namespace.
+//
+// The container is allowed to run for the specified duration before the initial
+// process and all processes originating from it is terminated. A zero or
+// negative timeout value is equivalent tp [ExecTimeoutDefault], a timeout value
+// greater than [ExecTimeoutMax] is equivalent to [ExecTimeoutMax].
+//
+// The user-facing name is not accessible from the container and does not
+// affect curing outcome. Because of this, it is omitted from parameter data
+// for computing identifier.
+func NewExec(
+	name string,
+	checksum *Checksum,
+	timeout time.Duration,
+
+	dir *check.Absolute,
+	env []string,
+	pathname *check.Absolute,
+	args []string,
+
+	paths ...ExecPath,
+) Artifact {
+	if name == "" {
+		name = "exec-" + path.Base(pathname.String())
+	}
+	if timeout <= 0 {
+		timeout = ExecTimeoutDefault
+	}
+	if timeout > ExecTimeoutMax {
+		timeout = ExecTimeoutMax
+	}
+	a := execArtifact{name, paths, dir, env, pathname, args, timeout}
+	if checksum == nil {
+		return &a
+	}
+	return &execNetArtifact{*checksum, a}
+}
+
+// Kind returns the hardcoded [Kind] constant.
+func (a *execArtifact) Kind() Kind { return KindExec }
+
+// Params returns paths, executable pathname and args concatenated together.
+func (a *execArtifact) Params() []byte {
+	var buf bytes.Buffer
+	for _, p := range a.paths {
+		if p.W {
+			buf.WriteByte(1)
+		} else {
+			buf.WriteByte(0)
+		}
+		if p.P != nil {
+			buf.WriteString(p.P.String())
+		} else {
+			buf.WriteString("invalid P\x00")
+		}
+		buf.WriteByte(0)
+		for _, d := range p.A {
+			id := Ident(d)
+			buf.Write(id[:])
+		}
+		buf.WriteByte(0)
+	}
+	buf.WriteByte(0)
+	buf.WriteString(a.dir.String())
+	buf.WriteByte(0)
+	for _, e := range a.env {
+		buf.WriteString(e)
+	}
+	buf.WriteByte(0)
+	buf.WriteString(a.path.String())
+	buf.WriteByte(0)
+	for _, arg := range a.args {
+		buf.WriteString(arg)
+	}
+	return buf.Bytes()
+}
+
+// Dependencies returns a slice of all artifacts collected from caller-supplied
+// [ExecPath].
+func (a *execArtifact) Dependencies() []Artifact {
+	artifacts := make([][]Artifact, 0, len(a.paths))
+	for _, p := range a.paths {
+		artifacts = append(artifacts, p.A)
+	}
+	return slices.Concat(artifacts...)
+}
+
+// String returns the caller-supplied reporting name.
+func (a *execArtifact) String() string { return a.name }
+
+// Cure cures the [Artifact] in the container described by the caller.
+func (a *execArtifact) Cure(f *FContext) (err error) {
+	return a.cure(f, false)
+}
+
+const (
+	// execWaitDelay is passed through to [container.Params].
+	execWaitDelay = time.Nanosecond
+)
+
+// scanVerbose prefixes program output for a verbose [message.Msg].
+func scanVerbose(
+	msg message.Msg,
+	done chan<- struct{},
+	prefix string,
+	r io.Reader,
+) {
+	defer close(done)
+	s := bufio.NewScanner(r)
+	for s.Scan() {
+		msg.Verbose(prefix, s.Text())
+	}
+	if err := s.Err(); err != nil && !errors.Is(err, os.ErrClosed) {
+		msg.Verbose("*"+prefix, err)
+	}
+}
+
+// cure is like Cure but allows optional host net namespace. This is used for
+// the [KnownChecksum] variant where networking is allowed.
+func (a *execArtifact) cure(f *FContext, hostNet bool) (err error) {
+	overlayWorkIndex := -1
+	for i, p := range a.paths {
+		if p.P == nil || len(p.A) == 0 {
+			return os.ErrInvalid
+		}
+		if p.P.Is(AbsWork) {
+			overlayWorkIndex = i
+		}
+	}
+
+	var artifactCount int
+	for _, p := range a.paths {
+		artifactCount += len(p.A)
+	}
+
+	ctx, cancel := context.WithTimeout(f.Unwrap(), a.timeout)
+	defer cancel()
+
+	z := container.New(ctx, f.GetMessage())
+	z.WaitDelay = execWaitDelay
+	z.SeccompPresets |= std.PresetStrict
+	z.ParentPerm = 0700
+	z.HostNet = hostNet
+	z.Hostname = "cure"
+	if z.HostNet {
+		z.Hostname = "cure-net"
+	}
+	z.Uid, z.Gid = (1<<10)-1, (1<<10)-1
+	if msg := f.GetMessage(); msg.IsVerbose() {
+		var stdout, stderr io.ReadCloser
+		if stdout, err = z.StdoutPipe(); err != nil {
+			return
+		}
+		if stderr, err = z.StderrPipe(); err != nil {
+			_ = stdout.Close()
+			return
+		}
+		defer func() {
+			if err != nil && !errors.As(err, new(*exec.ExitError)) {
+				_ = stdout.Close()
+				_ = stderr.Close()
+			}
+		}()
+
+		stdoutDone, stderrDone := make(chan struct{}), make(chan struct{})
+		go scanVerbose(msg, stdoutDone, "("+a.name+":1)", stdout)
+		go scanVerbose(msg, stderrDone, "("+a.name+":2)", stderr)
+		defer func() { <-stdoutDone; <-stderrDone }()
+	}
+
+	z.Dir, z.Env, z.Path, z.Args = a.dir, a.env, a.path, a.args
+	z.Grow(len(a.paths) + 4)
+
+	temp, work := f.GetTempDir(), f.GetWorkDir()
+	for i, b := range a.paths {
+		layers := make([]*check.Absolute, len(b.A))
+		for j, d := range b.A {
+			layers[j] = f.Pathname(d)
+		}
+
+		if i == overlayWorkIndex {
+			if err = os.MkdirAll(work.String(), 0700); err != nil {
+				return
+			}
+			tempWork := temp.Append(".work")
+			if err = os.MkdirAll(tempWork.String(), 0700); err != nil {
+				return
+			}
+			z.Overlay(
+				AbsWork,
+				work,
+				tempWork,
+				layers...,
+			)
+			continue
+		}
+
+		if a.paths[i].W {
+			tempUpper, tempWork := temp.Append(
+				".upper", strconv.Itoa(i),
+			), temp.Append(
+				".work", strconv.Itoa(i),
+			)
+			if err = os.MkdirAll(tempUpper.String(), 0700); err != nil {
+				return
+			}
+			if err = os.MkdirAll(tempWork.String(), 0700); err != nil {
+				return
+			}
+			z.Overlay(b.P, tempUpper, tempWork, layers...)
+		} else if len(layers) == 1 {
+			z.Bind(layers[0], b.P, 0)
+		} else {
+			z.OverlayReadonly(b.P, layers...)
+		}
+	}
+	if overlayWorkIndex < 0 {
+		z.Bind(
+			work,
+			AbsWork,
+			std.BindWritable|std.BindEnsure,
+		)
+	}
+	z.Bind(
+		f.GetTempDir(),
+		fhs.AbsTmp,
+		std.BindWritable|std.BindEnsure,
+	)
+	z.Proc(fhs.AbsProc).Dev(fhs.AbsDev, true)
+
+	if err = z.Start(); err != nil {
+		return
+	}
+	if err = z.Serve(); err != nil {
+		return
+	}
+	if err = z.Wait(); err != nil {
+		return
+	}
+
+	// do not allow empty directories to succeed
+	for {
+		err = syscall.Rmdir(work.String())
+		if err != syscall.EINTR {
+			break
+		}
+	}
+	if err != nil && errors.Is(err, syscall.ENOTEMPTY) {
+		err = nil
+	}
+	return
+}

