diff --git a/common/bufio/copy.go b/common/bufio/copy.go
index 3fb61a5..d0acc2a 100644
--- a/common/bufio/copy.go
+++ b/common/bufio/copy.go
@@ -4,8 +4,6 @@ import (
 	"context"
 	"io"
 	"net"
-	"os"
-
 	"github.com/sagernet/sing/common"
 	"github.com/sagernet/sing/common/buf"
 	E "github.com/sagernet/sing/common/exceptions"
@@ -23,17 +21,34 @@ func (r *readOnlyReader) WriteTo(w io.Writer) (n int64, err error) {
 	return Copy(w, r.Reader)
 }
 
-func needReadFromWrapper(dst io.ReaderFrom, src io.Reader) bool {
-	_, isTCPConn := dst.(*net.TCPConn)
-	if !isTCPConn {
-		return false
-	}
-	switch src.(type) {
-	case *net.TCPConn, *net.UnixConn, *os.File:
-		return false
-	default:
-		return true
-	}
+func (r *readOnlyReader) Upstream() any {
+	return r.Reader
+}
+
+func (r *readOnlyReader) ReaderReplaceable() bool {
+	return true
+}
+
+type writeOnlyWriter struct {
+	io.Writer
+}
+
+func (w *writeOnlyWriter) ReadFrom(r io.Reader) (n int64, err error) {
+	return Copy(w.Writer, r)
+}
+
+func (w *writeOnlyWriter) Upstream() any {
+	return w.Writer
+}
+
+func (w *writeOnlyWriter) WriterReplaceable() bool {
+	return true
+}
+
+func needWrapper(src, dst any) bool {
+	_, srcTCPConn := src.(*net.TCPConn)
+	_, dstTCPConn := dst.(*net.TCPConn)
+	return (srcTCPConn || dstTCPConn) && !(srcTCPConn && dstTCPConn)
 }
 
 func Copy(dst io.Writer, src io.Reader) (n int64, err error) {
@@ -45,10 +60,13 @@ func Copy(dst io.Writer, src io.Reader) (n int64, err error) {
 	src = N.UnwrapReader(src)
 	dst = N.UnwrapWriter(dst)
 	if wt, ok := src.(io.WriterTo); ok {
+		if needWrapper(dst, src) {
+			dst = &writeOnlyWriter{dst}
+		}
 		return wt.WriteTo(dst)
 	}
 	if rt, ok := dst.(io.ReaderFrom); ok {
-		if needReadFromWrapper(rt, src) {
+		if needWrapper(rt, src) {
 			src = &readOnlyReader{src}
 		}
 		return rt.ReadFrom(src)
@@ -86,7 +104,7 @@ func CopyExtendedBuffer(dst N.ExtendedWriter, src N.ExtendedReader, buffer *buf.
 	frontHeadroom := N.CalculateFrontHeadroom(dst)
 	rearHeadroom := N.CalculateRearHeadroom(dst)
 	readBufferRaw := buffer.Slice()
-	readBuffer := buf.With(readBufferRaw[:cap(readBufferRaw)-rearHeadroom])
+	readBuffer := buf.With(readBufferRaw[:len(readBufferRaw)-rearHeadroom])
 	var notFirstTime bool
 	for {
 		readBuffer.Resize(frontHeadroom, 0)
@@ -143,7 +161,7 @@ func CopyExtendedWithPool(dst N.ExtendedWriter, src N.ExtendedReader) (n int64,
 	for {
 		buffer := buf.NewSize(bufferSize)
 		readBufferRaw := buffer.Slice()
-		readBuffer := buf.With(readBufferRaw[:cap(readBufferRaw)-rearHeadroom])
+		readBuffer := buf.With(readBufferRaw[:len(readBufferRaw)-rearHeadroom])
 		readBuffer.Resize(frontHeadroom, 0)
 		err = src.ReadBuffer(readBuffer)
 		if err != nil {
@@ -235,7 +253,7 @@ func CopyPacket(dst N.PacketWriter, src N.PacketReader) (n int64, err error) {
 	var destination M.Socksaddr
 	var notFirstTime bool
 	readBufferRaw := buffer.Slice()
-	readBuffer := buf.With(readBufferRaw[:cap(readBufferRaw)-rearHeadroom])
+	readBuffer := buf.With(readBufferRaw[:len(readBufferRaw)-rearHeadroom])
 	for {
 		readBuffer.Resize(frontHeadroom, 0)
 		destination, err = src.ReadPacket(readBuffer)
@@ -293,7 +311,7 @@ func CopyPacketWithPool(dst N.PacketWriter, src N.PacketReader) (n int64, err er
 	for {
 		buffer := buf.NewSize(bufferSize)
 		readBufferRaw := buffer.Slice()
-		readBuffer := buf.With(readBufferRaw[:cap(readBufferRaw)-rearHeadroom])
+		readBuffer := buf.With(readBufferRaw[:len(readBufferRaw)-rearHeadroom])
 		readBuffer.Resize(frontHeadroom, 0)
 		destination, err = src.ReadPacket(readBuffer)
 		if err != nil {
diff --git a/common/network/thread.go b/common/network/thread.go
index 3b9787e..ae16590 100644
--- a/common/network/thread.go
+++ b/common/network/thread.go
@@ -136,13 +136,13 @@ func calculateWriterMTU(writer any) int {
 	}
 	if upstream, hasUpstream := writer.(common.WithUpstream); hasUpstream {
 		upstreamMTU := calculateWriterMTU(upstream.Upstream())
-		if mtu == 0 && upstreamMTU < mtu {
+		if mtu == 0 || upstreamMTU > 0 && upstreamMTU < mtu {
 			mtu = upstreamMTU
 		}
 	}
 	if upstream, hasUpstream := writer.(WithUpstreamWriter); hasUpstream {
 		upstreamMTU := calculateWriterMTU(upstream.UpstreamWriter())
-		if mtu == 0 && upstreamMTU < mtu {
+		if mtu == 0 || upstreamMTU > 0 && upstreamMTU < mtu {
 			mtu = upstreamMTU
 		}
 	}
diff --git a/protocol/trojan/protocol.go b/protocol/trojan/protocol.go
index b56061f..be45cae 100644
--- a/protocol/trojan/protocol.go
+++ b/protocol/trojan/protocol.go
@@ -13,6 +13,7 @@ import (
 	"github.com/sagernet/sing/common/bufio"
 	E "github.com/sagernet/sing/common/exceptions"
 	M "github.com/sagernet/sing/common/metadata"
+	N "github.com/sagernet/sing/common/network"
 	"github.com/sagernet/sing/common/rw"
 )
 
