message: relocate from container

This package is quite useful. This change allows it to be imported without importing container.

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

15 files changed, 58 insertions, 583 deletions

diff --git a/container/autoroot.go b/container/autoroot.go
index 0ebe6b2b..f555acad 100644
--- a/container/autoroot.go
+++ b/container/autoroot.go
@@ -6,6 +6,7 @@ import (
 
 	"hakurei.app/container/check"
 	"hakurei.app/container/fhs"
+	"hakurei.app/message"
 )
 
 func init() { gob.Register(new(AutoRootOp)) }
@@ -81,7 +82,7 @@ func (r *AutoRootOp) String() string {
 }
 
 // IsAutoRootBindable returns whether a dir entry name is selected for AutoRoot.
-func IsAutoRootBindable(msg Msg, name string) bool {
+func IsAutoRootBindable(msg message.Msg, name string) bool {
 	switch name {
 	case "proc", "dev", "tmp", "mnt", "etc":
 
diff --git a/container/autoroot_test.go b/container/autoroot_test.go
index 8c72b789..d53edc71 100644
--- a/container/autoroot_test.go
+++ b/container/autoroot_test.go
@@ -8,6 +8,7 @@ import (
 	"hakurei.app/container/bits"
 	"hakurei.app/container/check"
 	"hakurei.app/container/stub"
+	"hakurei.app/message"
 )
 
 func TestAutoRootOp(t *testing.T) {
@@ -195,7 +196,7 @@ func TestIsAutoRootBindable(t *testing.T) {
 	}
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {
-			var msg Msg
+			var msg message.Msg
 			if tc.log {
 				msg = &kstub{nil, stub.New(t, func(s *stub.Stub[syscallDispatcher]) syscallDispatcher { panic("unreachable") }, stub.Expect{Calls: []stub.Call{
 					call("verbose", stub.ExpectArgs{[]any{"got unexpected root entry"}}, nil, nil),
diff --git a/container/container.go b/container/container.go
index 5b6514d4..ae83fc30 100644
--- a/container/container.go
+++ b/container/container.go
@@ -18,6 +18,7 @@ import (
 	"hakurei.app/container/check"
 	"hakurei.app/container/fhs"
 	"hakurei.app/container/seccomp"
+	"hakurei.app/message"
 )
 
 const (
@@ -52,7 +53,7 @@ type (
 
 		cmd *exec.Cmd
 		ctx context.Context
-		msg Msg
+		msg message.Msg
 		Params
 	}
 
@@ -396,9 +397,9 @@ func (p *Container) ProcessState() *os.ProcessState {
 }
 
 // New returns the address to a new instance of [Container] that requires further initialisation before use.
-func New(ctx context.Context, msg Msg) *Container {
+func New(ctx context.Context, msg message.Msg) *Container {
 	if msg == nil {
-		msg = NewMsg(nil)
+		msg = message.NewMsg(nil)
 	}
 
 	p := &Container{ctx: ctx, msg: msg, Params: Params{Ops: new(Ops)}}
@@ -409,7 +410,7 @@ func New(ctx context.Context, msg Msg) *Container {
 }
 
 // NewCommand calls [New] and initialises the [Params.Path] and [Params.Args] fields.
-func NewCommand(ctx context.Context, msg Msg, pathname *check.Absolute, name string, args ...string) *Container {
+func NewCommand(ctx context.Context, msg message.Msg, pathname *check.Absolute, name string, args ...string) *Container {
 	z := New(ctx, msg)
 	z.Path = pathname
 	z.Args = append([]string{name}, args...)
diff --git a/container/container_test.go b/container/container_test.go
index 2d60f29d..6a85869f 100644
--- a/container/container_test.go
+++ b/container/container_test.go
@@ -26,6 +26,7 @@ import (
 	"hakurei.app/container/vfs"
 	"hakurei.app/hst"
 	"hakurei.app/ldd"
+	"hakurei.app/message"
 )
 
 func TestStartError(t *testing.T) {
@@ -152,13 +153,13 @@ func TestStartError(t *testing.T) {
 			})
 
 			t.Run("msg", func(t *testing.T) {
-				if got, ok := container.GetErrorMessage(tc.err); !ok {
+				if got, ok := message.GetMessage(tc.err); !ok {
 					if tc.msg != "" {
-						t.Errorf("GetErrorMessage: err does not implement MessageError")
+						t.Errorf("GetMessage: err does not implement MessageError")
 					}
 					return
 				} else if got != tc.msg {
-					t.Errorf("GetErrorMessage: %q, want %q", got, tc.msg)
+					t.Errorf("GetMessage: %q, want %q", got, tc.msg)
 				}
 			})
 		})
@@ -545,7 +546,7 @@ func testContainerCancel(
 }
 
 func TestContainerString(t *testing.T) {
-	msg := container.NewMsg(nil)
+	msg := message.NewMsg(nil)
 	c := container.NewCommand(t.Context(), msg, check.MustAbs("/run/current-system/sw/bin/ldd"), "ldd", "/usr/bin/env")
 	c.SeccompFlags |= seccomp.AllowMultiarch
 	c.SeccompRules = seccomp.Preset(
@@ -711,7 +712,7 @@ func TestMain(m *testing.M) {
 }
 
