fix buffered writer

common/io/buffered_writer.go

@@ -17,7 +17,7 @@ type BufferedWriter struct {
 func NewBufferedWriter(rawWriter io.Writer) *BufferedWriter {
 	return &BufferedWriter{
 		writer: rawWriter,
-		buffer: alloc.NewBuffer().Clear(),
+		buffer: alloc.NewSmallBuffer().Clear(),
 		cached: true,
 	}
 }
@@ -55,11 +55,22 @@ func (v *BufferedWriter) Write(b []byte) (int, error) {
 	if !v.cached {
 		return v.writer.Write(b)
 	}
-	nBytes, _ := v.buffer.Write(b)
-	if v.buffer.IsFull() {
-		v.FlushWithoutLock()
+	nBytes, err := v.buffer.Write(b)
+	if err != nil {
+		return 0, err
 	}
-	return nBytes, nil
+	if v.buffer.IsFull() {
+		err := v.FlushWithoutLock()
+		if err != nil {
+			return 0, err
+		}
+		if nBytes < len(b) {
+			if _, err := v.writer.Write(b[nBytes:]); err != nil {
+				return nBytes, err
+			}
+		}
+	}
+	return len(b), nil
 }
 
 func (v *BufferedWriter) Flush() error {

common/io/buffered_writer_test.go

@@ -1,6 +1,7 @@
 package io_test
 
 import (
+	"crypto/rand"
 	"testing"
 
 	"v2ray.com/core/common/alloc"
@@ -27,3 +28,26 @@ func TestBufferedWriter(t *testing.T) {
 	writer.SetCached(false)
 	assert.Int(content.Len()).Equals(16)
 }
+
+func TestBufferedWriterLargePayload(t *testing.T) {
+	assert := assert.On(t)
+
+	content := alloc.NewLocalBuffer(128 * 1024).Clear()
+
+	writer := NewBufferedWriter(content)
+	assert.Bool(writer.Cached()).IsTrue()
+
+	payload := make([]byte, 64*1024)
+	rand.Read(payload)
+
+	nBytes, err := writer.Write(payload[:1024])
+	assert.Int(nBytes).Equals(1024)
+	assert.Error(err).IsNil()
+
+	assert.Bool(content.IsEmpty()).IsTrue()
+
+	nBytes, err = writer.Write(payload[1024:])
+	assert.Error(err).IsNil()
+	assert.Int(nBytes).Equals(63 * 1024)
+	assert.Bytes(content.Value).Equals(payload)
+}