From b50414f5adfe48a85275a4b92b5580b2477722d8 Mon Sep 17 00:00:00 2001
From: Cassondra Foesch <puellanivis@gmail.com>
Date: Tue, 12 May 2026 13:01:16 +0000
Subject: [PATCH 01/15] fixes

---
 client.go             | 86 +++++++++++++++++++++++++++++++++++--------
 client_test.go        | 35 ++++++++++++++++++
 internal/sync/pool.go | 12 +++++-
 3 files changed, 116 insertions(+), 17 deletions(-)

diff --git a/client.go b/client.go
index 7428cdf6..9b918584 100644
--- a/client.go
+++ b/client.go
@@ -281,6 +281,10 @@ func (c *clientConn) recv(ctx context.Context, reqid uint32, ch chan result) (*s
 		c.discard(ch)
 		return nil, ctx.Err()
 
+	case <-c.closed:
+		c.discard(ch)
+		return nil, sshfx.StatusConnectionLost
+
 	case res := <-ch:
 		c.resPool.Put(ch)
 
@@ -488,7 +492,6 @@ func statusToError(status *sshfx.StatusPacket, okExpected bool) error {
 			return fmt.Errorf("unexpected SSH_FX_OK")
 		}
 		return nil
-
 	case sshfx.StatusEOF:
 		return io.EOF
 	}
@@ -705,11 +708,17 @@ func (cl *Client) ReportPoolMetrics(wr io.Writer) {
 	}
 }
 
+// Wait blocks until the connection has shut down,
+// and returns the error causing the shutdown.
+// It can be called concurrently from multiple goroutines.
+func (cl *Client) Wait() error {
+	return cl.conn.Wait()
+}
+
 // Close closes the SFTP session.
 func (cl *Client) Close() error {
 	cl.conn.disconnect(nil)
-	cl.conn.wr.Close()
-	return nil
+	return cl.conn.wr.Close()
 }
 
 func wrapPathError(op, path string, err error) error {
@@ -753,11 +762,8 @@ func wrapLinkError(op, oldpath, newpath string, err error) error {
 func (cl *Client) Mkdir(name string, perm fs.FileMode) error {
 	return wrapPathError("mkdir", name,
 		cl.sendPacket(context.Background(), nil, &sshfx.MkdirPacket{
-			Path: name,
-			Attrs: sshfx.Attributes{
-				Flags:       sshfx.AttrPermissions,
-				Permissions: sshfx.FileMode(perm.Perm()),
-			},
+			Path:  name,
+			Attrs: attrsFromPerm(perm),
 		}),
 	)
 }
@@ -845,6 +851,45 @@ func (cl *Client) Remove(name string) error {
 	return wrapPathError("remove", name, errF)
 }
 
+// RemoveAll removes path and any children it contains.
+// It removes everything it can but returns the first error it encounters.
+// f the path does not exist, RemoveAll returns nil (no error).
+// If there is an error, it will be of type *PathError.
+func (cl *Client) RemoveAll(pathname string) error {
+	fi, err := cl.Stat(pathname)
+	if err != nil {
+		if errors.Is(err, fs.ErrNotExist) {
+			return nil
+		}
+		return err
+	}
+
+	if !fi.IsDir() {
+		return cl.Remove(pathname)
+	}
+
+	files, err := cl.ReadDir(pathname)
+	if err != nil {
+		return err
+	}
+
+	for _, file := range files {
+		filename := path.Join(pathname, file.Name())
+		switch {
+		case file.IsDir():
+			if err := cl.RemoveAll(filename); err != nil {
+				return err
+			}
+		default:
+			if err := cl.Remove(filename); err != nil {
+				return err
+			}
+		}
+	}
+
+	return nil
+}
+
 func (cl *Client) setstat(ctx context.Context, name string, attrs *sshfx.Attributes) error {
 	return wrapPathError("setstat", name,
 		cl.sendPacket(ctx, nil, &sshfx.SetStatPacket{
@@ -935,7 +980,7 @@ func (cl *Client) ReadLink(name string) (string, error) {
 // Server-specific restrictions may apply when old path and new path are in different directories.
 // Even within the same directory, on non-Unix servers Rename is not guaranteed to be an atomic operation.
 func (cl *Client) Rename(oldpath, newpath string) error {
-	if cl.hasExtension(openssh.ExtensionPOSIXRename()) {
+	if cl.HasExtension(openssh.ExtensionPOSIXRename()) {
 		return wrapLinkError("rename", oldpath, newpath,
 			cl.sendPacket(context.Background(), nil, &openssh.POSIXRenameExtendedPacket{
 				OldPath: oldpath,
@@ -963,7 +1008,11 @@ func (cl *Client) Symlink(oldname, newname string) error {
 	)
 }
 
-func (cl *Client) hasExtension(ext *sshfx.ExtensionPair) bool {
+func (cl *Client) GetExtension(name string) string {
+	return cl.exts[name]
+}
+
+func (cl *Client) HasExtension(ext *sshfx.ExtensionPair) bool {
 	return cl.exts[ext.Name] == ext.Data
 }
 
@@ -986,7 +1035,7 @@ func (cl *Client) StatVFS(path string) (*openssh.StatVFSExtendedReplyPacket, err
 // then no request will be sent,
 // and Link returns an *fs.LinkError wrapping sshfx.StatusOpUnsupported.
 func (cl *Client) Link(oldname, newname string) error {
-	if !cl.hasExtension(openssh.ExtensionHardlink()) {
+	if !cl.HasExtension(openssh.ExtensionHardlink()) {
 		return wrapLinkError("hardlink", oldname, newname, sshfx.StatusOpUnsupported)
 	}
 
@@ -1422,6 +1471,14 @@ func (cl *Client) Create(name string) (*File, error) {
 	return cl.OpenFile(name, OpenFlagReadWrite|OpenFlagCreate|OpenFlagTruncate, 0666)
 }
 
+func attrsFromPerm(perm fs.FileMode) sshfx.Attributes {
+	var attrs sshfx.Attributes
+	if perm != 0 {
+		attrs.SetPermissions(sshfx.FileMode(perm.Perm()))
+	}
+	return attrs
+}
+
 // OpenFile is the generalized open call;
 // most users can use the simplified Open or Create methods instead.
 // It opens the named file with the specified flag (OpenFlagReadOnly, etc.).
@@ -1434,10 +1491,7 @@ func (cl *Client) OpenFile(name string, flag int, perm fs.FileMode) (*File, erro
 	handle, err := cl.getHandle(context.Background(), nil, &sshfx.OpenPacket{
 		Filename: name,
 		PFlags:   toPortableFlags(flag),
-		Attrs: sshfx.Attributes{
-			Flags:       sshfx.AttrPermissions,
-			Permissions: sshfx.FileMode(perm.Perm()),
-		},
+		Attrs:    attrsFromPerm(perm),
 	})
 	if err != nil {
 		return nil, wrapPathError("openfile", name, err)
@@ -2468,7 +2522,7 @@ func (f *File) Sync() error {
 		return f.wrapErr("fsync", err)
 	}
 
-	if !f.cl.hasExtension(openssh.ExtensionFSync()) {
+	if !f.cl.HasExtension(openssh.ExtensionFSync()) {
 		return f.wrapErr("fsync", sshfx.StatusOpUnsupported)
 	}
 
diff --git a/client_test.go b/client_test.go
index e9e68eab..2892b0a0 100644
--- a/client_test.go
+++ b/client_test.go
@@ -1,9 +1,13 @@
 package sftp
 
 import (
+	"bytes"
+	"errors"
 	"io"
 	"io/fs"
 	"testing"
+
+	sshfx "github.com/pkg/sftp/v2/encoding/ssh/filexfer"
 )
 
 func TestClient(t *testing.T) {
@@ -36,3 +40,34 @@ func TestClient(t *testing.T) {
 
 	var _ allFS = new(fsys)
 }
+
+type sink struct{}
+
+func (sink) Close() error { return nil }
+func (sink) Write(p []byte) (int, error) { return len(p), nil }
+
+// Issue #418: panic in clientConn.recv when the sid is incomplete.
+func TestClientNoSid(t *testing.T) {
+	initPkt := &sshfx.VersionPacket{
+		Version: sftpProtocolVersion,
+	}
+
+	initData, err := initPkt.MarshalBinary()
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+
+	stream := new(bytes.Buffer)
+	stream.Write(initData)
+	stream.Write([]byte{ 0, 0, 0, 10, 0, 0 })
+
+	cl, err := NewClientPipe(t.Context(), stream, sink{})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	_, err = cl.Stat("anything")
+	if !errors.Is(err, sshfx.StatusConnectionLost) {
+		t.Errorf("cl.Stat = %v, expected sshfx.StatusConnectionLost", err)
+	}
+}
diff --git a/internal/sync/pool.go b/internal/sync/pool.go
index 9c3e6dc2..7ffe6b98 100644
--- a/internal/sync/pool.go
+++ b/internal/sync/pool.go
@@ -168,7 +168,8 @@ func (p *Pool[T]) Put(v *T) {
 // relieving pressure on the garbage collector and amortizing allocation overhead.
 // While also co-ordinating outstanding work, so the caller can wait for all work to be complete.
 type WorkPool[T any] struct {
-	wg sync.WaitGroup
+	wg     sync.WaitGroup
+	closed chan struct{}
 
 	ch chan chan T
 }
@@ -178,6 +179,8 @@ type WorkPool[T any] struct {
 // It will panic if given a negative depth, the same as making a negative-buffer channel.
 func NewWorkPool[T any](depth int) *WorkPool[T] {
 	p := &WorkPool[T]{
+		closed: make(chan struct{}),
+
 		ch: make(chan chan T, depth),
 	}
 
