Contact emailsnidhij...@chromium.org

ExplainerNone

Specificationhttps://fetch.spec.whatwg.org/#http-network-fetch

Summary

Makes Response.body be a readable byte stream instead of a "default"
readable stream. This enables it to be used with bring-your-own-buffer
(BYOB) readers, reducing garbage collection overhead and copies.

As mentioned in the Activation section below, we plan to ship the
ReadableStreamTeeCloneForBranch2 feature first, and then the FetchBYOB
feature later.
Blink componentBlink>Network>FetchAPI
<https://bugs.chromium.org/p/chromium/issues/list?q=component:Blink%3ENetwork%3EFetchAPI>

TAG reviewNone

TAG review statusNot applicable

Risks


Interoperability and Compatibility

Low risk because streams and fetch have already been standardized for a
long time. Other browsers have implemented other parts of the standard, and
Firefox has already shipped this behavior for many months and others will
most likely also adapt this feature as well soon.


*Gecko*: Shipped/Shipping (
https://github.com/whatwg/fetch/issues/267#issuecomment-1350303670) Already
shipped in Firefox in 2022.

*WebKit*: Positive (https://github.com/whatwg/fetch/pull/1593) @annevk from
Apple approved the PR to update the spec with relevant changes and
expressed interest as an implementer on behalf of Apple.

*Web developers*: No signals

*Other signals*: Deno is also interested in, and somewhat shipped, this
behavior (https://github.com/denoland/deno/issues/17386).

Activation

Currently, to clone a body, we tee the body's stream, but teeing always
returns two "default" streams, where the chunks are not cloned for both
streams. Making Response.body into a byte stream, will mean that cloning it
will result in cloning the chunks for the second stream, which is different
behavior. In order to mitigate activation risks, we are splitting this
change into two releases. One where the default teeing behavior will also
start to clone for the second stream behind the
"ReadableStreamTeeCloneForBranch2" feature flag, and then make
Response.body a readable byte stream behind the "FetchBYOB" feature flag.


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?



Debuggability

No special support needed.


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

This feature will be purely implemented in Blink and so cross-platform
support is automatic.


Is this feature fully tested by web-platform-tests
<https://chromium.googlesource.com/chromium/src/+/main/docs/testing/web_platform_tests.md>
?Yes

Flag nameReadableStreamTeeCloneForBranch2 and FetchBYOB

Requires code in //chrome?False

Tracking bughttps://bugs.chromium.org/p/chromium/issues/detail?id=1243329

Estimated milestones
Shipping on desktop 116
Shipping on Android 116
Shipping on WebView 116

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. The spec change for BYOB support for Fetch was already landed at
https://github.com/whatwg/fetch/pull/1593.

Link to entry on the Chrome Platform Status
https://chromestatus.com/feature/5192003450568704

Links to previous Intent discussionsIntent to prototype:
https://groups.google.com/a/chromium.org/g/blink-dev/c/Iyt6Ca9PiJQ/m/s_D7A0YwCgAJ

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