Overview

dart_libp2p_webrtc is the libp2p WebRTC transport for dart_libp2p. It lets a Dart or Flutter app and a web app running js-libp2p in a browser connect directly to each other. Two Dart apps can use it too.

Browsers can’t open raw TCP or UDP connections, so they can’t use the transports dart_libp2p speaks natively. They can use WebRTC, and libp2p specifies how: the /webrtc transport, also called private-to-private WebRTC. The two peers find each other through a circuit relay, exchange SDP over a stream on the relayed connection, and then talk peer to peer over WebRTC data channels. The relay only carries the signaling.

sequenceDiagram
    participant B as Browser (js-libp2p)
    participant R as Circuit relay
    participant P as App (dart_libp2p)
    P->>R: reserve (TCP or UDX)
    B->>R: reserve (WebSockets)
    B->>R: connect to P through the relay
    R->>P: relayed connection
    B->>P: /webrtc-signaling/0.0.1: SDP offer
    P->>B: SDP answer, ICE candidates
    B-->>P: direct WebRTC connection (DTLS, data channels)

Under the hood it uses libdatachannel, a C/C++ WebRTC library, through dart:ffi. The package’s build hook compiles it from source for Android, iOS, Linux and macOS, so there’s no separate native install.

dart pub add dart_libp2p_webrtc

What you get

Feature	Notes
libp2p /webrtc	Dials and accepts /p2p-circuit/webrtc connections, per the libp2p WebRTC spec. Interoperates with js-libp2p in Chrome, Firefox and WebKit.
Swarm integration	WebRTC connections join the dart_libp2p swarm like TCP or UDX ones: your stream handlers, identify and ping work over them unchanged.
Streams	Data channels with the spec’s framing: half-close (FIN, FIN_ACK), STOP_SENDING and resets, so they behave like any libp2p stream.
upgrade(peer)	Moves a peer you reach through a relay onto a direct connection.
NAT traversal	ICE with STUN, and TURN for networks with no direct path.
Data channels without libp2p	RtcPeerConnection and RtcDataChannel, for WebRTC outside libp2p.

Guides

• Getting started: install, then connect two hosts through a relay and move them onto WebRTC.
• Browsers: connect a js-libp2p web app and a Dart app, in both directions.
• Flutter and mobile: building for Android and iOS, and what changes on a phone.
• Networks: relays, STUN, TURN and NAT, and which networks connect directly.
• Running a TURN server: coturn for Dart apps and browsers, with time-limited credentials.
• Data channels without libp2p: the lower-level WebRTC API.
• How it works: signaling, stream framing, the swarm, and the native layer.
• Interoperability: what this package is tested against, and how.

Every code sample in these guides comes from a program in example/ or from the browser page the interop tests run, and the test suite runs them.