RTCPeerConnection.setLocalDescription() that implicitly creates the offer or answer

Category: Miscellaneous
Type: New or changed feature
Status: Enabled by default (Chrome 80)
Intent stage: Shipped

Summary

Makes the RTCSessionDescription argument optional for setLocalDescription(). Previously, it required a value returned by createOffer() or createAnswer(). With this change Chromium generates the the offer or answer implicitly when no argument is provided. This avoids possible edge-case races.

Motivation

This is part of "Perfect Negotiation", which makes signaling in WebRTC race-free and less error-prone. For more details, see https://docs.google.com/presentation/d/1xcvf0udNeSH7s1FOY7RRqr1dEFvokZjn-MZPjwy3iXQ/edit?usp=sharing.

Standards & signals

Specification: https://github.com/w3c/webrtc-pc/pull/2234
Firefox: In development — Confirmed in a public W3C WebRTC WG meeting
Safari: No signal
Web developers: No signals
Tracking bug: https://bugs.chromium.org/p/chromium/issues/detail?id=980885

Docs: N/A

Explainers: https://docs.google.com/presentation/d/1xcvf0udNeSH7s1FOY7RRqr1dEFvokZjn-MZPjwy3iXQ/edit?usp=sharing

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