@@ -25,7 +26,7 @@ const (
 var CRLF = []byte{'\r', '\n'}
 
 type ClientConn struct {
-	net.Conn
+	N.ExtendedConn
 	key           [KeyLength]byte
 	destination   M.Socksaddr
 	headerWritten bool
@@ -33,17 +34,17 @@ type ClientConn struct {
 
 func NewClientConn(conn net.Conn, key [KeyLength]byte, destination M.Socksaddr) *ClientConn {
 	return &ClientConn{
-		Conn:        conn,
-		key:         key,
-		destination: destination,
+		ExtendedConn: bufio.NewExtendedConn(conn),
+		key:          key,
+		destination:  destination,
 	}
 }
 
 func (c *ClientConn) Write(p []byte) (n int, err error) {
 	if c.headerWritten {
-		return c.Conn.Write(p)
+		return c.ExtendedConn.Write(p)
 	}
-	err = ClientHandshake(c.Conn, c.key, c.destination, p)
+	err = ClientHandshake(c.ExtendedConn, c.key, c.destination, p)
 	if err != nil {
 		return
 	}
@@ -54,10 +55,9 @@ func (c *ClientConn) Write(p []byte) (n int, err error) {
 
 func (c *ClientConn) WriteBuffer(buffer *buf.Buffer) error {
 	if c.headerWritten {
-		defer buffer.Release()
-		return common.Error(c.Conn.Write(buffer.Bytes()))
+		return c.ExtendedConn.WriteBuffer(buffer)
 	}
-	err := ClientHandshakeBuffer(c.Conn, c.key, c.destination, buffer)
+	err := ClientHandshakeBuffer(c.ExtendedConn, c.key, c.destination, buffer)
 	if err != nil {
 		return err
 	}
@@ -69,11 +69,11 @@ func (c *ClientConn) ReadFrom(r io.Reader) (n int64, err error) {
 	if !c.headerWritten {
 		return bufio.ReadFrom0(c, r)
 	}
-	return bufio.Copy(c.Conn, r)
+	return bufio.Copy(c.ExtendedConn, r)
 }
 
 func (c *ClientConn) WriteTo(w io.Writer) (n int64, err error) {
-	return bufio.Copy(w, c.Conn)
+	return bufio.Copy(w, c.ExtendedConn)
 }
 
 func (c *ClientConn) FrontHeadroom() int {
@@ -84,7 +84,7 @@ func (c *ClientConn) FrontHeadroom() int {
 }
 
 func (c *ClientConn) Upstream() any {
-	return c.Conn
+	return c.ExtendedConn
 }
 
 type ClientPacketConn struct {