protocol/rtcp: wrote body for Timestamp and added testing.

protocol/rtcp/parse.go

@@ -0,0 +1,26 @@
+package rtcp
+
+import (
+	"encoding/binary"
+	"errors"
+)
+
+// Timestamp gets the timestamp from a receiver report and returns as the most
+// significant word, and the least significant word. If the given bytes do not
+// represent a valid receiver report, and error is returned.
+func Timestamp(buf []byte) (msw, lsw uint32, err error) {
+	// First check version of rtcp
+	if (buf[0] & 0xc0 >> 6) != 2 {
+		return 0, 0, errors.New("incompatible RTCP version")
+	}
+
+	// Check type of packet
+	if buf[1] != typeSenderReport {
+		return 0, 0, errors.New("rtcp packet is not of sender report type")
+	}
+
+	msw = binary.BigEndian.Uint32(buf[8:])
+	lsw = binary.BigEndian.Uint32(buf[12:])
+
+	return
+}

protocol/rtcp/parse_test.go

@@ -0,0 +1,34 @@
+package rtcp
+
+import (
+	"testing"
+)
+
+// TestTimestamp checks that Timestamp correctly returns the most signicicant
+// word, and least signiciant word, of a receiver report timestamp.
+func TestTimestamp(t *testing.T) {
+	const expectedMSW = 2209003992
+	const expectedLSW = 1956821460
+	report := []byte{
+		0x80, 0xc8, 0x00, 0x06,
+		0x6f, 0xad, 0x40, 0xc6,
+		0x83, 0xaa, 0xb9, 0xd8, // Most significant word of timestamp (2209003992)
+		0x74, 0xa2, 0xb9, 0xd4, // Least significant word of timestamp (1956821460)
+		0x4b, 0x1c, 0x5a, 0xa5,
+		0x00, 0x00, 0x00, 0x66,
+		0x00, 0x01, 0xc2, 0xc5,
+	}
+
+	msw, lsw, err := Timestamp(report)
+	if err != nil {
+		t.Fatalf("did not expect error: %v", err)
+	}
+
+	if msw != expectedMSW {
+		t.Errorf("most significant word of timestamp is not what's expected. \nGot: %v\n Want: %v\n", msw, expectedMSW)
+	}
+
+	if lsw != expectedLSW {
+		t.Errorf("least significant word of timestamp is not what's expected. \nGot: %v\n Want: %v\n", lsw, expectedLSW)
+	}
+}