libdatachannel

libdatachannel - C/C++ WebRTC Data Channels

libdatachannel is a standalone implementation of WebRTC Data Channels and WebSockets in C++17 with C bindings for POSIX platforms (including Linux and Apple macOS) and Microsoft Windows. It enables direct connectivity between native applications and web browsers without the pain of importing the entire WebRTC stack. Its API is modelled as a simplified version of the JavaScript WebRTC and WebSocket browser API, in order to ease the design of cross-environment applications.

It can be compiled with multiple backends:

• The security layer can be provided through GnuTLS or OpenSSL.
• The connectivity for WebRTC can be provided through my ad-hoc ICE library libjuice as submodule or through libnice.

This projet is originally inspired by librtcdcpp, however it is a complete rewrite from scratch, because the messy architecture of librtcdcpp made solving its implementation issues difficult.

Licensed under LGPLv2, see LICENSE.

Compatibility

The library aims at implementing the following communication protocols:

WebRTC Data Channel

The WebRTC stack has been tested to be compatible with Firefox and Chromium.

Protocol stack:

• SCTP-based Data Channels (draft-ietf-rtcweb-data-channel-13)
• DTLS/UDP (RFC7350 and RFC8261)
• ICE (RFC8445) with STUN RFC5389

Features:

• Full IPv6 support
• Trickle ICE draft-ietf-ice-trickle-21
• Multicast DNS candidates (draft-ietf-rtcweb-mdns-ice-candidates-04)
• TURN relaying RFC5766 with libnice as ICE backend.

WebSocket

WebSocket is the protocol of choice for WebRTC signaling. The support is optional and can be disabled at compile time.

Protocol stack:

• WebSocket protocol (RFC6455), client-side only
• HTTP over TLS (RFC2818)

Features:

• IPv6 and IPv4/IPv6 dual-stack support
• Keepalive with ping/pong

Dependencies

• GnuTLS: https://www.gnutls.org/ or OpenSSL: https://www.openssl.org/

Optional:

• libnice: https://nice.freedesktop.org/ (substituable with libjuice)

Submodules:

• libjuice: https://github.com/paullouisageneau/libjuice
• usrsctp: https://github.com/sctplab/usrsctp

Building

Building with CMake (preferred)

$ git submodule update --init --recursive
$ mkdir build
$ cd build
$ cmake -DUSE_JUICE=1 -DUSE_GNUTLS=1 ..
$ make

Building directly with Make

$ git submodule update --init --recursive
$ make USE_JUICE=1 USE_GNUTLS=1

Examples

See examples for a complete usage example with signaling server (under GPLv2).

Additionnaly, you might want to have a look at the C API.

Signal a PeerConnection

#include "rtc/rtc.hpp"

rtc::Configuration config;
config.iceServers.emplace_back("mystunserver.org:3478");

auto pc = make_shared<rtc::PeerConnection>(config);

pc->onLocalDescription([](const rtc::Description &sdp) {
    // Send the SDP to the remote peer
    MY_SEND_DESCRIPTION_TO_REMOTE(string(sdp));
});

pc->onLocalCandidate([](const rtc::Candidate &candidate) {
    // Send the candidate to the remote peer
    MY_SEND_CANDIDATE_TO_REMOTE(candidate.candidate(), candidate.mid());
});

MY_ON_RECV_DESCRIPTION_FROM_REMOTE([pc](string sdp) {
    pc->setRemoteDescription(rtc::Description(sdp));
});

MY_ON_RECV_CANDIDATE_FROM_REMOTE([pc](string candidate, string mid) {
    pc->addRemoteCandidate(rtc::Candidate(candidate, mid));
});

Observe the PeerConnection state

pc->onStateChange([](PeerConnection::State state) {
    cout << "State: " << state << endl;
});

pc->onGatheringStateChange([](PeerConnection::GatheringState state) {
    cout << "Gathering state: " << state << endl;
});

Create a DataChannel

auto dc = pc->createDataChannel("test");

dc->onOpen([]() {
    cout << "Open" << endl;
});

dc->onMessage([](const variant<binary, string> &message) {
    if (holds_alternative<string>(message)) {
        cout << "Received: " << get<string>(message) << endl;
    }
});

Receive a DataChannel

shared_ptr<rtc::DataChannel> dc;
pc->onDataChannel([&dc](shared_ptr<rtc::DataChannel> incoming) {
    dc = incoming;
    dc->send("Hello world!");
});

Open a WebSocket

auto ws = make_shared<rtc::WebSocket>();

ws->onOpen([]() {
	cout << "WebSocket open" << endl;
});

ws->onMessage([](const variant<binary, string> &message) {
    if (holds_alternative<string>(message)) {
        cout << "WebSocket received: " << get<string>(message) << endl;
    }
});

ws->open("wss://my.websocket/service");