internal/app/sppulse: correctly handle small cookie

The trailing zero bytes need to be sliced off, so send cookie size alongside buffer content.

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

3 files changed, 282 insertions, 29 deletions

diff --git a/internal/app/dispatcher_test.go b/internal/app/dispatcher_test.go
index b87fae66..7e91b816 100644
--- a/internal/app/dispatcher_test.go
+++ b/internal/app/dispatcher_test.go
@@ -124,24 +124,39 @@ func paramsWantEnv(config *hst.Config, wantEnv map[string]string, next extraChec
 	}
 }
 
+// opBehaviourTestCase checks outcomeOp behaviour against outcomeStateSys and outcomeStateParams.
 type opBehaviourTestCase struct {
-	name      string
-	newOp     func(isShim, clearUnexported bool) outcomeOp
+	name string
+	// newOp returns a new instance of outcomeOp under testing that is safe to clobber.
+	newOp func(isShim, clearUnexported bool) outcomeOp
+	// newConfig returns a new instance of [hst.Config] that is checked not to be clobbered by outcomeOp.
 	newConfig func() *hst.Config
 
-	pStateSys     pStateSysFunc
-	toSystem      []stub.Call
-	wantSys       *system.I
+	// pStateSys is called before outcomeOp.toSystem to prepare outcomeStateSys.
+	pStateSys pStateSysFunc
+	// toSystem are expected syscallDispatcher calls during outcomeOp.toSystem.
+	toSystem []stub.Call
+	// wantSys is the expected [system.I] state after outcomeOp.toSystem.
+	wantSys *system.I
+	// extraCheckSys is called after outcomeOp.toSystem to check the state of outcomeStateSys.
 	extraCheckSys extraCheckSysFunc
+	// wantErrSystem is the expected error value returned by outcomeOp.toSystem.
+	// Further testing is skipped if not nil.
 	wantErrSystem error
 
-	pStateContainer  pStateContainerFunc
-	toContainer      []stub.Call
-	wantParams       *container.Params
+	// pStateContainer is called before outcomeOp.toContainer to prepare outcomeStateParams.
+	pStateContainer pStateContainerFunc
+	// toContainer are expected syscallDispatcher calls during outcomeOp.toContainer.
+	toContainer []stub.Call
+	// wantParams is the expected [container.Params] after outcomeOp.toContainer.
+	wantParams *container.Params
+	// extraCheckParams is called after outcomeOp.toContainer to check the state of outcomeStateParams.
 	extraCheckParams extraCheckParamsFunc
+	// wantErrContainer is the expected error value returned by outcomeOp.toContainer.
 	wantErrContainer error
 }
 
+// checkOpBehaviour runs a slice of opBehaviourTestCase.
 func checkOpBehaviour(t *testing.T, testCases []opBehaviourTestCase) {
 	t.Helper()
 
@@ -258,6 +273,40 @@ func checkOpBehaviour(t *testing.T, testCases []opBehaviourTestCase) {
 
 func newI() *system.I { return system.New(panicMsgContext{}, panicMsgContext{}, checkExpectUid) }
 
+// simpleTestCase is a simple freeform test case utilising kstub.
+type simpleTestCase struct {
+	name string
+	f    func(k *kstub) error
+	// want are expected syscallDispatcher calls during f.
+	want stub.Expect
+	// wantErr is the expected error value returned by f.
+	wantErr error
+}
+
+// checkSimple runs a slice of simpleTestCase.
+func checkSimple(t *testing.T, fname string, testCases []simpleTestCase) {
+	t.Helper()
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Helper()
+			t.Parallel()
+
+			defer stub.HandleExit(t)
+			k := &kstub{panicDispatcher{}, stub.New(t, func(s *stub.Stub[syscallDispatcher]) syscallDispatcher { return &kstub{panicDispatcher{}, s} }, tc.want)}
+			if err := tc.f(k); !reflect.DeepEqual(err, tc.wantErr) {
+				t.Errorf("%s: error = %#v, want %#v", fname, err, tc.wantErr)
+			}
+			k.VisitIncomplete(func(s *stub.Stub[syscallDispatcher]) {
+				t.Helper()
+
+				t.Errorf("%s: %d calls, want %d", fname, s.Pos(), s.Len())
+			})
+		})
+	}
+}
+
+// kstub partially implements syscallDispatcher via [stub.Stub].
 type kstub struct {
 	panicDispatcher
 	*stub.Stub[syscallDispatcher]
@@ -416,6 +465,11 @@ func (nameDentry) IsDir() bool                { panic("unreachable") }
 func (nameDentry) Type() fs.FileMode          { panic("unreachable") }
 func (nameDentry) Info() (fs.FileInfo, error) { panic("unreachable") }
 