internal/pkg/exec_test.go

@@ -0,0 +1,297 @@
+package pkg_test
+
+//go:generate env CGO_ENABLED=0 go build -tags testtool -o testdata/testtool ./testdata
+
+import (
+	_ "embed"
+	"encoding/gob"
+	"errors"
+	"net"
+	"os"
+	"os/exec"
+	"slices"
+	"testing"
+
+	"hakurei.app/container/check"
+	"hakurei.app/container/stub"
+	"hakurei.app/hst"
+	"hakurei.app/internal/pkg"
+)
+
+// testtoolBin is the container test tool binary made available to the
+// execArtifact for testing its curing environment.
+//
+//go:embed testdata/testtool
+var testtoolBin []byte
+
+func TestExec(t *testing.T) {
+	t.Parallel()
+
+	wantChecksumOffline := pkg.MustDecode(
+		"GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9",
+	)
+
+	checkWithCache(t, []cacheTestCase{
+		{"offline", nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
+			c.SetStrict(true)
+			testtool, testtoolDestroy := newTesttool()
+
+			cureMany(t, c, []cureStep{
+				{"container", pkg.NewExec(
+					"", nil, 0,
+					pkg.AbsWork,
+					[]string{"HAKUREI_TEST=1"},
+					check.MustAbs("/opt/bin/testtool"),
+					[]string{"testtool"},
+
+					pkg.MustPath("/file", false, newStubFile(
+						pkg.KindHTTPGet,
+						pkg.ID{0xfe, 0},
+						nil,
+						nil, nil,
+					)),
+					pkg.MustPath("/.hakurei", false, stubArtifact{
+						kind:   pkg.KindTar,
+						params: []byte("empty directory"),
+						cure: func(t *pkg.TContext) error {
+							return os.MkdirAll(t.GetWorkDir().String(), 0700)
+						},
+					}),
+					pkg.MustPath("/opt", false, testtool),
+				), ignorePathname, wantChecksumOffline, nil},
+
+				{"error passthrough", pkg.NewExec(
+					"", nil, 0,
+					pkg.AbsWork,
+					[]string{"HAKUREI_TEST=1"},
+					check.MustAbs("/opt/bin/testtool"),
+					[]string{"testtool"},
+
+					pkg.MustPath("/proc/nonexistent", false, stubArtifact{
+						kind:   pkg.KindTar,
+						params: []byte("doomed artifact"),
+						cure: func(t *pkg.TContext) error {
+							return stub.UniqueError(0xcafe)
+						},
+					}),
+				), nil, pkg.Checksum{}, errors.Join(stub.UniqueError(0xcafe))},
+
+				{"invalid paths", pkg.NewExec(
+					"", nil, 0,
+					pkg.AbsWork,
+					[]string{"HAKUREI_TEST=1"},
+					check.MustAbs("/opt/bin/testtool"),
+					[]string{"testtool"},
+
+					pkg.ExecPath{},
+				), nil, pkg.Checksum{}, os.ErrInvalid},
+			})
+
+			// check init failure passthrough
+			var exitError *exec.ExitError
+			if _, _, err := c.Cure(pkg.NewExec(
+				"", nil, 0,
+				pkg.AbsWork,
+				nil,
+				check.MustAbs("/opt/bin/testtool"),
+				[]string{"testtool"},
+			)); !errors.As(err, &exitError) ||
+				exitError.ExitCode() != hst.ExitFailure {
+				t.Fatalf("Cure: error = %v, want init exit status 1", err)
+			}
+
+			testtoolDestroy(t, base, c)
+		}, pkg.MustDecode("UiV6kMz7KrTsc_yphiyQzFLqjRanHxUOwrBMtkKuWo4mOO6WgPFAcoUEeSp7eVIW")},
+
+		{"net", nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
+			c.SetStrict(true)
+			testtool, testtoolDestroy := newTesttool()
+
+			wantChecksum := pkg.MustDecode(
+				"a1F_i9PVQI4qMcoHgTQkORuyWLkC1GLIxOhDt2JpU1NGAxWc5VJzdlfRK-PYBh3W",
+			)
+			cureMany(t, c, []cureStep{
+				{"container", pkg.NewExec(
+					"", &wantChecksum, 0,
+					pkg.AbsWork,
+					[]string{"HAKUREI_TEST=1"},
+					check.MustAbs("/opt/bin/testtool"),
+					[]string{"testtool", "net"},
+
+					pkg.MustPath("/file", false, newStubFile(
+						pkg.KindHTTPGet,
+						pkg.ID{0xfe, 0},
+						nil,
+						nil, nil,
+					)),
+					pkg.MustPath("/.hakurei", false, stubArtifact{
+						kind:   pkg.KindTar,
+						params: []byte("empty directory"),
+						cure: func(t *pkg.TContext) error {
+							return os.MkdirAll(t.GetWorkDir().String(), 0700)
+						},
+					}),
+					pkg.MustPath("/opt", false, testtool),
+				), ignorePathname, wantChecksum, nil},
+			})
+
+			testtoolDestroy(t, base, c)
+		}, pkg.MustDecode("ek4K-0d4iRSArkY2TCs3WK34DbiYeOmhE_4vsJTSu_6roY4ZF3YG6eKRooal-i1o")},
+
+		{"overlay root", nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
+			c.SetStrict(true)
+			testtool, testtoolDestroy := newTesttool()
+
+			cureMany(t, c, []cureStep{
+				{"container", pkg.NewExec(
+					"", nil, 0,
+					pkg.AbsWork,
+					[]string{"HAKUREI_TEST=1", "HAKUREI_ROOT=1"},
+					check.MustAbs("/opt/bin/testtool"),
+					[]string{"testtool"},
+
+					pkg.MustPath("/", true, stubArtifact{
+						kind:   pkg.KindTar,
+						params: []byte("empty directory"),
+						cure: func(t *pkg.TContext) error {
+							return os.MkdirAll(t.GetWorkDir().String(), 0700)
+						},
+					}),
+					pkg.MustPath("/opt", false, testtool),
+				), ignorePathname, wantChecksumOffline, nil},
+			})
+
+			testtoolDestroy(t, base, c)
+		}, pkg.MustDecode("VIqqpf0ip9jcyw63i6E8lCMGUcLivQBe4Bevt3WusNac-1MSy5bzB647qGUBzl-W")},
+
+		{"overlay work", nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
+			c.SetStrict(true)
+			testtool, testtoolDestroy := newTesttool()
+
+			cureMany(t, c, []cureStep{
+				{"container", pkg.NewExec(
+					"", nil, 0,
+					pkg.AbsWork,
+					[]string{"HAKUREI_TEST=1", "HAKUREI_ROOT=1"},
+					check.MustAbs("/work/bin/testtool"),
+					[]string{"testtool"},
+
+					pkg.MustPath("/", true, stubArtifact{
+						kind:   pkg.KindTar,
+						params: []byte("empty directory"),
+						cure: func(t *pkg.TContext) error {
+							return os.MkdirAll(t.GetWorkDir().String(), 0700)
+						},
+					}), pkg.MustPath("/work/", false, stubArtifact{
+						kind:   pkg.KindTar,
+						params: []byte("empty directory"),
+						cure: func(t *pkg.TContext) error {
+							return os.MkdirAll(t.GetWorkDir().String(), 0700)
+						},
+					}), pkg.Path(pkg.AbsWork, false /* ignored */, testtool),
+				), ignorePathname, wantChecksumOffline, nil},
+			})
+
+			testtoolDestroy(t, base, c)
+		}, pkg.MustDecode("q8x2zQg4YZbKpPqKlEBj_uxXD9vOBaZ852qOuIsl9QdO73I_UMNpuUoPLtunxUYl")},
+
+		{"multiple layers", nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
+			c.SetStrict(true)
+			testtool, testtoolDestroy := newTesttool()
+
+			cureMany(t, c, []cureStep{
+				{"container", pkg.NewExec(
+					"", nil, 0,
+					pkg.AbsWork,
+					[]string{"HAKUREI_TEST=1", "HAKUREI_ROOT=1"},
+					check.MustAbs("/opt/bin/testtool"),
+					[]string{"testtool", "layers"},
+
+					pkg.MustPath("/", true, stubArtifact{
+						kind:   pkg.KindTar,
+						params: []byte("empty directory"),
+						cure: func(t *pkg.TContext) error {
+							return os.MkdirAll(t.GetWorkDir().String(), 0700)
+						},
+					}, stubArtifactF{
+						kind:   pkg.KindExec,
+						params: []byte("test sample with dependencies"),
+
+						deps: slices.Repeat([]pkg.Artifact{newStubFile(
+							pkg.KindHTTPGet,
+							pkg.ID{0xfe, 0},
+							nil,
+							nil, nil,
+						), stubArtifact{
+							kind:   pkg.KindTar,
+							params: []byte("empty directory"),
+
+							// this is queued and might run instead of the other
+							// one so do not leave it as nil
+							cure: func(t *pkg.TContext) error {
+								return os.MkdirAll(t.GetWorkDir().String(), 0700)
+							},
+						}}, 1<<5 /* concurrent cache hits */), cure: func(f *pkg.FContext) error {
+							work := f.GetWorkDir()
+							if err := os.MkdirAll(work.String(), 0700); err != nil {
+								return err
+							}
+							return os.WriteFile(work.Append("check").String(), []byte("layers"), 0400)
+						},
+					}),
+					pkg.MustPath("/opt", false, testtool),
+				), ignorePathname, wantChecksumOffline, nil},
+			})
+
+			testtoolDestroy(t, base, c)
+		}, pkg.MustDecode("SITnQ6PTV12PAQQjIuLUxkvsXQiC9Gq_HJQlcb4BPL5YnRHnx8lsW7PRM9YMLBsx")},
+	})
+}
+
+// newTesttool returns an [Artifact] that cures into testtoolBin. The returned
+// function must be called at the end of the test but not deferred.
+func newTesttool() (
+	testtool pkg.Artifact,
+	testtoolDestroy func(t *testing.T, base *check.Absolute, c *pkg.Cache),
+) {
+	// testtoolBin is built during go:generate and is not deterministic
+	testtool = overrideIdent{pkg.ID{0xfe, 0xff}, stubArtifact{
+		kind: pkg.KindTar,
+		cure: func(t *pkg.TContext) error {
+			work := t.GetWorkDir()
+			if err := os.MkdirAll(
+				work.Append("bin").String(),
+				0700,
+			); err != nil {
+				return err
+			}
+
+			if ift, err := net.Interfaces(); err != nil {
+				return err
+			} else {
+				var f *os.File
+				if f, err = os.Create(t.GetWorkDir().Append(
+					"ift",
+				).String()); err != nil {
+					return err
+				} else {
+					err = gob.NewEncoder(f).Encode(ift)
+					closeErr := f.Close()
+					if err != nil {
+						return err
+					}
+					if closeErr != nil {
+						return closeErr
+					}
+				}
+			}
+
+			return os.WriteFile(t.GetWorkDir().Append(
+				"bin",
+				"testtool",
+			).String(), testtoolBin, 0500)
+		},
+	}}
+	testtoolDestroy = newDestroyArtifactFunc(testtool)
+	return
+}

internal/pkg/file.go

@@ -0,0 +1,54 @@
+package pkg
+
+import (
+	"context"
+	"crypto/sha512"
+	"fmt"
+)
+
+// A fileArtifact is an [Artifact] that cures into data known ahead of time.
+type fileArtifact []byte
+
+var _ KnownChecksum = fileArtifact{}
+
+// fileArtifactNamed embeds fileArtifact alongside a caller-supplied name.
+type fileArtifactNamed struct {
+	fileArtifact
+	// Caller-supplied user-facing reporting name.
+	name string
+}
+
+var _ fmt.Stringer = fileArtifactNamed{}
+
+// String returns the caller-supplied reporting name.
+func (a fileArtifactNamed) String() string { return a.name }
+
+// NewFile returns a [File] that cures into a caller-supplied byte slice.
+//
+// Caller must not modify data after NewFile returns.
+func NewFile(name string, data []byte) File {
+	f := fileArtifact(data)
+	if name != "" {
+		return fileArtifactNamed{f, name}
+	}
+	return f
+}
+
+// Kind returns the hardcoded [Kind] constant.
+func (a fileArtifact) Kind() Kind { return KindFile }
+
+// Params returns the result of Data.
+func (a fileArtifact) Params() []byte { return a }
+
+// Dependencies returns a nil slice.
+func (a fileArtifact) Dependencies() []Artifact { return nil }
+
+// Checksum computes and returns the checksum of caller-supplied data.
+func (a fileArtifact) Checksum() Checksum {
+	h := sha512.New384()
+	h.Write(a)
+	return Checksum(h.Sum(nil))
+}
+
+// Cure returns the caller-supplied data.
+func (a fileArtifact) Cure(context.Context) ([]byte, error) { return a, nil }

internal/pkg/file_test.go

@@ -0,0 +1,29 @@
+package pkg_test
+
+import (
+	"testing"
+
+	"hakurei.app/container/check"
+	"hakurei.app/internal/pkg"
+)
+
+func TestFile(t *testing.T) {
+	t.Parallel()
+
+	checkWithCache(t, []cacheTestCase{
+		{"file", nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
+			c.SetStrict(true)
+
+			cureMany(t, c, []cureStep{
+				{"short", pkg.NewFile("null", []byte{0}), base.Append(
+					"identifier",
+					"lIx_W4M7tVOcQ8jh08EJOfXf4brRmkEEjvUa7c17vVUzlmtUxlhhrgqmc9aZhjbn",
+				), pkg.MustDecode(
+					"vsAhtPNo4waRNOASwrQwcIPTqb3SBuJOXw2G4T1mNmVZM-wrQTRllmgXqcIIoRcX",
+				), nil},
+			})
+		}, pkg.MustDecode(
+			"hnrfmJtivNKcgtETsKnU9gP_OwPgpNY3DSUJnmxnmeOODSO-YBvEBiTgieY4AAd7",
+		)},
+	})
+}

internal/pkg/net.go

@@ -0,0 +1,124 @@
+package pkg
+
+import (
+	"context"
+	"crypto/sha512"
+	"fmt"
+	"io"
+	"net/http"
+	"path"
+	"sync"
+)
+
+// An httpArtifact is an [Artifact] backed by a [http] url string. The method is
+// hardcoded as [http.MethodGet]. Request body is not allowed because it cannot
+// be deterministically represented by Params.
+type httpArtifact struct {
+	// Caller-supplied url string.
+	url string
+
+	// Caller-supplied checksum of the response body. This is validated during
+	// curing and the first call to Data.
+	checksum Checksum
+
+	// doFunc is the Do method of [http.Client] supplied by the caller.
+	doFunc func(req *http.Request) (*http.Response, error)
+
+	// Response body read to EOF.
+	data []byte
+
+	// Synchronises access to data.
+	mu sync.Mutex
+}
+
+var _ KnownChecksum = new(httpArtifact)
+var _ fmt.Stringer = new(httpArtifact)
+
+// NewHTTPGet returns a new [File] backed by the supplied client. A GET request
+// is set up for url. If c is nil, [http.DefaultClient] is used instead.
+func NewHTTPGet(
+	c *http.Client,
+	url string,
+	checksum Checksum,
+) File {
+	if c == nil {
+		c = http.DefaultClient
+	}
+	return &httpArtifact{url: url, checksum: checksum, doFunc: c.Do}
+}
+
+// Kind returns the hardcoded [Kind] constant.
+func (a *httpArtifact) Kind() Kind { return KindHTTPGet }
+
+// Params returns the backing url string. Context is not represented as it does
+// not affect [Cache.Cure] outcome.
+func (a *httpArtifact) Params() []byte { return []byte(a.url) }
+
+// Dependencies returns a nil slice.
+func (a *httpArtifact) Dependencies() []Artifact { return nil }
+
+// Checksum returns the caller-supplied checksum.
+func (a *httpArtifact) Checksum() Checksum { return a.checksum }
+
+// String returns [path.Base] over the backing url.
+func (a *httpArtifact) String() string { return path.Base(a.url) }
+
+// ResponseStatusError is returned for a response returned by an [http.Client]
+// with a status code other than [http.StatusOK].
+type ResponseStatusError int
+
+func (e ResponseStatusError) Error() string {
+	return "the requested URL returned non-OK status: " + http.StatusText(int(e))
+}
+
+// do sends the caller-supplied request on the caller-supplied [http.Client]
+// and reads its response body to EOF and returns the resulting bytes.
+func (a *httpArtifact) do(ctx context.Context) (data []byte, err error) {
+	var req *http.Request
+	req, err = http.NewRequestWithContext(ctx, http.MethodGet, a.url, nil)
+	if err != nil {
+		return
+	}
+
+	var resp *http.Response
+	if resp, err = a.doFunc(req); err != nil {
+		return
+	}
+
+	if resp.StatusCode != http.StatusOK {
+		_ = resp.Body.Close()
+		return nil, ResponseStatusError(resp.StatusCode)
+	}
+
+	if data, err = io.ReadAll(resp.Body); err != nil {
+		_ = resp.Body.Close()
+		return
+	}
+
+	err = resp.Body.Close()
+	return
+}
+
+// Cure completes the http request and returns the resulting response body read
+// to EOF. Data does not interact with the filesystem.
+func (a *httpArtifact) Cure(ctx context.Context) (data []byte, err error) {
+	a.mu.Lock()
+	defer a.mu.Unlock()
+
+	if a.data != nil {
+		// validated by cache or a previous call to Data
+		return a.data, nil
+	}
+
+	if data, err = a.do(ctx); err != nil {
+		return
+	}
+
+	h := sha512.New384()
+	h.Write(data)
+	if got := (Checksum)(h.Sum(nil)); got != a.checksum {
+		return nil, &ChecksumMismatchError{got, a.checksum}
+	}
+	a.data = data
+	return
+}