@@ -203,6 +206,7 @@ func (p *WorkPool[T]) Close() error {
 		return errors.New("cannot close nil work pool")
 	}
 
+	close(p.closed)
 	close(p.ch)
 
 	p.wg.Wait()
@@ -243,6 +247,12 @@ func (p *WorkPool[T]) Put(v chan T) {
 		return
 	}
 
+	select {
+	case <-p.closed:
+		return
+	default:
+	}
+
 	select {
 	case p.ch <- v:
 		p.wg.Done()

From 972cbeb5c3d02b0084e42744ce0caa815f1001da Mon Sep 17 00:00:00 2001
From: Cassondra Foesch <puellanivis@gmail.com>
Date: Tue, 12 May 2026 13:46:39 +0000
Subject: [PATCH 02/15] Client.ReaddirContext

---
 client.go | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/client.go b/client.go
index 9b918584..7a88f25f 100644
--- a/client.go
+++ b/client.go
@@ -1051,13 +1051,20 @@ func (cl *Client) Link(oldname, newname string) error {
 // If an error occurs reading the directory,
 // Readdir returns the entries it was able to read before the error, along with the error.
 func (cl *Client) Readdir(name string) ([]fs.FileInfo, error) {
+	return cl.ReaddirContext(context.Background(), name)
+}
+
+// ReaddirContext reads the named directory, returning all its directory entries as [fs.FileInfo] sorted by filename.
+// If an error occurs reading the directory, including the context being canceled,
+// Readdir returns the entries it was able to read before the error, along with the error.
+func (cl *Client) ReaddirContext(ctx context.Context, name string) ([]fs.FileInfo, error) {
 	d, err := cl.OpenDir(name)
 	if err != nil {
 		return nil, err
 	}
 	defer d.Close()
 
-	fis, err := d.Readdir(0)
+	fis, err := d.ReaddirContext(ctx, 0)
 
 	slices.SortFunc(fis, func(a, b fs.FileInfo) int {
 		return cmp.Compare(a.Name(), b.Name())

From b2536a6351f2a38aa71a917a950f51c094607b3b Mon Sep 17 00:00:00 2001
From: Cassondra Foesch <puellanivis@gmail.com>
Date: Tue, 12 May 2026 14:42:43 +0000
Subject: [PATCH 03/15] =?UTF-8?q?path=20import=20=E2=86=92=20stdpath?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 client.go | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/client.go b/client.go
index 7a88f25f..8b47d533 100644
--- a/client.go
+++ b/client.go
@@ -11,7 +11,7 @@ import (
 	"iter"
 	"math"
 	"os"
-	"path"
+	stdpath "path"
 	"slices"
 	"sync/atomic"
 	"syscall"
@@ -783,7 +783,7 @@ func (cl *Client) MkdirAll(name string, perm fs.FileMode) error {
 
 	// Slow path: make sure parent exists and then call Mkdir for name.
 
-	if parent := path.Dir(name); parent != "" {
+	if parent := stdpath.Dir(name); parent != "" {
 		err = cl.MkdirAll(parent, perm)
 		if err != nil {
 			return err
@@ -874,7 +874,7 @@ func (cl *Client) RemoveAll(pathname string) error {
 	}
 
 	for _, file := range files {
-		filename := path.Join(pathname, file.Name())
+		filename := stdpath.Join(pathname, file.Name())
 		switch {
 		case file.IsDir():
 			if err := cl.RemoveAll(filename); err != nil {
@@ -1267,6 +1267,7 @@ func (d *Dir) rangedir(ctx context.Context, grow func(int)) iter.Seq2[*sshfx.Nam
 
 			// Pull from saved entries first.
 			for i, ent := range d.entries {
+				switch ent.Name() {
 				if !yield(ent, nil) {
 					// This is a break condition.
 					// We need to remove all entries that have been consumed,

From c3fd5a1a6e4ae4d3833875d08762730f7a3cb6c9 Mon Sep 17 00:00:00 2001
From: Cassondra Foesch <puellanivis@gmail.com>
Date: Tue, 12 May 2026 14:43:21 +0000
Subject: [PATCH 04/15] rangedir: bug: skip . and ..

---
 client.go | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/client.go b/client.go
index 8b47d533..b9bd00de 100644
--- a/client.go
+++ b/client.go
@@ -1268,6 +1268,10 @@ func (d *Dir) rangedir(ctx context.Context, grow func(int)) iter.Seq2[*sshfx.Nam
 			// Pull from saved entries first.
 			for i, ent := range d.entries {
 				switch ent.Name() {
+				case ".", "..": // skip useless names.
+					continue
+				}
+
 				if !yield(ent, nil) {
 					// This is a break condition.
 					// We need to remove all entries that have been consumed,

From 77c75f658209398f8b63f774d340f606458930ea Mon Sep 17 00:00:00 2001
From: Cassondra Foesch <puellanivis@gmail.com>
Date: Tue, 12 May 2026 14:51:44 +0000
Subject: [PATCH 05/15] go fmt; golint

---
 client.go                                      | 14 ++++++++++++--
 client_test.go                                 |  4 ++--
 encoding/ssh/filexfer/buffer.go                |  2 +-
 encoding/ssh/filexfer/extended_packets_test.go |  4 ++--
 encoding/ssh/filexfer/response_packets.go      |  2 +-
 5 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/client.go b/client.go
index b9bd00de..8e220364 100644
--- a/client.go
+++ b/client.go
@@ -580,6 +580,8 @@ func (cl *Client) getDataBuf(size int) []byte {
 	return hint[:size] // trim our buffer to length, it might be longer than chunkSize.
 }
 
+// SSHSession is an interface for x/crypto/ssh.Session,
+// in order to break the dependency on x/crypto.
 type SSHSession interface {
 	StdinPipe() (io.WriteCloser, error)
 	StdoutPipe() (io.Reader, error)
@@ -591,6 +593,8 @@ type SSHSession interface {
 	Wait() error
 }
 
+// SSHClient is an interface for x/crypto/ssh.Client,
+// in order to break the dependency on x/crypto.
 type SSHClient[Session SSHSession] interface {
 	NewSession() (Session, error)
 }
@@ -1008,12 +1012,18 @@ func (cl *Client) Symlink(oldname, newname string) error {
 	)
 }
 
+// GetExtension returns the data associated with the extension name.
+// If there is no data associated with the extension name, it returns the empty string.
 func (cl *Client) GetExtension(name string) string {
 	return cl.exts[name]
 }
 
-func (cl *Client) HasExtension(ext *sshfx.ExtensionPair) bool {
-	return cl.exts[ext.Name] == ext.Data
+// HasExtension returns true if the data associated with the extension name is the same as extension data.
+//
+// This is a much more strict test for extensions than simple existence of data associated with the extension name.
+// To test for anything wider than extension data, use [Client.GetExtension].
+func (cl *Client) HasExtension(extension *sshfx.ExtensionPair) bool {
+	return cl.exts[extension.Name] == extension.Data
 }
 
 // StatVFS retrieves VFS statistics from a remote host.
diff --git a/client_test.go b/client_test.go
index 2892b0a0..91d99080 100644
--- a/client_test.go
+++ b/client_test.go
@@ -43,7 +43,7 @@ func TestClient(t *testing.T) {
 
 type sink struct{}
 
-func (sink) Close() error { return nil }
+func (sink) Close() error                { return nil }
 func (sink) Write(p []byte) (int, error) { return len(p), nil }
 
 // Issue #418: panic in clientConn.recv when the sid is incomplete.
@@ -59,7 +59,7 @@ func TestClientNoSid(t *testing.T) {
 
 	stream := new(bytes.Buffer)
 	stream.Write(initData)
-	stream.Write([]byte{ 0, 0, 0, 10, 0, 0 })
+	stream.Write([]byte{0, 0, 0, 10, 0, 0})
 
 	cl, err := NewClientPipe(t.Context(), stream, sink{})
 	if err != nil {
diff --git a/encoding/ssh/filexfer/buffer.go b/encoding/ssh/filexfer/buffer.go
index 0d8cec1c..8dde0101 100644
--- a/encoding/ssh/filexfer/buffer.go
+++ b/encoding/ssh/filexfer/buffer.go
@@ -197,7 +197,7 @@ func (b *Buffer) ConsumeUint32() uint32 {
 func (b *Buffer) AppendUint32(v uint32) {
 	b.b = binary.BigEndian.AppendUint32(b.b, v)
 }
-//*/
+
 // ConsumeCount consumes a single uint32 count from the buffer, in network byte order (big-endian) as an int.
 // If the buffer does not have enough data, it will set Err to ErrShortPacket.
 func (b *Buffer) ConsumeCount() (int, error) {
diff --git a/encoding/ssh/filexfer/extended_packets_test.go b/encoding/ssh/filexfer/extended_packets_test.go
index e097e5b9..79843f2a 100644
--- a/encoding/ssh/filexfer/extended_packets_test.go
+++ b/encoding/ssh/filexfer/extended_packets_test.go
@@ -183,7 +183,7 @@ func TestExtendedPacketTestData(t *testing.T) {
 		t.Errorf("UnmarshalPacketBody(): ExtendedRequest was %q, but expected %q", p.ExtendedRequest, extendedRequest)
 	}
 