+// errorReader implements [io.Reader] that unconditionally returns -1, val.
+type errorReader struct{ val error }
+
+func (r errorReader) Read([]byte) (int, error) { return -1, r.val }
+
 // panicMsgContext implements [message.Msg] and [context.Context] with methods wrapping panic.
 // This should be assigned to test cases to be checked against.
 type panicMsgContext struct{}
diff --git a/internal/app/sppulse.go b/internal/app/sppulse.go
index 9cc172da..fe63f366 100644
--- a/internal/app/sppulse.go
+++ b/internal/app/sppulse.go
@@ -24,6 +24,8 @@ func init() { gob.Register(new(spPulseOp)) }
 type spPulseOp struct {
 	// PulseAudio cookie data, populated during toSystem if a cookie is present.
 	Cookie *[pulseCookieSizeMax]byte
+	// PulseAudio cookie size, populated during toSystem if a cookie is present.
+	CookieSize int
 }
 
 func (s *spPulseOp) toSystem(state *outcomeStateSys) error {
@@ -60,7 +62,7 @@ func (s *spPulseOp) toSystem(state *outcomeStateSys) error {
 		return err
 	} else if a != nil {
 		s.Cookie = new([pulseCookieSizeMax]byte)
-		if err = loadFile(state.msg, state.k, "PulseAudio cookie", a.String(), s.Cookie[:]); err != nil {
+		if s.CookieSize, err = loadFile(state.msg, state.k, "PulseAudio cookie", a.String(), s.Cookie[:]); err != nil {
 			return err
 		}
 	} else {
@@ -80,8 +82,12 @@ func (s *spPulseOp) toContainer(state *outcomeStateParams) error {
 
 	if s.Cookie != nil {
 		innerDst := hst.AbsPrivateTmp.Append("/pulse-cookie")
+
+		if s.CookieSize < 0 || s.CookieSize > pulseCookieSizeMax {
+			return newWithMessage("unexpected PulseAudio cookie size")
+		}
 		state.env["PULSE_COOKIE"] = innerDst.String()
-		state.params.Place(innerDst, s.Cookie[:])
+		state.params.Place(innerDst, s.Cookie[:s.CookieSize])
 	}
 
 	return nil
@@ -161,44 +167,44 @@ func discoverPulseCookie(k syscallDispatcher) (*check.Absolute, error) {
 func loadFile(
 	msg message.Msg, k syscallDispatcher,
 	description, pathname string, buf []byte,
-) error {
+) (int, error) {
 	n := len(buf)
 	if n == 0 {
-		return errors.New("invalid buffer")
+		return -1, errors.New("invalid buffer")
 	}
-	msg.Verbosef("loading up to %d bytes from %q", n, pathname)
 
 	if fi, err := k.stat(pathname); err != nil {
-		return &hst.AppError{Step: "access " + description, Err: err}
+		return -1, &hst.AppError{Step: "access " + description, Err: err}
 	} else {
 		if fi.IsDir() {
-			return &hst.AppError{Step: "read " + description,
+			return -1, &hst.AppError{Step: "read " + description,
 				Err: &os.PathError{Op: "stat", Path: pathname, Err: syscall.EISDIR}}
 		}
 		if s := fi.Size(); s > int64(n) {
-			return newWithMessageError(
-				description+" at "+strconv.Quote(pathname)+" exceeds maximum expected size",
+			return -1, newWithMessageError(
+				description+" at "+strconv.Quote(pathname)+" exceeds expected size",
 				&os.PathError{Op: "stat", Path: pathname, Err: syscall.ENOMEM},
 			)
 		} else if s < int64(n) {
-			msg.Verbosef("%s at %q is %d bytes longer than expected", description, pathname, int64(n)-s)
+			msg.Verbosef("%s at %q is %d bytes shorter than expected", description, pathname, int64(n)-s)
+		} else {
+			msg.Verbosef("loading %d bytes from %q", n, pathname)
 		}
 	}
 