internal/pkg/net_test.go

@@ -0,0 +1,133 @@
+package pkg_test
+
+import (
+	"crypto/sha512"
+	"net/http"
+	"reflect"
+	"testing"
+	"testing/fstest"
+
+	"hakurei.app/container/check"
+	"hakurei.app/internal/pkg"
+)
+
+func TestHTTPGet(t *testing.T) {
+	t.Parallel()
+
+	const testdata = "\x7f\xe1\x69\xa2\xdd\x63\x96\x26\x83\x79\x61\x8b\xf0\x3f\xd5\x16\x9a\x39\x3a\xdb\xcf\xb1\xbc\x8d\x33\xff\x75\xee\x62\x56\xa9\xf0\x27\xac\x13\x94\x69"
+
+	testdataChecksum := func() pkg.Checksum {
+		h := sha512.New384()
+		h.Write([]byte(testdata))
+		return (pkg.Checksum)(h.Sum(nil))
+	}()
+
+	var transport http.Transport
+	client := http.Client{Transport: &transport}
+	transport.RegisterProtocol("file", http.NewFileTransportFS(fstest.MapFS{
+		"testdata": {Data: []byte(testdata), Mode: 0400},
+	}))
+
+	checkWithCache(t, []cacheTestCase{
+		{"direct", nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
+			f := pkg.NewHTTPGet(
+				&client,
+				"file:///testdata",
+				testdataChecksum,
+			)
+			wantIdent := pkg.KindHTTPGet.Ident([]byte("file:///testdata"))
+			if got, err := f.Cure(t.Context()); err != nil {
+				t.Fatalf("Cure: error = %v", err)
+			} else if string(got) != testdata {
+				t.Fatalf("Cure: %x, want %x", got, testdata)
+			} else if gotIdent := pkg.Ident(f); gotIdent != wantIdent {
+				t.Fatalf("Ident: %s, want %s", pkg.Encode(gotIdent), pkg.Encode(wantIdent))
+			}
+
+			// check direct validation
+			f = pkg.NewHTTPGet(
+				&client,
+				"file:///testdata",
+				pkg.Checksum{},
+			)
+			wantErrMismatch := &pkg.ChecksumMismatchError{
+				Got: testdataChecksum,
+			}
+			if _, err := f.Cure(t.Context()); !reflect.DeepEqual(err, wantErrMismatch) {
+				t.Fatalf("Cure: error = %#v, want %#v", err, wantErrMismatch)
+			} else if gotIdent := pkg.Ident(f); gotIdent != wantIdent {
+				t.Fatalf("Ident: %s, want %s", pkg.Encode(gotIdent), pkg.Encode(wantIdent))
+			}
+
+			// check direct response error
+			f = pkg.NewHTTPGet(
+				&client,
+				"file:///nonexistent",
+				pkg.Checksum{},
+			)
+			wantIdentNonexistent := pkg.KindHTTPGet.Ident([]byte("file:///nonexistent"))
+			wantErrNotFound := pkg.ResponseStatusError(http.StatusNotFound)
+			if _, err := f.Cure(t.Context()); !reflect.DeepEqual(err, wantErrNotFound) {
+				t.Fatalf("Cure: error = %#v, want %#v", err, wantErrNotFound)
+			} else if gotIdent := pkg.Ident(f); gotIdent != wantIdentNonexistent {
+				t.Fatalf("Ident: %s, want %s", pkg.Encode(gotIdent), pkg.Encode(wantIdentNonexistent))
+			}
+		}, pkg.MustDecode("E4vEZKhCcL2gPZ2Tt59FS3lDng-d_2SKa2i5G_RbDfwGn6EemptFaGLPUDiOa94C")},
+
+		{"cure", nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
+			f := pkg.NewHTTPGet(
+				&client,
+				"file:///testdata",
+				testdataChecksum,
+			)
+			wantIdent := pkg.KindHTTPGet.Ident([]byte("file:///testdata"))
+			wantPathname := base.Append(
+				"identifier",
+				pkg.Encode(wantIdent),
+			)
+			if pathname, checksum, err := c.Cure(f); err != nil {
+				t.Fatalf("Cure: error = %v", err)
+			} else if !pathname.Is(wantPathname) {
+				t.Fatalf("Cure: %q, want %q", pathname, wantPathname)
+			} else if checksum != testdataChecksum {
+				t.Fatalf("Cure: %x, want %x", checksum, testdataChecksum)
+			}
+
+			if got, err := f.Cure(t.Context()); err != nil {
+				t.Fatalf("Cure: error = %v", err)
+			} else if string(got) != testdata {
+				t.Fatalf("Cure: %x, want %x", got, testdata)
+			} else if gotIdent := pkg.Ident(f); gotIdent != wantIdent {
+				t.Fatalf("Ident: %s, want %s", pkg.Encode(gotIdent), pkg.Encode(wantIdent))
+			}
+
+			// check load from cache
+			f = pkg.NewHTTPGet(
+				&client,
+				"file:///testdata",
+				testdataChecksum,
+			)
+			if got, err := f.Cure(t.Context()); err != nil {
+				t.Fatalf("Cure: error = %v", err)
+			} else if string(got) != testdata {
+				t.Fatalf("Cure: %x, want %x", got, testdata)
+			} else if gotIdent := pkg.Ident(f); gotIdent != wantIdent {
+				t.Fatalf("Ident: %s, want %s", pkg.Encode(gotIdent), pkg.Encode(wantIdent))
+			}
+
+			// check error passthrough
+			f = pkg.NewHTTPGet(
+				&client,
+				"file:///nonexistent",
+				pkg.Checksum{},
+			)
+			wantIdentNonexistent := pkg.KindHTTPGet.Ident([]byte("file:///nonexistent"))
+			wantErrNotFound := pkg.ResponseStatusError(http.StatusNotFound)
+			if _, _, err := c.Cure(f); !reflect.DeepEqual(err, wantErrNotFound) {
+				t.Fatalf("Pathname: error = %#v, want %#v", err, wantErrNotFound)
+			} else if gotIdent := pkg.Ident(f); gotIdent != wantIdentNonexistent {
+				t.Fatalf("Ident: %s, want %s", pkg.Encode(gotIdent), pkg.Encode(wantIdentNonexistent))
+			}
+		}, pkg.MustDecode("bqtn69RkV5E7V7GhhgCFjcvbxmaqrO8DywamM4Tyjf10F6EJBHjXiIa_tFRtF4iN")},
+	})
+}

