internal/params: relocate from package container

This does not make sense as part of the public API, so make it internal.

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

container/container_test.go

@@ -26,6 +26,7 @@ import (
 	"hakurei.app/fhs"
 	"hakurei.app/hst"
 	"hakurei.app/internal/info"
+	"hakurei.app/internal/params"
 	"hakurei.app/ldd"
 	"hakurei.app/message"
 	"hakurei.app/vfs"
@@ -84,9 +85,9 @@ func TestStartError(t *testing.T) {
 		{"params env", &container.StartError{
 			Fatal: true,
 			Step:  "set up params stream",
-			Err:   container.ErrReceiveEnv,
+			Err:   params.ErrReceiveEnv,
 		}, "set up params stream: environment variable not set",
-			container.ErrReceiveEnv, syscall.EBADF,
+			params.ErrReceiveEnv, syscall.EBADF,
 			"cannot set up params stream: environment variable not set"},
 
 		{"params", &container.StartError{

container/dispatcher.go

@@ -16,6 +16,7 @@ import (
 	"hakurei.app/container/std"
 	"hakurei.app/ext"
 	"hakurei.app/internal/netlink"
+	"hakurei.app/internal/params"
 	"hakurei.app/message"
 )
 
@@ -56,7 +57,7 @@ type syscallDispatcher interface {
 	// isatty provides [Isatty].
 	isatty(fd int) bool
 	// receive provides [Receive].
-	receive(key string, e any, fdp *uintptr) (closeFunc func() error, err error)
+	receive(key string, e any, fdp *int) (closeFunc func() error, err error)
 
 	// bindMount provides procPaths.bindMount.
 	bindMount(msg message.Msg, source, target string, flags uintptr) error
@@ -155,8 +156,8 @@ func (direct) capBoundingSetDrop(cap uintptr) error            { return capBound
 func (direct) capAmbientClearAll() error                       { return capAmbientClearAll() }
 func (direct) capAmbientRaise(cap uintptr) error               { return capAmbientRaise(cap) }
 func (direct) isatty(fd int) bool                              { return ext.Isatty(fd) }
-func (direct) receive(key string, e any, fdp *uintptr) (func() error, error) {
-	return Receive(key, e, fdp)
+func (direct) receive(key string, e any, fdp *int) (func() error, error) {
+	return params.Receive(key, e, fdp)
 }
 
 func (direct) bindMount(msg message.Msg, source, target string, flags uintptr) error {

container/dispatcher_test.go

@@ -390,7 +390,7 @@ func (k *kstub) isatty(fd int) bool {
 	return expect.Ret.(bool)
 }
 
-func (k *kstub) receive(key string, e any, fdp *uintptr) (closeFunc func() error, err error) {
+func (k *kstub) receive(key string, e any, fdp *int) (closeFunc func() error, err error) {
 	k.Helper()
 	expect := k.Expects("receive")
 
@@ -408,10 +408,17 @@ func (k *kstub) receive(key string, e any, fdp *uintptr) (closeFunc func() error
 		}
 		return nil
 	}
+
+	// avoid changing test cases
+	var fdpComp *uintptr
+	if fdp != nil {
+		fdpComp = new(uintptr(*fdp))
+	}
+
 	err = expect.Error(
 		stub.CheckArg(k.Stub, "key", key, 0),
 		stub.CheckArgReflect(k.Stub, "e", e, 1),
-		stub.CheckArgReflect(k.Stub, "fdp", fdp, 2))
+		stub.CheckArgReflect(k.Stub, "fdp", fdpComp, 2))
 
 	// 3 is unused so stores params
 	if expect.Args[3] != nil {
@@ -426,7 +433,7 @@ func (k *kstub) receive(key string, e any, fdp *uintptr) (closeFunc func() error
 	if expect.Args[4] != nil {
 		if v, ok := expect.Args[4].(uintptr); ok && v >= 3 {
 			if fdp != nil {
-				*fdp = v
+				*fdp = int(v)
 			}
 		}
 	}

container/init.go

@@ -19,6 +19,7 @@ import (
 	"hakurei.app/container/seccomp"
 	"hakurei.app/ext"
 	"hakurei.app/fhs"
+	"hakurei.app/internal/params"
 	"hakurei.app/message"
 )
 