 	if f, err := k.open(pathname); err != nil {
-		return &hst.AppError{Step: "open " + description, Err: err}
+		return -1, &hst.AppError{Step: "open " + description, Err: err}
 	} else {
 		if n, err = f.Read(buf); err != nil {
 			if !errors.Is(err, io.EOF) {
 				_ = f.Close()
-				return &hst.AppError{Step: "read " + description, Err: err}
+				return n, &hst.AppError{Step: "read " + description, Err: err}
 			}
-			msg.Verbosef("copied %d bytes from %q", n, pathname)
-		} // nil error indicates a partial read, which is handled after stat
+		}
 
 		if err = f.Close(); err != nil {
-			return &hst.AppError{Step: "close " + description, Err: err}
+			return n, &hst.AppError{Step: "close " + description, Err: err}
 		}
-		return nil
+		return n, nil
 	}
 }
diff --git a/internal/app/sppulse_test.go b/internal/app/sppulse_test.go
index 75b1db0f..7c050bf5 100644
--- a/internal/app/sppulse_test.go
+++ b/internal/app/sppulse_test.go
@@ -2,7 +2,9 @@ package app
 
 import (
 	"bytes"
+	"errors"
 	"os"
+	"syscall"
 	"testing"
 
 	"hakurei.app/container"
@@ -28,7 +30,7 @@ func TestSpPulseOp(t *testing.T) {
 			return c
 		}, nil, nil, nil, nil, errNotEnabled, nil, nil, nil, nil, nil},
 
-		{"socketDir stat", func(isShim bool, _ bool) outcomeOp {
+		{"socketDir stat", func(isShim, _ bool) outcomeOp {
 			if !isShim {
 				return new(spPulseOp)
 			}
@@ -99,25 +101,94 @@ func TestSpPulseOp(t *testing.T) {
 			call("stat", stub.ExpectArgs{wantRuntimePath + "/pulse"}, (*stubFi)(nil), nil),
 			call("stat", stub.ExpectArgs{wantRuntimePath + "/pulse/native"}, &stubFi{mode: 0666}, nil),
 			call("lookupEnv", stub.ExpectArgs{"PULSE_COOKIE"}, "/proc/nonexistent/cookie", nil),
-			call("verbosef", stub.ExpectArgs{"loading up to %d bytes from %q", []any{1 << 8, "/proc/nonexistent/cookie"}}, nil, nil),
 			call("stat", stub.ExpectArgs{"/proc/nonexistent/cookie"}, &stubFi{isDir: false, size: 1 << 8}, nil),
+			call("verbosef", stub.ExpectArgs{"loading %d bytes from %q", []any{1 << 8, "/proc/nonexistent/cookie"}}, nil, nil),
 			call("open", stub.ExpectArgs{"/proc/nonexistent/cookie"}, (*stubOsFile)(nil), stub.UniqueError(0)),
 		}, nil, nil, &hst.AppError{
 			Step: "open PulseAudio cookie",
 			Err:  stub.UniqueError(0),
 		}, nil, nil, nil, nil, nil},
 
