diff --git a/common/buf/buffered_writer.go b/common/buf/buffered_writer.go
index 2ab504dbf..b3ff77a37 100644
--- a/common/buf/buffered_writer.go
+++ b/common/buf/buffered_writer.go
@@ -15,6 +15,7 @@ func NewBufferedWriter(writer io.Writer) *BufferedWriter {
 	return NewBufferedWriterSize(writer, 1024)
 }
 
+// NewBufferedWriterSize creates a BufferedWriter with specified buffer size.
 func NewBufferedWriterSize(writer io.Writer, size uint32) *BufferedWriter {
 	return &BufferedWriter{
 		writer:   writer,
diff --git a/common/buf/buffered_writer_test.go b/common/buf/buffered_writer_test.go
index c2254dd54..97cb923be 100644
--- a/common/buf/buffered_writer_test.go
+++ b/common/buf/buffered_writer_test.go
@@ -4,6 +4,7 @@ import (
 	"crypto/rand"
 	"testing"
 
+	"v2ray.com/core/common"
 	. "v2ray.com/core/common/buf"
 	"v2ray.com/core/testing/assert"
 )
@@ -37,7 +38,7 @@ func TestBufferedWriterLargePayload(t *testing.T) {
 	assert.Bool(writer.IsBuffered()).IsTrue()
 
 	payload := make([]byte, 64*1024)
-	rand.Read(payload)
+	common.Must2(rand.Read(payload))
 
 	nBytes, err := writer.Write(payload[:512])
 	assert.Int(nBytes).Equals(512)
diff --git a/common/buf/io.go b/common/buf/io.go
index 0fe9e4f9e..c66a1f782 100644
--- a/common/buf/io.go
+++ b/common/buf/io.go
@@ -11,6 +11,7 @@ type Reader interface {
 	Read() (MultiBuffer, error)
 }
 
+// ErrReadTimeout is an error that happens with IO timeout.
 var ErrReadTimeout = newError("IO timeout")
 
 type TimeoutReader interface {