-	wantBuffer := []byte{ textValue^0x2a }
+	wantBuffer := []byte{textValue ^ 0x2a}
 
 	if buf, ok := p.Data.(*Buffer); !ok {
 		t.Errorf("UnmarshalPacketBody(): Data was type %T, but expected %T", p.Data, buf)
@@ -243,7 +243,7 @@ func TestExtendedPacketTestBuffer(t *testing.T) {
 		t.Errorf("UnmarshalPacketBody(): ExtendedRequest was %q, but expected %q", p.ExtendedRequest, extendedRequest)
 	}
 
-	wantBuffer := []byte{ 0x00, 0x00, 0x00, 0x03, 'b', 'a', 'r' }
+	wantBuffer := []byte{0x00, 0x00, 0x00, 0x03, 'b', 'a', 'r'}
 
 	if buf, ok := p.Data.(*Buffer); !ok {
 		t.Errorf("UnmarshalPacketBody(): Data was type %T, but expected %T", p.Data, buf)
diff --git a/encoding/ssh/filexfer/response_packets.go b/encoding/ssh/filexfer/response_packets.go
index 60ec6d04..c85fcdd8 100644
--- a/encoding/ssh/filexfer/response_packets.go
+++ b/encoding/ssh/filexfer/response_packets.go
@@ -44,7 +44,7 @@ func (p *StatusPacket) MarshalSize() int {
 	// uint32(length) + uint8(type) + uint32(request-id)
 	const size = 4 + 1 + 4
 
- 	// uint32(error/status code) + string(error message) + string(language tag)
+	// uint32(error/status code) + string(error message) + string(language tag)
 	return size + 4 + 4 + len(p.ErrorMessage) + 4 + len(p.LanguageTag)
 }
 

From 7fa0a047ca1f5ad68aad05f13e75422fc4de8216 Mon Sep 17 00:00:00 2001
From: Cassondra Foesch <puellanivis@gmail.com>
Date: Tue, 19 May 2026 11:56:22 +0000
Subject: [PATCH 06/15] update go tags

---
 errno_posix.go | 1 -
 fuzz.go        | 2 --
 ls_plan9.go    | 1 -
 ls_stub.go     | 1 -
 ls_unix.go     | 1 -
 5 files changed, 6 deletions(-)

diff --git a/errno_posix.go b/errno_posix.go
index bc5bbcd5..45a1f914 100644
--- a/errno_posix.go
+++ b/errno_posix.go
@@ -1,5 +1,4 @@
 //go:build !plan9
-// +build !plan9
 
 package sftp
 
diff --git a/fuzz.go b/fuzz.go
index 72202818..324eb20b 100644
--- a/fuzz.go
+++ b/fuzz.go
@@ -1,6 +1,4 @@
-// go:build gofuzz
 //go:build gofuzz
-// +build gofuzz
 
 package sftp
 
diff --git a/ls_plan9.go b/ls_plan9.go
index ed7dc044..21e8f11e 100644
--- a/ls_plan9.go
+++ b/ls_plan9.go
@@ -1,5 +1,4 @@
 //go:build plan9
-// +build plan9
 
 package sftp
 
diff --git a/ls_stub.go b/ls_stub.go
index 1cf29cd6..b584d695 100644
--- a/ls_stub.go
+++ b/ls_stub.go
@@ -1,5 +1,4 @@
 //go:build windows || android
-// +build windows android
 
 package sftp
 
diff --git a/ls_unix.go b/ls_unix.go
index ec4efa2f..2e659801 100644
--- a/ls_unix.go
+++ b/ls_unix.go
@@ -1,5 +1,4 @@
 //go:build aix || darwin || dragonfly || freebsd || (!android && linux) || netbsd || openbsd || solaris || js || wasip1 || zos
-// +build aix darwin dragonfly freebsd !android,linux netbsd openbsd solaris js wasip1 zos
 
 package sftp
 

From 5524c1065a24994ad15cc8da896db798497c456d Mon Sep 17 00:00:00 2001
From: Cassondra Foesch <puellanivis@gmail.com>
Date: Tue, 19 May 2026 12:01:12 +0000
Subject: [PATCH 07/15] sync.WorkPool: if closed Get returns false, wg.Done
 before testing if closed

---
 internal/sync/pool.go | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/internal/sync/pool.go b/internal/sync/pool.go
index 7ffe6b98..54bb1e4b 100644
--- a/internal/sync/pool.go
+++ b/internal/sync/pool.go
@@ -229,6 +229,13 @@ func (p *WorkPool[T]) Get() (chan T, bool) {
 		return make(chan T, 1), true
 	}
 
+	select {
+	case <-p.closed:
+		var ch chan T
+		return ch, false
+	default:
+	}
+
 	v, ok := <-p.ch
 	if ok {
 		p.wg.Add(1)
@@ -247,6 +254,8 @@ func (p *WorkPool[T]) Put(v chan T) {
 		return
 	}
 
+	p.wg.Done()
+
 	select {
 	case <-p.closed:
 		return
@@ -255,7 +264,6 @@ func (p *WorkPool[T]) Put(v chan T) {
 
 	select {
 	case p.ch <- v:
-		p.wg.Done()
 	default:
 		panic("worker pool overfill")
 		// This is an overfill, which shouldn't happen, but just in case...

From 87fe5f4808e385a6bc4478e7e4514a073f5bb578 Mon Sep 17 00:00:00 2001
From: Cassondra Foesch <puellanivis@gmail.com>
Date: Tue, 19 May 2026 12:01:37 +0000
Subject: [PATCH 08/15] sync: include Once alias

---
 internal/sync/aliases.go | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/internal/sync/aliases.go b/internal/sync/aliases.go
index d611b71e..53d72e1f 100644
--- a/internal/sync/aliases.go
+++ b/internal/sync/aliases.go
@@ -12,3 +12,6 @@ type RWMutex = sync.RWMutex
 
 // WaitGroup is an alias to [sync.WaitGroup]
 type WaitGroup = sync.WaitGroup
+
+// Once is an alias to [sync.Once]
+type Once = sync.Once

From 09c2367c37214cac20bd6512facafe05f4969866 Mon Sep 17 00:00:00 2001
From: Cassondra Foesch <puellanivis@gmail.com>
Date: Tue, 19 May 2026 12:03:50 +0000
Subject: [PATCH 09/15] import tests from v1

---
 Makefile                   |  33 +-
 client_integration_test.go | 819 +++++++++++++++++++++++++++++++++++++
 client_test.go             | 121 +++++-
 3 files changed, 960 insertions(+), 13 deletions(-)
 create mode 100644 client_integration_test.go

diff --git a/Makefile b/Makefile
index 65c6ae99..789c8ce4 100644
--- a/Makefile
+++ b/Makefile
@@ -1,9 +1,36 @@
 .PHONY: integration integration_w_race
 
+DELAY ?= 0
+
+ifneq ($(DELAY),0)
+DELAY_FLAG=-delay $(DELAY)
+endif
+
+TAGS=integration,sftp.sync.metrics
+
 integration:
-	go test -v ./...
+	go test -v $(DELAY_FLAG) -tags=$(TAGS)
+	go test ./encoding/... ./internal/...
 	make -C localfs integration
 