-		{"success cookie", func(isShim bool, _ bool) outcomeOp {
+		{"cookie bad shim size", func(isShim, clearUnexported bool) outcomeOp {
 			if !isShim {
 				return new(spPulseOp)
 			}
-			return &spPulseOp{Cookie: (*[256]byte)(sampleCookie)}
+			op := &spPulseOp{Cookie: (*[pulseCookieSizeMax]byte)(sampleCookie), CookieSize: pulseCookieSizeMax}
+			if clearUnexported {
+				op.CookieSize += +0xfd
+			}
+			return op
+		}, hst.Template, nil, []stub.Call{
+			call("stat", stub.ExpectArgs{wantRuntimePath + "/pulse"}, (*stubFi)(nil), nil),
+			call("stat", stub.ExpectArgs{wantRuntimePath + "/pulse/native"}, &stubFi{mode: 0666}, nil),
+			call("lookupEnv", stub.ExpectArgs{"PULSE_COOKIE"}, "/proc/nonexistent/cookie", nil),
+			call("stat", stub.ExpectArgs{"/proc/nonexistent/cookie"}, &stubFi{isDir: false, size: 1 << 8}, nil),
+			call("verbosef", stub.ExpectArgs{"loading %d bytes from %q", []any{1 << 8, "/proc/nonexistent/cookie"}}, nil, nil),
+			call("open", stub.ExpectArgs{"/proc/nonexistent/cookie"}, &stubOsFile{Reader: bytes.NewReader(sampleCookie)}, nil),
+		}, newI().
+			// state.ensureRuntimeDir
+			Ensure(m(wantRunDirPath), 0700).
+			UpdatePermType(system.User, m(wantRunDirPath), acl.Execute).
+			Ensure(m(wantRuntimePath), 0700).
+			UpdatePermType(system.User, m(wantRuntimePath), acl.Execute).
+			// state.runtime
+			Ephemeral(system.Process, m(wantRuntimeSharePath), 0700).
+			UpdatePerm(m(wantRuntimeSharePath), acl.Execute).
+			// toSystem
+			Link(m(wantRuntimePath+"/pulse/native"), m(wantRuntimeSharePath+"/pulse")), sysUsesRuntime(nil), nil, insertsOps(afterSpRuntimeOp(nil)), []stub.Call{
+			// this op configures the container state and does not make calls during toContainer
+		}, nil, nil, &hst.AppError{
+			Step: "finalise",
+			Err:  os.ErrInvalid,
+			Msg:  "unexpected PulseAudio cookie size",
+		}},
+
+		{"success cookie short", func(isShim, _ bool) outcomeOp {
+			if !isShim {
+				return new(spPulseOp)
+			}
+			sampleCookieTrunc := make([]byte, pulseCookieSizeMax)
+			copy(sampleCookieTrunc, sampleCookie[:len(sampleCookie)-0xe])
+			return &spPulseOp{Cookie: (*[pulseCookieSizeMax]byte)(sampleCookieTrunc), CookieSize: pulseCookieSizeMax - 0xe}
+		}, hst.Template, nil, []stub.Call{
+			call("stat", stub.ExpectArgs{wantRuntimePath + "/pulse"}, (*stubFi)(nil), nil),
+			call("stat", stub.ExpectArgs{wantRuntimePath + "/pulse/native"}, &stubFi{mode: 0666}, nil),
+			call("lookupEnv", stub.ExpectArgs{"PULSE_COOKIE"}, "/proc/nonexistent/cookie", nil),
+			call("stat", stub.ExpectArgs{"/proc/nonexistent/cookie"}, &stubFi{isDir: false, size: pulseCookieSizeMax - 0xe}, nil),
+			call("verbosef", stub.ExpectArgs{"%s at %q is %d bytes shorter than expected", []any{"PulseAudio cookie", "/proc/nonexistent/cookie", int64(0xe)}}, nil, nil),
+			call("open", stub.ExpectArgs{"/proc/nonexistent/cookie"}, &stubOsFile{Reader: bytes.NewReader(sampleCookie[:len(sampleCookie)-0xe])}, nil),
+		}, newI().
+			// state.ensureRuntimeDir
+			Ensure(m(wantRunDirPath), 0700).
+			UpdatePermType(system.User, m(wantRunDirPath), acl.Execute).
+			Ensure(m(wantRuntimePath), 0700).
+			UpdatePermType(system.User, m(wantRuntimePath), acl.Execute).
+			// state.runtime
+			Ephemeral(system.Process, m(wantRuntimeSharePath), 0700).
+			UpdatePerm(m(wantRuntimeSharePath), acl.Execute).
+			// toSystem
+			Link(m(wantRuntimePath+"/pulse/native"), m(wantRuntimeSharePath+"/pulse")), sysUsesRuntime(nil), nil, insertsOps(afterSpRuntimeOp(nil)), []stub.Call{
+			// this op configures the container state and does not make calls during toContainer