 func helperNewContainerLibPaths(ctx context.Context, libPaths *[]*check.Absolute, args ...string) (c *container.Container) {
-	msg := container.NewMsg(nil)
+	msg := message.NewMsg(nil)
 	c = container.NewCommand(ctx, msg, absHelperInnerPath, "helper", args...)
 	c.Env = append(c.Env, envDoCheck+"=1")
 	c.Bind(check.MustAbs(os.Args[0]), absHelperInnerPath, 0)
diff --git a/container/dispatcher.go b/container/dispatcher.go
index 65881cc7..5f8c72cb 100644
--- a/container/dispatcher.go
+++ b/container/dispatcher.go
@@ -11,6 +11,7 @@ import (
 	"syscall"
 
 	"hakurei.app/container/seccomp"
+	"hakurei.app/message"
 )
 
 type osFile interface {
@@ -37,7 +38,7 @@ type syscallDispatcher interface {
 	setNoNewPrivs() error
 
 	// lastcap provides [LastCap].
-	lastcap(msg Msg) uintptr
+	lastcap(msg message.Msg) uintptr
 	// capset provides capset.
 	capset(hdrp *capHeader, datap *[2]capData) error
 	// capBoundingSetDrop provides capBoundingSetDrop.
@@ -52,9 +53,9 @@ type syscallDispatcher interface {
 	receive(key string, e any, fdp *uintptr) (closeFunc func() error, err error)
 
 	// bindMount provides procPaths.bindMount.
-	bindMount(msg Msg, source, target string, flags uintptr) error
+	bindMount(msg message.Msg, source, target string, flags uintptr) error
 	// remount provides procPaths.remount.
-	remount(msg Msg, target string, flags uintptr) error
+	remount(msg message.Msg, target string, flags uintptr) error
 	// mountTmpfs provides mountTmpfs.
 	mountTmpfs(fsname, target string, flags uintptr, size int, perm os.FileMode) error
 	// ensureFile provides ensureFile.
@@ -122,11 +123,11 @@ type syscallDispatcher interface {
 	wait4(pid int, wstatus *syscall.WaitStatus, options int, rusage *syscall.Rusage) (wpid int, err error)
 
 	// printf provides the Printf method of [log.Logger].
-	printf(msg Msg, format string, v ...any)
+	printf(msg message.Msg, format string, v ...any)
 	// fatal provides the Fatal method of [log.Logger]
-	fatal(msg Msg, v ...any)
+	fatal(msg message.Msg, v ...any)
 	// fatalf provides the Fatalf method of [log.Logger]
-	fatalf(msg Msg, format string, v ...any)
+	fatalf(msg message.Msg, format string, v ...any)
 }
 
 // direct implements syscallDispatcher on the current kernel.
@@ -140,7 +141,7 @@ func (direct) setPtracer(pid uintptr) error       { return SetPtracer(pid) }
 func (direct) setDumpable(dumpable uintptr) error { return SetDumpable(dumpable) }
 func (direct) setNoNewPrivs() error               { return SetNoNewPrivs() }
 
-func (direct) lastcap(msg Msg) uintptr                         { return LastCap(msg) }
+func (direct) lastcap(msg message.Msg) uintptr                 { return LastCap(msg) }
 func (direct) capset(hdrp *capHeader, datap *[2]capData) error { return capset(hdrp, datap) }
 func (direct) capBoundingSetDrop(cap uintptr) error            { return capBoundingSetDrop(cap) }
 func (direct) capAmbientClearAll() error                       { return capAmbientClearAll() }
@@ -150,10 +151,10 @@ func (direct) receive(key string, e any, fdp *uintptr) (func() error, error) {
 	return Receive(key, e, fdp)
 }
 
-func (direct) bindMount(msg Msg, source, target string, flags uintptr) error {
+func (direct) bindMount(msg message.Msg, source, target string, flags uintptr) error {
 	return hostProc.bindMount(msg, source, target, flags)
 }
-func (direct) remount(msg Msg, target string, flags uintptr) error {
+func (direct) remount(msg message.Msg, target string, flags uintptr) error {
 	return hostProc.remount(msg, target, flags)
 }
 func (k direct) mountTmpfs(fsname, target string, flags uintptr, size int, perm os.FileMode) error {
@@ -221,6 +222,6 @@ func (direct) wait4(pid int, wstatus *syscall.WaitStatus, options int, rusage *s
 	return syscall.Wait4(pid, wstatus, options, rusage)
 }
 
-func (direct) printf(msg Msg, format string, v ...any) { msg.GetLogger().Printf(format, v...) }
-func (direct) fatal(msg Msg, v ...any)                 { msg.GetLogger().Fatal(v...) }
-func (direct) fatalf(msg Msg, format string, v ...any) { msg.GetLogger().Fatalf(format, v...) }
+func (direct) printf(msg message.Msg, format string, v ...any) { msg.GetLogger().Printf(format, v...) }
+func (direct) fatal(msg message.Msg, v ...any)                 { msg.GetLogger().Fatal(v...) }
+func (direct) fatalf(msg message.Msg, format string, v ...any) { msg.GetLogger().Fatalf(format, v...) }
diff --git a/container/dispatcher_test.go b/container/dispatcher_test.go
index 2a2685fd..4e6ee76f 100644
--- a/container/dispatcher_test.go
+++ b/container/dispatcher_test.go
@@ -18,6 +18,7 @@ import (
 