 integration_w_race:
-	go test -race -v ./...
-	make -C localfs integration
+	go test -race -v $(DELAY_FLAG) -tags=$(TAGS)
+	go test -race ./encoding/... ./internal/...
+	make -C localfs integration_w_race
+
+COUNT ?= 1
+BENCHMARK_PATTERN ?= "."
+
+benchmark:
+	go test -v -run=NONE -bench=$(BENCHMARK_PATTERN) -benchmem -count=$(COUNT) $(DELAY_FLAG) -tags=$(TAGS)
+	make -C localfs benchmark
+
+benchmark_w_memprofile:
+ifneq ($(DELAY),0)
+	@echo "memprofile with DELAY produces invalid data" >&2
+	@exit 1
+endif
+	go test -v -run=NONE -bench=$(BENCHMARK_PATTERN) -benchmem -count=$(COUNT) -memprofile memprofile.out -tags=integration
+	go tool pprof -sample_index=alloc_space -svg -output=memprofile-space.svg memprofile.out
+	go tool pprof -sample_index=alloc_objects -svg -output=memprofile-allocs.svg memprofile.out
+	make -C localfs benchmark_w_memprofile
diff --git a/client_integration_test.go b/client_integration_test.go
new file mode 100644
index 00000000..6c60e9f8
--- /dev/null
+++ b/client_integration_test.go
@@ -0,0 +1,819 @@
+//go:build integration && !windows
+
+package sftp
+
+import (
+	"bytes"
+	"errors"
+	"flag"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"slices"
+	"testing"
+	"time"
+
+	sshfx "github.com/pkg/sftp/v2/encoding/ssh/filexfer"
+	"github.com/pkg/sftp/v2/internal/sync"
+)
+
+const (
+	kibi = 1024
+	mebi = 1024 * 1024
+)
+
+const (
+	ReadOnly                = true
+	ReadWrite               = false
+	NoDelay   time.Duration = 0
+)
+
+const debuglevel = "ERROR" // set to "DEBUG" for debugging
+
+var testSftp *string
+
+func TestMain(m *testing.M) {
+	sftpServerLocations := []string{
+		"/usr/libexec/ssh/sftp-server",
+		"/usr/libexec/sftp-server",
+		"/usr/lib/openssh/sftp-server",
+		"/usr/lib/ssh/sftp-server",
+		`C:\Program Files\Git\usr\lib\ssh\sftp-server.exe`,
+	}
+
+	sftpServer, _ := exec.LookPath("sftp-server")
+	if sftpServer == "" {
+		for _, loc := range sftpServerLocations {
+			if _, err := os.Stat(loc); err == nil {
+				sftpServer = loc
+				break
+			}
+		}
+
+		if sftpServer == "" {
+			fmt.Fprintln(os.Stdout, "FAIL: could not find sftp-server")
+			os.Exit(1)
+		}
+	}
+
+	testSftp = flag.String("sftp", sftpServer, "location of the sftp server binary")
+	flag.Parse()
+
+	os.Exit(m.Run())
+}
+
+type delayedWrite struct {
+	t time.Time
+	b []byte
+}
+
+// delayedWriter wraps a writer and artificially delays the write.
+// This is meant to mimic connections with various latencies.
+// Errors returned from the underlying writer will panic so this should only be used over reliable connections.
+type delayedWriter struct {
+	ch      chan delayedWrite
+	closing chan struct{}
+
+	wg     sync.WaitGroup
+	closed <-chan struct{}
+}
+
+func newDelayedWriter(t testing.TB, wr io.WriteCloser, delay time.Duration) *delayedWriter {
+	closed := make(chan struct{})
+
+	dw := &delayedWriter{
+		ch:      make(chan delayedWrite, 128),
+		closing: make(chan struct{}),
+		closed:  closed,
+	}
+
+	ctx := t.Context()
+
+	go func() {
+		defer close(closed)
+
+		defer wr.Close()
+
+		for write := range dw.ch {
+			select {
+			case <-ctx.Done():
+				return
+			case <-time.After(time.Until(write.t.Add(delay))):
+			}
+
+			n, err := wr.Write(write.b)
+			if err != nil {
+				panic(err)
+			}
+
+			if n < len(write.b) {
+				panic(io.ErrShortWrite)
+			}
+		}
+	}()
+
+	return dw
+}
+
+func (dw *delayedWriter) Write(b []byte) (int, error) {
+	select {
+	case <-dw.closing:
+		return 0, io.ErrClosedPipe
+	default:
+	}
+
+	dw.wg.Add(1)
+	defer dw.wg.Done()
+
+	dw.ch <- delayedWrite{
+		t: time.Now(),
+		b: slices.Clone(b),
+	}
+
+	return len(b), nil
+}
+
+func (dw *delayedWriter) Close() error {
+	close(dw.closing)
+
+	dw.wg.Wait() // wait for any outstanding blocking writes
+
+	close(dw.ch)
+
+	<-dw.closed // wait for writer goroutine to finish.
+
+	return nil
+}
+
+func testClient(t testing.TB, readonly bool, delay time.Duration, opts ...ClientOption) (*Client, *exec.Cmd) {
+	args := []string{
+		"-e",
+		"-l", debuglevel,
+	}
+	if readonly {
+		args = append(args, "-R")
+	}
+
+	cmd := exec.Command(*testSftp, args...)
+
+	cmd.Stderr = os.Stdout
+	pw, err := cmd.StdinPipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if delay > 0 {
+		pw = newDelayedWriter(t, pw, delay)
+	}
+
+	pr, err := cmd.StdoutPipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if err := cmd.Start(); err != nil {
+		t.Skip("could not start sftp-server process:", err)
+	}
+
+	cl, err := newClientPipe(t.Context(), pr, nil, pw, nil, opts)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	return cl, cmd
+}
+
+// github.com/pkg/sftp/issues/42, abrupt server hangup would result in client hangs.
+func TestServerRoughDisconnect(t *testing.T) {
+	cl, cmd := testClient(t, ReadOnly, NoDelay)
+	defer cmd.Wait()
+	defer cl.Close()
+
+	f, err := cl.Open("/dev/zero")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer f.Close()
+
+	go func() {
+		time.Sleep(100 * time.Millisecond)
+		cmd.Process.Kill()
+	}()
+
+	_, err = io.Copy(io.Discard, f)
+	if !errors.Is(err, sshfx.StatusConnectionLost) {
+		t.Errorf("io.Copy error = %#v, but wanted sshfx.StatusConnectionLost", err)
+	}
+}
+
+// github.com/pkg/sftp/issues/181, abrupt server hangup would result in client hangs.
+// due to broadcastErr filling up the request channel
+// this reproduces it about 50% of the time
+func TestServerRoughDisconnect2(t *testing.T) {
+	cl, cmd := testClient(t, ReadOnly, NoDelay)
+	defer cmd.Wait()
+	defer cl.Close()
+
+	f, err := cl.Open("/dev/zero")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer f.Close()
+
+	b := make([]byte, 100*32*kibi)
+
+	go func() {
+		time.Sleep(100 * time.Millisecond)
+		cmd.Process.Kill()
+	}()
+
+	for {
+		if _, err := f.Read(b); err != nil {
+			if !errors.Is(err, sshfx.StatusConnectionLost) {
+				t.Errorf("File.Read error = %#v, but wanted sshfx.StatusConnectionLost", err)
+			}
+			break
+		}
+	}
+}
+
+// github.com/pkg/sftp/issues/234 - abrupt shutdown during ReadFrom hangs client
+func TestServerRoughDisconnect3(t *testing.T) {
+	cl, cmd := testClient(t, ReadWrite, NoDelay)
+	defer cmd.Wait()
+	defer cl.Close()
+
+	dst, err := cl.OpenFile("/dev/null", OpenFlagReadWrite, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer dst.Close()
+
+	src, err := os.Open("/dev/zero")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer src.Close()
+
+	go func() {
+		time.Sleep(100 * time.Millisecond)
+		cmd.Process.Kill()
+	}()
+
+	_, err = io.Copy(dst, src)
+	if !errors.Is(err, sshfx.StatusConnectionLost) {
+		t.Errorf("io.Copy error = %#v, but wanted sshfx.StatusConnectionLost", err)
+	}
+}
+
+// github.com/pkg/sftp/issues/234 - also affected Write
+func TestServerRoughDisconnect4(t *testing.T) {
+	cl, cmd := testClient(t, ReadWrite, NoDelay)
+	defer cmd.Wait()
+	defer cl.Close()
+
+	dst, err := cl.OpenFile("/dev/null", OpenFlagReadWrite, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer dst.Close()
+
+	src, err := os.Open("/dev/zero")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer src.Close()
+
+	b := make([]byte, 200*32*kibi)
+
+	if _, err = src.Read(b); err != nil {
+		t.Fatal(err)
+	}
+
+	go func() {
+		time.Sleep(100 * time.Millisecond)
+		cmd.Process.Kill()
+	}()
+
+	for {
+		if _, err := dst.Write(b); err != nil {
+			if !errors.Is(err, sshfx.StatusConnectionLost) {
+				t.Errorf("dst.Write error = %#v, but wanted sshfx.StatusConnectionLost", err)
+			}
+			break
+		}
+	}
+
+	_, err = io.Copy(dst, src)
+	if !errors.Is(err, sshfx.StatusConnectionLost) {
+		t.Errorf("io.Copy error = %#v, but wanted sshfx.StatusConnectionLost", err)
+	}
+}
+
+func benchmarkRead(b *testing.B, bufsize int, delay time.Duration) {
+	size := 10*mebi + 123 // ~10MiB
+
+	cl, cmd := testClient(b, ReadOnly, delay)
+	defer cmd.Wait()
+	defer cl.Close()
+
+	buf := make([]byte, bufsize)
+
+	b.SetBytes(int64(size))
+
+	for b.Loop() {
+		offset := 0
+
+		f, err := cl.Open("/dev/zero")
+		if err != nil {
+			b.Fatal(err)
+		}
+
+		for offset < size {
+			remaining := size - offset
+			buf := buf[:min(remaining, len(buf))]
+
+			n, err := io.ReadFull(f, buf)
+			offset += n
+
+			if err != nil {
+				b.Fatalf("read error at %d: %v", offset, err)
+			}
+		}
+
+		switch {
+		case offset < size:
+			b.Fatalf("read too few bytes! read: %d, wanted: %d", offset, size)
+		case offset > size:
+			b.Fatalf("read too many bytes! read: %d, wanted: %d", offset, size)
+		}
+
+		f.Close()
+	}
+}
+
+func BenchmarkRead1k(b *testing.B) {
+	benchmarkRead(b, 1*kibi, NoDelay)
+}
+
+func BenchmarkRead16k(b *testing.B) {
+	benchmarkRead(b, 16*kibi, NoDelay)
+}
+
+func BenchmarkRead32k(b *testing.B) {
+	benchmarkRead(b, 32*kibi, NoDelay)
+}
+
+func BenchmarkRead128k(b *testing.B) {
+	benchmarkRead(b, 128*kibi, NoDelay)
+}
+
+func BenchmarkRead512k(b *testing.B) {
+	benchmarkRead(b, 512*kibi, NoDelay)
+}
+
+func BenchmarkRead1MiB(b *testing.B) {
+	benchmarkRead(b, mebi, NoDelay)
+}
+
+func BenchmarkRead4MiB(b *testing.B) {
+	benchmarkRead(b, 4*mebi, NoDelay)
+}
+
+func BenchmarkRead4MiBDelay10Msec(b *testing.B) {
+	benchmarkRead(b, 4*mebi, 10*time.Millisecond)
+}
+
+func BenchmarkRead4MiBDelay50Msec(b *testing.B) {
+	benchmarkRead(b, 4*mebi, 50*time.Millisecond)
+}
+
+func BenchmarkRead4MiBDelay150Msec(b *testing.B) {
+	benchmarkRead(b, 4*mebi, 150*time.Millisecond)
+}
+
+func benchmarkWrite(b *testing.B, bufsize int, delay time.Duration) {
+	size := 10*mebi + 0x123 // ~10MiB
+
+	cl, cmd := testClient(b, ReadWrite, delay)
+	defer cmd.Wait()
+	defer cl.Close()
+
+	data := make([]byte, size)
+	for i := range data {
+		data[i] = uint8(i >> ((i % 4) * 8))
+	}
+
+	b.SetBytes(int64(size))
+
+	for b.Loop() {
+		func() {
+			offset := 0
+
+			f, err := os.CreateTemp("", "sftptest-benchwrite")
+			if err != nil {
+				b.Fatal(err)
+			}
+			defer os.Remove(f.Name())
+			defer f.Close()
+
+			f2, err := cl.Create(f.Name())
+			if err != nil {
+				b.Fatal(err)
+			}
+			defer f2.Close()
+
+			for offset < size {
+				buf := data[offset:]
+				buf = buf[:min(len(buf), bufsize)]
+
+				n, err := f2.Write(buf)
+				offset += n
+				if err != nil {
+					b.Fatalf("write error at %d: %v", offset, err)
+				}
+
+				if n != len(buf) {
+					b.Fatalf("wrote too few bytes! written: %d, wanted: %d", n, len(buf))
+				}
+			}
+
+			fi, err := os.Stat(f.Name())
+			if err != nil {
+				b.Fatal(err)
+			}
+
+			if fi.Size() != int64(size) {
+				b.Fatalf("wrong file size: got: %d, want: %d", fi.Size(), size)
+			}
+		}()
+	}
+}
+
+func BenchmarkWrite1k(b *testing.B) {
+	benchmarkWrite(b, 1*kibi, NoDelay)
+}
+
+func BenchmarkWrite16k(b *testing.B) {
+	benchmarkWrite(b, 16*kibi, NoDelay)
+}
+
+func BenchmarkWrite32k(b *testing.B) {
+	benchmarkWrite(b, 32*kibi, NoDelay)
+}
+
+func BenchmarkWrite128k(b *testing.B) {
+	benchmarkWrite(b, 128*kibi, NoDelay)
+}
+
+func BenchmarkWrite512k(b *testing.B) {
+	benchmarkWrite(b, 512*kibi, NoDelay)
+}
+
+func BenchmarkWrite1MiB(b *testing.B) {
+	benchmarkWrite(b, mebi, NoDelay)
+}
+
+func BenchmarkWrite4MiB(b *testing.B) {
+	benchmarkWrite(b, 4*mebi, NoDelay)
+}
+
+func BenchmarkWrite4MiBDelay10Msec(b *testing.B) {
+	benchmarkWrite(b, 4*mebi, 10*time.Millisecond)
+}
+
+func BenchmarkWrite4MiBDelay50Msec(b *testing.B) {
+	benchmarkWrite(b, 4*mebi, 50*time.Millisecond)
+}
+
+func BenchmarkWrite4MiBDelay150Msec(b *testing.B) {
+	benchmarkWrite(b, 4*mebi, 150*time.Millisecond)
+}
+
+func benchmarkReadFrom(b *testing.B, bufsize int, delay time.Duration) {
+	size := 10*mebi + 123 // ~10MiB
+
+	// open sftp client
+	cl, cmd := testClient(b, ReadWrite, delay)
+	defer cmd.Wait()
+	defer cl.Close()
+
+	data := make([]byte, size)
+
+	b.SetBytes(int64(size))
+
+	for b.Loop() {
+		func() {
+			f, err := os.CreateTemp("", "sftptest-benchreadfrom")
+			if err != nil {
+				b.Fatal(err)
+			}
+			defer os.Remove(f.Name())
+			defer f.Close()
+
+			f2, err := cl.Create(f.Name())
+			if err != nil {
+				b.Fatal(err)
+			}
+			defer f2.Close()
+
+			f2.ReadFrom(bytes.NewReader(data))
+
+			fi, err := os.Stat(f.Name())
+			if err != nil {
+				b.Fatal(err)
+			}
+
+			if fi.Size() != int64(size) {
+				b.Fatalf("wrong file size: got: %d, want: %d", fi.Size(), size)
+			}
+		}()
+	}
+}
+
+func BenchmarkReadFrom1k(b *testing.B) {
+	benchmarkReadFrom(b, 1*kibi, NoDelay)
+}
+
+func BenchmarkReadFrom16k(b *testing.B) {
+	benchmarkReadFrom(b, 16*kibi, NoDelay)
+}
+
+func BenchmarkReadFrom32k(b *testing.B) {
+	benchmarkReadFrom(b, 32*kibi, NoDelay)
+}
+
+func BenchmarkReadFrom128k(b *testing.B) {
+	benchmarkReadFrom(b, 128*kibi, NoDelay)
+}
+
+func BenchmarkReadFrom512k(b *testing.B) {
+	benchmarkReadFrom(b, 512*kibi, NoDelay)
+}
+
+func BenchmarkReadFrom1MiB(b *testing.B) {
+	benchmarkReadFrom(b, mebi, NoDelay)
+}
+
+func BenchmarkReadFrom4MiB(b *testing.B) {
+	benchmarkReadFrom(b, 4*mebi, NoDelay)
+}
+
+func BenchmarkReadFrom4MiBDelay10Msec(b *testing.B) {
+	benchmarkReadFrom(b, 4*mebi, 10*time.Millisecond)
+}
+
+func BenchmarkReadFrom4MiBDelay50Msec(b *testing.B) {
+	benchmarkReadFrom(b, 4*mebi, 50*time.Millisecond)
+}
+
+func BenchmarkReadFrom4MiBDelay150Msec(b *testing.B) {
+	benchmarkReadFrom(b, 4*mebi, 150*time.Millisecond)
+}
+
+func benchmarkWriteTo(b *testing.B, bufsize int, delay time.Duration) {
+	size := 10*mebi + 123 // ~10MiB
+
+	// open sftp client
+	cl, cmd := testClient(b, false, delay)
+	defer cmd.Wait()
+	defer cl.Close()
+
+	f, err := os.CreateTemp("", "sftptest-benchwriteto")
+	if err != nil {
+		b.Fatal(err)
+	}
+	defer os.Remove(f.Name())
+
+	data := make([]byte, size)
+
+	if _, err = f.Write(data); err != nil {
+		b.Fatal(err)
+	}
+
+	if err = f.Close(); err != nil {
+		b.Fatal(err)
+	}
+
+	buf := bytes.NewBuffer(make([]byte, 0, size))
+
+	b.SetBytes(int64(size))
+
+	for i := 0; i < b.N; i++ {
+		buf.Reset()
+
+		f2, err := cl.Open(f.Name())
+		if err != nil {
+			b.Fatal(err)
+		}
+
+		if _, err = f2.WriteTo(buf); err != nil {
+			b.Fatal(err)
+		}
+
+		if err = f2.Close(); err != nil {
+			b.Fatal(err)
+		}
+
+		if buf.Len() != size {
+			b.Fatalf("wrong buffer size: got: %d, want: %d", buf.Len(), size)
+		}
+	}
+}
+
+func BenchmarkWriteTo1k(b *testing.B) {
+	benchmarkWriteTo(b, 1*kibi, NoDelay)
+}
+
+func BenchmarkWriteTo16k(b *testing.B) {
+	benchmarkWriteTo(b, 16*kibi, NoDelay)
+}
+
+func BenchmarkWriteTo32k(b *testing.B) {
+	benchmarkWriteTo(b, 32*kibi, NoDelay)
+}
+
+func BenchmarkWriteTo128k(b *testing.B) {
+	benchmarkWriteTo(b, 128*kibi, NoDelay)
+}
+
+func BenchmarkWriteTo512k(b *testing.B) {
+	benchmarkWriteTo(b, 512*kibi, NoDelay)
+}
+
+func BenchmarkWriteTo1MiB(b *testing.B) {
+	benchmarkWriteTo(b, mebi, NoDelay)
+}
+
+func BenchmarkWriteTo4MiB(b *testing.B) {
+	benchmarkWriteTo(b, 4*mebi, NoDelay)
+}
+
+func BenchmarkWriteTo4MiBDelay10Msec(b *testing.B) {
+	benchmarkWriteTo(b, 4*mebi, 10*time.Millisecond)
+}
+
+func BenchmarkWriteTo4MiBDelay50Msec(b *testing.B) {
+	benchmarkWriteTo(b, 4*mebi, 50*time.Millisecond)
+}
+
+func BenchmarkWriteTo4MiBDelay150Msec(b *testing.B) {
+	benchmarkWriteTo(b, 4*mebi, 150*time.Millisecond)
+}
+
+type zeroSource struct{}
+
+func (zeroSource) Read(b []byte) (n int, err error) {
+	for i := range b {
+		b[i] = 0
+	}
+	return len(b), nil
+}
+
+func (zeroSource) Close() error { return nil }
+
+func zeroFile(t testing.TB, filename string, filesize int64) string {
+	src, err := os.CreateTemp("", filename)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer src.Close()
+
+	n, err := io.Copy(src, io.LimitReader(zeroSource{}, filesize))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if n < filesize {
+		t.Fatal("short copy")
+	}
+
+	return src.Name()
+}
+
+func benchmarkCopyDown(b *testing.B, filesize int64, delay time.Duration) {
+	srcFilename := zeroFile(b, "sftptest-benchcopydown-src", filesize)
+	defer os.Remove(srcFilename)
+
+	cl, cmd := testClient(b, ReadOnly, delay)
+	defer cmd.Wait()
+	defer cl.Close()
+
+	b.SetBytes(filesize)
+
+	for b.Loop() {
+		func() {
+			dst, err := os.CreateTemp("", "sftptest-benchcopydown-dst")
+			if err != nil {
+				b.Fatal(err)
+			}
+			defer os.Remove(dst.Name())
+			defer dst.Close()
+
+			src, err := cl.Open(srcFilename)
+			if err != nil {
+				b.Fatal(err)
+			}
+			defer src.Close()
+
+			n, err := io.Copy(dst, src)
+			if err != nil {
+				b.Fatal("copy error:", err)
+			}
+
+			if n != filesize {
+				b.Fatalf("wrong bytes copied: got: %d, want: %d", n, filesize)
+			}
+
+			fi, err := dst.Stat()
+			if err != nil {
+				b.Fatal(err)
+			}
+
+			if fi.Size() != filesize {
+				b.Fatalf("wrong file size: got: %d, want: %d", fi.Size(), filesize)
+			}
+		}()
+	}
+}
+
+func BenchmarkCopyDown10MiBDelay10Msec(b *testing.B) {
+	benchmarkCopyDown(b, 10*mebi, 10*time.Millisecond)
+}
+
+func BenchmarkCopyDown10MiBDelay50Msec(b *testing.B) {
+	benchmarkCopyDown(b, 10*mebi, 50*time.Millisecond)
+}
+
+func BenchmarkCopyDown10MiBDelay150Msec(b *testing.B) {
+	benchmarkCopyDown(b, 10*mebi, 150*time.Millisecond)
+}
+
+func benchmarkCopyUp(b *testing.B, filesize int64, delay time.Duration) {
+	srcFilename := zeroFile(b, "sftptest-benchcopyup-src", filesize)
+	defer os.Remove(srcFilename)
+
+	sftp, cmd := testClient(b, false, delay)
+	defer cmd.Wait()
+	defer sftp.Close()
+
+	b.SetBytes(filesize)
+
+	for b.Loop() {
+		func() {
+			// We need to create the destination filename through the OS first.
+			tmpDst, err := os.CreateTemp("", "sftptest-benchcopyup-dst")
+			if err != nil {
+				b.Fatal(err)
+			}
+			dstFilename := tmpDst.Name()
+			tmpDst.Close()
+
+			defer os.Remove(dstFilename)
+
+			// Now, we can use the filename from above as our destination.
+			dst, err := sftp.Create(dstFilename)
+			if err != nil {
+				b.Fatal(err)
+			}
+			defer dst.Close()
+
+			src, err := os.Open(srcFilename)
+			if err != nil {
+				b.Fatal(err)
+			}
+			defer src.Close()
+
+			n, err := io.Copy(dst, src)
+			if err != nil {
+				b.Fatal("copy error:", err)
+			}
+
+			if n < filesize {
+				b.Error("unable to copy all bytes")
+			}
+
+			fi, err := os.Stat(dstFilename)
+			if err != nil {
+				b.Fatal(err)
+			}
+
+			if fi.Size() != filesize {
+				b.Errorf("wrong file size: got %d, want %d", fi.Size(), filesize)
+			}
+		}()
+	}
+}
+
+func BenchmarkCopyUp10MiBDelay10Msec(b *testing.B) {
+	benchmarkCopyUp(b, 10*mebi, 10*time.Millisecond)
+}
+
+func BenchmarkCopyUp10MiBDelay50Msec(b *testing.B) {
+	benchmarkCopyUp(b, 10*mebi, 50*time.Millisecond)
+}
+
+func BenchmarkCopyUp10MiBDelay150Msec(b *testing.B) {
+	benchmarkCopyUp(b, 10*mebi, 150*time.Millisecond)
+}
diff --git a/client_test.go b/client_test.go
index 91d99080..3a36afff 100644
--- a/client_test.go
+++ b/client_test.go
@@ -46,28 +46,129 @@ type sink struct{}
 func (sink) Close() error                { return nil }
 func (sink) Write(p []byte) (int, error) { return len(p), nil }
 