internal/pkg/pkg_test.go

@@ -0,0 +1,977 @@
+package pkg_test
+
+import (
+	"archive/tar"
+	"bytes"
+	"context"
+	"crypto/sha512"
+	"encoding/base64"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"io"
+	"io/fs"
+	"log"
+	"net/http"
+	"os"
+	"path/filepath"
+	"reflect"
+	"syscall"
+	"testing"
+	"unsafe"
+
+	"hakurei.app/container"
+	"hakurei.app/container/check"
+	"hakurei.app/container/stub"
+	"hakurei.app/internal/pkg"
+	"hakurei.app/message"
+)
+
+func TestMain(m *testing.M) { container.TryArgv0(nil); os.Exit(m.Run()) }
+
+// overrideIdent overrides the ID method of [Artifact].
+type overrideIdent struct {
+	id pkg.ID
+	pkg.TrivialArtifact
+}
+
+func (a overrideIdent) ID() pkg.ID { return a.id }
+
+// overrideIdentFile overrides the ID method of [File].
+type overrideIdentFile struct {
+	id pkg.ID
+	pkg.File
+}
+
+func (a overrideIdentFile) ID() pkg.ID { return a.id }
+
+// A knownIdentArtifact implements [pkg.KnownIdent] and [Artifact]
+type knownIdentArtifact interface {
+	pkg.KnownIdent
+	pkg.TrivialArtifact
+}
+
+// A knownIdentFile implements [pkg.KnownIdent] and [File]
+type knownIdentFile interface {
+	pkg.KnownIdent
+	pkg.File
+}
+
+// overrideChecksum overrides the Checksum method of [Artifact].
+type overrideChecksum struct {
+	checksum pkg.Checksum
+	knownIdentArtifact
+}
+
+func (a overrideChecksum) Checksum() pkg.Checksum { return a.checksum }
+
+// overrideChecksumFile overrides the Checksum method of [File].
+type overrideChecksumFile struct {
+	checksum pkg.Checksum
+	knownIdentFile
+}
+
+func (a overrideChecksumFile) Checksum() pkg.Checksum { return a.checksum }
+
+// A stubArtifact implements [TrivialArtifact] with hardcoded behaviour.
+type stubArtifact struct {
+	kind   pkg.Kind
+	params []byte
+	deps   []pkg.Artifact
+
+	cure func(t *pkg.TContext) error
+}
+
+func (a stubArtifact) Kind() pkg.Kind               { return a.kind }
+func (a stubArtifact) Params() []byte               { return a.params }
+func (a stubArtifact) Dependencies() []pkg.Artifact { return a.deps }
+func (a stubArtifact) Cure(t *pkg.TContext) error   { return a.cure(t) }
+
+// A stubArtifactF implements [FloodArtifact] with hardcoded behaviour.
+type stubArtifactF struct {
+	kind   pkg.Kind
+	params []byte
+	deps   []pkg.Artifact
+
+	cure func(f *pkg.FContext) error
+}
+
+func (a stubArtifactF) Kind() pkg.Kind               { return a.kind }
+func (a stubArtifactF) Params() []byte               { return a.params }
+func (a stubArtifactF) Dependencies() []pkg.Artifact { return a.deps }
+func (a stubArtifactF) Cure(f *pkg.FContext) error   { return a.cure(f) }
+
+// A stubFile implements [File] with hardcoded behaviour.
+type stubFile struct {
+	data []byte
+	err  error
+
+	stubArtifact
+}
+
+func (a stubFile) Cure(context.Context) ([]byte, error) { return a.data, a.err }
+
+// newStubFile returns an implementation of [pkg.File] with hardcoded behaviour.
+func newStubFile(
+	kind pkg.Kind,
+	id pkg.ID,
+	sum *pkg.Checksum,
+	data []byte,
+	err error,
+) pkg.File {
+	f := overrideIdentFile{id, stubFile{data, err, stubArtifact{
+		kind,
+		nil,
+		nil,
+		func(*pkg.TContext) error {
+			panic("unreachable")
+		},
+	}}}
+	if sum == nil {
+		return f
+	} else {
+		return overrideChecksumFile{*sum, f}
+	}
+}
+
+// destroyArtifact removes all traces of an [Artifact] from the on-disk cache.
+// Do not use this in a test case without a very good reason to do so.
+func destroyArtifact(
+	t *testing.T,
+	base *check.Absolute,
+	c *pkg.Cache,
+	a pkg.Artifact,
+) {
+	if pathname, checksum, err := c.Cure(a); err != nil {
+		t.Fatalf("Cure: error = %v", err)
+	} else if err = os.Remove(pathname.String()); err != nil {
+		t.Fatal(err)
+	} else {
+		p := base.Append(
+			"checksum",
+			pkg.Encode(checksum),
+		)
+		if err = filepath.WalkDir(p.String(), func(
+			path string,
+			d fs.DirEntry,
+			err error,
+		) error {
+			if err != nil {
+				return err
+			}
+			if d.IsDir() {
+				return os.Chmod(path, 0700)
+			}
+			return nil
+		}); err != nil && !errors.Is(err, os.ErrNotExist) {
+			t.Fatal(err)
+		}
+		if err = os.RemoveAll(p.String()); err != nil {
+			t.Fatal(err)
+		}
+	}
+}
+
+// newDestroyArtifactFunc returns a function that calls destroyArtifact.
+func newDestroyArtifactFunc(a pkg.Artifact) func(
+	t *testing.T,
+	base *check.Absolute,
+	c *pkg.Cache,
+) {
+	return func(
+		t *testing.T,
+		base *check.Absolute,
+		c *pkg.Cache,
+	) {
+		destroyArtifact(t, base, c, a)
+	}
+}
+
+func TestIdent(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name string
+		a    pkg.Artifact
+		want pkg.ID
+	}{
+		{"tar", stubArtifact{
+			pkg.KindTar,
+			[]byte{pkg.TarGzip, 0, 0, 0, 0, 0, 0, 0},
+			[]pkg.Artifact{
+				overrideIdent{pkg.ID{}, stubArtifact{}},
+			},
+			nil,
+		}, pkg.MustDecode(
+			"HnySzeLQvSBZuTUcvfmLEX_OmH4yJWWH788NxuLuv7kVn8_uPM6Ks4rqFWM2NZJY",
+		)},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			if got := pkg.Ident(tc.a); got != tc.want {
+				t.Errorf("Ident: %s, want %s",
+					pkg.Encode(got),
+					pkg.Encode(tc.want),
+				)
+			}
+		})
+	}
+}
+
+// cacheTestCase is a test case passed to checkWithCache where a new instance
+// of [pkg.Cache] is prepared for the test case, and is validated and removed
+// on test completion.
+type cacheTestCase struct {
+	name  string
+	early func(t *testing.T, base *check.Absolute)
+	f     func(t *testing.T, base *check.Absolute, c *pkg.Cache)
+	want  pkg.Checksum
+}
+
+// checkWithCache runs a slice of cacheTestCase.
+func checkWithCache(t *testing.T, testCases []cacheTestCase) {
+	t.Helper()
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Helper()
+			t.Parallel()
+
+			base := check.MustAbs(t.TempDir())
+			if err := os.Chmod(base.String(), 0700); err != nil {
+				t.Fatal(err)
+			}
+			t.Cleanup(func() {
+				if err := filepath.WalkDir(base.String(), func(path string, d fs.DirEntry, err error) error {
+					if err != nil {
+						t.Error(err)
+						return nil
+					}
+					if !d.IsDir() {
+						return nil
+					}
+					return os.Chmod(path, 0700)
+				}); err != nil {
+					t.Fatal(err)
+				}
+			})
+
+			msg := message.New(log.New(os.Stderr, "cache: ", 0))
+			msg.SwapVerbose(testing.Verbose())
+
+			var scrubFunc func() error // scrub after hashing
+			if c, err := pkg.New(t.Context(), msg, 0, base); err != nil {
+				t.Fatalf("New: error = %v", err)
+			} else {
+				t.Cleanup(c.Close)
+				if tc.early != nil {
+					tc.early(t, base)
+				}
+				tc.f(t, base, c)
+				scrubFunc = c.Scrub
+			}
+
+			var restoreTemp bool
+			if _, err := os.Lstat(base.Append("temp").String()); err != nil {
+				if !errors.Is(err, os.ErrNotExist) {
+					t.Fatal(err)
+				}
+			} else {
+				restoreTemp = true
+			}
+
+			if checksum, err := pkg.HashDir(base); err != nil {
+				t.Fatalf("HashDir: error = %v", err)
+			} else if checksum != tc.want {
+				t.Fatalf("HashDir: %v", &pkg.ChecksumMismatchError{
+					Got:  checksum,
+					Want: tc.want,
+				})
+			}
+
+			if err := scrubFunc(); err != nil {
+				t.Fatal("cache contains inconsistencies\n\n" + err.Error())
+			}
+
+			if restoreTemp {
+				if err := os.Mkdir(
+					base.Append("temp").String(),
+					0700,
+				); err != nil {
+					t.Fatal(err)
+				}
+			}
+
+			// validate again to make sure scrub did not condemn anything
+			if checksum, err := pkg.HashDir(base); err != nil {
+				t.Fatalf("HashDir: error = %v", err)
+			} else if checksum != tc.want {
+				t.Fatalf("(scrubbed) HashDir: %v", &pkg.ChecksumMismatchError{
+					Got:  checksum,
+					Want: tc.want,
+				})
+			}
+		})
+	}
+}
+
+// A cureStep contains an [Artifact] to be cured, and the expected outcome.
+type cureStep struct {
+	name string
+
+	a pkg.Artifact
+
+	pathname *check.Absolute
+	checksum pkg.Checksum
+	err      error
+}
+
+// ignorePathname is passed to cureMany to skip the pathname check.
+var ignorePathname = check.MustAbs("/\x00")
+
+// cureMany cures many artifacts against a [Cache] and checks their outcomes.
+func cureMany(t *testing.T, c *pkg.Cache, steps []cureStep) {
+	t.Helper()
+
+	for _, step := range steps {
+		t.Log("cure step:", step.name)
+		if pathname, checksum, err := c.Cure(step.a); !reflect.DeepEqual(err, step.err) {
+			t.Fatalf("Cure: error = %v, want %v", err, step.err)
+		} else if step.pathname != ignorePathname && !pathname.Is(step.pathname) {
+			t.Fatalf("Cure: pathname = %q, want %q", pathname, step.pathname)
+		} else if checksum != step.checksum {
+			t.Fatalf("Cure: checksum = %s, want %s", pkg.Encode(checksum), pkg.Encode(step.checksum))
+		} else {
+			v := any(err)
+			if err == nil {
+				v = pathname
+			}
+			t.Log(pkg.Encode(checksum)+":", v)
+		}
+	}
+}
+
+func TestCache(t *testing.T) {
+	t.Parallel()
+
+	const testdata = "" +
+		"\x00\x00\x00\x00" +
+		"\xad\x0b\x00" +
+		"\x04" +
+		"\xfe\xfe\x00\x00" +
+		"\xfe\xca\x00\x00"
+
+	testdataChecksum := func() pkg.Checksum {
+		h := sha512.New384()
+		h.Write([]byte(testdata))
+		return (pkg.Checksum)(h.Sum(nil))
+	}()
+
+	testCases := []cacheTestCase{
+		{"file", nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
+			c.SetStrict(true)
+
+			identifier := (pkg.ID)(bytes.Repeat([]byte{
+				0x75, 0xe6, 0x9d, 0x6d, 0xe7, 0x9f,
+			}, 8))
+			wantPathname := base.Append(
+				"identifier",
+				"deadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeef",
+			)
+			identifier0 := (pkg.ID)(bytes.Repeat([]byte{
+				0x71, 0xa7, 0xde, 0x6d, 0xa6, 0xde,
+			}, 8))
+			wantPathname0 := base.Append(
+				"identifier",
+				"cafebabecafebabecafebabecafebabecafebabecafebabecafebabecafebabe",
+			)
+
+			cureMany(t, c, []cureStep{
+				{"initial file", newStubFile(
+					pkg.KindHTTPGet,
+					identifier,
+					&testdataChecksum,
+					[]byte(testdata), nil,
+				), wantPathname, testdataChecksum, nil},
+
+				{"identical content", newStubFile(
+					pkg.KindHTTPGet,
+					identifier0,
+					&testdataChecksum,
+					[]byte(testdata), nil,
+				), wantPathname0, testdataChecksum, nil},
+
+				{"existing entry", newStubFile(
+					pkg.KindHTTPGet,
+					identifier,
+					&testdataChecksum,
+					[]byte(testdata), nil,
+				), wantPathname, testdataChecksum, nil},
+
+				{"checksum mismatch", newStubFile(
+					pkg.KindHTTPGet,
+					pkg.ID{0xff, 0},
+					new(pkg.Checksum),
+					[]byte(testdata), nil,
+				), nil, pkg.Checksum{}, &pkg.ChecksumMismatchError{
+					Got: testdataChecksum,
+				}},
+
+				{"store without validation", newStubFile(
+					pkg.KindHTTPGet,
+					pkg.MustDecode("vsAhtPNo4waRNOASwrQwcIPTqb3SBuJOXw2G4T1mNmVZM-wrQTRllmgXqcIIoRcX"),
+					nil,
+					[]byte{0}, nil,
+				), base.Append(
+					"identifier",
+					"vsAhtPNo4waRNOASwrQwcIPTqb3SBuJOXw2G4T1mNmVZM-wrQTRllmgXqcIIoRcX",
+				), pkg.Checksum{
+					0xbe, 0xc0, 0x21, 0xb4, 0xf3, 0x68,
+					0xe3, 0x06, 0x91, 0x34, 0xe0, 0x12,
+					0xc2, 0xb4, 0x30, 0x70, 0x83, 0xd3,
+					0xa9, 0xbd, 0xd2, 0x06, 0xe2, 0x4e,
+					0x5f, 0x0d, 0x86, 0xe1, 0x3d, 0x66,
+					0x36, 0x65, 0x59, 0x33, 0xec, 0x2b,
+					0x41, 0x34, 0x65, 0x96, 0x68, 0x17,
+					0xa9, 0xc2, 0x08, 0xa1, 0x17, 0x17,
+				}, nil},
+
+				{"incomplete implementation", struct{ pkg.Artifact }{stubArtifact{
+					kind:   pkg.KindExec,
+					params: []byte("artifact overridden to be incomplete"),
+				}}, nil, pkg.Checksum{}, pkg.InvalidArtifactError(pkg.MustDecode(
+					"da4kLKa94g1wN2M0qcKflqgf2-Y2UL36iehhczqsIIW8G0LGvM7S8jjtnBc0ftB0",
+				))},
+
+				{"error passthrough", newStubFile(
+					pkg.KindHTTPGet,
+					pkg.ID{0xff, 1},
+					nil,
+					nil, stub.UniqueError(0xcafe),
+				), nil, pkg.Checksum{}, stub.UniqueError(0xcafe)},
+
+				{"error caching", newStubFile(
+					pkg.KindHTTPGet,
+					pkg.ID{0xff, 1},
+					nil,
+					nil, nil,
+				), nil, pkg.Checksum{}, stub.UniqueError(0xcafe)},
+
+				{"cache hit bad type", overrideChecksum{testdataChecksum, overrideIdent{pkg.ID{0xff, 2}, stubArtifact{
+					kind: pkg.KindTar,
+				}}}, nil, pkg.Checksum{}, pkg.InvalidFileModeError(
+					0400,
+				)},
+			})
+
+			if c0, err := pkg.New(
+				t.Context(),
+				message.New(nil),
+				0, base,
+			); err != nil {
+				t.Fatalf("New: error = %v", err)
+			} else {
+				t.Cleanup(c.Close) // check doubled cancel
+				cureMany(t, c0, []cureStep{
+					{"cache hit ident", overrideIdent{
+						id: identifier,
+					}, wantPathname, testdataChecksum, nil},
+
+					{"cache miss checksum match", newStubFile(
+						pkg.KindHTTPGet,
+						testdataChecksum,
+						nil,
+						[]byte(testdata),
+						nil,
+					), base.Append(
+						"identifier",
+						pkg.Encode(testdataChecksum),
+					), testdataChecksum, nil},
+				})
+
+				// cure after close
+				c.Close()
+				if _, _, err = c.Cure(stubArtifactF{
+					kind:   pkg.KindExec,
+					params: []byte("unreachable artifact cured after cancel"),
+					deps:   []pkg.Artifact{pkg.NewFile("", []byte("unreachable dependency"))},
+				}); !reflect.DeepEqual(err, context.Canceled) {
+					t.Fatalf("(closed) Cure: error = %v", err)
+				}
+			}
+		}, pkg.MustDecode("St9rlE-mGZ5gXwiv_hzQ_B8bZP-UUvSNmf4nHUZzCMOumb6hKnheZSe0dmnuc4Q2")},
+
+		{"directory", nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
+			id := pkg.KindTar.Ident(
