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Update WebRTC message size limit #628

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Update WebRTC message size limit #628

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6 changes: 3 additions & 3 deletions webrtc/README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -88,9 +88,9 @@ QUIC. The libp2p WebRTC message framing is not concerned with flow-control and
thus does not need the `RESET_STREAM` frame to be send in reply to a
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@sukunrt sukunrt Mar 26, 2025

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Can you edit the webrtc-direct file to remove this line where we recommend a max-message size of 16kB
https://github.com/libp2p/specs/blob/1253e2a1deec908037fba924fcd350ec16df13a6/webrtc/webrtc-direct.md?plain=1#L79

`STOP_SENDING` frame.

Encoded messages including their length prefix MUST NOT exceed 16kiB to support
all major browsers. See ["Understanding message size
limits"](https://developer.mozilla.org/en-US/docs/Web/API/WebRTC_API/Using_data_channels#understanding_message_size_limits).
Encoded messages including their length prefix MUST NOT exceed 256kiB to support
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@sukunrt sukunrt Mar 26, 2025

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Why 256kB, can we support more? Can we add links for the browser specific limts here?

all major browsers. See ["Large Data Channel Messages"](https://blog.mozilla.org/webrtc/large-data-channel-messages/)
and [WebRTC#40644524](https://issues.webrtc.org/issues/40644524).
Comment on lines +91 to +93
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@lidel lidel Sep 5, 2024 •
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Based on internal discussions, I believe we've decided to keep it at 16KiB to remain compatible with Kubo 0.30.0.

@achingbrain what is the next step here? figure out next steps without breaking interop? (e.g. how to negotiate higher size limit per connection via something like RTCSctpTransport/maxMessageSize?)

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@achingbrain achingbrain Sep 5, 2024

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I’m doing some experiments in the test plans repo to validate that we do in fact see a throughput increase with larger messages.

Marking this as a draft pending the outcome of that.

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@achingbrain achingbrain Mar 11, 2025

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See linked performance graphs here: #628 (comment)

Implementations MAY choose to send smaller messages, e.g. to reduce delays
sending _flagged_ messages.
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@achingbrain achingbrain Sep 3, 2024

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Should we account for forwards compatibility with future implementations that aren't arbitrarily limited like browsers currently?

Suggested change
Implementations MAY choose to send smaller messages, e.g. to reduce delays
sending _flagged_ messages.
Implementations MAY choose to send smaller messages, e.g. to reduce delays
sending _flagged_ messages, and they MAY choose to accept larger messages
to allow for forwards compatibility with more capable implementations in the
future.

A "be liberal in what you accept, conservative in what you emit" sort of thing.

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@sukunrt sukunrt Mar 26, 2025

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I'd prefer separate sentences since they're both important and about different things.

Implementations MAY choose to send smaller messages, e.g. to reduce delays
sending _flagged_ messages.

Implementations MAY choose to accept larger messages
to allow for forwards compatibility with more capable implementations in the
future.


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