@@ -147,35 +148,33 @@ func initEntrypoint(k syscallDispatcher, msg message.Msg) {
 	}
 
 	var (
-		params      initParams
+		param      initParams
 		closeSetup func() error
-		setupFd     uintptr
-		offsetSetup int
+		setupFd    int
 	)
-	if f, err := k.receive(setupEnv, &params, &setupFd); err != nil {
+	if f, err := k.receive(setupEnv, &param, &setupFd); err != nil {
 		if errors.Is(err, EBADF) {
 			k.fatal(msg, "invalid setup descriptor")
 		}
-		if errors.Is(err, ErrReceiveEnv) {
+		if errors.Is(err, params.ErrReceiveEnv) {
 			k.fatal(msg, setupEnv+" not set")
 		}
 
 		k.fatalf(msg, "cannot decode init setup payload: %v", err)
 	} else {
-		if params.Ops == nil {
+		if param.Ops == nil {
 			k.fatal(msg, "invalid setup parameters")
 		}
-		if params.ParentPerm == 0 {
-			params.ParentPerm = 0755
+		if param.ParentPerm == 0 {
+			param.ParentPerm = 0755
 		}
 
-		msg.SwapVerbose(params.Verbose)
+		msg.SwapVerbose(param.Verbose)
 		msg.Verbose("received setup parameters")
 		closeSetup = f
-		offsetSetup = int(setupFd + 1)
 	}
 
-	if !params.HostNet {
+	if !param.HostNet {
 		ctx, cancel := signal.NotifyContext(context.Background(), CancelSignal,
 			os.Interrupt, SIGTERM, SIGQUIT)
 		defer cancel() // for panics
@@ -188,7 +187,7 @@ func initEntrypoint(k syscallDispatcher, msg message.Msg) {
 		k.fatalf(msg, "cannot set SUID_DUMP_USER: %v", err)
 	}
 	if err := k.writeFile(fhs.Proc+"self/uid_map",
-		append([]byte{}, strconv.Itoa(params.Uid)+" "+strconv.Itoa(params.HostUid)+" 1\n"...),
+		append([]byte{}, strconv.Itoa(param.Uid)+" "+strconv.Itoa(param.HostUid)+" 1\n"...),
 		0); err != nil {
 		k.fatalf(msg, "%v", err)
 	}
@@ -198,7 +197,7 @@ func initEntrypoint(k syscallDispatcher, msg message.Msg) {
 		k.fatalf(msg, "%v", err)
 	}
 	if err := k.writeFile(fhs.Proc+"self/gid_map",
-		append([]byte{}, strconv.Itoa(params.Gid)+" "+strconv.Itoa(params.HostGid)+" 1\n"...),
+		append([]byte{}, strconv.Itoa(param.Gid)+" "+strconv.Itoa(param.HostGid)+" 1\n"...),
 		0); err != nil {
 		k.fatalf(msg, "%v", err)
 	}
@@ -207,8 +206,8 @@ func initEntrypoint(k syscallDispatcher, msg message.Msg) {
 	}
 
 	oldmask := k.umask(0)
-	if params.Hostname != "" {
-		if err := k.sethostname([]byte(params.Hostname)); err != nil {
+	if param.Hostname != "" {
+		if err := k.sethostname([]byte(param.Hostname)); err != nil {
 			k.fatalf(msg, "cannot set hostname: %v", err)
 		}
 	}
@@ -221,7 +220,7 @@ func initEntrypoint(k syscallDispatcher, msg message.Msg) {
 	}
 
 	ctx, cancel := context.WithCancel(context.Background())
-	state := &setupState{process: make(map[int]WaitStatus), Params: &params.Params, Msg: msg, Context: ctx}
+	state := &setupState{process: make(map[int]WaitStatus), Params: &param.Params, Msg: msg, Context: ctx}
 	defer cancel()
 
