1577830 - RTCDataChannel.send order is wrong for blobs

Status: NEW

(Core :: WebRTC, defect, P2)

Description

[Jan-Ivar Bruaroey [:jib] (needinfo? me)]

Firefox does not preserve datachannel.send() call order when Blobs are sent (relative to other data sent).

STRs: https://jsfiddle.net/jib1/v2ctmg5L/ and web-platform-tests/wpt#18770.

For details see w3c/webrtc-pc#2215.

Comment 1

[guest271314]

The order is preserved when both data1 and data2 are Blobs https://plnkr.co/edit/7oYM0i?p=preview

Comment 2

[Michael Froman [:mjf]]

Marking as P2. :jib, please change if you disagree.

Comment 3

[Byron Campen [:bwc]]

This seems to be because we're doing a couple of extra dispatches when sending a Blob. These extra dispatches seem to be related to a performance optimization that offloads the reading of a Blob to another thread:

https://searchfox.org/mozilla-central/rev/f1e99da78fe6c3c68696358dac06aed90f8112d3/netwerk/sctp/datachannel/DataChannel.cpp#2765

We definitely should be waiting until after the blob is sent before sending other data.

Comment 4

[Byron Campen [:bwc]]

There's a test-case in webrtc/RTCDataChannel-send-blob-order.html that fails because of this bug, but now this test-case intermittently "succeeds" on fission for some reason.

Comment 5

[Jan-Ivar Bruaroey [:jib] (needinfo? me)]

FWIW https://jsfiddle.net/jib1/e0z61uo2/ shows WebSocket does not have this problem.

But until Chromium adds blob support (webrtc 2276) this is probably low priority.

Comment 6

[Jan-Ivar Bruaroey [:jib] (needinfo? me)]

Bumping back to P2 due to recent activity in other browsers.