+func TestClientZeroLengthPacket(t *testing.T) {
+	// Packet length zero (never valid). This used to crash the client.
+	r := bytes.NewReader([]byte{0, 0, 0, 0})
+
+	cl, err := NewClientPipe(t.Context(), r, sink{})
+	if err == nil {
+		t.Error("expected an error, got nil")
+	}
+	if cl != nil {
+		cl.Close()
+	}
+}
+
+func TestClientShortPacket(t *testing.T) {
+	// init packet too short.
+	r := bytes.NewReader([]byte{0, 0, 0, 1, 2})
+
+	cl, err := NewClientPipe(t.Context(), r, sink{})
+	if !errors.Is(err, sshfx.ErrShortPacket) {
+		t.Fatalf("got error %#v, but expected sshfx.ErrShortPacket", err)
+	}
+	if cl != nil {
+		cl.Close()
+	}
+}
+
+func streamPackets(t testing.TB, verPkt *sshfx.VersionPacket, packets ...sshfx.PacketMarshaller) io.ReadCloser {
+	pr, pw := io.Pipe()
+
+	go func() {
+		defer pw.Close()
+
+		bindata, err := verPkt.MarshalBinary()
+		if err != nil {
+			t.Errorf("could not binary marshal %#v: %v", verPkt, err)
+			return
+		}
+		pw.Write(bindata)
+
+		var reqid uint32
+		for _, packet := range packets {
+			reqid++
+
+			header, payload, err := packet.MarshalPacket(reqid, nil)
+			if err != nil {
+				t.Errorf("could not packet marshal %#v: %v", packet, err)
+				return
+			}
+
+			if _, err := pw.Write(header); err != nil {
+				t.Error("could not write packet header:", err)
+				return
+			}
+
+			if _, err := pw.Write(payload); err != nil {
+				t.Error("could not write packet payload:", err)
+				return
+			}
+		}
+	}()
+
+	return pr
+}
+
+type noSidBrokenPacket struct{}
+
+func (noSidBrokenPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) {
+	return []byte{0, 0, 0, 10, 0, 0}, nil, nil
+}
+
+func (noSidBrokenPacket) MarshalSize() int {
+	return 10
+}
+
 // Issue #418: panic in clientConn.recv when the sid is incomplete.
 func TestClientNoSid(t *testing.T) {
-	initPkt := &sshfx.VersionPacket{
-		Version: sftpProtocolVersion,
-	}
+	stream := streamPackets(t,
+		&sshfx.VersionPacket{
+			Version: sftpProtocolVersion,
+		},
+		noSidBrokenPacket{},
+	)
 
