Ready for Developer Testing: Source Specific Multicast for Direct Sockets API

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Feb 20, 2026, 9:39:13 PM (4 hours ago) Feb 20

to blin...@chromium.org, om...@blockcast.net

Contact emails

om...@blockcast.net

Explainer

https://github.com/kkroo/multicast-in-direct-sockets

Specification

https://github.com/WICG/direct-sockets/pull/81

Design docs

https://github.com/WICG/direct-sockets/blob/main/docs/multicast-explainer.md

Summary

Adds Source-Specific Multicast (SSM) support to the Direct Sockets API, allowing Isolated Web Apps to optionally specify a source address when joining multicast groups to receive UDP packets only from that source. The Direct Sockets API currently supports Any-Source Multicast (ASM), which receives packets from any source sending to the multicast group. SSM is essential to using multicast outside of private networks, simplifying packet routing, and filtering traffic at the network level by source address, preventing spoofing and denial of service attacks.

Blink component

Blink>Network->Direct Sockets

Web Feature ID

Missing feature

Risks

Interoperability and Compatibility

Other browsers may choose to implement this API.

Gecko: No signal

WebKit: No signal

Web developers: No signals

Other signals:

Security

Security and privacy considerations are explained https://github.com/WICG/direct-sockets/blob/main/docs/multicast-explainer.md Security considerations This API gives the opportunity to flood the network with packets. By only providing this API to Isolated Web Apps the user agent can be more confident that the application has not been compromised. This allows users and system administrators to confidently grant this capability to trusted applications. Additionally, routers have control, whether they send multicast packets or drop them. In many setups dropping multicast packets is the default setting.

WebView application risks

Does this intent deprecate or change behavior of existing APIs, such that it has potentially high risk for Android WebView-based applications?

No information provided

Debuggability

The code using this API can be debugged using the standard tools. Integrating the API with the DevTools Networking tab to enable easier introspection of the state of these connections as well as the data transferred could be a beneficial future improvement.

Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, ChromeOS, Android, and Android WebView)?

No
Windows, Mac, Linux, ChromeOS

Is this feature fully tested by web-platform-tests?

No
Cannot be tested in WPT, the issue https://github.com/web-platform-tests/wpt/issues/55304

DevTrial instructions

https://github.com/WICG/direct-sockets/blob/main/docs/multicast-how-to.md

Flag name on about://flags

source-specific-multicast-in-direct-sockets

Finch feature name

SourceSpecificMulticastInDirectSockets

Requires code in //chrome?

False