LGTM1
On 10/20/25 4:14 p.m., Reilly Grant wrote:
IWA OWNER LGTM
This is an extension to an existing IWA-only feature. Multicast
introduces additional privacy concerns because since content is
intended for consumption by multiple clients it cannot be encrypted in
a way which preserves confidentiality (this has been previously
discussed on this list an network-dev@). Requiring the user to
explicitly choose to install an application rather than making this
capability available to any site at least partially mitigates this
concern.
Reilly Grant | Software Engineer |[email protected] |Google Chrome
<https://www.google.com/chrome>
On Fri, Oct 17, 2025 at 3:11 AM Chromestatus
<[email protected]> wrote:
*Contact emails*
[email protected]
*Explainer*
https://github.com/explainers-by-googlers/Multicast-in-Direct-Sockets
*Specification*
https://github.com/WICG/direct-sockets/pull/79
*Design docs*
https://github.com/WICG/direct-sockets/blob/main/docs/multicast-explainer.md
https://docs.google.com/document/d/1Wna0lkTrhYoTxOO1GjOrut2nWHO19HEyo9YCk39tXqY/edit?usp=sharing
*Summary*
Allows Isolated Web Apps to subscribe to multicast groups and
receive UDP packets from there, and to specify additional
parameters when sending UDP packets to multicasts addresses.
*Blink component*
Blink>Network->Direct Sockets
<https://issues.chromium.org/issues?q=customfield1222907:%22Blink%3ENetwork-%3EDirect%20Sockets%22>
*Web Feature ID*
Missing feature
*Motivation*
1. Synchronous video stream from one device to the whole network
of devices. For example, imagine in a shopping mall there would be
multiple displays which show videos simultaneously on all devices.
2. Device discovery on a local network. mDNS protocol uses
multicast sockets under the hood. In short, when a device joins a
network, it sends a message: “Hello, I am headphones-10, my ip is
‘20.20.20.14’ . Who else is here?”, other devices reply and in
such a manner all devices can know about each other without a
central server.
*Initial public proposal*
https://github.com/WICG/proposals/issues/228
*TAG review*
Tag does not review Isolated Web Apps. It was stated publicly here
https://github.com/w3ctag/design-reviews/issues/842#issuecomment-2917031448
*TAG review status*
Not applicable
*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
This feature is implemented on desktop platforms, although it will
only be available to the end users on platforms that support
Isolated Web Apps, which is currently only ChromeOS. Android is
excluded for historical reasons, although there are no apparent
interoperability blockers here.
*Is this feature fully tested by web-platform-tests
<https://chromium.googlesource.com/chromium/src/+/main/docs/testing/web_platform_tests.md>?*
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*
MulticastInDirectSockets
*Finch feature name*
MulticastInDirectSockets
*Rollout plan*
Will ship enabled for all users
*Requires code in //chrome?*
False
*Measurement*
Separate programmatic counters for the .idl methods and attributes
(via MeasureAs) are included to track the stats for API usage:
MulticastControllerJoinGroupFunction
MulticastControllerLeaveGroupFunction
MulticastControllerJoinedGroupsAttribute
*Availability expectation*
Feature is available only in Isolated Web Apps on desktop
platforms. https://chromestatus.com/feature/5146307550248960
*Adoption expectation*
Expected to be used initially by a small number of developers
inside Isolated Web Apps.
*Adoption plan*
Working directly with developers that are planning to rely on the API.
*Estimated milestones*
Shipping on desktop 144
DevTrial on desktop 142
*Anticipated spec changes*
Open questions about a feature may be a source of future web
compat or interop issues. Please list open issues (e.g. links to
known github issues in the project for the feature specification)
whose resolution may introduce web compat/interop risk (e.g.,
changing to naming or structure of the API in a
non-backward-compatible way).
None
*Link to entry on the Chrome Platform Status*
https://chromestatus.com/feature/5073740211814400?gate=5084202819256320
*Links to previous Intent discussions*
Intent to Prototype:
https://groups.google.com/a/chromium.org/d/msgid/blink-dev/68aeedee.050a0220.27f047.019b.GAE%40google.com
This intent message was generated by Chrome Platform Status
<https://chromestatus.com>.
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