-	initData, err := initPkt.MarshalBinary()
+	cl, err := NewClientPipe(t.Context(), stream, sink{})
 	if err != nil {
-		t.Fatal("unexpected error:", err)
+		t.Fatal(err)
 	}
+	defer cl.Close()
 
-	stream := new(bytes.Buffer)
-	stream.Write(initData)
-	stream.Write([]byte{0, 0, 0, 10, 0, 0})
+	_, err = cl.Stat("anything")
+	if !errors.Is(err, sshfx.StatusConnectionLost) {
+		t.Errorf("cl.Stat = %q, expected sshfx.StatusConnectionLost", err)
+	}
+}
+
+// sftp/issue/390 - server disconnect should not cause io.EOF or
+// io.ErrUnexpectedEOF in sftp.File.Read, because those confuse io.ReadFull.
+func TestClientRoughDisconnectEOF(t *testing.T) {
+	stream := streamPackets(t,
+		&sshfx.VersionPacket{
+			Version: sftpProtocolVersion,
+		},
+		&sshfx.HandlePacket{
+			Handle: "foo",
+		},
+		&sshfx.DataPacket{
+			Data: []byte("foo"),
+		},
+	)
 
 	cl, err := NewClientPipe(t.Context(), stream, sink{})
 	if err != nil {
 		t.Fatal(err)
 	}
+	defer cl.Close()
 