 	"hakurei.app/container/seccomp"
 	"hakurei.app/container/stub"
+	"hakurei.app/message"
 )
 
 type opValidTestCase struct {
@@ -329,7 +330,7 @@ func (k *kstub) setDumpable(dumpable uintptr) error {
 }
 
 func (k *kstub) setNoNewPrivs() error { k.Helper(); return k.Expects("setNoNewPrivs").Err }
-func (k *kstub) lastcap(msg Msg) uintptr {
+func (k *kstub) lastcap(msg message.Msg) uintptr {
 	k.Helper()
 	k.checkMsg(msg)
 	return k.Expects("lastcap").Ret.(uintptr)
@@ -409,7 +410,7 @@ func (k *kstub) receive(key string, e any, fdp *uintptr) (closeFunc func() error
 	return
 }
 
-func (k *kstub) bindMount(msg Msg, source, target string, flags uintptr) error {
+func (k *kstub) bindMount(msg message.Msg, source, target string, flags uintptr) error {
 	k.Helper()
 	k.checkMsg(msg)
 	return k.Expects("bindMount").Error(
@@ -418,7 +419,7 @@ func (k *kstub) bindMount(msg Msg, source, target string, flags uintptr) error {
 		stub.CheckArg(k.Stub, "flags", flags, 2))
 }
 
-func (k *kstub) remount(msg Msg, target string, flags uintptr) error {
+func (k *kstub) remount(msg message.Msg, target string, flags uintptr) error {
 	k.Helper()
 	k.checkMsg(msg)
 	return k.Expects("remount").Error(
@@ -702,7 +703,7 @@ func (k *kstub) wait4(pid int, wstatus *syscall.WaitStatus, options int, rusage
 	return
 }
 
-func (k *kstub) printf(_ Msg, format string, v ...any) {
+func (k *kstub) printf(_ message.Msg, format string, v ...any) {
 	k.Helper()
 	if k.Expects("printf").Error(
 		stub.CheckArg(k.Stub, "format", format, 0),
@@ -711,7 +712,7 @@ func (k *kstub) printf(_ Msg, format string, v ...any) {
 	}
 }
 
-func (k *kstub) fatal(_ Msg, v ...any) {
+func (k *kstub) fatal(_ message.Msg, v ...any) {
 	k.Helper()
 	if k.Expects("fatal").Error(
 		stub.CheckArgReflect(k.Stub, "v", v, 0)) != nil {
@@ -720,7 +721,7 @@ func (k *kstub) fatal(_ Msg, v ...any) {
 	panic(stub.PanicExit)
 }
 
-func (k *kstub) fatalf(_ Msg, format string, v ...any) {
+func (k *kstub) fatalf(_ message.Msg, format string, v ...any) {
 	k.Helper()
 	if k.Expects("fatalf").Error(
 		stub.CheckArg(k.Stub, "format", format, 0),
@@ -730,7 +731,7 @@ func (k *kstub) fatalf(_ Msg, format string, v ...any) {
 	panic(stub.PanicExit)
 }
 
-func (k *kstub) checkMsg(msg Msg) {
+func (k *kstub) checkMsg(msg message.Msg) {
 	k.Helper()
 	var target *kstub
 
diff --git a/container/executable.go b/container/executable.go
index 9b6d4f66..f80a1f79 100644
--- a/container/executable.go
+++ b/container/executable.go
@@ -3,6 +3,8 @@ package container
 import (
 	"os"
 	"sync"
+
+	"hakurei.app/message"
 )
 
 var (
@@ -10,7 +12,7 @@ var (
 	executableOnce sync.Once
 )
 
-func copyExecutable(msg Msg) {
+func copyExecutable(msg message.Msg) {
 	if name, err := os.Executable(); err != nil {
 		msg.BeforeExit()
 		msg.GetLogger().Fatalf("cannot read executable path: %v", err)
@@ -19,7 +21,7 @@ func copyExecutable(msg Msg) {
 	}
 }
 
-func MustExecutable(msg Msg) string {
+func MustExecutable(msg message.Msg) string {
 	executableOnce.Do(func() { copyExecutable(msg) })
 	return executable
 }
diff --git a/container/executable_test.go b/container/executable_test.go
index 5608a8ae..33981bb6 100644
--- a/container/executable_test.go
+++ b/container/executable_test.go
@@ -5,11 +5,12 @@ import (
 	"testing"
 
 	"hakurei.app/container"
+	"hakurei.app/message"
 )
 
 func TestExecutable(t *testing.T) {
 	for i := 0; i < 16; i++ {
-		if got := container.MustExecutable(container.NewMsg(nil)); got != os.Args[0] {
+		if got := container.MustExecutable(message.NewMsg(nil)); got != os.Args[0] {
 			t.Errorf("MustExecutable: %q, want %q",
 				got, os.Args[0])
 		}
diff --git a/container/init.go b/container/init.go
index 9481acd1..923a36e8 100644
--- a/container/init.go
+++ b/container/init.go
@@ -14,6 +14,7 @@ import (
 
