SDP go implementation

RFC 4566 SDP: Session Description Protocol in golang.

In alpha stage.

Examples

See examples folder. Also there is online SDP example (temporary unavailable) 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 (
	"net"
	"time"
	"fmt"

	"github.com/gortc/sdp"
)

func main()  {
	var (
		s sdp.Session
		b []byte
	)
	// defining medias
	audio := sdp.Media{
		Description: sdp.MediaDescription{
			Type:     "audio",
			Port:     49170,
			Format:   "0",
			Protocol: "RTP/AVP",
		},
	}
	video := sdp.Media{
		Description: sdp.MediaDescription{
			Type:     "video",
			Port:     51372,
			Format:   "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"

	"github.com/gortc/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"

	"github.com/gortc/sdp"
)

func main() {
	var (
		s sdp.Session
		b []byte
	)
	b = s.AddVersion(0).
		AddMediaDescription(sdp.MediaDescription{
			Type:     "video",
			Port:     51372,
			Format:   "99",
			Protocol: "RTP/AVP",
		}).
		AddAttribute("rtpmap", "99", "h263-1998/90000").
		AddLine(sdp.TypeEmail, "[email protected]").
		AddRaw('ф', "ОПАСНО").
		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]
	//  ф=ОПАСНО
}

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.