internal/app/paths: defer extra formatting

This reduces payload size for params to shim.

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

cmd/hakurei/command.go

@@ -231,7 +231,7 @@ func buildCommand(ctx context.Context, msg container.Msg, early *earlyHardeningE
 		var flagShort bool
 		c.NewCommand("ps", "List active instances", func(args []string) error {
 			var sc hst.Paths
-			app.CopyPaths(&sc, new(app.Hsu).MustID())
+			app.CopyPaths().Copy(&sc, new(app.Hsu).MustID())
 			printPs(os.Stdout, time.Now().UTC(), state.NewMulti(msg, sc.RunDirPath.String()), flagShort, flagJSON)
 			return errSuccess
 		}).Flag(&flagShort, "short", command.BoolFlag(false), "Print instance id")

cmd/hakurei/parse.go

@@ -89,7 +89,7 @@ func tryShort(msg container.Msg, name string) (config *hst.Config, entry *state.
 		msg.Verbose("argument looks like prefix")
 
 		var sc hst.Paths
-		app.CopyPaths(&sc, new(app.Hsu).MustID())
+		app.CopyPaths().Copy(&sc, new(app.Hsu).MustID())
 		s := state.NewMulti(msg, sc.RunDirPath.String())
 		if entries, err := state.Join(s); err != nil {
 			log.Printf("cannot join store: %v", err)

cmd/hakurei/print.go

@@ -22,7 +22,7 @@ func printShowSystem(output io.Writer, short, flagJSON bool) {
 	defer t.MustFlush()
 
 	info := &hst.Info{User: new(app.Hsu).MustID()}
-	app.CopyPaths(&info.Paths, info.User)
+	app.CopyPaths().Copy(&info.Paths, info.User)
 
 	if flagJSON {
 		printJSON(output, short, info)

internal/app/dispatcher_test.go

@@ -0,0 +1,26 @@
+package app
+
+import (
+	"os"
+	"os/exec"
+
+	"hakurei.app/container"
+)
+
+type panicDispatcher struct{}
+
+func (panicDispatcher) new(func(k syscallDispatcher))         { panic("unreachable") }
+func (panicDispatcher) getuid() int                           { panic("unreachable") }
+func (panicDispatcher) getgid() int                           { panic("unreachable") }
+func (panicDispatcher) lookupEnv(string) (string, bool)       { panic("unreachable") }
+func (panicDispatcher) stat(string) (os.FileInfo, error)      { panic("unreachable") }
+func (panicDispatcher) readdir(string) ([]os.DirEntry, error) { panic("unreachable") }
+func (panicDispatcher) tempdir() string                       { panic("unreachable") }
+func (panicDispatcher) evalSymlinks(string) (string, error)   { panic("unreachable") }
+func (panicDispatcher) lookPath(string) (string, error)       { panic("unreachable") }
+func (panicDispatcher) lookupGroupId(string) (string, error)  { panic("unreachable") }
+func (panicDispatcher) cmdOutput(*exec.Cmd) ([]byte, error)   { panic("unreachable") }
+func (panicDispatcher) overflowUid(container.Msg) int         { panic("unreachable") }
+func (panicDispatcher) overflowGid(container.Msg) int         { panic("unreachable") }
+func (panicDispatcher) mustHsuPath() *container.Absolute      { panic("unreachable") }
+func (panicDispatcher) fatalf(string, ...any)                 { panic("unreachable") }

internal/app/finalise.go

@@ -275,7 +275,7 @@ func (k *outcome) finalise(ctx context.Context, msg container.Msg, config *hst.C
 
 	// TODO(ophestra): revert this after params to shim
 	share := &shareHost{seal: k}
-	copyPaths(k.syscallDispatcher, &share.sc, hsu.MustIDMsg(msg))
+	copyPaths(k.syscallDispatcher).Copy(&share.sc, hsu.MustIDMsg(msg))
 	msg.Verbosef("process share directory at %q, runtime directory at %q", share.sc.SharePath, share.sc.RunDirPath)
 
 	var mapuid, mapgid *stringPair[int]

internal/app/paths.go

@@ -7,28 +7,53 @@ import (
 	"hakurei.app/hst"
 )
 