+				binary.LittleEndian.AppendUint64(nil, pkg.TarGzip),
+				overrideIdent{testdataChecksum, stubArtifact{}},
+			)
+			makeSample := func(t *pkg.TContext) error {
+				work := t.GetWorkDir()
+				if err := os.Mkdir(work.String(), 0700); err != nil {
+					return err
+				}
+
+				if err := os.WriteFile(
+					work.Append("check").String(),
+					[]byte{0, 0},
+					0400,
+				); err != nil {
+					return err
+				}
+
+				if err := os.MkdirAll(work.Append(
+					"lib",
+					"pkgconfig",
+				).String(), 0700); err != nil {
+					return err
+				}
+
+				return os.Symlink(
+					"/proc/nonexistent/libedac.so",
+					work.Append(
+						"lib",
+						"libedac.so",
+					).String(),
+				)
+			}
+			wantChecksum := pkg.MustDecode(
+				"qRN6in76LndiiOZJheHkwyW8UT1N5-f-bXvHfDvwrMw2fSkOoZdh8pWE1qhLk65b",
+			)
+			wantPathname := base.Append(
+				"identifier",
+				pkg.Encode(id),
+			)
+
+			id0 := pkg.KindTar.Ident(
+				binary.LittleEndian.AppendUint64(nil, pkg.TarGzip),
+				overrideIdent{pkg.ID{}, stubArtifact{}},
+			)
+			wantPathname0 := base.Append(
+				"identifier",
+				pkg.Encode(id0),
+			)
+
+			makeGarbage := func(work *check.Absolute, wantErr error) error {
+				if err := os.Mkdir(work.String(), 0700); err != nil {
+					return err
+				}
+
+				mode := fs.FileMode(0)
+				if wantErr == nil {
+					mode = 0500
+				}
+
+				if err := os.MkdirAll(work.Append(
+					"lib",
+					"pkgconfig",
+				).String(), 0700); err != nil {
+					return err
+				}
+
+				if err := os.WriteFile(work.Append(
+					"lib",
+					"check",
+				).String(), nil, 0400&mode); err != nil {
+					return err
+				}
+
+				if err := os.Chmod(work.Append(
+					"lib",
+					"pkgconfig",
+				).String(), 0500&mode); err != nil {
+					return err
+				}
+				if err := os.Chmod(work.Append(
+					"lib",
+				).String(), 0500&mode); err != nil {
+					return err
+				}
+
+				return wantErr
+			}
+
+			cureMany(t, c, []cureStep{
+				{"initial directory", overrideChecksum{wantChecksum, overrideIdent{id, stubArtifact{
+					kind: pkg.KindTar,
+					cure: makeSample,
+				}}}, wantPathname, wantChecksum, nil},
+
+				{"identical identifier", overrideChecksum{wantChecksum, overrideIdent{id, stubArtifact{
+					kind: pkg.KindTar,
+				}}}, wantPathname, wantChecksum, nil},
+
+				{"identical checksum", overrideIdent{id0, stubArtifact{
+					kind: pkg.KindTar,
+					cure: makeSample,
+				}}, wantPathname0, wantChecksum, nil},
+
+				{"cure fault", overrideIdent{pkg.ID{0xff, 0}, stubArtifact{
+					kind: pkg.KindTar,
+					cure: func(t *pkg.TContext) error {
+						return makeGarbage(t.GetWorkDir(), stub.UniqueError(0xcafe))
+					},
+				}}, nil, pkg.Checksum{}, stub.UniqueError(0xcafe)},
+
+				{"checksum mismatch", overrideChecksum{pkg.Checksum{}, overrideIdent{pkg.ID{0xff, 1}, stubArtifact{
+					kind: pkg.KindTar,
+					cure: func(t *pkg.TContext) error {
+						return makeGarbage(t.GetWorkDir(), nil)
+					},
+				}}}, nil, pkg.Checksum{}, &pkg.ChecksumMismatchError{
+					Got: pkg.MustDecode(
+						"CUx-3hSbTWPsbMfDhgalG4Ni_GmR9TnVX8F99tY_P5GtkYvczg9RrF5zO0jX9XYT",
+					),
+				}},
+
+				{"cache hit bad type", newStubFile(
+					pkg.KindHTTPGet,
+					pkg.ID{0xff, 2},
+					&wantChecksum,
+					[]byte(testdata), nil,
+				), nil, pkg.Checksum{}, pkg.InvalidFileModeError(
+					fs.ModeDir | 0500,
+				)},
+
+				{"openFile directory", overrideIdent{pkg.ID{0xff, 3}, stubArtifact{
+					kind: pkg.KindTar,
+					cure: func(t *pkg.TContext) error {
+						r, err := t.Open(overrideChecksumFile{checksum: wantChecksum})
+						if err != nil {
+							panic(err)
+						}
+						_, err = io.ReadAll(r)
+						return err
+					},
+				}}, nil, pkg.Checksum{}, &os.PathError{
+					Op: "read",
+					Path: base.Append(
+						"checksum",
+						pkg.Encode(wantChecksum),
+					).String(),
+					Err: syscall.EISDIR,
+				}},
+
+				{"no output", overrideIdent{pkg.ID{0xff, 4}, stubArtifact{
+					kind: pkg.KindTar,
+					cure: func(t *pkg.TContext) error {
+						return nil
+					},
+				}}, nil, pkg.Checksum{}, pkg.NoOutputError{}},
+
+				{"file output", overrideIdent{pkg.ID{0xff, 5}, stubArtifact{
+					kind: pkg.KindTar,
+					cure: func(t *pkg.TContext) error {
+						return os.WriteFile(t.GetWorkDir().String(), []byte{0}, 0400)
+					},
+				}}, nil, pkg.Checksum{}, errors.New("non-file artifact produced regular file")},
+
+				{"symlink output", overrideIdent{pkg.ID{0xff, 6}, stubArtifact{
+					kind: pkg.KindTar,
+					cure: func(t *pkg.TContext) error {
+						return os.Symlink(
+							t.GetWorkDir().String(),
+							t.GetWorkDir().String(),
+						)
+					},
+				}}, nil, pkg.Checksum{}, pkg.InvalidFileModeError(
+					fs.ModeSymlink | 0777,
+				)},
+			})
+		}, pkg.MustDecode("WVpvsVqVKg9Nsh744x57h51AuWUoUR2nnh8Md-EYBQpk6ziyTuUn6PLtF2e0Eu_d")},
+
+		{"pending", nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
+			c.SetStrict(true)
+
+			wantErr := stub.UniqueError(0xcafe)
+			n, ready := make(chan struct{}), make(chan struct{})
+			go func() {
+				if _, _, err := c.Cure(overrideIdent{pkg.ID{0xff}, stubArtifact{
+					kind: pkg.KindTar,
+					cure: func(t *pkg.TContext) error {
+						close(ready)
+						<-n
+						return wantErr
+					},
+				}}); !reflect.DeepEqual(err, wantErr) {
+					panic(fmt.Sprintf("Cure: error = %v, want %v", err, wantErr))
+				}
+			}()
+
+			<-ready
+			wCureDone := make(chan struct{})
+			go func() {
+				if _, _, err := c.Cure(overrideIdent{pkg.ID{0xff}, stubArtifact{
+					kind: pkg.KindTar,
+				}}); !reflect.DeepEqual(err, wantErr) {
+					panic(fmt.Sprintf("Cure: error = %v, want %v", err, wantErr))
+				}
+				close(wCureDone)
+			}()
+
+			// check cache activity while a cure is blocking
+			cureMany(t, c, []cureStep{
+				{"error passthrough", newStubFile(
+					pkg.KindHTTPGet,
+					pkg.ID{0xff, 1},
+					nil,
+					nil, stub.UniqueError(0xbad),
+				), nil, pkg.Checksum{}, stub.UniqueError(0xbad)},
+
+				{"file output", overrideIdent{pkg.ID{0xff, 2}, stubArtifact{
+					kind: pkg.KindTar,
+					cure: func(t *pkg.TContext) error {
+						return os.WriteFile(
+							t.GetWorkDir().String(),
+							[]byte{0},
+							0400,
+						)
+					},
+				}}, nil, pkg.Checksum{}, errors.New(
+					"non-file artifact produced regular file",
+				)},
+			})
+
+			wantErrScrub := &pkg.ScrubError{
+				Errs: []error{errors.New("scrub began with pending artifacts")},
+			}
+			if err := c.Scrub(); !reflect.DeepEqual(err, wantErrScrub) {
+				t.Fatalf("Scrub: error = %#v, want %#v", err, wantErrScrub)
+			}
+
+			identPendingVal := reflect.ValueOf(c).Elem().FieldByName("identPending")
+			identPending := reflect.NewAt(
+				identPendingVal.Type(),
+				unsafe.Pointer(identPendingVal.UnsafeAddr()),
+			).Elem().Interface().(map[pkg.ID]<-chan struct{})
+			notify := identPending[pkg.ID{0xff}]
+			go close(n)
+			<-notify
+			<-wCureDone
+		}, pkg.MustDecode("E4vEZKhCcL2gPZ2Tt59FS3lDng-d_2SKa2i5G_RbDfwGn6EemptFaGLPUDiOa94C")},
+
+		{"scrub", nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
+			cureMany(t, c, []cureStep{
+				{"bad measured file", newStubFile(
+					pkg.KindHTTPGet,
+					pkg.Checksum{0xfe, 0},
+					&pkg.Checksum{0xff, 0},
+					[]byte{0}, nil,
+				), base.Append(
+					"identifier",
+					pkg.Encode(pkg.Checksum{0xfe, 0}),
+				), pkg.Checksum{0xff, 0}, nil},
+			})
+
+			for _, p := range [][]string{
+				{"identifier", "invalid"},
+				{"identifier", pkg.Encode(pkg.ID{0xfe, 0xff})},
+				{"checksum", "invalid"},
+			} {
+				if err := os.WriteFile(
+					base.Append(p...).String(),
+					nil,
+					0400,
+				); err != nil {
+					t.Fatal(err)
+				}
+			}
+
+			for _, p := range [][]string{
+				{"../nonexistent", "checksum", pkg.Encode(pkg.Checksum{0xff, 0xff})},
+				{"../nonexistent", "identifier", pkg.Encode(pkg.Checksum{0xfe, 0xfe})},
+			} {
+				if err := os.Symlink(
+					p[0],
+					base.Append(p[1:]...).String(),
+				); err != nil {
+					t.Fatal(err)
+				}
+			}
+
+			wantErr := &pkg.ScrubError{
+				ChecksumMismatches: []pkg.ChecksumMismatchError{
+					{Got: pkg.MustDecode(
+						"vsAhtPNo4waRNOASwrQwcIPTqb3SBuJOXw2G4T1mNmVZM-wrQTRllmgXqcIIoRcX",
+					), Want: pkg.Checksum{0xff, 0}},
+				},
+				DanglingIdentifiers: []pkg.ID{
+					{0xfe, 0},
+					{0xfe, 0xfe},
+					{0xfe, 0xff},
+				},
+				Errs: []error{
+					pkg.InvalidFileModeError(fs.ModeSymlink),
+					base64.CorruptInputError(4),
+					base64.CorruptInputError(8),
+					&os.PathError{
+						Op:   "readlink",
+						Path: base.Append("identifier", pkg.Encode(pkg.ID{0xfe, 0xff})).String(),
+						Err:  syscall.EINVAL,
+					},
+					base64.CorruptInputError(4),
+				},
+			}
+			if err := c.Scrub(); !reflect.DeepEqual(err, wantErr) {
+				t.Fatalf("Scrub: error =\n%s\nwant\n%s", err, wantErr)
+			}
+		}, pkg.MustDecode("E4vEZKhCcL2gPZ2Tt59FS3lDng-d_2SKa2i5G_RbDfwGn6EemptFaGLPUDiOa94C")},
+	}
+	checkWithCache(t, testCases)
+}
+
+func TestErrors(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name string
+		err  error
+		want string
+	}{
+		{"InvalidLookupError", pkg.InvalidLookupError{
+			0xff, 0xf0,
+		}, "attempting to look up non-dependency artifact __AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"},
+
+		{"InvalidArtifactError", pkg.InvalidArtifactError{
+			0xff, 0xfd,
+		}, "artifact __0AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA cannot be cured"},
+
+		{"ChecksumMismatchError", &pkg.ChecksumMismatchError{
+			Want: (pkg.Checksum)(bytes.Repeat([]byte{
+				0x75, 0xe6, 0x9d, 0x6d, 0xe7, 0x9f,
+			}, 8)),
+		}, "got AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" +
+			" instead of deadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeef"},
+
+		{"ResponseStatusError", pkg.ResponseStatusError(
+			http.StatusNotAcceptable,
+		), "the requested URL returned non-OK status: Not Acceptable"},
+
+		{"DisallowedTypeflagError", pkg.DisallowedTypeflagError(
+			tar.TypeChar,
+		), "disallowed typeflag '3'"},
+
+		{"InvalidFileModeError", pkg.InvalidFileModeError(
+			fs.ModeSymlink | 0777,
+		), "artifact did not produce a regular file or directory"},
+
+		{"NoOutputError", pkg.NoOutputError{
+			// empty struct
+		}, "artifact cured successfully but did not produce any output"},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			if got := tc.err.Error(); got != tc.want {
+				t.Errorf("Error: %q, want %q", got, tc.want)
+			}
+		})
+	}
+}
+
+func TestScrubError(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name   string
+		err    pkg.ScrubError
+		want   string
+		unwrap []error
+	}{
+		{"full", pkg.ScrubError{
+			ChecksumMismatches: []pkg.ChecksumMismatchError{
+				{Want: pkg.MustDecode("CH3AiUrCCcVOjOYLaMKKK1Da78989JtfHeIsxMzWOQFiN4mrCLDYpoDxLWqJWCUN")},
+			},
+			DanglingIdentifiers: []pkg.ID{
+				(pkg.ID)(bytes.Repeat([]byte{0x75, 0xe6, 0x9d, 0x6d, 0xe7, 0x9f}, 8)),
+				(pkg.ID)(bytes.Repeat([]byte{0x71, 0xa7, 0xde, 0x6d, 0xa6, 0xde}, 8)),
+			},
+			Errs: []error{
+				stub.UniqueError(0xcafe),
+				stub.UniqueError(0xbad),
+				stub.UniqueError(0xff),
+			},
+		}, `checksum mismatches:
+got AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA instead of CH3AiUrCCcVOjOYLaMKKK1Da78989JtfHeIsxMzWOQFiN4mrCLDYpoDxLWqJWCUN
+
+dangling identifiers:
+deadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeef
+cafebabecafebabecafebabecafebabecafebabecafebabecafebabecafebabe
+
+errors during scrub:
+unique error 51966 injected by the test suite
+unique error 2989 injected by the test suite
+unique error 255 injected by the test suite
+`, []error{
+			&pkg.ChecksumMismatchError{Want: pkg.MustDecode("CH3AiUrCCcVOjOYLaMKKK1Da78989JtfHeIsxMzWOQFiN4mrCLDYpoDxLWqJWCUN")},
+			stub.UniqueError(0xcafe),
+			stub.UniqueError(0xbad),
+			stub.UniqueError(0xff),
+		}},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			if got := tc.err.Error(); got != tc.want {
+				t.Errorf("Error:\n\n%s\n\nwant\n\n%s", got, tc.want)
+			}
+
+			if unwrap := tc.err.Unwrap(); !reflect.DeepEqual(unwrap, tc.unwrap) {
+				t.Errorf("Unwrap: %#v, want %#v", unwrap, tc.unwrap)
+			}
+		})
+	}
+}
+
+func TestNew(t *testing.T) {
+	t.Parallel()
+
+	t.Run("nonexistent", func(t *testing.T) {
+		t.Parallel()
+
+		wantErr := &os.PathError{
+			Op:   "mkdir",
+			Path: container.Nonexistent,
+			Err:  syscall.ENOENT,
+		}
+		if _, err := pkg.New(
+			t.Context(),
+			message.New(nil),
+			0, check.MustAbs(container.Nonexistent),
+		); !reflect.DeepEqual(err, wantErr) {
+			t.Errorf("New: error = %#v, want %#v", err, wantErr)
+		}
+	})
+
+	t.Run("permission", func(t *testing.T) {
+		t.Parallel()
+
+		tempDir := check.MustAbs(t.TempDir())
+		if err := os.Chmod(tempDir.String(), 0); err != nil {
+			t.Fatal(err)
+		} else {
+			t.Cleanup(func() {
+				if err = os.Chmod(tempDir.String(), 0700); err != nil {
+					t.Fatal(err)
+				}
+			})
+		}
+
+		wantErr := &os.PathError{
+			Op:   "mkdir",
+			Path: tempDir.Append("cache").String(),
+			Err:  syscall.EACCES,
+		}
+		if _, err := pkg.New(
+			t.Context(),
+			message.New(nil),
+			0, tempDir.Append("cache"),
+		); !reflect.DeepEqual(err, wantErr) {
+			t.Errorf("New: error = %#v, want %#v", err, wantErr)
+		}
+	})
+}

