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

Breaking change: No
Enterprise impact: None
Spec maturity: Incubation
Web Platform Tests: No

WPT details: This will be added as part of development

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

Ecosystem

Web Platform Tests: https://wpt.fyi/results/?q=rtcpeerconnection-setlocaldescription-that-implicitly-creates-the-offer-or-answer
Chrome Platform Showcase: https://chrome-platform-showcase.paulkinlan-ea.deno.net/features
GenDN reference: https://gendn.paulkinlan-ea.deno.net/features
chrome.dev demos search: https://www.google.com/search?q=site%3Achrome.dev+RTCPeerConnection.setLocalDescription()%20that%20implicitly%20creates%20the%20offer%20or%20answer
MDN Web Docs: https://developer.mozilla.org/en-US/search?q=RTCPeerConnection.setLocalDescription()%20that%20implicitly%20creates%20the%20offer%20or%20answer
Baseline status: https://webstatus.dev/?q=RTCPeerConnection.setLocalDescription()%20that%20implicitly%20creates%20the%20offer%20or%20answer

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

View on chromestatus.com