-// CopyPaths populates a [hst.Paths] struct.
-func CopyPaths(v *hst.Paths, userid int) { copyPaths(direct{}, v, userid) }
-
-// copyPaths populates a [hst.Paths] struct.
-func copyPaths(k syscallDispatcher, v *hst.Paths, userid int) {
-	const xdgRuntimeDir = "XDG_RUNTIME_DIR"
-
-	if tempDir, err := container.NewAbs(k.tempdir()); err != nil {
-		k.fatalf("invalid TMPDIR: %v", err)
-	} else {
-		v.TempDir = tempDir
+// EnvPaths holds paths copied from the environment and is used to create [hst.Paths].
+type EnvPaths struct {
+	// TempDir is returned by [os.TempDir].
+	TempDir *container.Absolute
+	// RuntimePath is copied from $XDG_RUNTIME_DIR.
+	RuntimePath *container.Absolute
 }
 
-	v.SharePath = v.TempDir.Append("hakurei." + strconv.Itoa(userid))
+// Copy expands [EnvPaths] into [hst.Paths].
+func (env *EnvPaths) Copy(v *hst.Paths, userid int) {
+	if env == nil || env.TempDir == nil || v == nil {
+		panic("attempting to use an invalid EnvPaths")
+	}
 
-	r, _ := k.lookupEnv(xdgRuntimeDir)
-	if a, err := container.NewAbs(r); err != nil {
+	v.TempDir = env.TempDir
+	v.SharePath = env.TempDir.Append("hakurei." + strconv.Itoa(userid))
+
+	if env.RuntimePath == nil {
 		// fall back to path in share since hakurei has no hard XDG dependency
 		v.RunDirPath = v.SharePath.Append("run")
 		v.RuntimePath = v.RunDirPath.Append("compat")
 	} else {
-		v.RuntimePath = a
-		v.RunDirPath = v.RuntimePath.Append("hakurei")
+		v.RuntimePath = env.RuntimePath
+		v.RunDirPath = env.RuntimePath.Append("hakurei")
 	}
 }
+
+// CopyPaths returns a populated [EnvPaths].
+func CopyPaths() *EnvPaths { return copyPaths(direct{}) }
+
+// copyPaths returns a populated [EnvPaths].
+func copyPaths(k syscallDispatcher) *EnvPaths {
+	const xdgRuntimeDir = "XDG_RUNTIME_DIR"
+
+	var env EnvPaths
+
+	if tempDir, err := container.NewAbs(k.tempdir()); err != nil {
+		k.fatalf("invalid TMPDIR: %v", err)
+		panic("unreachable")
+	} else {
+		env.TempDir = tempDir
+	}
+
+	r, _ := k.lookupEnv(xdgRuntimeDir)
+	if a, err := container.NewAbs(r); err == nil {
+		env.RuntimePath = a
+	}
+
+	return &env
+}

