webrtc(browser-browser): specify init channel for connection establishment

[sukunrt]

Connection establishment doesn't work if we don't create a channel before creating the SDP offer.
Not exactly very helpful but some info on this SO question: https://stackoverflow.com/questions/38867763/why-i-have-to-open-data-channel-before-send-peer-connection-offer/38872920#38872920

js-libp2p already does this: https://github.com/libp2p/js-libp2p/blob/master/packages/transport-webrtc/src/private-to-private/handler.ts#L116-L119

go-libp2p: https://github.com/libp2p/go-libp2p/blob/webrtcprivate/transport/p2p/transport/webrtcprivate/transport.go#L242

I think this should be a part of the spec.

[thomaseizinger]

I think in Rust we handle this by including the relevant m-line?

https://github.com/libp2p/rust-libp2p/blob/484fc5693c0a7ad9ad2acb0a08445a7a4f5f7fd9/misc/webrtc-utils/src/sdp.rs#L84

[sukunrt]

I think that's for webrtc-direct. Can something similar can be done for webrtc browser-browser too?

[thomaseizinger]

I think that's for webrtc-direct. Can something similar can be done for webrtc browser-browser too?

You are right, that is for webrtc-direct. We haven't implemented webrtc yet so I can't say.

[mxinden]

Thank you for improving the specs.