diff --git a/transport/internet/kcp/segment.go b/transport/internet/kcp/segment.go
index 5acf25be..9af1629d 100644
--- a/transport/internet/kcp/segment.go
+++ b/transport/internet/kcp/segment.go
@@ -31,6 +31,7 @@ type Segment interface {
 	Command() Command
 	ByteSize() int
 	Bytes() buf.Supplier
+	parse(conv uint16, cmd Command, opt SegmentOption, buf []byte) (bool, []byte)
 }
 
 const (
@@ -53,6 +54,34 @@ func NewDataSegment() *DataSegment {
 	return new(DataSegment)
 }
 
+func (s *DataSegment) parse(conv uint16, cmd Command, opt SegmentOption, buf []byte) (bool, []byte) {
+	s.Conv = conv
+	s.Option = opt
+	if len(buf) < 15 {
+		return false, nil
+	}
+	s.Timestamp = serial.BytesToUint32(buf)
+	buf = buf[4:]
+
+	s.Number = serial.BytesToUint32(buf)
+	buf = buf[4:]
+
+	s.SendingNext = serial.BytesToUint32(buf)
+	buf = buf[4:]
+
+	dataLen := int(serial.BytesToUint16(buf))
+	buf = buf[2:]
+
+	if len(buf) < dataLen {
+		return false, nil
+	}
+	s.Data().Clear()
+	s.Data().Append(buf[:dataLen])
+	buf = buf[dataLen:]
+
+	return true, buf
+}
+
 func (s *DataSegment) Conversation() uint16 {
 	return s.Conv
 }
@@ -113,6 +142,36 @@ func NewAckSegment() *AckSegment {
 	}
 }
 
+func (s *AckSegment) parse(conv uint16, cmd Command, opt SegmentOption, buf []byte) (bool, []byte) {
+	s.Conv = conv
+	s.Option = opt
+	if len(buf) < 13 {
+		return false, nil
+	}
+
+	s.ReceivingWindow = serial.BytesToUint32(buf)
+	buf = buf[4:]
+
+	s.ReceivingNext = serial.BytesToUint32(buf)
+	buf = buf[4:]
+
+	s.Timestamp = serial.BytesToUint32(buf)
+	buf = buf[4:]
+
+	count := int(buf[0])
+	buf = buf[1:]
+
+	if len(buf) < count*4 {
+		return false, nil
+	}
+	for i := 0; i < count; i++ {
+		s.PutNumber(serial.BytesToUint32(buf))
+		buf = buf[4:]
+	}
+
+	return true, buf
+}
+
 func (s *AckSegment) Conversation() uint16 {
 	return s.Conv
 }
@@ -176,6 +235,27 @@ func NewCmdOnlySegment() *CmdOnlySegment {
 	return new(CmdOnlySegment)
 }
 
+func (s *CmdOnlySegment) parse(conv uint16, cmd Command, opt SegmentOption, buf []byte) (bool, []byte) {
+	s.Conv = conv
+	s.Cmd = cmd
+	s.Option = opt
+
+	if len(buf) < 12 {
+		return false, nil
+	}
+
+	s.SendingNext = serial.BytesToUint32(buf)
+	buf = buf[4:]
+
+	s.ReceivingNext = serial.BytesToUint32(buf)
+	buf = buf[4:]
+
+	s.PeerRTO = serial.BytesToUint32(buf)
+	buf = buf[4:]
+
+	return true, buf
+}
+
 func (s *CmdOnlySegment) Conversation() uint16 {
 	return s.Conv
 }
@@ -213,83 +293,19 @@ func ReadSegment(buf []byte) (Segment, []byte) {
 	opt := SegmentOption(buf[1])
 	buf = buf[2:]
 
-	if cmd == CommandData {
-		seg := NewDataSegment()
-		seg.Conv = conv
-		seg.Option = opt
-		if len(buf) < 15 {
-			return nil, nil
-		}
-		seg.Timestamp = serial.BytesToUint32(buf)
-		buf = buf[4:]
-
-		seg.Number = serial.BytesToUint32(buf)
-		buf = buf[4:]
-
-		seg.SendingNext = serial.BytesToUint32(buf)
-		buf = buf[4:]
-
-		dataLen := int(serial.BytesToUint16(buf))
-		buf = buf[2:]
-
-		if len(buf) < dataLen {
-			return nil, nil
-		}
-		seg.Data().Clear()
-		seg.Data().Append(buf[:dataLen])
-		buf = buf[dataLen:]
-
-		return seg, buf
+	var seg Segment
+	switch cmd {
+	case CommandData:
+		seg = NewDataSegment()
+	case CommandACK:
+		seg = NewAckSegment()
+	default:
+		seg = NewCmdOnlySegment()
 	}
 
-	if cmd == CommandACK {
-		seg := NewAckSegment()
-		seg.Conv = conv
-		seg.Option = opt
-		if len(buf) < 13 {
-			return nil, nil
-		}
-
-		seg.ReceivingWindow = serial.BytesToUint32(buf)
-		buf = buf[4:]
-
-		seg.ReceivingNext = serial.BytesToUint32(buf)
-		buf = buf[4:]
-
-		seg.Timestamp = serial.BytesToUint32(buf)
-		buf = buf[4:]
-
-		count := int(buf[0])
-		buf = buf[1:]
-
-		if len(buf) < count*4 {
-			return nil, nil
-		}
-		for i := 0; i < count; i++ {
-			seg.PutNumber(serial.BytesToUint32(buf))
-			buf = buf[4:]
-		}
-
-		return seg, buf
-	}
-
-	seg := NewCmdOnlySegment()
-	seg.Conv = conv
-	seg.Cmd = cmd
-	seg.Option = opt
-
-	if len(buf) < 12 {
+	valid, extra := seg.parse(conv, cmd, opt, buf)
+	if !valid {
 		return nil, nil
 	}
-
-	seg.SendingNext = serial.BytesToUint32(buf)
-	buf = buf[4:]
-
-	seg.ReceivingNext = serial.BytesToUint32(buf)
-	buf = buf[4:]
-
-	seg.PeerRTO = serial.BytesToUint32(buf)
-	buf = buf[4:]
-
-	return seg, buf
+	return seg, extra
 }