internal/pkg/tar.go

@@ -0,0 +1,238 @@
+package pkg
+
+import (
+	"archive/tar"
+	"compress/bzip2"
+	"compress/gzip"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"io"
+	"io/fs"
+	"net/http"
+	"os"
+
+	"hakurei.app/container/check"
+)
+
+const (
+	// TarUncompressed denotes an uncompressed tarball.
+	TarUncompressed = iota
+	// TarGzip denotes a tarball compressed via [gzip].
+	TarGzip
+	// TarBzip2 denotes a tarball compressed via [bzip2].
+	TarBzip2
+)
+
+// A tarArtifact is an [Artifact] unpacking a tarball backed by a [File].
+type tarArtifact struct {
+	// Caller-supplied backing tarball.
+	f Artifact
+	// Compression on top of the tarball.
+	compression uint64
+}
+
+// tarArtifactNamed embeds tarArtifact for a [fmt.Stringer] tarball.
+type tarArtifactNamed struct {
+	tarArtifact
+	// Copied from tarArtifact.f.
+	name string
+}
+
+var _ fmt.Stringer = new(tarArtifactNamed)
+
+// String returns the name of the underlying [Artifact] suffixed with unpack.
+func (a *tarArtifactNamed) String() string { return a.name + "-unpack" }
+
+// NewTar returns a new [Artifact] backed by the supplied [Artifact] and
+// compression method. The source [Artifact] must be compatible with
+// [TContext.Open].
+func NewTar(a Artifact, compression uint64) Artifact {
+	ta := tarArtifact{a, compression}
+	if s, ok := a.(fmt.Stringer); ok {
+		if name := s.String(); name != "" {
+			return &tarArtifactNamed{ta, name}
+		}
+	}
+	return &ta
+}
+
+// NewHTTPGetTar is abbreviation for NewHTTPGet passed to NewTar.
+func NewHTTPGetTar(
+	hc *http.Client,
+	url string,
+	checksum Checksum,
+	compression uint64,
+) Artifact {
+	return NewTar(NewHTTPGet(hc, url, checksum), compression)
+}
+
+// Kind returns the hardcoded [Kind] constant.
+func (a *tarArtifact) Kind() Kind { return KindTar }
+
+// Params returns compression encoded in little endian.
+func (a *tarArtifact) Params() []byte {
+	return binary.LittleEndian.AppendUint64(nil, a.compression)
+}
+
+// Dependencies returns a slice containing the backing file.
+func (a *tarArtifact) Dependencies() []Artifact {
+	return []Artifact{a.f}
+}
+
+// A DisallowedTypeflagError describes a disallowed typeflag encountered while
+// unpacking a tarball.
+type DisallowedTypeflagError byte
+
+func (e DisallowedTypeflagError) Error() string {
+	return "disallowed typeflag '" + string(e) + "'"
+}
+
+// Cure cures the [Artifact], producing a directory located at work.
+func (a *tarArtifact) Cure(t *TContext) (err error) {
+	temp := t.GetTempDir()
+	var tr io.ReadCloser
+	if tr, err = t.Open(a.f); err != nil {
+		return
+	}
+
+	defer func(f io.ReadCloser) {
+		closeErr := tr.Close()
+		if err == nil {
+			err = closeErr
+		}
+
+		closeErr = f.Close()
+		if err == nil {
+			err = closeErr
+		}
+	}(tr)
+	tr = io.NopCloser(tr)
+
+	switch a.compression {
+	case TarUncompressed:
+		break
+
+	case TarGzip:
+		if tr, err = gzip.NewReader(tr); err != nil {
+			return
+		}
+		break
+
+	case TarBzip2:
+		tr = io.NopCloser(bzip2.NewReader(tr))
+		break
+
+	default:
+		return os.ErrInvalid
+	}
+
+	type dirTargetPerm struct {
+		path *check.Absolute
+		mode fs.FileMode
+	}
+	var madeDirectories []dirTargetPerm
+
+	if err = os.MkdirAll(temp.String(), 0700); err != nil {
+		return
+	}
+
+	var header *tar.Header
+	r := tar.NewReader(tr)
+	for header, err = r.Next(); err == nil; header, err = r.Next() {
+		typeflag := header.Typeflag
+		if typeflag == 0 {
+			if len(header.Name) > 0 && header.Name[len(header.Name)-1] == '/' {
+				typeflag = tar.TypeDir
+			} else {
+				typeflag = tar.TypeReg
+			}
+		}
+
+		pathname := temp.Append(header.Name)
+		if typeflag >= '0' && typeflag <= '9' && typeflag != tar.TypeDir {
+			if err = os.MkdirAll(pathname.Dir().String(), 0700); err != nil {
+				return
+			}
+		}
+
+		switch typeflag {
+		case tar.TypeReg:
+			var f *os.File
+			if f, err = os.OpenFile(
+				pathname.String(),
+				os.O_CREATE|os.O_EXCL|os.O_WRONLY,
+				header.FileInfo().Mode()&0500,
+			); err != nil {
+				return
+			}
+			if _, err = io.Copy(f, r); err != nil {
+				_ = f.Close()
+				return
+			} else if err = f.Close(); err != nil {
+				return
+			}
+			break
+
+		case tar.TypeLink:
+			if err = os.Link(header.Linkname, pathname.String()); err != nil {
+				return
+			}
+			break
+
+		case tar.TypeSymlink:
+			if err = os.Symlink(header.Linkname, pathname.String()); err != nil {
+				return
+			}
+			break
+
+		case tar.TypeDir:
+			madeDirectories = append(madeDirectories, dirTargetPerm{
+				path: pathname,
+				mode: header.FileInfo().Mode(),
+			})
+			if err = os.MkdirAll(pathname.String(), 0700); err != nil {
+				return
+			}
+			break
+
+		case tar.TypeXGlobalHeader:
+			continue // ignore
+
+		default:
+			return DisallowedTypeflagError(typeflag)
+		}
+	}
+	if errors.Is(err, io.EOF) {
+		err = nil
+	}
+	if err == nil {
+		for _, e := range madeDirectories {
+			if err = os.Chmod(e.path.String(), e.mode&0500); err != nil {
+				return
+			}
+		}
+	} else {
+		return
+	}
+
+	if err = os.Chmod(temp.String(), 0700); err != nil {
+		return
+	}
+
+	var entries []os.DirEntry
+	if entries, err = os.ReadDir(temp.String()); err != nil {
+		return
+	}
+
+	if len(entries) == 1 && entries[0].IsDir() {
+		p := temp.Append(entries[0].Name())
+		if err = os.Chmod(p.String(), 0700); err != nil {
+			return
+		}
+		err = os.Rename(p.String(), t.GetWorkDir().String())
+	} else {
+		err = os.Rename(temp.String(), t.GetWorkDir().String())
+	}
+	return
+}

