libdatachannel - C/C++ WebRTC Data Channels

libdatachannel is a standalone implementation of WebRTC Data Channels, WebRTC Media Transport, and WebSockets in C++17 with C bindings for POSIX platforms (including GNU/Linux, Android, 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. The interface consists of simplified versions of the JavaScript WebRTC and WebSocket APIs present in browsers, in order to ease the design of cross-environment applications. It can be compiled with multiple backends:

• The security layer can be provided through OpenSSL or GnuTLS.
• 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 Channels and Media Transport

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)
• SRTP-based Media Transport (draft-ietf-rtcweb-rtp-usage-26)
• DTLS/UDP (RFC7350 and RFC8261)
• ICE (RFC8445) with STUN (RFC8489) and its extension TURN (RFC8656)

Features:

• Full IPv6 support
• Trickle ICE (draft-ietf-ice-trickle-21)
• JSEP compatible (draft-ietf-rtcweb-jsep-26)
• Multicast DNS candidates (draft-ietf-rtcweb-mdns-ice-candidates-04)
• SRTP and SRTCP key derivation from DTLS (RFC5764)
• Differentiated Services QoS (draft-ietf-tsvwg-rtcweb-qos-18)

Note only SDP BUNDLE mode is supported for media multiplexing (draft-ietf-mmusic-sdp-bundle-negotiation-54). The behavior is equivalent to the JSEP bundle-only policy: the library always negociates one unique network component, where SRTP media streams are multiplexed with SRTCP control packets (RFC5761) and SCTP/DTLS data traffic (RFC5764).

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

Dependencies:

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

Submodules:

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

Optional dependencies:

• libnice: https://nice.freedesktop.org/ (if selected as ICE backend instead of libjuice)
• libsrtp: https://github.com/cisco/libsrtp (if selected instead of the submodule)

Building

Clone repository and submodules

$ git clone https://github.com/paullouisageneau/libdatachannel.git
$ cd libdatachannel
$ git submodule update --init --recursive

Building with CMake

The CMake library targets libdatachannel and libdatachannel-static respectively correspond to the shared and static libraries. The default target will build tests and examples. The option USE_GNUTLS allows to switch between OpenSSL (default) and GnuTLS, and the option USE_NICE allows to switch between libjuice as submodule (default) and libnice.

If you only need Data Channels, the option NO_MEDIA allows to make the library lighter by removing media support. Similarly, NO_WEBSOCKET removes WebSocket support.

POSIX-compliant operating systems (including Linux and Apple macOS)

$ cmake -B build -DUSE_GNUTLS=1 -DUSE_NICE=0
$ cd build
$ make -j2

Apple macOS with XCode project

$ cmake -B "$BUILD_DIR" -DUSE_GNUTLS=0 -DUSE_NICE=0 -G Xcode

Xcode project is generated in build/ directory.

Solving Could NOT find OpenSSL error

You need to add OpenSSL root directory if your build fails with the following message:

Could NOT find OpenSSL, try to set the path to OpenSSL root folder in the
system variable OPENSSL_ROOT_DIR (missing: OPENSSL_CRYPTO_LIBRARY
OPENSSL_INCLUDE_DIR)

for example:

$ cmake -B build -DUSE_GNUTLS=0 -DUSE_NICE=0 -G Xcode -DOPENSSL_ROOT_DIR=/usr/local/Cellar/openssl\@1.1/1.1.1h/

Microsoft Windows with MinGW cross-compilation

$ cmake -B build -DCMAKE_TOOLCHAIN_FILE=/usr/share/mingw/toolchain-x86_64-w64-mingw32.cmake # replace with your toolchain file
$ cd build
$ make -j2

Microsoft Windows with Microsoft Visual C++

$ cmake -B build -G "NMake Makefiles"
$ cd build
$ nmake

Building directly with Make (Linux only)

The option USE_GNUTLS allows to switch between OpenSSL (default) and GnuTLS, and the option USE_NICE allows to switch between libjuice as submodule (default) and libnice.

If you only need Data Channels, the option NO_MEDIA removes media support. Similarly, NO_WEBSOCKET removes WebSocket support.

$ make USE_GNUTLS=1 USE_NICE=0

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([](rtc::Description sdp) {
    // Send the SDP to the remote peer
    MY_SEND_DESCRIPTION_TO_REMOTE(string(sdp));
});

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

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

External resources

• Rust wrapper for libdatachannel: datachannel-rs
• Node.js wrapper for libdatachannel: node-datachannel
• Unity wrapper for Windows 10 and Hololens: datachannel-unity
• WebAssembly wrapper compatible with libdatachannel: datachannel-wasm