+		}, &container.Params{
+			Ops: new(container.Ops).
+				Bind(m(wantRuntimeSharePath+"/pulse"), m("/run/user/1000/pulse/native"), 0).
+				Place(m("/.hakurei/pulse-cookie"), sampleCookie[:len(sampleCookie)-0xe]),
+		}, paramsWantEnv(config, map[string]string{
+			"PULSE_SERVER": "unix:/run/user/1000/pulse/native",
+			"PULSE_COOKIE": "/.hakurei/pulse-cookie",
+		}, nil), nil},
+
+		{"success cookie", func(isShim, _ bool) outcomeOp {
+			if !isShim {
+				return new(spPulseOp)
+			}
+			return &spPulseOp{Cookie: (*[pulseCookieSizeMax]byte)(sampleCookie), CookieSize: pulseCookieSizeMax}
 		}, hst.Template, nil, []stub.Call{
 			call("stat", stub.ExpectArgs{wantRuntimePath + "/pulse"}, (*stubFi)(nil), nil),
 			call("stat", stub.ExpectArgs{wantRuntimePath + "/pulse/native"}, &stubFi{mode: 0666}, nil),
 			call("lookupEnv", stub.ExpectArgs{"PULSE_COOKIE"}, "/proc/nonexistent/cookie", nil),
-			call("verbosef", stub.ExpectArgs{"loading up to %d bytes from %q", []any{1 << 8, "/proc/nonexistent/cookie"}}, nil, nil),
 			call("stat", stub.ExpectArgs{"/proc/nonexistent/cookie"}, &stubFi{isDir: false, size: 1 << 8}, nil),
+			call("verbosef", stub.ExpectArgs{"loading %d bytes from %q", []any{1 << 8, "/proc/nonexistent/cookie"}}, nil, nil),
 			call("open", stub.ExpectArgs{"/proc/nonexistent/cookie"}, &stubOsFile{Reader: bytes.NewReader(sampleCookie)}, nil),
 		}, newI().
 			// state.ensureRuntimeDir
@@ -169,3 +240,125 @@ func TestSpPulseOp(t *testing.T) {
 		}, nil), nil},
 	})
 }
+
+func TestLoadFile(t *testing.T) {
+	t.Parallel()
+
+	sampleCookie := bytes.Repeat([]byte{0xfc}, pulseCookieSizeMax)
+	checkSimple(t, "loadFile", []simpleTestCase{
+		{"buf", func(k *kstub) error {
+			n, err := loadFile(k, k,
+				"simulated PulseAudio cookie",
+				"/home/ophestra/xdg/config/pulse/cookie",
+				nil)
+			k.Verbose(n)
+			return err
+		}, stub.Expect{Calls: []stub.Call{
+			call("verbose", stub.ExpectArgs{[]any{-1}}, nil, nil),
+		}}, errors.New("invalid buffer")},
+
+		{"stat", func(k *kstub) error {
+			n, err := loadFile(k, k,
+				"simulated PulseAudio cookie",
+				"/home/ophestra/xdg/config/pulse/cookie",
+				make([]byte, 1<<8+0xfd))
+			k.Verbose(n)
+			return err
+		}, stub.Expect{Calls: []stub.Call{
+			call("stat", stub.ExpectArgs{"/home/ophestra/xdg/config/pulse/cookie"}, (*stubFi)(nil), stub.UniqueError(3)),
+			call("verbose", stub.ExpectArgs{[]any{-1}}, nil, nil),
+		}}, &hst.AppError{
+			Step: "access simulated PulseAudio cookie",
+			Err:  stub.UniqueError(3),
+		}},
+
+		{"dir", func(k *kstub) error {
+			n, err := loadFile(k, k,
+				"simulated PulseAudio cookie",
+				"/home/ophestra/xdg/config/pulse/cookie",
+				make([]byte, 1<<8+0xfd))
+			k.Verbose(n)
+			return err
+		}, stub.Expect{Calls: []stub.Call{
+			call("stat", stub.ExpectArgs{"/home/ophestra/xdg/config/pulse/cookie"}, &stubFi{isDir: true}, nil),
+			call("verbose", stub.ExpectArgs{[]any{-1}}, nil, nil),
+		}}, &hst.AppError{
+			Step: "read simulated PulseAudio cookie",
+			Err:  &os.PathError{Op: "stat", Path: "/home/ophestra/xdg/config/pulse/cookie", Err: syscall.EISDIR},
+		}},
+
+		{"oob", func(k *kstub) error {
+			n, err := loadFile(k, k,
+				"simulated PulseAudio cookie",
+				"/home/ophestra/xdg/config/pulse/cookie",
+				make([]byte, 1<<8+0xfd))
+			k.Verbose(n)
+			return err
+		}, stub.Expect{Calls: []stub.Call{
+			call("stat", stub.ExpectArgs{"/home/ophestra/xdg/config/pulse/cookie"}, &stubFi{size: 1<<8 + 0xff}, nil),
+			call("verbose", stub.ExpectArgs{[]any{-1}}, nil, nil),