 	/* early is called right before pivot_root into intermediate root;
@@ -229,7 +228,7 @@ func initEntrypoint(k syscallDispatcher, msg message.Msg) {
 	difficult to obtain via library functions after pivot_root, and
 	implementations are expected to avoid changing the state of the mount
 	namespace */
-	for i, op := range *params.Ops {
+	for i, op := range *param.Ops {
 		if op == nil || !op.Valid() {
 			k.fatalf(msg, "invalid op at index %d", i)
 		}
@@ -272,7 +271,7 @@ func initEntrypoint(k syscallDispatcher, msg message.Msg) {
 	step sets up the container filesystem, and implementations are expected to
 	keep the host root and sysroot mount points intact but otherwise can do
 	whatever they need to. Calling chdir is allowed but discouraged. */
-	for i, op := range *params.Ops {
+	for i, op := range *param.Ops {
 		// ops already checked during early setup
 		if prefix, ok := op.prefix(); ok {
 			msg.Verbosef("%s %s", prefix, op)
@@ -328,7 +327,7 @@ func initEntrypoint(k syscallDispatcher, msg message.Msg) {
 		k.fatalf(msg, "cannot clear the ambient capability set: %v", err)
 	}
 	for i := uintptr(0); i <= lastcap; i++ {
-		if params.Privileged && i == CAP_SYS_ADMIN {
+		if param.Privileged && i == CAP_SYS_ADMIN {
 			continue
 		}
 		if err := k.capBoundingSetDrop(i); err != nil {
@@ -337,7 +336,7 @@ func initEntrypoint(k syscallDispatcher, msg message.Msg) {
 	}
 
 	var keep [2]uint32
-	if params.Privileged {
+	if param.Privileged {
 		keep[capToIndex(CAP_SYS_ADMIN)] |= capToMask(CAP_SYS_ADMIN)
 
 		if err := k.capAmbientRaise(CAP_SYS_ADMIN); err != nil {
@@ -351,13 +350,13 @@ func initEntrypoint(k syscallDispatcher, msg message.Msg) {
 		k.fatalf(msg, "cannot capset: %v", err)
 	}
 
-	if !params.SeccompDisable {
-		rules := params.SeccompRules
+	if !param.SeccompDisable {
+		rules := param.SeccompRules
 		if len(rules) == 0 { // non-empty rules slice always overrides presets
-			msg.Verbosef("resolving presets %#x", params.SeccompPresets)
-			rules = seccomp.Preset(params.SeccompPresets, params.SeccompFlags)
+			msg.Verbosef("resolving presets %#x", param.SeccompPresets)
+			rules = seccomp.Preset(param.SeccompPresets, param.SeccompFlags)
 		}
-		if err := k.seccompLoad(rules, params.SeccompFlags); err != nil {
+		if err := k.seccompLoad(rules, param.SeccompFlags); err != nil {
 			// this also indirectly asserts PR_SET_NO_NEW_PRIVS
 			k.fatalf(msg, "cannot load syscall filter: %v", err)
 		}
@@ -366,10 +365,10 @@ func initEntrypoint(k syscallDispatcher, msg message.Msg) {
 		msg.Verbose("syscall filter not configured")
 	}
 
-	extraFiles := make([]*os.File, params.Count)
+	extraFiles := make([]*os.File, param.Count)
 	for i := range extraFiles {
 		// setup fd is placed before all extra files
-		extraFiles[i] = k.newFile(uintptr(offsetSetup+i), "extra file "+strconv.Itoa(i))
+		extraFiles[i] = k.newFile(uintptr(setupFd+1+i), "extra file "+strconv.Itoa(i))
 	}
 	k.umask(oldmask)
 
@@ -447,7 +446,7 @@ func initEntrypoint(k syscallDispatcher, msg message.Msg) {
 
 	// called right before startup of initial process, all state changes to the
 	// current process is prohibited during late
-	for i, op := range *params.Ops {
+	for i, op := range *param.Ops {
 		// ops already checked during early setup
 		if err := op.late(state, k); err != nil {
 			if m, ok := messageFromError(err); ok {
@@ -468,14 +467,14 @@ func initEntrypoint(k syscallDispatcher, msg message.Msg) {
 		k.fatalf(msg, "cannot close setup pipe: %v", err)
 	}
 