-	_, err = cl.Stat("anything")
+	f, err := cl.Open("anything")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	_, err = io.ReadFull(f, make([]byte, 10))
 	if !errors.Is(err, sshfx.StatusConnectionLost) {
-		t.Errorf("cl.Stat = %v, expected sshfx.StatusConnectionLost", err)
+		t.Errorf("io.ReadFull error = %q, but wanted sshfx.StatusConnectionLost", err)
 	}
 }

From c44c329e8ff71b8074ceb51ba0b4c197eb799e83 Mon Sep 17 00:00:00 2001
From: Cassondra Foesch <puellanivis@gmail.com>
Date: Tue, 19 May 2026 12:05:11 +0000
Subject: [PATCH 10/15] bugfixes

---
 client.go | 49 ++++++++++++++++++++++++++++++-------------------
 1 file changed, 30 insertions(+), 19 deletions(-)

diff --git a/client.go b/client.go
index 8e220364..754f9954 100644
--- a/client.go
+++ b/client.go
@@ -226,12 +226,6 @@ func (c *clientConn) dispatch(cancel <-chan struct{}, req sshfx.PacketMarshaller
 	default:
 	}
 
-	if c.inflight == nil {
-		c.inflight = make(map[uint32]chan<- result)
-	}
-
-	c.inflight[reqid] = ch
-
 	if _, err := c.wr.Write(header); err != nil {
 		c.resPool.Put(ch)
 		return reqid, nil, fmt.Errorf("sftp: write packet header: %w", err)
@@ -244,6 +238,11 @@ func (c *clientConn) dispatch(cancel <-chan struct{}, req sshfx.PacketMarshaller
 		}
 	}
 
+	if c.inflight == nil {
+		c.inflight = make(map[uint32]chan<- result)
+	}
+	c.inflight[reqid] = ch
+
 	return reqid, ch, nil
 }
 
@@ -253,10 +252,18 @@ func (c *clientConn) returnRaw(raw *sshfx.RawPacket) {
 }
 
 func (c *clientConn) discardBlocking(ch chan result) {
-	res := <-ch
+	select {
+	case <-c.closed:
+		// We've been disconnected.
+		// We have to return something to the work pool, or resPool.Close will deadlock.
+		// It also has to be able to receive a result,
+		// otherwise a broadcasted error will lock up on a send.
+		c.resPool.Put(make(chan result, 1))
 
-	c.returnRaw(res.pkt)
-	c.resPool.Put(ch)
+	case res := <-ch:
+		c.returnRaw(res.pkt)
+		c.resPool.Put(ch)
+	}
 }
 
 func (c *clientConn) discard(ch chan result) {
@@ -492,6 +499,7 @@ func statusToError(status *sshfx.StatusPacket, okExpected bool) error {
 			return fmt.Errorf("unexpected SSH_FX_OK")
 		}
 		return nil
+
 	case sshfx.StatusEOF:
 		return io.EOF
 	}
@@ -1778,14 +1786,12 @@ func (f *File) writeat(ctx context.Context, b []byte, off int64) (written int, e
 		//
 		// Either way, this should be the last successfully written offset.
 		written := int64(firstErr.off) - f.offset
-		f.offset = int64(firstErr.off)
 
 		return int(written), f.wrapErr("writeat", firstErr.err)
 	}
 
 	// We didn't hit any errors, so we must have written all the bytes in the buffer.
 	written = len(b)
-	f.offset += int64(written)
 
 	return written, nil
 }
@@ -1911,6 +1917,7 @@ func (f *File) ReadFrom(r io.Reader) (read int64, err error) {
 	workCh := make(chan work, f.cl.maxInflight)
 
 	type rwErr struct {
+		op  string
 		off uint64
 		err error
 	}
@@ -1936,7 +1943,11 @@ func (f *File) ReadFrom(r io.Reader) (read int64, err error) {
 		for {
 			n, err := io.ReadFull(r, b)
 			if n < 0 {
-				errCh <- rwErr{req.Offset, panicInstead("sftp: readfrom: read returned negative count")}
+				errCh <- rwErr{
+					op:  "read",
+					off: req.Offset,
+					err: panicInstead("sftp: readfrom: read returned negative count"),
+				}
 				return
 			}
 
@@ -1966,7 +1977,7 @@ func (f *File) ReadFrom(r io.Reader) (read int64, err error) {
 
 			if err != nil {
 				if !errors.Is(err, io.EOF) && !errors.Is(err, io.ErrUnexpectedEOF) {
-					errCh <- rwErr{req.Offset, err}
+					errCh <- rwErr{"read", req.Offset, err}
 				}
 				return
 			}
@@ -1984,7 +1995,7 @@ func (f *File) ReadFrom(r io.Reader) (read int64, err error) {
 		for work := range workCh {
 			err := f.cl.recvStatus(ctx, work.reqid, work.res, statusHint)
 			if err != nil {
-				errCh <- rwErr{work.off, err}
+				errCh <- rwErr{"write", work.off, err}
 
 				// DO NOT return.
 				// We want to ensure that workCh is drained before errCh is closed.
@@ -2020,7 +2031,7 @@ func (f *File) ReadFrom(r io.Reader) (read int64, err error) {
 		}
 
 		// ReadFrom is defined to return the read bytes, regardless of any write errors.
-		return read, f.wrapErr("readfrom", firstErr.err)
+		return read, f.wrapErr(firstErr.op, firstErr.err)
 	}
 
 	// We didn't hit any errors, so we must have written all the bytes that we read until EOF.
@@ -2341,7 +2352,7 @@ func (f *File) WriteTo(w io.Writer) (written int64, err error) {
 		}
 	}()
 
-	var writeErr error
+	var readErr error
 
 	// Dispatch: Dispatch into any number of Reads of length <= f.cl.maxDataLen.
 	go func() {
@@ -2358,7 +2369,7 @@ func (f *File) WriteTo(w io.Writer) (written int64, err error) {
 		for {
 			reqid, res, err := f.cl.conn.dispatch(closed, req)
 			if err != nil {
-				writeErr = err
+				readErr = err
 				return
 			}
 
@@ -2418,11 +2429,11 @@ func (f *File) WriteTo(w io.Writer) (written int64, err error) {
 				return written, nil // return nil instead of EOF
 			}
 
-			return written, f.wrapErr("writeto", err)
+			return written, f.wrapErr("recv", err)
 		}
 	}
 
-	return written, f.wrapErr("writeto", writeErr)
+	return written, f.wrapErr("read", readErr)
 }
 
 // WriteFile writes data to the named file, creating it if neccessary.

From d86f5dfefa812240fa7d4ffdb7d47cecf7428b89 Mon Sep 17 00:00:00 2001
From: Cassondra Foesch <puellanivis@gmail.com>
Date: Tue, 19 May 2026 12:10:01 +0000
Subject: [PATCH 11/15] writeat: we shouldn't be using f.offset at all

---
 client.go | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/client.go b/client.go
index 754f9954..470bed4f 100644
--- a/client.go
+++ b/client.go
@@ -1716,7 +1716,7 @@ func (f *File) writeat(ctx context.Context, b []byte, off int64) (written int, e
 
 		req := &sshfx.WritePacket{
 			Handle: handle,
-			Offset: uint64(f.offset),
+			Offset: uint64(off),
 		}
 
 		for len(b) > 0 {
@@ -1785,7 +1785,7 @@ func (f *File) writeat(ctx context.Context, b []byte, off int64) (written int, e
 		// * the offset of the start of the first error received dispatching a write packet offset.
 		//
 		// Either way, this should be the last successfully written offset.
-		written := int64(firstErr.off) - f.offset
+		written := int64(firstErr.off) - off
 
 		return int(written), f.wrapErr("writeat", firstErr.err)
 	}

From a711c561b996b90fd410bc4a347fc5bc95f853ce Mon Sep 17 00:00:00 2001
From: Cassondra Foesch <puellanivis@gmail.com>
Date: Tue, 19 May 2026 13:00:23 +0000
Subject: [PATCH 12/15] fix race condition between chan close and chan write

---
 client_test.go        | 59 ++++++++++++++++++++++++++++++++++++++-----
 internal/sync/pool.go |  9 ++++---
 2 files changed, 57 insertions(+), 11 deletions(-)

diff --git a/client_test.go b/client_test.go
index 3a36afff..f259ffc6 100644
--- a/client_test.go
+++ b/client_test.go
@@ -5,9 +5,11 @@ import (
 	"errors"
 	"io"
 	"io/fs"
+	"sync/atomic"
 	"testing"
 
 	sshfx "github.com/pkg/sftp/v2/encoding/ssh/filexfer"
+	"github.com/pkg/sftp/v2/internal/sync"
 )
 
 func TestClient(t *testing.T) {
@@ -72,10 +74,46 @@ func TestClientShortPacket(t *testing.T) {
 	}
 }
 
