With prenegotiated channels, the data-channel protocol is not used and instead the channel's negotiation is intended to be performed out of band in some application-specific manner. Comes with test!
Mostly follows the W3C specification https://www.w3.org/TR/webrtc/#peer-to-peer-data-api With contributions from: Mathieu Duponchelle <mathieu@centricular.com> https://bugzilla.gnome.org/show_bug.cgi?id=794351