diff --git a/app/proxyman/outbound/handler.go b/app/proxyman/outbound/handler.go
index 804788fee..76208e66f 100644
--- a/app/proxyman/outbound/handler.go
+++ b/app/proxyman/outbound/handler.go
@@ -122,6 +122,11 @@ func (h *Handler) Dial(ctx context.Context, dest v2net.Destination) (internet.Co
 	return internet.Dial(ctx, dest)
 }
 
+var (
+	_ buf.MultiBufferReader = (*Connection)(nil)
+	_ buf.MultiBufferWriter = (*Connection)(nil)
+)
+
 type Connection struct {
 	stream     ray.Ray
 	closed     bool
@@ -170,11 +175,11 @@ func (v *Connection) Write(b []byte) (int, error) {
 	return buf.ToBytesWriter(v.writer).Write(b)
 }
 
-func (v *Connection) WriteMultiBuffer(mb buf.MultiBuffer) (int, error) {
+func (v *Connection) WriteMultiBuffer(mb buf.MultiBuffer) error {
 	if v.closed {
-		return 0, io.ErrClosedPipe
+		return io.ErrClosedPipe
 	}
-	return mb.Len(), v.writer.Write(mb)
+	return v.writer.Write(mb)
 }
 
 // Close implements net.Conn.Close().
diff --git a/common/buf/multi_buffer.go b/common/buf/multi_buffer.go
index e6d54de3d..5c11c8305 100644
--- a/common/buf/multi_buffer.go
+++ b/common/buf/multi_buffer.go
@@ -3,7 +3,7 @@ package buf
 import "net"
 
 type MultiBufferWriter interface {
-	WriteMultiBuffer(MultiBuffer) (int, error)
+	WriteMultiBuffer(MultiBuffer) error
 }
 
 type MultiBufferReader interface {
diff --git a/common/buf/writer.go b/common/buf/writer.go
index 262879fd8..988580d1c 100644
--- a/common/buf/writer.go
+++ b/common/buf/writer.go
@@ -22,8 +22,7 @@ type writerAdapter struct {
 
 // Write implements buf.MultiBufferWriter.
 func (w *writerAdapter) Write(mb MultiBuffer) error {
-	_, err := w.writer.WriteMultiBuffer(mb)
-	return err
+	return w.writer.WriteMultiBuffer(mb)
 }
 
 type mergingWriter struct {
@@ -62,6 +61,10 @@ func (w *seqWriter) Write(mb MultiBuffer) error {
 	return nil
 }
 
+var (
+	_ MultiBufferWriter = (*bytesToBufferWriter)(nil)
+)
+
 type bytesToBufferWriter struct {
 	writer Writer
 }
@@ -81,8 +84,8 @@ func (w *bytesToBufferWriter) Write(payload []byte) (int, error) {
 	return len(payload), nil
 }
 
-func (w *bytesToBufferWriter) WriteMultiBuffer(mb MultiBuffer) (int, error) {
-	return mb.Len(), w.writer.Write(mb)
+func (w *bytesToBufferWriter) WriteMultiBuffer(mb MultiBuffer) error {
+	return w.writer.Write(mb)
 }
 
 func (w *bytesToBufferWriter) ReadFrom(reader io.Reader) (int64, error) {
diff --git a/common/crypto/io.go b/common/crypto/io.go
index 133094f7b..60e593e52 100644
--- a/common/crypto/io.go
+++ b/common/crypto/io.go
@@ -27,6 +27,10 @@ func (r *CryptionReader) Read(data []byte) (int, error) {
 	return nBytes, err
 }
 
+var (
+	_ buf.MultiBufferWriter = (*CryptionWriter)(nil)
+)
+
 type CryptionWriter struct {
 	stream cipher.Stream
 	writer io.Writer
@@ -46,11 +50,11 @@ func (w *CryptionWriter) Write(data []byte) (int, error) {
 	return w.writer.Write(data)
 }
 
-func (w *CryptionWriter) WriteMultiBuffer(mb buf.MultiBuffer) (int, error) {
+func (w *CryptionWriter) WriteMultiBuffer(mb buf.MultiBuffer) error {
 	bs := mb.ToNetBuffers()
 	for _, b := range bs {
 		w.stream.XORKeyStream(b, b)
 	}
-	nBytes, err := bs.WriteTo(w.writer)
-	return int(nBytes), err
+	_, err := bs.WriteTo(w.writer)
+	return err
 }
diff --git a/transport/internet/kcp/connection.go b/transport/internet/kcp/connection.go
index a395a162a..5dd15705d 100644
--- a/transport/internet/kcp/connection.go
+++ b/transport/internet/kcp/connection.go
@@ -375,11 +375,11 @@ func (v *Connection) Write(b []byte) (int, error) {
 	}
 }
 
-func (c *Connection) WriteMultiBuffer(mb buf.MultiBuffer) (int, error) {
+func (c *Connection) WriteMultiBuffer(mb buf.MultiBuffer) error {
 	if c.mergingWriter == nil {
 		c.mergingWriter = buf.NewMergingWriterSize(c, c.mss)
 	}
-	return mb.Len(), c.mergingWriter.Write(mb)
+	return c.mergingWriter.Write(mb)
 }
 
 func (v *Connection) SetState(state State) {
diff --git a/transport/internet/tls/tls.go b/transport/internet/tls/tls.go
index 4b4f3f689..12f5a155a 100644
--- a/transport/internet/tls/tls.go
+++ b/transport/internet/tls/tls.go
@@ -9,6 +9,11 @@ import (
 
 //go:generate go run $GOPATH/src/v2ray.com/core/tools/generrorgen/main.go -pkg tls -path Transport,Internet,TLS
 
+var (
+	_ buf.MultiBufferReader = (*conn)(nil)
+	_ buf.MultiBufferWriter = (*conn)(nil)
+)
+
 type conn struct {
 	net.Conn
 
@@ -23,11 +28,11 @@ func (c *conn) ReadMultiBuffer() (buf.MultiBuffer, error) {
 	return c.mergingReader.Read()
 }
 
-func (c *conn) WriteMultiBuffer(mb buf.MultiBuffer) (int, error) {
+func (c *conn) WriteMultiBuffer(mb buf.MultiBuffer) error {
 	if c.mergingWriter == nil {
 		c.mergingWriter = buf.NewMergingWriter(c.Conn)
 	}
-	return mb.Len(), c.mergingWriter.Write(mb)
+	return c.mergingWriter.Write(mb)
 }
 
 func Client(c net.Conn, config *tls.Config) net.Conn {
diff --git a/transport/internet/websocket/connection.go b/transport/internet/websocket/connection.go
index 01bfccef2..5b7db36d3 100644
--- a/transport/internet/websocket/connection.go
+++ b/transport/internet/websocket/connection.go
@@ -69,11 +69,11 @@ func (c *connection) Write(b []byte) (int, error) {
 	return len(b), nil
 }
 
-func (c *connection) WriteMultiBuffer(mb buf.MultiBuffer) (int, error) {
+func (c *connection) WriteMultiBuffer(mb buf.MultiBuffer) error {
 	if c.mergingWriter == nil {
 		c.mergingWriter = buf.NewMergingWriter(c)
 	}
-	return mb.Len(), c.mergingWriter.Write(mb)
+	return c.mergingWriter.Write(mb)
 }
 
 func (c *connection) Close() error {