-	cmd := exec.Command(params.Path.String())
+	cmd := exec.Command(param.Path.String())
 	cmd.Stdin, cmd.Stdout, cmd.Stderr = os.Stdin, os.Stdout, os.Stderr
-	cmd.Args = params.Args
-	cmd.Env = params.Env
+	cmd.Args = param.Args
+	cmd.Env = param.Env
 	cmd.ExtraFiles = extraFiles
-	cmd.Dir = params.Dir.String()
+	cmd.Dir = param.Dir.String()
 
-	msg.Verbosef("starting initial process %s", params.Path)
+	msg.Verbosef("starting initial process %s", param.Path)
 	if err := k.start(cmd); err != nil {
 		k.fatalf(msg, "%v", err)
 	}
@@ -493,7 +492,7 @@ func initEntrypoint(k syscallDispatcher, msg message.Msg) {
 	for {
 		select {
 		case s := <-sig:
-			if s == CancelSignal && params.ForwardCancel && cmd.Process != nil {
+			if s == CancelSignal && param.ForwardCancel && cmd.Process != nil {
 				msg.Verbose("forwarding context cancellation")
 				if err := k.signal(cmd, os.Interrupt); err != nil && !errors.Is(err, os.ErrProcessDone) {
 					k.printf(msg, "cannot forward cancellation: %v", err)
@@ -525,7 +524,7 @@ func initEntrypoint(k syscallDispatcher, msg message.Msg) {
 				cancel()
 
 				// start timeout early
-				go func() { time.Sleep(params.AdoptWaitDelay); close(timeout) }()
+				go func() { time.Sleep(param.AdoptWaitDelay); close(timeout) }()
 
 				// close initial process files; this also keeps them alive
 				for _, f := range extraFiles {

container/init_test.go

@@ -10,6 +10,7 @@ import (
 	"hakurei.app/check"
 	"hakurei.app/container/seccomp"
 	"hakurei.app/container/std"
+	"hakurei.app/internal/params"
 	"hakurei.app/internal/stub"
 )
 
@@ -40,7 +41,7 @@ func TestInitEntrypoint(t *testing.T) {
 				call("lockOSThread", stub.ExpectArgs{}, nil, nil),
 				call("getpid", stub.ExpectArgs{}, 1, nil),
 				call("setPtracer", stub.ExpectArgs{uintptr(0)}, nil, nil),
-				call("receive", stub.ExpectArgs{"HAKUREI_SETUP", new(initParams), new(uintptr)}, nil, ErrReceiveEnv),
+				call("receive", stub.ExpectArgs{"HAKUREI_SETUP", new(initParams), new(uintptr)}, nil, params.ErrReceiveEnv),
 				call("fatal", stub.ExpectArgs{[]any{"HAKUREI_SETUP not set"}}, nil, nil),
 			},
 		}, nil},

container/params.go

@@ -1,36 +0,0 @@
-package container
-
-import (
-	"encoding/gob"
-	"errors"
-	"os"
-	"strconv"
-	"syscall"
-)
-
-var (
-	ErrReceiveEnv = errors.New("environment variable not set")
-)
-
-// Receive retrieves setup fd from the environment and receives params.
-func Receive(key string, e any, fdp *uintptr) (func() error, error) {
-	var setup *os.File
-
-	if s, ok := os.LookupEnv(key); !ok {
-		return nil, ErrReceiveEnv
-	} else {
-		if fd, err := strconv.Atoi(s); err != nil {
-			return nil, optionalErrorUnwrap(err)
-		} else {
-			setup = os.NewFile(uintptr(fd), "setup")
-			if setup == nil {
-				return nil, syscall.EDOM
-			}
-			if fdp != nil {
-				*fdp = setup.Fd()
-			}
-		}
-	}
-
-	return setup.Close, gob.NewDecoder(setup).Decode(e)
-}

