protocol/rtcp: wrote struct for RTCP sender report

protocol/rtcp/rtcp.go

@@ -18,7 +18,8 @@ const (
 
 // MISC.
 const (
-	reportBlockSize = 6
+	reportBlockSize  = 6
+	senderReportSize = 28
 )
 
 // ReceiverReport describes an RTCP receiver report packet.
@@ -115,6 +116,37 @@ func (d *SourceDescription) bodyLen() int {
 	return l
 }
 
+// SenderReport describes an RTCP sender report.
+type SenderReport struct {
+	Header              // Standard RTCP header.
+	SSRC         uint32 // SSRC of sender.
+	TimestampMSW uint32 // Most significant word of timestamp.
+	TimestampLSW uint32 // Least significant word of timestamp.
+	RTPTimestamp uint32 // Current RTP timestamp.
+	PacketCount  uint32 // Senders packet count.
+	OctetCount   uint32 // Senders octet count.
+
+	// Report blocks (unimplemented)
+	// ...
+}
+
+// Bytes returns a []byte of the SenderReport.
+func (r *SenderReport) Bytes() []byte {
+	buf := make([]byte, senderReportSize)
+	r.writeHeader(buf, senderReportSize-1)
+	for i, w := range []uint32{
+		r.SSRC,
+		r.TimestampMSW,
+		r.TimestampLSW,
+		r.RTPTimestamp,
+		r.PacketCount,
+		r.OctetCount,
+	} {
+		binary.BigEndian.PutUint32(buf[i+1:], w)
+	}
+	return buf
+}
+
 // Header describes a standard RTCP packet header.
 type Header struct {
 	Version     uint8 // RTCP version.