 	"hakurei.app/container/fhs"
 	"hakurei.app/container/seccomp"
+	"hakurei.app/message"
 )
 
 const (
@@ -61,7 +62,7 @@ type (
 	setupState struct {
 		nonrepeatable uintptr
 		*Params
-		Msg
+		message.Msg
 	}
 )
 
@@ -95,14 +96,14 @@ type initParams struct {
 }
 
 // Init is called by [TryArgv0] if the current process is the container init.
-func Init(msg Msg) {
+func Init(msg message.Msg) {
 	if msg == nil {
 		panic("attempting to call initEntrypoint with nil msg")
 	}
 	initEntrypoint(direct{}, msg)
 }
 
-func initEntrypoint(k syscallDispatcher, msg Msg) {
+func initEntrypoint(k syscallDispatcher, msg message.Msg) {
 	k.lockOSThread()
 
 	if k.getpid() != 1 {
@@ -125,7 +126,7 @@ func initEntrypoint(k syscallDispatcher, msg Msg) {
 			k.fatal(msg, "invalid setup descriptor")
 		}
 		if errors.Is(err, ErrReceiveEnv) {
-			k.fatal(msg, "HAKUREI_SETUP not set")
+			k.fatal(msg, setupEnv+" not set")
 		}
 
 		k.fatalf(msg, "cannot decode init setup payload: %v", err)
@@ -448,11 +449,11 @@ const initName = "init"
 
 // TryArgv0 calls [Init] if the last element of argv0 is "init".
 // If a nil msg is passed, the system logger is used instead.
-func TryArgv0(msg Msg) {
+func TryArgv0(msg message.Msg) {
 	if msg == nil {
 		log.SetPrefix(initName + ": ")
 		log.SetFlags(0)
-		msg = NewMsg(log.Default())
+		msg = message.NewMsg(log.Default())
 	}
 
 	if len(os.Args) > 0 && path.Base(os.Args[0]) == initName {
diff --git a/container/mount.go b/container/mount.go
index 0c459c9c..360a71dc 100644
--- a/container/mount.go
+++ b/container/mount.go
@@ -7,6 +7,7 @@ import (
 	. "syscall"
 
 	"hakurei.app/container/vfs"
+	"hakurei.app/message"
 )
 
 /*
@@ -87,7 +88,7 @@ const (
 )
 
 // bindMount mounts source on target and recursively applies flags if MS_REC is set.
-func (p *procPaths) bindMount(msg Msg, source, target string, flags uintptr) error {
+func (p *procPaths) bindMount(msg message.Msg, source, target string, flags uintptr) error {
 	// syscallDispatcher.bindMount and procPaths.remount must not be called from this function
 
 	if err := p.k.mount(source, target, FstypeNULL, MS_SILENT|MS_BIND|flags&MS_REC, zeroString); err != nil {
@@ -97,7 +98,7 @@ func (p *procPaths) bindMount(msg Msg, source, target string, flags uintptr) err
 }
 
 // remount applies flags on target, recursively if MS_REC is set.
-func (p *procPaths) remount(msg Msg, target string, flags uintptr) error {
+func (p *procPaths) remount(msg message.Msg, target string, flags uintptr) error {
 	// syscallDispatcher methods bindMount, remount must not be called from this function
 
 	var targetFinal string
@@ -159,7 +160,7 @@ func (p *procPaths) remount(msg Msg, target string, flags uintptr) error {
 }
 
 // remountWithFlags remounts mount point described by [vfs.MountInfoNode].
-func remountWithFlags(k syscallDispatcher, msg Msg, n *vfs.MountInfoNode, mf uintptr) error {
+func remountWithFlags(k syscallDispatcher, msg message.Msg, n *vfs.MountInfoNode, mf uintptr) error {
 	// syscallDispatcher methods bindMount, remount must not be called from this function
 