container/params_test.go

@@ -1,53 +0,0 @@
-package container_test
-
-import (
-	"errors"
-	"os"
-	"strconv"
-	"syscall"
-	"testing"
-
-	"hakurei.app/container"
-)
-
-func TestSetupReceive(t *testing.T) {
-	t.Run("not set", func(t *testing.T) {
-		const key = "TEST_ENV_NOT_SET"
-		{
-			v, ok := os.LookupEnv(key)
-			t.Cleanup(func() {
-				if ok {
-					if err := os.Setenv(key, v); err != nil {
-						t.Fatalf("Setenv: error = %v", err)
-					}
-				} else {
-					if err := os.Unsetenv(key); err != nil {
-						t.Fatalf("Unsetenv: error = %v", err)
-					}
-				}
-			})
-		}
-
-		if _, err := container.Receive(key, nil, nil); !errors.Is(err, container.ErrReceiveEnv) {
-			t.Errorf("Receive: error = %v, want %v", err, container.ErrReceiveEnv)
-		}
-	})
-
-	t.Run("format", func(t *testing.T) {
-		const key = "TEST_ENV_FORMAT"
-		t.Setenv(key, "")
-
-		if _, err := container.Receive(key, nil, nil); !errors.Is(err, strconv.ErrSyntax) {
-			t.Errorf("Receive: error = %v, want %v", err, strconv.ErrSyntax)
-		}
-	})
-
-	t.Run("range", func(t *testing.T) {
-		const key = "TEST_ENV_RANGE"
-		t.Setenv(key, "-1")
-
-		if _, err := container.Receive(key, nil, nil); !errors.Is(err, syscall.EDOM) {
-			t.Errorf("Receive: error = %v, want %v", err, syscall.EDOM)
-		}
-	})
-}

internal/outcome/dispatcher.go

@@ -17,6 +17,7 @@ import (
 	"hakurei.app/ext"
 	"hakurei.app/internal/dbus"
 	"hakurei.app/internal/info"
+	"hakurei.app/internal/params"
 	"hakurei.app/message"
 )
 
@@ -84,7 +85,7 @@ type syscallDispatcher interface {
 	// setDumpable provides [container.SetDumpable].
 	setDumpable(dumpable uintptr) error
 	// receive provides [container.Receive].
-	receive(key string, e any, fdp *uintptr) (closeFunc func() error, err error)
+	receive(key string, e any, fdp *int) (closeFunc func() error, err error)
 
 	// containerStart provides the Start method of [container.Container].
 	containerStart(z *container.Container) error
@@ -154,8 +155,8 @@ func (direct) prctl(op, arg2, arg3 uintptr) error { return ext.Prctl(op, arg2, a
 func (direct) overflowUid(msg message.Msg) int    { return container.OverflowUid(msg) }
 func (direct) overflowGid(msg message.Msg) int    { return container.OverflowGid(msg) }
 func (direct) setDumpable(dumpable uintptr) error { return ext.SetDumpable(dumpable) }
-func (direct) receive(key string, e any, fdp *uintptr) (func() error, error) {
-	return container.Receive(key, e, fdp)
+func (direct) receive(key string, e any, fdp *int) (func() error, error) {
+	return params.Receive(key, e, fdp)
 }
 
 func (direct) containerStart(z *container.Container) error { return z.Start() }

internal/outcome/dispatcher_test.go

@@ -401,12 +401,12 @@ func (k *kstub) setDumpable(dumpable uintptr) error {
 		stub.CheckArg(k.Stub, "dumpable", dumpable, 0))
 }
 
-func (k *kstub) receive(key string, e any, fdp *uintptr) (closeFunc func() error, err error) {
+func (k *kstub) receive(key string, e any, fdp *int) (closeFunc func() error, err error) {
 	k.Helper()
 	expect := k.Expects("receive")
 	reflect.ValueOf(e).Elem().Set(reflect.ValueOf(expect.Args[1]))
 	if expect.Args[2] != nil {
-		*fdp = expect.Args[2].(uintptr)
+		*fdp = int(expect.Args[2].(uintptr))
 	}
 	return func() error { return k.Expects("closeReceive").Err }, expect.Error(
 		stub.CheckArg(k.Stub, "key", key, 0))
@@ -712,7 +712,7 @@ func (panicDispatcher) cmdOutput(*exec.Cmd) ([]byte, error)                 { pa
 func (panicDispatcher) overflowUid(message.Msg) int                        { panic("unreachable") }
 func (panicDispatcher) overflowGid(message.Msg) int                        { panic("unreachable") }
 func (panicDispatcher) setDumpable(uintptr) error                          { panic("unreachable") }
-func (panicDispatcher) receive(string, any, *uintptr) (func() error, error) { panic("unreachable") }
+func (panicDispatcher) receive(string, any, *int) (func() error, error)    { panic("unreachable") }
 func (panicDispatcher) containerStart(*container.Container) error          { panic("unreachable") }
 func (panicDispatcher) containerServe(*container.Container) error          { panic("unreachable") }
 func (panicDispatcher) containerWait(*container.Container) error           { panic("unreachable") }