internal/pkg/tar_test.go

@@ -0,0 +1,204 @@
+package pkg_test
+
+import (
+	"archive/tar"
+	"bytes"
+	"compress/gzip"
+	"crypto/sha512"
+	"errors"
+	"io/fs"
+	"net/http"
+	"os"
+	"testing"
+	"testing/fstest"
+
+	"hakurei.app/container/check"
+	"hakurei.app/container/stub"
+	"hakurei.app/internal/pkg"
+)
+
+func TestTar(t *testing.T) {
+	t.Parallel()
+
+	checkWithCache(t, []cacheTestCase{
+		{"http", nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
+			checkTarHTTP(t, base, c, fstest.MapFS{
+				".": {Mode: fs.ModeDir | 0700},
+
+				"checksum": {Mode: fs.ModeDir | 0700},
+				"checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP":                {Mode: fs.ModeDir | 0700},
+				"checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP/check":          {Mode: 0400, Data: []byte{0, 0}},
+				"checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP/lib":            {Mode: fs.ModeDir | 0700},
+				"checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP/lib/pkgconfig":  {Mode: fs.ModeDir | 0700},
+				"checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP/lib/libedac.so": {Mode: fs.ModeSymlink | 0777, Data: []byte("/proc/nonexistent/libedac.so")},
+
+				"identifier": {Mode: fs.ModeDir | 0700},
+				"identifier/HnySzeLQvSBZuTUcvfmLEX_OmH4yJWWH788NxuLuv7kVn8_uPM6Ks4rqFWM2NZJY": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP")},
+				"identifier/Zx5ZG9BAwegNT3zQwCySuI2ktCXxNgxirkGLFjW4FW06PtojYVaCdtEw8yuntPLa": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/1TL00Qb8dcqayX7wTO8WNaraHvY6b-KCsctLDTrb64QBCmxj_-byK1HdIUwMaFEP")},
+
+				"work": {Mode: fs.ModeDir | 0700},
+			}, pkg.MustDecode(
+				"cTw0h3AmYe7XudSoyEMByduYXqGi-N5ZkTZ0t9K5elsu3i_jNIVF5T08KR1roBFM",
+			))
+		}, pkg.MustDecode("sxbgyX-bPoezbha214n2lbQhiVfTUBkhZ0EX6zI7mmkMdrCdwuMwhMBJphLQsy94")},
+
+		{"http expand", nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
+			checkTarHTTP(t, base, c, fstest.MapFS{
+				".": {Mode: fs.ModeDir | 0700},
+
+				"lib":            {Mode: fs.ModeDir | 0700},
+				"lib/libedac.so": {Mode: fs.ModeSymlink | 0777, Data: []byte("/proc/nonexistent/libedac.so")},
+			}, pkg.MustDecode(
+				"CH3AiUrCCcVOjOYLaMKKK1Da78989JtfHeIsxMzWOQFiN4mrCLDYpoDxLWqJWCUN",
+			))
+		}, pkg.MustDecode("4I8wx_h7NSJTlG5lbuz-GGEXrOg0GYC3M_503LYEBhv5XGWXfNIdIY9Q3eVSYldX")},
+	})
+}
+
+func checkTarHTTP(
+	t *testing.T,
+	base *check.Absolute,
+	c *pkg.Cache,
+	testdataFsys fs.FS,
+	wantChecksum pkg.Checksum,
+) {
+	var testdata string
+	{
+		var buf bytes.Buffer
+		w := tar.NewWriter(&buf)
+		if err := w.AddFS(testdataFsys); err != nil {
+			t.Fatalf("AddFS: error = %v", err)
+		}
+		if err := w.Close(); err != nil {
+			t.Fatalf("Close: error = %v", err)
+		}
+
+		var zbuf bytes.Buffer
+		gw := gzip.NewWriter(&zbuf)
+		if _, err := gw.Write(buf.Bytes()); err != nil {
+			t.Fatalf("Write: error = %v", err)
+		}
+		if err := gw.Close(); err != nil {
+			t.Fatalf("Close: error = %v", err)
+		}
+		testdata = zbuf.String()
+	}
+
+	testdataChecksum := func() pkg.Checksum {
+		h := sha512.New384()
+		h.Write([]byte(testdata))
+		return (pkg.Checksum)(h.Sum(nil))
+	}()
+
+	var transport http.Transport
+	client := http.Client{Transport: &transport}
+	transport.RegisterProtocol("file", http.NewFileTransportFS(fstest.MapFS{
+		"testdata": {Data: []byte(testdata), Mode: 0400},
+	}))
+
+	wantIdent := func() pkg.ID {
+		h := sha512.New384()
+		h.Write([]byte{byte(pkg.KindTar), 0, 0, 0, 0, 0, 0, 0})
+		h.Write([]byte{pkg.TarGzip, 0, 0, 0, 0, 0, 0, 0})
+		h.Write([]byte{byte(pkg.KindHTTPGet), 0, 0, 0, 0, 0, 0, 0})
+		httpIdent := pkg.KindHTTPGet.Ident([]byte("file:///testdata"))
+		h.Write(httpIdent[:])
+		return pkg.ID(h.Sum(nil))
+	}()
+
+	a := pkg.NewHTTPGetTar(
+		&client,
+		"file:///testdata",
+		testdataChecksum,
+		pkg.TarGzip,
+	)
+
+	if id := pkg.Ident(a); id != wantIdent {
+		t.Fatalf("Ident: %s, want %s", pkg.Encode(id), pkg.Encode(wantIdent))
+	}
+
+	tarDir := stubArtifact{
+		kind:   pkg.KindExec,
+		params: []byte("directory containing a single regular file"),
+		cure: func(t *pkg.TContext) error {
+			work := t.GetWorkDir()
+			if err := os.MkdirAll(work.String(), 0700); err != nil {
+				return err
+			}
+			return os.WriteFile(
+				work.Append("sample.tar.gz").String(),
+				[]byte(testdata),
+				0400,
+			)
+		},
+	}
+	tarDirMulti := stubArtifact{
+		kind:   pkg.KindExec,
+		params: []byte("directory containing a multiple entries"),
+		cure: func(t *pkg.TContext) error {
+			work := t.GetWorkDir()
+			if err := os.MkdirAll(work.Append(
+				"garbage",
+			).String(), 0700); err != nil {
+				return err
+			}
+			return os.WriteFile(
+				work.Append("sample.tar.gz").String(),
+				[]byte(testdata),
+				0400,
+			)
+		},
+	}
+	tarDirType := stubArtifact{
+		kind:   pkg.KindExec,
+		params: []byte("directory containing a symbolic link"),
+		cure: func(t *pkg.TContext) error {
+			work := t.GetWorkDir()
+			if err := os.MkdirAll(work.String(), 0700); err != nil {
+				return err
+			}
+			return os.Symlink(
+				work.String(),
+				work.Append("sample.tar.gz").String(),
+			)
+		},
+	}
+	// destroy these to avoid including it in flatten test case
+	defer newDestroyArtifactFunc(tarDir)(t, base, c)
+	defer newDestroyArtifactFunc(tarDirMulti)(t, base, c)
+	defer newDestroyArtifactFunc(tarDirType)(t, base, c)
+
+	cureMany(t, c, []cureStep{
+		{"file", a, base.Append(
+			"identifier",
+			pkg.Encode(wantIdent),
+		), wantChecksum, nil},
+
+		{"directory", pkg.NewTar(
+			tarDir,
+			pkg.TarGzip,
+		), ignorePathname, wantChecksum, nil},
+
+		{"multiple entries", pkg.NewTar(
+			tarDirMulti,
+			pkg.TarGzip,
+		), nil, pkg.Checksum{}, errors.New(
+			"input directory does not contain a single regular file",
+		)},
+
+		{"bad type", pkg.NewTar(
+			tarDirType,
+			pkg.TarGzip,
+		), nil, pkg.Checksum{}, errors.New(
+			"input directory does not contain a single regular file",
+		)},
+
+		{"error passthrough", pkg.NewTar(stubArtifact{
+			kind:   pkg.KindExec,
+			params: []byte("doomed artifact"),
+			cure: func(t *pkg.TContext) error {
+				return stub.UniqueError(0xcafe)
+			},
+		}, pkg.TarGzip), nil, pkg.Checksum{}, stub.UniqueError(0xcafe)},
+	})
+}

internal/pkg/testdata/main.go

@@ -0,0 +1,260 @@
+//go:build testtool
+
+package main
+
+import (
+	"encoding/gob"
+	"log"
+	"net"
+	"os"
+	"path"
+	"reflect"
+	"slices"
+	"strings"
+
+	"hakurei.app/container/check"
+	"hakurei.app/container/fhs"
+	"hakurei.app/container/vfs"
+)
+
+func main() {
+	log.SetFlags(0)
+	log.SetPrefix("testtool: ")
+
+	var hostNet, layers bool
+	if len(os.Args) == 2 && os.Args[0] == "testtool" {
+		switch os.Args[1] {
+		case "net":
+			hostNet = true
+			log.SetPrefix("testtool(net): ")
+			break
+
+		case "layers":
+			layers = true
+			log.SetPrefix("testtool(layers): ")
+			break
+
+		default:
+			log.Fatalf("Args: %q", os.Args)
+			return
+		}
+	} else if wantArgs := []string{"testtool"}; !slices.Equal(os.Args, wantArgs) {
+		log.Fatalf("Args: %q, want %q", os.Args, wantArgs)
+	}
+
+	var overlayRoot bool
+	wantEnv := []string{"HAKUREI_TEST=1"}
+	if len(os.Environ()) == 2 {
+		overlayRoot = true
+		if !layers {
+			log.SetPrefix("testtool(overlay root): ")
+		}
+		wantEnv = []string{"HAKUREI_TEST=1", "HAKUREI_ROOT=1"}
+	}
+	if !slices.Equal(wantEnv, os.Environ()) {
+		log.Fatalf("Environ: %q, want %q", os.Environ(), wantEnv)
+	}
+
+	var overlayWork bool
+	const (
+		wantExec     = "/opt/bin/testtool"
+		wantExecWork = "/work/bin/testtool"
+	)
+	var iftPath string
+	if got, err := os.Executable(); err != nil {
+		log.Fatalf("Executable: error = %v", err)
+	} else {
+		iftPath = path.Join(path.Dir(path.Dir(got)), "ift")
+
+		if got != wantExec {
+			switch got {
+			case wantExecWork:
+				overlayWork = true
+				log.SetPrefix("testtool(overlay work): ")
+
+			default:
+				log.Fatalf("Executable: %q, want %q", got, wantExec)
+			}
+		}
+	}
+
+	wantHostname := "cure"
+	if hostNet {
+		wantHostname += "-net"
+	}
+
+	if hostname, err := os.Hostname(); err != nil {
+		log.Fatalf("Hostname: error = %v", err)
+	} else if hostname != wantHostname {
+		log.Fatalf("Hostname: %q, want %q", hostname, wantHostname)
+	}
+
+	var m *vfs.MountInfo
+	if f, err := os.Open(fhs.Proc + "self/mountinfo"); err != nil {
+		log.Fatalf("Open: error = %v", err)
+	} else {
+		err = vfs.NewMountInfoDecoder(f).Decode(&m)
+		closeErr := f.Close()
+		if err != nil {
+			log.Fatalf("Decode: error = %v", err)
+		}
+		if closeErr != nil {
+			log.Fatalf("Close: error = %v", err)
+		}
+	}
+
+	if ift, err := net.Interfaces(); err != nil {
+		log.Fatal(err)
+	} else if !hostNet {
+		if len(ift) != 1 || ift[0].Name != "lo" {
+			log.Fatalln("got interfaces", strings.Join(slices.Collect(func(yield func(ifn string) bool) {
+				for _, ifi := range ift {
+					if !yield(ifi.Name) {
+						break
+					}
+				}
+			}), ", "))
+		}
+	} else {
+		var iftParent []net.Interface
+
+		var r *os.File
+		if r, err = os.Open(iftPath); err != nil {
+			log.Fatal(err)
+		} else {
+			err = gob.NewDecoder(r).Decode(&iftParent)
+			closeErr := r.Close()
+			if err != nil {
+				log.Fatal(err)
+			}
+			if closeErr != nil {
+				log.Fatal(closeErr)
+			}
+		}
+
+		if !reflect.DeepEqual(ift, iftParent) {
+			log.Fatalf("Interfaces: %#v, want %#v", ift, iftParent)
+		}
+	}
+
+	const checksumEmptyDir = "MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU"
+	ident := "U2cbgVgEtjfRuvHfE1cQnZ3t8yoexULQyo_VLgvxAVJSsobMcNaFIsuDWtmt7kzK"
+	log.Println(m)
+	next := func() { m = m.Next; log.Println(m) }
+
+	if overlayRoot {
+		ident = "5ey2wpmMpj483YYa7ZZQciYLA2cx3_l167JCqWW4Pd-5DVp81dj9EsBtVTwYptF6"
+
+		if m.Root != "/" || m.Target != "/" ||
+			m.Source != "overlay" || m.FsType != "overlay" {
+			log.Fatal("unexpected root mount entry")
+		}
+		var lowerdir string
+		for _, o := range strings.Split(m.FsOptstr, ",") {
+			const lowerdirKey = "lowerdir="
+			if strings.HasPrefix(o, lowerdirKey) {
+				lowerdir = o[len(lowerdirKey):]
+			}
+		}
+		if !layers {
+			if path.Base(lowerdir) != checksumEmptyDir {
+				log.Fatal("unexpected artifact checksum")
+			}
+		} else {
+			ident = "tfjrsVuBuFgzWgwz-yPppFtylYuC1VFWnKhyBiHbWTGkyz8lt7Ee9QXWaIHPXs4x"
+
+			lowerdirsEscaped := strings.Split(lowerdir, ":")
+			lowerdirs := lowerdirsEscaped[:0]
+			// ignore the option separator since it does not appear in ident
+			for i, e := range lowerdirsEscaped {
+				if len(e) > 0 &&
+					e[len(e)-1] == check.SpecialOverlayEscape[0] &&
+					(len(e) == 1 || e[len(e)-2] != check.SpecialOverlayEscape[0]) {
+					// ignore escaped pathname separator since it does not
+					// appear in ident
+
+					e = e[:len(e)-1]
+					if len(lowerdirsEscaped) != i {
+						lowerdirsEscaped[i+1] = e + lowerdirsEscaped[i+1]
+						continue
+					}
+				}
+				lowerdirs = append(lowerdirs, e)
+			}
+
+			if len(lowerdirs) != 2 ||
+				path.Base(lowerdirs[0]) != "MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU" ||
+				path.Base(lowerdirs[1]) != "nY_CUdiaUM1OL4cPr5TS92FCJ3rCRV7Hm5oVTzAvMXwC03_QnTRfQ5PPs7mOU9fK" {
+				log.Fatalf("unexpected lowerdirs %s", strings.Join(lowerdirs, ", "))
+			}
+		}
+	} else {
+		if hostNet {
+			ident = "QdsJhGgnk5N2xdUNGcndXQxFKifxf1V_2t9X8CQ-pDcg24x6mGJC_BiLfGbs6Qml"
+		}
+
+		if m.Root != "/sysroot" || m.Target != "/" {
+			log.Fatal("unexpected root mount entry")
+		}
+
+		next()
+		if path.Base(m.Root) != "OLBgp1GsljhM2TJ-sbHjaiH9txEUvgdDTAzHv2P24donTt6_529l-9Ua0vFImLlb" {
+			log.Fatal("unexpected file artifact checksum")
+		}
+
+		next()
+		if path.Base(m.Root) != checksumEmptyDir {
+			log.Fatal("unexpected artifact checksum")
+		}
+	}
+
+	next() // testtool artifact
+
+	next()
+	if overlayWork {
+		ident = "acaDzHZv40dZaz4cGAXayqbRMgbEOuiuiUijZL8IgDQvyeCNMFE3onBMYfny-kXA"
+		if m.Root != "/" || m.Target != "/work" ||
+			m.Source != "overlay" || m.FsType != "overlay" {
+			log.Fatal("unexpected work mount entry")
+		}
+	} else {
+		if path.Base(m.Root) != ident || m.Target != "/work" {
+			log.Fatal("unexpected work mount entry")
+		}
+	}
+
+	next()
+	if path.Base(m.Root) != ident || m.Target != "/tmp" {
+		log.Fatal("unexpected temp mount entry")
+	}
+
+	next()
+	if m.Root != "/" || m.Target != "/proc" || m.Source != "proc" || m.FsType != "proc" {
+		log.Fatal("unexpected proc mount entry")
+	}
+
+	next()
+	if m.Root != "/" || m.Target != "/dev" || m.Source != "devtmpfs" || m.FsType != "tmpfs" {
+		log.Fatal("unexpected dev mount entry")
+	}
+
+	for i := 0; i < 9; i++ { // private /dev entries
+		next()
+	}
+
+	if m.Next != nil {
+		log.Println("unexpected extra mount entries")
+		for m.Next != nil {
+			next()
+		}
+		os.Exit(1)
+	}
+
+	checkData := []byte{0}
+	if hostNet {
+		checkData = []byte("net")
+	}
+	if err := os.WriteFile("check", checkData, 0400); err != nil {
+		log.Fatal(err)
+	}
+}