 	kf, unmatched := n.Flags()
diff --git a/container/msg.go b/container/msg.go
deleted file mode 100644
index 38c38ecd..00000000
--- a/container/msg.go
+++ /dev/null
@@ -1,110 +0,0 @@
-package container
-
-import (
-	"errors"
-	"log"
-	"sync/atomic"
-)
-
-// MessageError is an error with a user-facing message.
-type MessageError interface {
-	// Message returns a user-facing error message.
-	Message() string
-
-	error
-}
-
-// GetErrorMessage returns whether an error implements [MessageError], and the message if it does.
-func GetErrorMessage(err error) (string, bool) {
-	var e MessageError
-	if !errors.As(err, &e) || e == nil {
-		return zeroString, false
-	}
-	return e.Message(), true
-}
-
-// Msg is used for package-wide verbose logging.
-type Msg interface {
-	// GetLogger returns the address of the underlying [log.Logger].
-	GetLogger() *log.Logger
-
-	// IsVerbose atomically loads and returns whether [Msg] has verbose logging enabled.
-	IsVerbose() bool
-	// SwapVerbose atomically stores a new verbose state and returns the previous value held by [Msg].
-	SwapVerbose(verbose bool) bool
-	// Verbose passes its argument to the Println method of the underlying [log.Logger] if IsVerbose returns true.
-	Verbose(v ...any)
-	// Verbosef passes its argument to the Printf method of the underlying [log.Logger] if IsVerbose returns true.
-	Verbosef(format string, v ...any)
-
-	// Suspend causes the embedded [Suspendable] to withhold writes to its downstream [io.Writer].
-	// Suspend returns false and is a noop if called between calls to Suspend and Resume.
-	Suspend() bool
-
-	// Resume dumps the entire buffer held by the embedded [Suspendable] and stops withholding future writes.
-	// Resume returns false and is a noop if a call to Suspend does not precede it.
-	Resume() bool
-
-	// BeforeExit runs implementation-specific cleanup code, and optionally prints warnings.
-	// BeforeExit is called before [os.Exit].
-	BeforeExit()
-}
-
-// defaultMsg is the default implementation of the [Msg] interface.
-// The zero value is not safe for use. Callers should use the [NewMsg] function instead.
-type defaultMsg struct {
-	verbose atomic.Bool
-
-	logger *log.Logger
-	Suspendable
-}
-
-// NewMsg initialises a downstream [log.Logger] for a new [Msg].
-// The [log.Logger] should no longer be configured after NewMsg returns.
-// If downstream is nil, a new logger is initialised in its place.
-func NewMsg(downstream *log.Logger) Msg {
-	if downstream == nil {
-		downstream = log.New(log.Writer(), "container: ", 0)
-	}
-
-	m := defaultMsg{logger: downstream}
-	m.Suspendable.Downstream = downstream.Writer()
-	downstream.SetOutput(&m.Suspendable)
-	return &m
-}
-
-func (msg *defaultMsg) GetLogger() *log.Logger { return msg.logger }
-
-func (msg *defaultMsg) IsVerbose() bool               { return msg.verbose.Load() }
-func (msg *defaultMsg) SwapVerbose(verbose bool) bool { return msg.verbose.Swap(verbose) }
-func (msg *defaultMsg) Verbose(v ...any) {
-	if msg.verbose.Load() {
-		msg.logger.Println(v...)
-	}
-}
-func (msg *defaultMsg) Verbosef(format string, v ...any) {
-	if msg.verbose.Load() {
-		msg.logger.Printf(format, v...)
-	}
-}
-
-// Resume calls [Suspendable.Resume] and prints a message if buffer was filled
-// between calls to [Suspendable.Suspend] and Resume.
-func (msg *defaultMsg) Resume() bool {
-	resumed, dropped, _, err := msg.Suspendable.Resume()
-	if err != nil {
-		// probably going to result in an error as well, so this message is as good as unreachable
-		msg.logger.Printf("cannot dump buffer on resume: %v", err)
-	}
-	if resumed && dropped > 0 {
-		msg.logger.Printf("dropped %d bytes while output is suspended", dropped)
-	}
-	return resumed
-}
-
-// BeforeExit prints a message if called between calls to [Suspendable.Suspend] and Resume.
-func (msg *defaultMsg) BeforeExit() {
-	if msg.Resume() {
-		msg.logger.Printf("beforeExit reached on suspended output")
-	}
-}
diff --git a/container/msg_test.go b/container/msg_test.go
deleted file mode 100644
index ed5c0c59..00000000
--- a/container/msg_test.go
+++ /dev/null
@@ -1,177 +0,0 @@
-package container_test
-
-import (
-	"bytes"
-	"errors"
-	"io"
-	"log"
-	"strings"
-	"syscall"
-	"testing"
-
-	"hakurei.app/container"
-	"hakurei.app/container/stub"
-)
-
-func TestMessageError(t *testing.T) {
-	testCases := []struct {
-		name   string
-		err    error
-		want   string
-		wantOk bool
-	}{
-		{"nil", nil, "", false},
-		{"new", errors.New(":3"), "", false},
-		{"start", &container.StartError{
-			Step: "meow",
-			Err:  syscall.ENOTRECOVERABLE,
-		}, "cannot meow: state not recoverable", true},
-	}
-	for _, tc := range testCases {
-		t.Run(tc.name, func(t *testing.T) {
-			got, ok := container.GetErrorMessage(tc.err)
-			if got != tc.want {
-				t.Errorf("GetErrorMessage: %q, want %q", got, tc.want)
-			}
-			if ok != tc.wantOk {
-				t.Errorf("GetErrorMessage: ok = %v, want %v", ok, tc.wantOk)
-			}
-		})
-	}
-}
-
-func TestDefaultMsg(t *testing.T) {
-	// copied from output.go
-	const suspendBufMax = 1 << 24
-
-	t.Run("logger", func(t *testing.T) {
-		t.Run("nil", func(t *testing.T) {
-			got := container.NewMsg(nil).GetLogger()
-
-			if out := got.Writer().(*container.Suspendable).Downstream; out != log.Writer() {
-				t.Errorf("GetLogger: Downstream = %#v", out)