internal/outcome/shim.go

@@ -20,6 +20,7 @@ import (
 	"hakurei.app/ext"
 	"hakurei.app/fhs"
 	"hakurei.app/hst"
+	"hakurei.app/internal/params"
 	"hakurei.app/internal/pipewire"
 	"hakurei.app/message"
 )
@@ -197,7 +198,7 @@ func shimEntrypoint(k syscallDispatcher) {
 		if errors.Is(err, syscall.EBADF) {
 			k.fatal("invalid config descriptor")
 		}
-		if errors.Is(err, container.ErrReceiveEnv) {
+		if errors.Is(err, params.ErrReceiveEnv) {
 			k.fatal(shimEnv + " not set")
 		}
 

internal/outcome/shim_test.go

@@ -16,6 +16,7 @@ import (
 	"hakurei.app/fhs"
 	"hakurei.app/hst"
 	"hakurei.app/internal/env"
+	"hakurei.app/internal/params"
 	"hakurei.app/internal/stub"
 )
 
@@ -172,7 +173,7 @@ func TestShimEntrypoint(t *testing.T) {
 			call("setDumpable", stub.ExpectArgs{uintptr(ext.SUID_DUMP_DISABLE)}, nil, nil),
 			call("getppid", stub.ExpectArgs{}, 0xbad, nil),
 			call("setupContSignal", stub.ExpectArgs{0xbad}, 0, nil),
-			call("receive", stub.ExpectArgs{"HAKUREI_SHIM", outcomeState{}, nil}, nil, container.ErrReceiveEnv),
+			call("receive", stub.ExpectArgs{"HAKUREI_SHIM", outcomeState{}, nil}, nil, params.ErrReceiveEnv),
 			call("fatal", stub.ExpectArgs{[]any{"HAKUREI_SHIM not set"}}, nil, nil),
 
 			// deferred

internal/params/params.go

@@ -0,0 +1,42 @@
+// Package params provides helpers for receiving setup payload from parent.
+package params
+
+import (
+	"encoding/gob"
+	"errors"
+	"os"
+	"strconv"
+	"syscall"
+)
+
+// ErrReceiveEnv is returned by [Receive] if setup fd is not present in environment.
+var ErrReceiveEnv = errors.New("environment variable not set")
+
+// Receive retrieves setup fd from the environment and receives params.
+//
+// The file descriptor written to the value pointed to by fdp must not be passed
+// to any system calls. It is made available for ordering file descriptor only.
+func Receive(key string, v any, fdp *int) (func() error, error) {
+	var setup *os.File
+
+	if s, ok := os.LookupEnv(key); !ok {
+		return nil, ErrReceiveEnv
+	} else {
+		if fd, err := strconv.Atoi(s); err != nil {
+			if _err := errors.Unwrap(err); _err != nil {
+				err = _err
+			}
+			return nil, err
+		} else {
+			setup = os.NewFile(uintptr(fd), "setup")
+			if setup == nil {
+				return nil, syscall.EDOM
+			}
+			if fdp != nil {
+				*fdp = fd
+			}
+		}
+	}
+
+	return setup.Close, gob.NewDecoder(setup).Decode(v)
+}

