Merged in rtp-parsing (pull request #179)

protocol/rtp: can parse payload from RTP packet

Approved-by: Alan Noble <anoble@gmail.com>
Approved-by: kortschak <dan@kortschak.io>

protocol/rtp/parse.go

@@ -0,0 +1,67 @@
+/*
+NAME
+  parse.go
+
+DESCRIPTION
+  parse.go provides functionality for parsing RTP packets.
+
+AUTHOR
+  Saxon A. Nelson-Milton <saxon@ausocean.org>
+
+LICENSE
+  Copyright (C) 2019 the Australian Ocean Lab (AusOcean)
+
+  This is free software: you can redistribute it and/or modify them
+  under the terms of the GNU General Public License as published by the
+  Free Software Foundation, either version 3 of the License, or (at your
+  option) any later version.
+
+  It is distributed in the hope that it will be useful, but WITHOUT
+  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+  for more details.
+
+  You should have received a copy of the GNU General Public License
+  in gpl.txt.  If not, see http://www.gnu.org/licenses.
+*/
+
+package rtp
+
+import (
+	"encoding/binary"
+	"errors"
+)
+
+const badVer = "incompatible RTP version"
+
+// Payload returns the payload from an RTP packet provided the version is
+// compatible, otherwise an error is returned.
+func Payload(d []byte) ([]byte, error) {
+	if len(d) < defaultHeadSize {
+		panic("invalid RTP packet length")
+	}
+	if version(d) != rtpVer {
+		return nil, errors.New(badVer)
+	}
+	extLen := 0
+	if hasExt(d) {
+		extLen = 4 + 4*(int(binary.BigEndian.Uint16(d[optionalFieldIdx+4*csrcCount(d)+2:])))
+	}
+	payloadIdx := optionalFieldIdx + 4*csrcCount(d) + extLen
+	return d[payloadIdx:], nil
+}
+
+// hasExt returns true if an extension is present in the RTP packet.
+func hasExt(d []byte) bool {
+	return (d[0] & 0x10 >> 4) == 1
+}
+
+// csrcCount returns the number of CSRC fields.
+func csrcCount(d []byte) int {
+	return int(d[0] & 0x0f)
+}
+
+// version returns the version of the RTP packet.
+func version(d []byte) int {
+	return int(d[0] & 0xc0 >> 6)
+}

protocol/rtp/parse_test.go

@@ -0,0 +1,140 @@
+/*
+NAME
+  parse_test.go
+
+DESCRIPTION
+  parse_test.go provides testing for behaviour of functionality in parse.go.
+
+AUTHOR
+  Saxon A. Nelson-Milton <saxon@ausocean.org>
+
+LICENSE
+  Copyright (C) 2019 the Australian Ocean Lab (AusOcean)
+
+  This is free software: you can redistribute it and/or modify them
+  under the terms of the GNU General Public License as published by the
+  Free Software Foundation, either version 3 of the License, or (at your
+  option) any later version.
+
+  It is distributed in the hope that it will be useful, but WITHOUT
+  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+  for more details.
+
+  You should have received a copy of the GNU General Public License
+  in gpl.txt.  If not, see http://www.gnu.org/licenses.
+*/
+
+package rtp
+
+import (
+	"bytes"
+	"testing"
+)
+
+// TestVersion checks that we can correctly get the version from an RTP packet.
+func TestVersion(t *testing.T) {
+	const expect = 1
+	got := version((&Pkt{V: expect}).Bytes(nil))
+	if got != expect {
+		t.Errorf("unexpected version for RTP packet. Got: %v\n Want: %v\n", got, expect)
+	}
+}
+
+// TestCsrcCount checks that we can correctly obtain the csrc count from an
+// RTP packet.
+func TestCsrcCount(t *testing.T) {
+	const ver, expect = 2, 2
+
+	pkt := (&Pkt{
+		V:    ver,
+		CC:   expect,
+		CSRC: make([][4]byte, expect),
+	}).Bytes(nil)
+
+	got := csrcCount(pkt)
+	if got != expect {
+		t.Errorf("unexpected csrc count for RTP packet. Got: %v\n Want: %v\n", got, expect)
+	}
+}
+
+// TestHasExt checks the behaviour of hasExt with an RTP packet that has the
+// extension indicator true, and one with the extension indicator set to false.
+func TestHasExt(t *testing.T) {
+	const ver = 2
+
+	// First check for when there is an extension field.
+	pkt := &Pkt{
+		V: ver,
+		X: true,
+		Extension: ExtensionHeader{
+			ID:     0,
+			Header: make([][4]byte, 0),
+		},
+	}
+
+	got := hasExt(pkt.Bytes(nil))
+	if !got {
+		t.Error("RTP packet did not have true extension indicator as expected")
+	}
+
+	// Now check when there is not an extension field.
+	pkt.X = false
+	got = hasExt(pkt.Bytes(nil))
+	if got {
+		t.Error("did not expect to have extension indicator as true")
+	}
+}
+
+// TestPayload checks that we can correctly get the payload of an RTP packet
+// using Payload for a variety of RTP packet configurations.
+func TestPayload(t *testing.T) {
+	const ver = 2
+	expect := []byte{0x01, 0x02, 0x03, 0x04, 0x05}
+
+	testPkts := [][]byte{
+		(&Pkt{
+			V:       ver,
+			Payload: expect,
+		}).Bytes(nil),
+
+		(&Pkt{
+			V:       ver,
+			CC:      3,
+			CSRC:    make([][4]byte, 3),
+			Payload: expect,
+		}).Bytes(nil),
+
+		(&Pkt{
+			V: ver,
+			X: true,
+			Extension: ExtensionHeader{
+				ID:     0,
+				Header: make([][4]byte, 3),
+			},
+			Payload: expect,
+		}).Bytes(nil),
+
+		(&Pkt{
+			V:    ver,
+			CC:   3,
+			CSRC: make([][4]byte, 3),
+			Extension: ExtensionHeader{
+				ID:     0,
+				Header: make([][4]byte, 3),
+			},
+			Payload: expect,
+		}).Bytes(nil),
+	}
+
+	for i, p := range testPkts {
+		got, err := Payload(p)
+		if err != nil {
+			t.Errorf("unexpected error from Payload with pkt: %v", i)
+		}
+
+		if !bytes.Equal(got, expect) {
+			t.Errorf("unexpected payload data from RTP packet: %v.\n Got: %v\n Want: %v\n", i, got, expect)
+		}
+	}
+}

protocol/rtp/rtp.go

@@ -37,10 +37,11 @@ import (
 )
 
 const (
-	rtpVer          = 2
-	defaultHeadSize = 3 * 4                            // Header size of an rtp packet.
-	defPayloadSize  = sendSize                         // Default payload size for the rtp packet.
-	defPktSize      = defaultHeadSize + defPayloadSize // Default packet size is header size + payload size.
+	rtpVer           = 2                                // Version of RTP that this package is compatible with.
+	defaultHeadSize  = 12                               // Header size of an rtp packet.
+	defPayloadSize   = sendSize                         // Default payload size for the rtp packet.
+	defPktSize       = defaultHeadSize + defPayloadSize // Default packet size is header size + payload size.
+	optionalFieldIdx = 12                               // This is the idx of optional fields including CSRC and extension header in an RTP packet.
 )
 
 // Pkt provides fields consistent with RFC3550 definition of an rtp packet