internal/app/paths_test.go

@@ -0,0 +1,129 @@
+package app
+
+import (
+	"fmt"
+	"reflect"
+	"testing"
+
+	"hakurei.app/container"
+	"hakurei.app/container/stub"
+	"hakurei.app/hst"
+)
+
+func TestEnvPaths(t *testing.T) {
+	testCases := []struct {
+		name string
+		env  *EnvPaths
+		want hst.Paths
+
+		wantPanic string
+	}{
+		{"nil", nil, hst.Paths{}, "attempting to use an invalid EnvPaths"},
+		{"zero", new(EnvPaths), hst.Paths{}, "attempting to use an invalid EnvPaths"},
+
+		{"nil tempdir", &EnvPaths{
+			RuntimePath: container.AbsFHSTmp,
+		}, hst.Paths{}, "attempting to use an invalid EnvPaths"},
+
+		{"nil runtime", &EnvPaths{
+			TempDir: container.AbsFHSTmp,
+		}, hst.Paths{
+			TempDir:     container.AbsFHSTmp,
+			SharePath:   container.AbsFHSTmp.Append("hakurei.3735928559"),
+			RuntimePath: container.AbsFHSTmp.Append("hakurei.3735928559/run/compat"),
+			RunDirPath:  container.AbsFHSTmp.Append("hakurei.3735928559/run"),
+		}, ""},
+
+		{"full", &EnvPaths{
+			TempDir:     container.AbsFHSTmp,
+			RuntimePath: container.AbsFHSRunUser.Append("1000"),
+		}, hst.Paths{
+			TempDir:     container.AbsFHSTmp,
+			SharePath:   container.AbsFHSTmp.Append("hakurei.3735928559"),
+			RuntimePath: container.AbsFHSRunUser.Append("1000"),
+			RunDirPath:  container.AbsFHSRunUser.Append("1000/hakurei"),
+		}, ""},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			if tc.wantPanic != "" {
+				defer func() {
+					if r := recover(); r != tc.wantPanic {
+						t.Errorf("Copy: panic = %#v, want %q", r, tc.wantPanic)
+					}
+				}()
+			}
+
+			var sc hst.Paths
+			tc.env.Copy(&sc, 0xdeadbeef)
+			if !reflect.DeepEqual(&sc, &tc.want) {
+				t.Errorf("Copy: %#v, want %#v", sc, tc.want)
+			}
+		})
+	}
+}
+
+func TestCopyPaths(t *testing.T) {
+	testCases := []struct {
+		name  string
+		env   map[string]string
+		tmp   string
+		fatal string
+		want  EnvPaths
+	}{
+		{"invalid tempdir", nil, "\x00",
+			"invalid TMPDIR: path \"\\x00\" is not absolute", EnvPaths{}},
+		{"empty environment", make(map[string]string), container.Nonexistent,
+			"", EnvPaths{TempDir: container.MustAbs(container.Nonexistent)}},
+		{"invalid XDG_RUNTIME_DIR", map[string]string{"XDG_RUNTIME_DIR": "\x00"}, container.Nonexistent,
+			"", EnvPaths{TempDir: container.MustAbs(container.Nonexistent)}},
+		{"full", map[string]string{"XDG_RUNTIME_DIR": "/\x00"}, container.Nonexistent,
+			"", EnvPaths{TempDir: container.MustAbs(container.Nonexistent), RuntimePath: container.MustAbs("/\x00")}},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			if tc.fatal != "" {
+				defer stub.HandleExit(t)
+			}
+
+			k := copyPathsDispatcher{t: t, env: tc.env, tmp: tc.tmp, expectsFatal: tc.fatal}
+			got := copyPaths(k)
+
+			if tc.fatal != "" {
+				t.Fatalf("copyPaths: expected fatal %q", tc.fatal)
+			}
+
+			if !reflect.DeepEqual(got, &tc.want) {
+				t.Errorf("copyPaths: %#v, want %#v", got, &tc.want)
+			}
+		})
+	}
+}
+
+// copyPathsDispatcher implements enough of syscallDispatcher for all copyPaths code paths.
+type copyPathsDispatcher struct {
+	env map[string]string
+	tmp string
+
+	// must be checked at the conclusion of the test
+	expectsFatal string
+
+	t *testing.T
+	panicDispatcher
+}
+
+func (k copyPathsDispatcher) tempdir() string { return k.tmp }
+func (k copyPathsDispatcher) lookupEnv(key string) (value string, ok bool) {
+	value, ok = k.env[key]
+	return
+}
+func (k copyPathsDispatcher) fatalf(format string, v ...any) {
+	if k.expectsFatal == "" {
+		k.t.Fatalf("unexpected call to fatalf: format = %q, v = %#v", format, v)
+	}
+
+	if got := fmt.Sprintf(format, v...); got != k.expectsFatal {
+		k.t.Fatalf("fatalf: %q, want %q", got, k.expectsFatal)
+	}
+	panic(stub.PanicExit)
+}