internal/params/params_test.go

@@ -0,0 +1,131 @@
+package params_test
+
+import (
+	"encoding/gob"
+	"errors"
+	"os"
+	"slices"
+	"strconv"
+	"syscall"
+	"testing"
+
+	"hakurei.app/internal/params"
+)
+
+func TestSetupReceive(t *testing.T) {
+	t.Run("not set", func(t *testing.T) {
+		const key = "TEST_ENV_NOT_SET"
+		{
+			v, ok := os.LookupEnv(key)
+			t.Cleanup(func() {
+				if ok {
+					if err := os.Setenv(key, v); err != nil {
+						t.Fatalf("Setenv: error = %v", err)
+					}
+				} else {
+					if err := os.Unsetenv(key); err != nil {
+						t.Fatalf("Unsetenv: error = %v", err)
+					}
+				}
+			})
+		}
+
+		if _, err := params.Receive(key, nil, nil); !errors.Is(err, params.ErrReceiveEnv) {
+			t.Errorf("Receive: error = %v, want %v", err, params.ErrReceiveEnv)
+		}
+	})
+
+	t.Run("format", func(t *testing.T) {
+		const key = "TEST_ENV_FORMAT"
+		t.Setenv(key, "")
+
+		if _, err := params.Receive(key, nil, nil); !errors.Is(err, strconv.ErrSyntax) {
+			t.Errorf("Receive: error = %v, want %v", err, strconv.ErrSyntax)
+		}
+	})
+
+	t.Run("range", func(t *testing.T) {
+		const key = "TEST_ENV_RANGE"
+		t.Setenv(key, "-1")
+
+		if _, err := params.Receive(key, nil, nil); !errors.Is(err, syscall.EDOM) {
+			t.Errorf("Receive: error = %v, want %v", err, syscall.EDOM)
+		}
+	})
+
+	t.Run("setup receive", func(t *testing.T) {
+		check := func(t *testing.T, useNilFdp bool) {
+			const key = "TEST_SETUP_RECEIVE"
+			payload := []uint64{syscall.MS_MGC_VAL, syscall.MS_MGC_MSK, syscall.MS_ASYNC, syscall.MS_ACTIVE}
+
+			encoderDone := make(chan error, 1)
+			extraFiles := make([]*os.File, 0, 1)
+			if r, w, err := os.Pipe(); err != nil {
+				t.Fatalf("Setup: error = %v", err)
+			} else {
+				t.Cleanup(func() {
+					if err = errors.Join(r.Close(), w.Close()); err != nil {
+						t.Fatal(err)
+					}
+				})
+
+				extraFiles = append(extraFiles, r)
+				if deadline, ok := t.Deadline(); ok {
+					if err = w.SetDeadline(deadline); err != nil {
+						t.Fatal(err)
+					}
+				}
+				go func() { encoderDone <- gob.NewEncoder(w).Encode(payload) }()
+			}
+
+			if len(extraFiles) != 1 {
+				t.Fatalf("extraFiles: len = %v, want 1", len(extraFiles))
+			}
+
+			var dupFd int
+			if fd, err := syscall.Dup(int(extraFiles[0].Fd())); err != nil {
+				t.Fatalf("Dup: error = %v", err)
+			} else {
+				syscall.CloseOnExec(fd)
+				dupFd = fd
+				t.Setenv(key, strconv.Itoa(fd))
+			}
+
+			var (
+				gotPayload []uint64
+				fdp        *int
+			)
+			if !useNilFdp {
+				fdp = new(int)
+			}
+			var closeFile func() error
+			if f, err := params.Receive(key, &gotPayload, fdp); err != nil {
+				t.Fatalf("Receive: error = %v", err)
+			} else {
+				closeFile = f
+
+				if !slices.Equal(payload, gotPayload) {
+					t.Errorf("Receive: %#v, want %#v", gotPayload, payload)
+				}
+			}
+			if !useNilFdp {
+				if *fdp != dupFd {
+					t.Errorf("Fd: %d, want %d", *fdp, dupFd)
+				}
+			}
+
+			if err := <-encoderDone; err != nil {
+				t.Errorf("Encode: error = %v", err)
+			}
+
+			if closeFile != nil {
+				if err := closeFile(); err != nil {
+					t.Errorf("Close: error = %v", err)
+				}
+			}
+		}
+
+		t.Run("fp", func(t *testing.T) { check(t, false) })
+		t.Run("nil", func(t *testing.T) { check(t, true) })
+	})
+}