-			}
-
-			if prefix := got.Prefix(); prefix != "container: " {
-				t.Errorf("GetLogger: prefix = %q", prefix)
-			}
-		})
-
-		t.Run("takeover", func(t *testing.T) {
-			l := log.New(io.Discard, "\x00", 0xdeadbeef)
-			got := container.NewMsg(l)
-
-			if logger := got.GetLogger(); logger != l {
-				t.Errorf("GetLogger: %#v, want %#v", logger, l)
-			}
-
-			if ds := l.Writer().(*container.Suspendable).Downstream; ds != io.Discard {
-				t.Errorf("GetLogger: Downstream = %#v", ds)
-			}
-		})
-	})
-
-	dw := expectWriter{t: t}
-
-	steps := []struct {
-		name     string
-		pt, next []byte
-		err      error
-
-		f func(t *testing.T, msg container.Msg)
-	}{
-		{"zero verbose", nil, nil, nil, func(t *testing.T, msg container.Msg) {
-			if msg.IsVerbose() {
-				t.Error("IsVerbose unexpected true")
-			}
-		}},
-
-		{"swap false", nil, nil, nil, func(t *testing.T, msg container.Msg) {
-			if msg.SwapVerbose(false) {
-				t.Error("SwapVerbose unexpected true")
-			}
-		}},
-		{"write discard", nil, nil, nil, func(_ *testing.T, msg container.Msg) {
-			msg.Verbose("\x00")
-			msg.Verbosef("\x00")
-		}},
-		{"verbose false", nil, nil, nil, func(t *testing.T, msg container.Msg) {
-			if msg.IsVerbose() {
-				t.Error("IsVerbose unexpected true")
-			}
-		}},
-
-		{"swap true", nil, nil, nil, func(t *testing.T, msg container.Msg) {
-			if msg.SwapVerbose(true) {
-				t.Error("SwapVerbose unexpected true")
-			}
-		}},
-		{"write verbose", []byte("test: \x00\n"), nil, nil, func(_ *testing.T, msg container.Msg) {
-			msg.Verbose("\x00")
-		}},
-		{"write verbosef", []byte(`test: "\x00"` + "\n"), nil, nil, func(_ *testing.T, msg container.Msg) {
-			msg.Verbosef("%q", "\x00")
-		}},
-		{"verbose true", nil, nil, nil, func(t *testing.T, msg container.Msg) {
-			if !msg.IsVerbose() {
-				t.Error("IsVerbose unexpected false")
-			}
-		}},
-
-		{"resume noop", nil, nil, nil, func(t *testing.T, msg container.Msg) {
-			if msg.Resume() {
-				t.Error("Resume unexpected success")
-			}
-		}},
-		{"beforeExit noop", nil, nil, nil, func(_ *testing.T, msg container.Msg) {
-			msg.BeforeExit()
-		}},
-
-		{"beforeExit suspend", nil, nil, nil, func(_ *testing.T, msg container.Msg) {
-			msg.Suspend()
-		}},
-		{"beforeExit message", []byte("test: beforeExit reached on suspended output\n"), nil, nil, func(_ *testing.T, msg container.Msg) {
-			msg.BeforeExit()
-		}},
-		{"post beforeExit resume noop", nil, nil, nil, func(t *testing.T, msg container.Msg) {
-			if msg.Resume() {
-				t.Error("Resume unexpected success")
-			}
-		}},
-
-		{"suspend", nil, nil, nil, func(_ *testing.T, msg container.Msg) {
-			msg.Suspend()
-		}},
-		{"suspend write", nil, nil, nil, func(_ *testing.T, msg container.Msg) {
-			msg.GetLogger().Print("\x00")
-		}},
-		{"resume error", []byte("test: \x00\n"), []byte("test: cannot dump buffer on resume: unique error 0 injected by the test suite\n"), stub.UniqueError(0), func(t *testing.T, msg container.Msg) {
-			if !msg.Resume() {
-				t.Error("Resume unexpected failure")
-			}
-		}},
-
-		{"suspend drop", nil, nil, nil, func(_ *testing.T, msg container.Msg) {
-			msg.Suspend()
-		}},
-		{"suspend write fill", nil, nil, nil, func(_ *testing.T, msg container.Msg) {
-			msg.GetLogger().Print(strings.Repeat("\x00", suspendBufMax))
-		}},
-		{"resume dropped", append([]byte("test: "), bytes.Repeat([]byte{0}, suspendBufMax-6)...), []byte("test: dropped 7 bytes while output is suspended\n"), nil, func(t *testing.T, msg container.Msg) {
-			if !msg.Resume() {
-				t.Error("Resume unexpected failure")
-			}
-		}},
-	}
-
-	msg := container.NewMsg(log.New(&dw, "test: ", 0))
-	for _, step := range steps {
-		// these share the same writer, so cannot be subtests
-		t.Logf("running step %q", step.name)
-		dw.expect, dw.next, dw.err = step.pt, step.next, step.err
-		step.f(t, msg)
-		if dw.expect != nil {
-			t.Errorf("expect: %q", string(dw.expect))
-		}
-	}
-}
diff --git a/container/output.go b/container/output.go
deleted file mode 100644
index 4d799eb4..00000000
--- a/container/output.go
+++ /dev/null
@@ -1,77 +0,0 @@
-package container
-
-import (
-	"bytes"
-	"io"
-	"sync"
-	"sync/atomic"
-	"syscall"
-)
-
-const (
-	suspendBufInitial = 1 << 12
-	suspendBufMax     = 1 << 24
-)
-
-// Suspendable proxies writes to a downstream [io.Writer] but optionally withholds writes
-// between calls to Suspend and Resume.
-type Suspendable struct {
-	Downstream io.Writer
-
-	s atomic.Bool
-
-	buf bytes.Buffer
-	// for growing buf
-	bufOnce sync.Once
-	// for synchronising all other buf operations
-	bufMu sync.Mutex
-
-	dropped int
-}
-
-func (s *Suspendable) Write(p []byte) (n int, err error) {
-	if !s.s.Load() {
-		return s.Downstream.Write(p)
-	}
-	s.bufOnce.Do(func() { s.buf.Grow(suspendBufInitial) })
-
-	s.bufMu.Lock()
-	defer s.bufMu.Unlock()
-
-	if free := suspendBufMax - s.buf.Len(); free < len(p) {
-		// fast path
-		if free <= 0 {
-			s.dropped += len(p)
-			return 0, syscall.ENOMEM
-		}
-
-		n, _ = s.buf.Write(p[:free])
-		err = syscall.ENOMEM
-		s.dropped += len(p) - n
-		return
-	}
-
-	return s.buf.Write(p)
-}
-
-// IsSuspended returns whether [Suspendable] is currently between a call to Suspend and Resume.
-func (s *Suspendable) IsSuspended() bool { return s.s.Load() }
-
