SDP

Package sdp implements SDP: Session Description Protocol [RFC4566]. Complies to gortc principles as core package.

Examples

See examples folder. Also there is online SDP example that gets RTCPeerConnection.localDescription.sdp using WebRTC, sends it to server, decodes as sdp.Session and renders it on web page.

SDP example:

v=0
o=jdoe 2890844526 2890842807 IN IP4 10.47.16.5
s=SDP Seminar
i=A Seminar on the session description protocol
u=http://www.example.com/seminars/sdp.pdf
[email protected] (Jane Doe)
p=12345
c=IN IP4 224.2.17.12/127
b=CT:154798
t=2873397496 2873404696
r=7d 1h 0 25h
k=clear:ab8c4df8b8f4as8v8iuy8re
a=recvonly
m=audio 49170 RTP/AVP 0
m=video 51372 RTP/AVP 99
b=AS:66781
k=prompt
a=rtpmap:99 h263-1998/90000

Encode:

package main

import (
	"fmt"
	"net"
	"time"
	
	"gortc.io/sdp"
)

func main()  {
	var (
		s sdp.Session
		b []byte
	)
	// defining medias
	audio := sdp.Media{
		Description: sdp.MediaDescription{
			Type:     "audio",
			Port:     49170,
			Formats:   []string{"0"},
			Protocol: "RTP/AVP",
		},
	}
	video := sdp.Media{
		Description: sdp.MediaDescription{
			Type:     "video",
			Port:     51372,
			Formats:   []string{"99"},
			Protocol: "RTP/AVP",
		},
		Bandwidths: sdp.Bandwidths{
			sdp.BandwidthApplicationSpecific: 66781,
		},
		Encryption: sdp.Encryption{
			Method: "prompt",
		},
	}
	video.AddAttribute("rtpmap", "99", "h263-1998/90000")

	// defining message
	m := &sdp.Message{
		Origin: sdp.Origin{
			Username:       "jdoe",
			SessionID:      2890844526,
			SessionVersion: 2890842807,
			Address:        "10.47.16.5",
		},
		Name:  "SDP Seminar",
		Info:  "A Seminar on the session description protocol",
		URI:   "http://www.example.com/seminars/sdp.pdf",
		Email: "[email protected] (Jane Doe)",
		Phone: "12345",
		Connection: sdp.ConnectionData{
			IP:  net.ParseIP("224.2.17.12"),
			TTL: 127,
		},
		Bandwidths: sdp.Bandwidths{
			sdp.BandwidthConferenceTotal: 154798,
		},
		Timing: []sdp.Timing{
			{
				Start:  sdp.NTPToTime(2873397496),
				End:    sdp.NTPToTime(2873404696),
				Repeat: 7 * time.Hour * 24,
				Active: 3600 * time.Second,
				Offsets: []time.Duration{
					0,
					25 * time.Hour,
				},
			},
		},
		Encryption: sdp.Encryption{
			Method: "clear",
			Key: "ab8c4df8b8f4as8v8iuy8re",
		},
		Medias: []sdp.Media{audio, video},
	}
	m.AddFlag("recvonly")

	// appending message to session
	s = m.Append(s)

	// appending session to byte buffer
	b = s.AppendTo(b)
	fmt.Println(string(b))
}

Decode:

package main

import (
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"os"

	"gortc.io/sdp"
)

func main() {
	name := "example.sdp"
	if len(os.Args) > 1 {
		name = os.Args[1]
	}
	var (
		s   sdp.Session
		b   []byte
		err error
		f   io.ReadCloser
	)
	fmt.Println("sdp file:", name)
	if f, err = os.Open(name); err != nil {
		log.Fatal("err:", err)
	}
	defer f.Close()
	if b, err = ioutil.ReadAll(f); err != nil {
		log.Fatal("err:", err)
	}
	if s, err = sdp.DecodeSession(b, s); err != nil {
		log.Fatal("err:", err)
	}
	for k, v := range s {
		fmt.Println(k, v)
	}
	d := sdp.NewDecoder(s)
	m := new(sdp.Message)
	if err = d.Decode(m); err != nil {
		log.Fatal("err:", err)
	}
	fmt.Println("Decoded session", m.Name)
	fmt.Println("Info:", m.Info)
	fmt.Println("Origin:", m.Origin)
}

Also, low-level Session struct can be used directly to compose SDP message:

package main

import (
	"fmt"

	"gortc.io/sdp"
)

func main() {
	var (
		s sdp.Session
		b []byte
	)
	b = s.AddVersion(0).
		AddMediaDescription(sdp.MediaDescription{
			Type:     "video",
			Port:     51372,
			Formats:   []string{"99"},
			Protocol: "RTP/AVP",
		}).
		AddAttribute("rtpmap", "99", "h263-1998/90000").
		AddLine(sdp.TypeEmail, "[email protected]").
		AddRaw('ü', "vαlue").
		AppendTo(b)
	// and so on
	fmt.Println(string(b))
	// Output:
	//	v=0
	//	m=video 51372 RTP/AVP 99
	//	a=rtpmap:99 h263-1998/90000
	//	[email protected]
	//	ü=vαlue
}

Supported params

• v (protocol version)
• o (originator and session identifier)
• s (session name)
• i (session information)
• u (URI of description)
• e (email address)
• p (phone number)
• c (connection information)
• b (zero or more bandwidth information lines)
• t (time)
• r (repeat)
• z (time zone adjustments)
• k (encryption key)
• a (zero or more session attribute lines)
• m (media name and transport address)

TODO:

• Encoding
• Parsing
• High level encoding
• High level decoding
• Examples
• CI
• More examples and docs
• Online example
• io.Reader and io.Writer interop
• Include to high-level CI

Possible optimizations

There are comments // ALLOCATIONS: suboptimal. and // CPU: suboptimal. that indicate suboptimal implementation that can be optimized. There are often a benchmarks for this pieces.

Benchmarks

goos: linux
goarch: amd64
pkg: github.com/gortc/sdp
PASS
benchmark                                    iter       time/iter   bytes alloc         allocs
---------                                    ----       ---------   -----------         ------
BenchmarkDecoder_Decode-12                 300000   4884.00 ns/op     3166 B/op   93 allocs/op
BenchmarkEncode-12                        1000000   1577.00 ns/op        0 B/op    0 allocs/op
BenchmarkSession_AddConnectionData-12    20000000    114.00 ns/op        0 B/op    0 allocs/op
BenchmarkAppendIP-12                     50000000     37.90 ns/op        0 B/op    0 allocs/op
BenchmarkAppendByte-12                  100000000     11.00 ns/op        0 B/op    0 allocs/op
BenchmarkAppendInt-12                   100000000     11.90 ns/op        0 B/op    0 allocs/op
BenchmarkSession_EX1-12                   3000000    578.00 ns/op       16 B/op    1 allocs/op
BenchmarkAppendRune-12                  200000000      6.70 ns/op        0 B/op    0 allocs/op
BenchmarkDecode-12                      100000000     13.10 ns/op        0 B/op    0 allocs/op
BenchmarkDecodeSession-12                 5000000    234.00 ns/op        0 B/op    0 allocs/op
ok  	github.com/gortc/sdp	16.820s

Build status

License