internal/system/pipewire_test.go

@@ -6,6 +6,7 @@ import (
 	"path"
 	"syscall"
 	"testing"
+	"time"
 
 	"hakurei.app/container/stub"
 	"hakurei.app/internal/acl"
@@ -497,6 +498,12 @@ type stubPipeWireConn struct {
 	curSendmsg int
 }
 
+func (conn *stubPipeWireConn) MightBlock(timeout time.Duration) {
+	if timeout != 5*time.Second {
+		panic("unexpected timeout " + timeout.String())
+	}
+}
+
 // Recvmsg marshals and copies a stubMessage prepared ahead of time.
 func (conn *stubPipeWireConn) Recvmsg(p, _ []byte, _ int) (n, _, recvflags int, err error) {
 	defer func() { conn.curRecvmsg++ }()

ldd/ldd_test.go

@@ -36,7 +36,7 @@ libzstd.so.1 = /usr/lib/libzstd.so.1 (0x7ff71bfd2000)
 
 		{"path not absolute", `
 libzstd.so.1 => usr/lib/libzstd.so.1 (0x7ff71bfd2000)
-`, &check.AbsoluteError{Pathname: "usr/lib/libzstd.so.1"}},
+`, check.AbsoluteError("usr/lib/libzstd.so.1")},
 
 		{"unexpected segments", `
 meow libzstd.so.1 => /usr/lib/libzstd.so.1 (0x7ff71bfd2000)

nixos.nix

@@ -24,11 +24,38 @@ let
   getsubuid = userid: appid: userid * 100000 + 10000 + appid;
   getsubname = userid: appid: "u${toString userid}_a${toString appid}";
   getsubhome = userid: appid: "${cfg.stateDir}/u${toString userid}/a${toString appid}";
+
+  mountpoints = {
+    ${cfg.sharefs.name} = mkIf (cfg.sharefs.source != null) {
+      depends = [ cfg.sharefs.source ];
+      device = "sharefs";
+      fsType = "fuse.sharefs";
+      noCheck = true;
+      options = [
+        "rw"
+        "noexec"
+        "nosuid"
+        "nodev"
+        "noatime"
+        "allow_other"
+        "mkdir"
+        "source=${cfg.sharefs.source}"
+        "setuid=${toString config.users.users.${cfg.sharefs.user}.uid}"
+        "setgid=${toString config.users.groups.${cfg.sharefs.group}.gid}"
+      ];
+    };
+  };
 in
 
 {
   imports = [ (import ./options.nix packages) ];
 
+  options = {
+    # Forward declare a dummy option for VM filesystems since the real one won't exist
+    # unless the VM module is actually imported.
+    virtualisation.fileSystems = lib.mkOption { };
+  };
+
   config = mkIf cfg.enable {
     assertions = [
       (
@@ -66,6 +93,10 @@ in
       ) "" cfg.users;
     };
 
+    environment.systemPackages = optional (cfg.sharefs.source != null) cfg.sharefs.package;
+    fileSystems = mountpoints;
+    virtualisation.fileSystems = mountpoints;
+
     home-manager =
       let
         privPackages = mapAttrs (_: userid: {
@@ -322,25 +353,57 @@ in
       in
       {
         users = mkMerge (
-          foldlAttrs (
+          foldlAttrs
-            acc: _: fid:
+            (
-            acc
+              acc: _: fid:
-            ++ foldlAttrs (
+              acc
-              acc': _: app:
+              ++ foldlAttrs (
-              acc' ++ [ { ${getsubname fid app.identity} = getuser fid app.identity; } ]
+                acc': _: app:
-            ) [ { ${getsubname fid 0} = getuser fid 0; } ] cfg.apps
+                acc' ++ [ { ${getsubname fid app.identity} = getuser fid app.identity; } ]
-          ) [ ] cfg.users
+              ) [ { ${getsubname fid 0} = getuser fid 0; } ] cfg.apps
+            )
+            (
+              if (cfg.sharefs.source != null) then
+                [
+                  {
+                    ${cfg.sharefs.user} = {
+                      uid = lib.mkDefault 1023;
+                      inherit (cfg.sharefs) group;
+                      isSystemUser = true;
+                      home = cfg.sharefs.source;
+                    };
+
+                  }
+                ]
+              else
+                [ ]
+            )
+            cfg.users
         );
 
         groups = mkMerge (
-          foldlAttrs (
+          foldlAttrs
-            acc: _: fid:
+            (
-            acc
+              acc: _: fid:
-            ++ foldlAttrs (
+              acc
-              acc': _: app:
+              ++ foldlAttrs (
-              acc' ++ [ { ${getsubname fid app.identity} = getgroup fid app.identity; } ]
+                acc': _: app:
-            ) [ { ${getsubname fid 0} = getgroup fid 0; } ] cfg.apps
+                acc' ++ [ { ${getsubname fid app.identity} = getgroup fid app.identity; } ]
-          ) [ ] cfg.users
+              ) [ { ${getsubname fid 0} = getgroup fid 0; } ] cfg.apps
+            )
+            (
+              if (cfg.sharefs.source != null) then
+                [
+                  {
+                    ${cfg.sharefs.group} = {
+                      gid = lib.mkDefault 1023;
+                    };
+                  }
+                ]
+              else
+                [ ]
+            )
+            cfg.users
         );
       };
   };

options.md

@@ -809,6 +809,96 @@ package
 
 
 
+## environment\.hakurei\.sharefs\.package
+
+
+
+The sharefs package to use\.
+
+
+
+*Type:*
+package
+
+
+
+*Default:*
+` <derivation sharefs> `
+
+
+
+## environment\.hakurei\.sharefs\.group
+
+
+
+Name of the group to run the sharefs daemon as\.
+
+
+
+*Type:*
+string
+
+
+
+*Default:*
+` "sharefs" `
+
+
+
+## environment\.hakurei\.sharefs\.name
+
+
+
+Host path to mount sharefs on\.
+
+
+
+*Type:*
+string
+
+
+
+*Default:*
+` "/sdcard" `
+
+
+
+## environment\.hakurei\.sharefs\.source
+
+
+
+Writable backing directory\. Setting this to null disables sharefs\.
+
+
+
+*Type:*
+null or string
+
+
+
+*Default:*
+` null `
+
+
+
+## environment\.hakurei\.sharefs\.user
+
+
+
+Name of the user to run the sharefs daemon as\.
+
+
+
+*Type:*
+string
+
+
+
+*Default:*
+` "sharefs" `
+
+
+
 ## environment\.hakurei\.shell
 
 

options.nix

@@ -1,8 +1,15 @@
 packages:
-{ lib, pkgs, ... }:
+{
+  lib,
+  pkgs,
+  config,
+  ...
+}:
 
 let
   inherit (lib) types mkOption mkEnableOption;
+
+  cfg = config.environment.hakurei;
 in
 
 {
@@ -40,6 +47,49 @@ in
         '';
       };
 
+      sharefs = {
+        package = mkOption {
+          type = types.package;
+          default = pkgs.linkFarm "sharefs" {
+            "bin/sharefs" = "${cfg.package}/libexec/sharefs";
+            "bin/mount.fuse.sharefs" = "${cfg.package}/libexec/sharefs";
+          };
+          description = "The sharefs package to use.";
+        };
+
+        user = mkOption {
+          type = types.str;
+          default = "sharefs";
+          description = ''
+            Name of the user to run the sharefs daemon as.
+          '';
+        };
+
+        group = mkOption {
+          type = types.str;
+          default = "sharefs";
+          description = ''
+            Name of the group to run the sharefs daemon as.
+          '';
+        };
+
+        name = mkOption {
+          type = types.str;
+          default = "/sdcard";
+          description = ''
+            Host path to mount sharefs on.
+          '';
+        };
+
+        source = mkOption {
+          type = types.nullOr types.str;
+          default = null;
+          description = ''
+            Writable backing directory. Setting this to null disables sharefs.
+          '';
+        };
+      };
+
       apps = mkOption {
         type =
           let

package.nix

@@ -13,6 +13,9 @@
   wayland-scanner,
   xorg,
 
+  # for sharefs
+  fuse3,
+
   # for hpkg
   zstd,
   gnutar,
@@ -92,6 +95,7 @@ buildGoModule rec {
   buildInputs = [
     libffi
     libseccomp
+    fuse3
     acl
     wayland
   ]

test/interactive/hakurei.nix

@@ -1,8 +1,9 @@
 { pkgs, ... }:
 {
-  environment.hakurei = {
+  environment.hakurei = rec {
     enable = true;
     stateDir = "/var/lib/hakurei";
+    sharefs.source = "${stateDir}/sdcard";
     users.alice = 0;
     apps = {
       "cat.gensokyo.extern.foot.noEnablements" = {