-// Suspend causes [Suspendable] to start withholding output in its buffer.
-func (s *Suspendable) Suspend() bool { return s.s.CompareAndSwap(false, true) }
-
-// Resume undoes the effect of Suspend and dumps the buffered into the downstream [io.Writer].
-func (s *Suspendable) Resume() (resumed bool, dropped uintptr, n int64, err error) {
-	if s.s.CompareAndSwap(true, false) {
-		s.bufMu.Lock()
-		defer s.bufMu.Unlock()
-
-		resumed = true
-		dropped = uintptr(s.dropped)
-
-		s.dropped = 0
-		n, err = io.Copy(s.Downstream, &s.buf)
-		s.buf.Reset()
-	}
-	return
-}
diff --git a/container/output_test.go b/container/output_test.go
deleted file mode 100644
index b6dedf16..00000000
--- a/container/output_test.go
+++ /dev/null
@@ -1,173 +0,0 @@
-package container_test
-
-import (
-	"bytes"
-	"errors"
-	"reflect"
-	"strconv"
-	"syscall"
-	"testing"
-
-	"hakurei.app/container"
-	"hakurei.app/container/stub"
-)
-
-func TestSuspendable(t *testing.T) {
-	// copied from output.go
-	const suspendBufMax = 1 << 24
-
-	const (
-		// equivalent to len(want.pt)
-		nSpecialPtEquiv = -iota - 1
-		// equivalent to len(want.w)
-		nSpecialWEquiv
-		// suspends writer before executing test case, implies nSpecialWEquiv
-		nSpecialSuspend
-		// offset: resume writer and measure against dump instead, implies nSpecialPtEquiv
-		nSpecialDump
-	)
-
-	// shares the same writer
-	steps := []struct {
-		name    string
-		w, pt   []byte
-		err     error
-		wantErr error
-		n       int
-	}{
-		{"simple", []byte{0xde, 0xad, 0xbe, 0xef}, []byte{0xde, 0xad, 0xbe, 0xef},
-			nil, nil, nSpecialPtEquiv},
-
-		{"error", []byte{0xb, 0xad}, []byte{0xb, 0xad},
-			stub.UniqueError(0), stub.UniqueError(0), nSpecialPtEquiv},
-
-		{"suspend short", []byte{0}, nil,
-			nil, nil, nSpecialSuspend},
-		{"sw short 0", []byte{0xca, 0xfe, 0xba, 0xbe}, nil,
-			nil, nil, nSpecialWEquiv},
-		{"sw short 1", []byte{0xff}, nil,
-			nil, nil, nSpecialWEquiv},
-		{"resume short", nil, []byte{0, 0xca, 0xfe, 0xba, 0xbe, 0xff}, nil, nil,
-			nSpecialDump},
-
-		{"long pt", bytes.Repeat([]byte{0xff}, suspendBufMax+1), bytes.Repeat([]byte{0xff}, suspendBufMax+1),
-			nil, nil, nSpecialPtEquiv},
-
-		{"suspend fill", bytes.Repeat([]byte{0xfe}, suspendBufMax), nil,
-			nil, nil, nSpecialSuspend},
-		{"drop", []byte{0}, nil,
-			nil, syscall.ENOMEM, 0},
-		{"drop error", []byte{0}, nil,
-			stub.UniqueError(1), syscall.ENOMEM, 0},
-		{"resume fill", nil, bytes.Repeat([]byte{0xfe}, suspendBufMax),
-			nil, nil, nSpecialDump - 2},
-
-		{"suspend fill partial", bytes.Repeat([]byte{0xfd}, suspendBufMax-0xf), nil,
-			nil, nil, nSpecialSuspend},
-		{"partial write", bytes.Repeat([]byte{0xad}, 0x1f), nil,
-			nil, syscall.ENOMEM, 0xf},
-		{"full drop", []byte{0}, nil,
-			nil, syscall.ENOMEM, 0},
-		{"resume fill partial", nil, append(bytes.Repeat([]byte{0xfd}, suspendBufMax-0xf), bytes.Repeat([]byte{0xad}, 0xf)...),
-			nil, nil, nSpecialDump - 0x10 - 1},
-	}
-
-	var dw expectWriter
-
-	w := container.Suspendable{Downstream: &dw}
-	for _, step := range steps {
-		// these share the same writer, so cannot be subtests
-		t.Logf("writing step %q", step.name)
-		dw.expect, dw.err = step.pt, step.err
-
-		var (
-			gotN   int
-			gotErr error
-		)
-
-		wantN := step.n
-		switch wantN {
-		case nSpecialPtEquiv:
-			wantN = len(step.pt)
-			gotN, gotErr = w.Write(step.w)
-
-		case nSpecialWEquiv:
-			wantN = len(step.w)
-			gotN, gotErr = w.Write(step.w)
-
-		case nSpecialSuspend:
-			s := w.IsSuspended()
-			if ok := w.Suspend(); s && ok {
-				t.Fatal("Suspend: unexpected success")
-			}
-
-			wantN = len(step.w)
-			gotN, gotErr = w.Write(step.w)
-
-		default:
-			if wantN <= nSpecialDump {
-				if !w.IsSuspended() {
-					t.Fatal("IsSuspended unexpected false")
-				}
-
-				resumed, dropped, n, err := w.Resume()
-				if !resumed {
-					t.Fatal("Resume: resumed = false")
-				}
-				if wantDropped := nSpecialDump - wantN; int(dropped) != wantDropped {
-					t.Errorf("Resume: dropped = %d, want %d", dropped, wantDropped)
-				}
-
-				wantN = len(step.pt)
-				gotN, gotErr = int(n), err
-			} else {
-				gotN, gotErr = w.Write(step.w)
-			}
-		}
-
-		if gotN != wantN {
-			t.Errorf("Write: n = %d, want %d", gotN, wantN)
-		}
-
-		if !reflect.DeepEqual(gotErr, step.wantErr) {
-			t.Errorf("Write: %v", gotErr)
-		}
-
-		if dw.expect != nil {
-			t.Errorf("expect: %q", string(dw.expect))
-		}
-	}
-}
-
-// expectWriter compares Write calls to expect.
-type expectWriter struct {
-	expect []byte
-	err    error
-
-	// optional consecutive write
-	next []byte
-
-	// optional, calls Error on failure if not nil
-	t *testing.T
-}
-
-func (w *expectWriter) Write(p []byte) (n int, err error) {
-	defer func() { w.expect = w.next; w.next = nil }()
-
-	n, err = len(p), w.err
-	if w.expect == nil {
-		n, err = 0, errors.New("unexpected call to Write: "+strconv.Quote(string(p)))
-		if w.t != nil {
-			w.t.Error(err.Error())
-		}
-		return
-	}
-	if string(p) != string(w.expect) {
-		n, err = 0, errors.New("p = "+strconv.Quote(string(p))+", want "+strconv.Quote(string(w.expect)))
-		if w.t != nil {
-			w.t.Error(err.Error())
-		}
-		return
-	}
-	return
-}
diff --git a/container/sysctl.go b/container/sysctl.go
index 9a1e818e..4387c4da 100644
--- a/container/sysctl.go
+++ b/container/sysctl.go
@@ -7,6 +7,7 @@ import (
 	"sync"
 
