add resetFragments() to all fragment-based decoders (#637)

pkg/format/rtpac3/decoder.go

@@ -42,12 +42,16 @@ func (d *Decoder) Init() error {
 	return nil
 }
 
+func (d *Decoder) resetFragments() {
+	d.fragments = d.fragments[:0]
+	d.fragmentsSize = 0
+}
+
 // Decode decodes frames from a RTP packet.
 // It returns the frames and the PTS of the first frame.
 func (d *Decoder) Decode(pkt *rtp.Packet) ([][]byte, error) {
 	if len(pkt.Payload) < 2 {
-		d.fragments = d.fragments[:0] // discard pending fragments
-		d.fragmentsSize = 0
+		d.resetFragments()
 		return nil, fmt.Errorf("payload is too short")
 	}
 
@@ -55,8 +59,7 @@ func (d *Decoder) Decode(pkt *rtp.Packet) ([][]byte, error) {
 	ft := pkt.Payload[0] & 0b11
 
 	if mbz != 0 {
-		d.fragments = d.fragments[:0] // discard pending fragments
-		d.fragmentsSize = 0
+		d.resetFragments()
 		return nil, fmt.Errorf("invalid MBZ: %v", mbz)
 	}
 
@@ -64,8 +67,7 @@ func (d *Decoder) Decode(pkt *rtp.Packet) ([][]byte, error) {
 
 	switch ft {
 	case 0:
-		d.fragments = d.fragments[:0] // discard pending fragments
-		d.fragmentsSize = 0
+		d.resetFragments()
 		d.firstPacketReceived = true
 
 		buf := pkt.Payload[2:]
@@ -91,8 +93,7 @@ func (d *Decoder) Decode(pkt *rtp.Packet) ([][]byte, error) {
 		}
 
 	case 1, 2:
-		d.fragments = d.fragments[:0] // discard pending fragments
-		d.fragmentsSize = 0
+		d.resetFragments()
 
 		var syncInfo ac3.SyncInfo
 		err := syncInfo.Unmarshal(pkt.Payload[2:])
@@ -122,8 +123,7 @@ func (d *Decoder) Decode(pkt *rtp.Packet) ([][]byte, error) {
 		d.fragmentsExpected -= le
 
 		if d.fragmentsExpected < 0 {
-			d.fragments = d.fragments[:0] // discard pending fragments
-			d.fragmentsSize = 0
+			d.resetFragments()
 			return nil, fmt.Errorf("fragment is too big")
 		}
 
@@ -134,8 +134,7 @@ func (d *Decoder) Decode(pkt *rtp.Packet) ([][]byte, error) {
 		}
 
 		frames = [][]byte{joinFragments(d.fragments, d.fragmentsSize)}
-		d.fragments = d.fragments[:0]
-		d.fragmentsSize = 0
+		d.resetFragments()
 	}
 
 	return frames, nil