-func streamPackets(t testing.TB, verPkt *sshfx.VersionPacket, packets ...sshfx.PacketMarshaller) io.ReadCloser {
+type tickWriter struct {
+	count atomic.Uint32
+	steps atomic.Uint32
+
+	once sync.Once
+	step chan struct{}
+}
+
+func (t *tickWriter) wait() {
+	_ = t.steps.Add(1)
+
+	<-t.step
+}
+
+func (t *tickWriter) Write(b []byte) (written int, err error) {
+	_ = t.count.Add(1)
+
+	t.step <- struct{}{}
+
+	return len(b), nil
+}
+
+func (t *tickWriter) Close() error {
+	t.once.Do(func() { close(t.step) })
+	return nil
+}
+
+func streamPackets(t testing.TB, verPkt *sshfx.VersionPacket, packets ...sshfx.PacketMarshaller) (io.ReadCloser, io.WriteCloser) {
 	pr, pw := io.Pipe()
 
+	ticker := &tickWriter{
+		step: make(chan struct{}),
+	}
+
 	go func() {
+		defer func() {
+			for range ticker.step {
+			}
+		}()
+
 		defer pw.Close()
 
 		bindata, err := verPkt.MarshalBinary()
@@ -83,7 +121,12 @@ func streamPackets(t testing.TB, verPkt *sshfx.VersionPacket, packets ...sshfx.P
 			t.Errorf("could not binary marshal %#v: %v", verPkt, err)
 			return
 		}
-		pw.Write(bindata)
+
+		ticker.wait()
+		if _, err := pw.Write(bindata); err != nil {
+			t.Error(err)
+			return
+		}
 
 		var reqid uint32
 		for _, packet := range packets {
@@ -95,6 +138,8 @@ func streamPackets(t testing.TB, verPkt *sshfx.VersionPacket, packets ...sshfx.P
 				return
 			}
 
+			ticker.wait()
+
 			if _, err := pw.Write(header); err != nil {
 				t.Error("could not write packet header:", err)
 				return
@@ -107,7 +152,7 @@ func streamPackets(t testing.TB, verPkt *sshfx.VersionPacket, packets ...sshfx.P
 		}
 	}()
 
-	return pr
+	return pr, ticker
 }
 
 type noSidBrokenPacket struct{}
@@ -122,14 +167,14 @@ func (noSidBrokenPacket) MarshalSize() int {
 
 // Issue #418: panic in clientConn.recv when the sid is incomplete.
 func TestClientNoSid(t *testing.T) {
-	stream := streamPackets(t,
+	rd, wr := streamPackets(t,
 		&sshfx.VersionPacket{
 			Version: sftpProtocolVersion,
 		},
 		noSidBrokenPacket{},
 	)
 
-	cl, err := NewClientPipe(t.Context(), stream, sink{})
+	cl, err := NewClientPipe(t.Context(), rd, wr)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -144,7 +189,7 @@ func TestClientNoSid(t *testing.T) {
 // sftp/issue/390 - server disconnect should not cause io.EOF or
 // io.ErrUnexpectedEOF in sftp.File.Read, because those confuse io.ReadFull.
 func TestClientRoughDisconnectEOF(t *testing.T) {
-	stream := streamPackets(t,
+	rd, wr := streamPackets(t,
 		&sshfx.VersionPacket{
 			Version: sftpProtocolVersion,
 		},
@@ -156,7 +201,7 @@ func TestClientRoughDisconnectEOF(t *testing.T) {
 		},
 	)
 
-	cl, err := NewClientPipe(t.Context(), stream, sink{})
+	cl, err := NewClientPipe(t.Context(), rd, wr)
 	if err != nil {
 		t.Fatal(err)
 	}
diff --git a/internal/sync/pool.go b/internal/sync/pool.go
index 54bb1e4b..5d706f2d 100644
--- a/internal/sync/pool.go
+++ b/internal/sync/pool.go
@@ -180,8 +180,7 @@ type WorkPool[T any] struct {
 func NewWorkPool[T any](depth int) *WorkPool[T] {
 	p := &WorkPool[T]{
 		closed: make(chan struct{}),
-
-		ch: make(chan chan T, depth),
+		ch:     make(chan chan T, depth),
 	}
 
 	for len(p.ch) < cap(p.ch) {
@@ -207,10 +206,11 @@ func (p *WorkPool[T]) Close() error {
 	}
 
 	close(p.closed)
-	close(p.ch)
 
 	p.wg.Wait()
 
+	close(p.ch)
+
 	for range p.ch {
 		// drain the pool and drop them on all on the ground for GC.
 	}
@@ -254,7 +254,7 @@ func (p *WorkPool[T]) Put(v chan T) {
 		return
 	}
 
-	p.wg.Done()
+	defer p.wg.Done()
 
 	select {
 	case <-p.closed:
@@ -263,6 +263,7 @@ func (p *WorkPool[T]) Put(v chan T) {
 	}
 
 	select {
+	case <-p.closed:
 	case p.ch <- v:
 	default:
 		panic("worker pool overfill")

From 2587c66fd1a6c7e61c4c22a4cd73333f4e79ad91 Mon Sep 17 00:00:00 2001
From: Cassondra Foesch <puellanivis@gmail.com>
Date: Tue, 19 May 2026 14:06:08 +0000
Subject: [PATCH 13/15] lock unlock around closed

---
 client_test.go | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/client_test.go b/client_test.go
index f259ffc6..c4c33c73 100644
--- a/client_test.go
+++ b/client_test.go
@@ -78,8 +78,10 @@ type tickWriter struct {
 	count atomic.Uint32
 	steps atomic.Uint32
 
-	once sync.Once
-	step chan struct{}
+	mu     sync.Mutex
+	once   sync.Once
+	closed bool
+	step   chan struct{}
 }
 
 func (t *tickWriter) wait() {
@@ -89,6 +91,13 @@ func (t *tickWriter) wait() {
 }
 
 func (t *tickWriter) Write(b []byte) (written int, err error) {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+
+	if t.closed {
+		return 0, io.ErrClosedPipe
+	}
+
 	_ = t.count.Add(1)
 
 	t.step <- struct{}{}
@@ -97,7 +106,13 @@ func (t *tickWriter) Write(b []byte) (written int, err error) {
 }
 
 func (t *tickWriter) Close() error {
-	t.once.Do(func() { close(t.step) })
+	t.once.Do(func() {
+		t.mu.Lock()
+		defer t.mu.Unlock()
+
+		t.closed = true
+		close(t.step)
+	})
 	return nil
 }
 

From d36cabc7ec137618d7921c878edddbeaee92581b Mon Sep 17 00:00:00 2001
From: Cassondra Foesch <puellanivis@gmail.com>
Date: Tue, 19 May 2026 14:07:43 +0000
Subject: [PATCH 14/15] lock before respool.Get

---
 client.go | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/client.go b/client.go
index 470bed4f..0daf8f96 100644
--- a/client.go
+++ b/client.go
@@ -208,6 +208,9 @@ func (c *clientConn) dispatch(cancel <-chan struct{}, req sshfx.PacketMarshaller
 	}
 	defer c.bufPool.Put(header)
 
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
 	// payload by design of the API is all but guaranteed to alias a caller-held byte slice,
 	// so, _do not_ put it into the bufPool.
 
@@ -216,9 +219,6 @@ func (c *clientConn) dispatch(cancel <-chan struct{}, req sshfx.PacketMarshaller
 		return reqid, nil, sshfx.StatusConnectionLost
 	}
 
-	c.mu.Lock()
-	defer c.mu.Unlock()
-
 	select {
 	case <-cancel:
 		c.resPool.Put(ch)

From 7029f9de0592ece929c3acf826dcaf4ea0181c30 Mon Sep 17 00:00:00 2001
From: Cassondra Foesch <puellanivis@gmail.com>
Date: Tue, 19 May 2026 14:08:04 +0000
Subject: [PATCH 15/15] more stabbing at deadlocks

---
 internal/sync/pool.go | 29 ++++++++++++++---------------
 1 file changed, 14 insertions(+), 15 deletions(-)

diff --git a/internal/sync/pool.go b/internal/sync/pool.go
index 5d706f2d..7215efa7 100644
--- a/internal/sync/pool.go
+++ b/internal/sync/pool.go
@@ -210,7 +210,6 @@ func (p *WorkPool[T]) Close() error {
 	p.wg.Wait()
 
 	close(p.ch)
-
 	for range p.ch {
 		// drain the pool and drop them on all on the ground for GC.
 	}
@@ -231,16 +230,22 @@ func (p *WorkPool[T]) Get() (chan T, bool) {
 
 	select {
 	case <-p.closed:
-		var ch chan T
-		return ch, false
-	default:
-	}
+		return nil, false
 
-	v, ok := <-p.ch
-	if ok {
-		p.wg.Add(1)
+	case v, ok := <-p.ch:
+		if !ok {
+			return nil, false
+		}
+
+		select {
+		case <-p.closed:
+			return nil, false
+
+		default:
+			p.wg.Add(1)
+			return v, true
+		}
 	}
-	return v, ok
 }
 
 // Put returns the given work channel to the pool.
@@ -256,12 +261,6 @@ func (p *WorkPool[T]) Put(v chan T) {
 
 	defer p.wg.Done()
 
-	select {
-	case <-p.closed:
-		return
-	default:
-	}
-
 	select {
 	case <-p.closed:
 	case p.ch <- v: