diff --git a/internal/common/copy.go b/internal/common/copy.go
index 1d57b97..bf5ffb7 100644
--- a/internal/common/copy.go
+++ b/internal/common/copy.go
@@ -41,18 +41,18 @@ import (
 // copyBuffer is the actual implementation of Copy and CopyBuffer.
 // if buf is nil, one is allocated.
 func Copy(dst net.Conn, src net.Conn, srcReadTimeout time.Duration) (written int64, err error) {
-	/*
-		// If the reader has a WriteTo method, use it to do the copy.
-		// Avoids an allocation and a copy.
-		if wt, ok := src.(WriterTo); ok {
-			return wt.WriteTo(dst)
-		}
-		// Similarly, if the writer has a ReadFrom method, use it to do the copy.
-		if rt, ok := dst.(ReaderFrom); ok {
-			return rt.ReadFrom(src)
-		}
+	defer func() { src.Close(); dst.Close() }()
+
+	// If the reader has a WriteTo method, use it to do the copy.
+	// Avoids an allocation and a copy.
+	if wt, ok := src.(io.WriterTo); ok {
+		return wt.WriteTo(dst)
+	}
+	// Similarly, if the writer has a ReadFrom method, use it to do the copy.
+	if rt, ok := dst.(io.ReaderFrom); ok {
+		return rt.ReadFrom(src)
+	}
 
-	*/
 	//if buf == nil {
 	size := 32 * 1024
 	/*
@@ -97,7 +97,5 @@ func Copy(dst net.Conn, src net.Conn, srcReadTimeout time.Duration) (written int
 			break
 		}
 	}
-	src.Close()
-	dst.Close()
 	return written, err
 }
diff --git a/internal/multiplex/session.go b/internal/multiplex/session.go
index 86451af..948d323 100644
--- a/internal/multiplex/session.go
+++ b/internal/multiplex/session.go
@@ -84,6 +84,7 @@ func MakeSession(id uint32, config SessionConfig) *Session {
 	if config.MaxFrameSize <= 0 {
 		sesh.MaxFrameSize = defaultSendRecvBufSize - 1024
 	}
+	// todo: validation. this must be smaller than the buffer sizes
 	sesh.maxStreamUnitWrite = sesh.MaxFrameSize - HEADER_LEN - sesh.Obfuscator.minOverhead
 
 	sbConfig := switchboardConfig{
@@ -156,12 +157,11 @@ func (sesh *Session) closeStream(s *Stream, active bool) error {
 		s.writingM.Lock()
 		defer s.writingM.Unlock()
 		// Notify remote that this stream is closed
-		pad := genRandomPadding()
 		f := &Frame{
 			StreamID: s.id,
 			Seq:      atomic.AddUint64(&s.nextSendSeq, 1) - 1,
 			Closing:  C_STREAM,
-			Payload:  pad,
+			Payload:  genRandomPadding(),
 		}
 
 		if s.obfsBuf == nil {
diff --git a/internal/multiplex/stream.go b/internal/multiplex/stream.go
index 3dfb8a2..a4d5dd6 100644
--- a/internal/multiplex/stream.go
+++ b/internal/multiplex/stream.go
@@ -80,7 +80,11 @@ func (s *Stream) Read(buf []byte) (n int, err error) {
 	}
 	log.Tracef("%v read from stream %v with err %v", n, s.id, err)
 	return
+}
 
+func (s *Stream) WriteTo(w io.Writer) (int64, error) {
+	// will keep writing until the underlying buffer is closed
+	return s.recvBuf.WriteTo(w)
 }
 
 // Write implements io.Write
@@ -91,7 +95,6 @@ func (s *Stream) Write(in []byte) (n int, err error) {
 	// in the middle of the execution of Write. This may cause the closing frame
 	// to be sent before the data frame and cause loss of packet.
 	//log.Tracef("attempting to write %v bytes to stream %v",len(in),s.id)
-	// todo: forbid concurrent write
 	s.writingM.Lock()
 	defer s.writingM.Unlock()
 	if s.isClosed() {