WebRTC transport for peer-to-peer networking

[tomaka]

The Vision

In order for browsers-embedded applications to be able to directly connect to the peer-to-peer network of a chain, there exists three protocols: WebSocket, WebTransport, or WebRTC.

Unfortunately, the first two require the server you connect to to expose a (non-self-signed) TLS certificate. This is ideologically problematic, as we don't want users of our software to have to deal with registering certificates. Browser-embedded applications should have a wide range of accessible peers, and the higher the barrier to making a client accessible, the fewer peers will be accessible.

WebSocket and WebTransport also come with a known security issue w.r.t. to our use case which I would prefer to not disclose publicly in an issue.

For these reasons, we want to use WebRTC. WebRTC has the advantage of existing specifically for peer-to-peer networking, meaning that even if changes are ever made to the WebRTC protocol (such as extra security requirements), we should be able to accommodate them.

The Plan

• WebRTC should be implemented in Substrate:
  • General umbrella issue in Substrate: Roadmap for allowing browser-embedded nodes to connect to Substrate networks polkadot-sdk#547
  • Libp2p issue: Native implementation of WebRTC libp2p/rust-libp2p#1066
    • At the time of writing, a PR is in progress: feat: Add WebRTC transport libp2p/rust-libp2p#2622
• WebRTC should be implemented in smoldot: wasm-node: Add support for WebRTC smoldot#1712 (nearly done at the time of writing)

As a side note, we're currently sponsoring the webrtc-rs library, which is not owned by us but will be used by the Substrate implementation: https://opencollective.com/webrtc-rs

Open Questions

The quality of the webrtc-rs library is unfortunately not the best. Is it wise to enable it by default on all Substrate nodes? A bug in the library could make it possible for an attacker to crash nodes.