# libdatachannel - C/C++ WebRTC DataChannels

libdatachannel is a standalone implementation of WebRTC DataChannels in C++17 with C bindings for POSIX platforms 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 API, in order to ease the design of cross-environment applications.

This projet is originally inspired by [librtcdcpp](https://github.com/chadnickbok/librtcdcpp), however it is a complete rewrite from scratch, because the messy architecture of librtcdcpp made solving its implementation issues difficult.

The connectivity can be provided through my ad-hoc ICE library [libjuice](https://github.com/paullouisageneau/libjuice) as submodule or through [libnice](https://github.com/libnice/libnice). The security layer can be provided through [GnuTLS](https://www.gnutls.org/) or [OpenSSL](https://www.openssl.org/).

Licensed under LGPLv2, see [LICENSE](https://github.com/paullouisageneau/libdatachannel/blob/master/LICENSE).

## Compatibility

The library aims at fully implementing WebRTC SCTP DataChannels ([draft-ietf-rtcweb-data-channel-13](https://tools.ietf.org/html/draft-ietf-rtcweb-data-channel-13)) over DTLS/UDP ([RFC7350](https://tools.ietf.org/html/rfc7350) and [RFC8261](https://tools.ietf.org/html/rfc8261)) with ICE ([RFC8445](https://tools.ietf.org/html/rfc8445)). It has been tested to be compatible with Firefox and Chromium. It supports IPv6 and Multicast DNS candidates resolution ([draft-ietf-rtcweb-mdns-ice-candidates-03](https://tools.ietf.org/html/draft-ietf-rtcweb-mdns-ice-candidates-03)) provided the operating system also supports it.

## Dependencies

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

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

Submodules:
- usrsctp: https://github.com/sctplab/usrsctp
- libjuice: https://github.com/paullouisageneau/libjuice

## Building
### Building with CMake (preferred)

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

### Building directly with Make

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

## Example

In the following example, note the callbacks are called in another thread.

### Signal a PeerConnection

```cpp
#include "rtc/rtc.hpp"
```

```cpp
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

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

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

```

### Create a DataChannel

```cpp
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

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

```

See [test/connectivity.cpp](https://github.com/paullouisageneau/libdatachannel/blob/master/test/connectivity.cpp) for a complete local connection example.

See [test/cpai.cpp](https://github.com/paullouisageneau/libdatachannel/blob/master/test/capi.cpp) for a C API example.