 	"hakurei.app/container/fhs"
+	"hakurei.app/message"
 )
 
 var (
@@ -23,7 +24,7 @@ const (
 	kernelCapLastCapPath  = fhs.ProcSys + "kernel/cap_last_cap"
 )
 
-func mustReadSysctl(msg Msg) {
+func mustReadSysctl(msg message.Msg) {
 	sysctlOnce.Do(func() {
 		if v, err := os.ReadFile(kernelOverflowuidPath); err != nil {
 			msg.GetLogger().Fatalf("cannot read %q: %v", kernelOverflowuidPath, err)
@@ -45,6 +46,6 @@ func mustReadSysctl(msg Msg) {
 	})
 }
 
-func OverflowUid(msg Msg) int { mustReadSysctl(msg); return kernelOverflowuid }
-func OverflowGid(msg Msg) int { mustReadSysctl(msg); return kernelOverflowgid }
-func LastCap(msg Msg) uintptr { mustReadSysctl(msg); return uintptr(kernelCapLastCap) }
+func OverflowUid(msg message.Msg) int { mustReadSysctl(msg); return kernelOverflowuid }
+func OverflowGid(msg message.Msg) int { mustReadSysctl(msg); return kernelOverflowgid }
+func LastCap(msg message.Msg) uintptr { mustReadSysctl(msg); return uintptr(kernelCapLastCap) }