+		}}, &hst.AppError{
+			Step: "finalise",
+			Err:  &os.PathError{Op: "stat", Path: "/home/ophestra/xdg/config/pulse/cookie", Err: syscall.ENOMEM},
+			Msg:  `simulated PulseAudio cookie at "/home/ophestra/xdg/config/pulse/cookie" exceeds expected size`,
+		}},
+
+		{"open", func(k *kstub) error {
+			n, err := loadFile(k, k,
+				"simulated PulseAudio cookie",
+				"/home/ophestra/xdg/config/pulse/cookie",
+				make([]byte, 1<<8+0xfd))
+			k.Verbose(n)
+			return err
+		}, stub.Expect{Calls: []stub.Call{
+			call("stat", stub.ExpectArgs{"/home/ophestra/xdg/config/pulse/cookie"}, &stubFi{size: 1 << 8}, nil),
+			call("verbosef", stub.ExpectArgs{"%s at %q is %d bytes shorter than expected", []any{"simulated PulseAudio cookie", "/home/ophestra/xdg/config/pulse/cookie", int64(0xfd)}}, nil, nil),
+			call("open", stub.ExpectArgs{"/home/ophestra/xdg/config/pulse/cookie"}, (*stubOsFile)(nil), stub.UniqueError(2)),
+			call("verbose", stub.ExpectArgs{[]any{-1}}, nil, nil),
+		}}, &hst.AppError{Step: "open simulated PulseAudio cookie", Err: stub.UniqueError(2)}},
+
+		{"read", func(k *kstub) error {
+			n, err := loadFile(k, k,
+				"simulated PulseAudio cookie",
+				"/home/ophestra/xdg/config/pulse/cookie",
+				make([]byte, 1<<8+0xfd))
+			k.Verbose(n)
+			return err
+		}, stub.Expect{Calls: []stub.Call{
+			call("stat", stub.ExpectArgs{"/home/ophestra/xdg/config/pulse/cookie"}, &stubFi{size: 1 << 8}, nil),
+			call("verbosef", stub.ExpectArgs{"%s at %q is %d bytes shorter than expected", []any{"simulated PulseAudio cookie", "/home/ophestra/xdg/config/pulse/cookie", int64(0xfd)}}, nil, nil),
+			call("open", stub.ExpectArgs{"/home/ophestra/xdg/config/pulse/cookie"}, &stubOsFile{Reader: errorReader{stub.UniqueError(1)}}, nil),
+			call("verbose", stub.ExpectArgs{[]any{-1}}, nil, nil),
+		}}, &hst.AppError{Step: "read simulated PulseAudio cookie", Err: stub.UniqueError(1)}},
+
+		{"short close", func(k *kstub) error {
+			buf := make([]byte, 1<<8+0xfd)
+			n, err := loadFile(k, k,
+				"simulated PulseAudio cookie",
+				"/home/ophestra/xdg/config/pulse/cookie",
+				buf)
+			k.Verbose(buf[:n])
+			return err
+		}, stub.Expect{Calls: []stub.Call{
+			call("stat", stub.ExpectArgs{"/home/ophestra/xdg/config/pulse/cookie"}, &stubFi{size: 1 << 8}, nil),
+			call("verbosef", stub.ExpectArgs{"%s at %q is %d bytes shorter than expected", []any{"simulated PulseAudio cookie", "/home/ophestra/xdg/config/pulse/cookie", int64(0xfd)}}, nil, nil),
+			call("open", stub.ExpectArgs{"/home/ophestra/xdg/config/pulse/cookie"}, &stubOsFile{closeErr: stub.UniqueError(0), Reader: bytes.NewReader(sampleCookie)}, nil),
+			call("verbose", stub.ExpectArgs{[]any{sampleCookie}}, nil, nil),
+		}}, &hst.AppError{Step: "close simulated PulseAudio cookie", Err: stub.UniqueError(0)}},
+
+		{"success", func(k *kstub) error {
+			buf := make([]byte, 1<<8)
+			n, err := loadFile(k, k,
+				"simulated PulseAudio cookie",
+				"/home/ophestra/xdg/config/pulse/cookie",
+				buf)
+			k.Verbose(buf[:n])
+			return err
+		}, stub.Expect{Calls: []stub.Call{
+			call("stat", stub.ExpectArgs{"/home/ophestra/xdg/config/pulse/cookie"}, &stubFi{size: 1 << 8}, nil),
+			call("verbosef", stub.ExpectArgs{"loading %d bytes from %q", []any{1 << 8, "/home/ophestra/xdg/config/pulse/cookie"}}, nil, nil),
+			call("open", stub.ExpectArgs{"/home/ophestra/xdg/config/pulse/cookie"}, &stubOsFile{Reader: bytes.NewReader(sampleCookie)}, nil),
+			call("verbose", stub.ExpectArgs{[]any{sampleCookie}}, nil, nil),
+		}}, nil},
+	})
+}