Add a textStream() method to the Body mixin by foolip · Pull Request #1862 · whatwg/fetch

foolip · 2025-10-02T12:10:07Z

textStream() is a convenience method that pipes a body through a utf-8 TextDecoderStream,
as it's a common use case for e.g. HTML streaming or any other text streaming.

Fixes #1861.

At least two implementers are interested (and none opposed):
- Chromium
- WebKit (see below)
Tests are written and can be reviewed and commented upon at:
- Un-tentative textStream() tests (for Blob and Body) web-platform-tests/wpt#60356
Implementation bugs
- Chromium: Implemented
- Gecko: https://bugzilla.mozilla.org/show_bug.cgi?id=2044628
- WebKit: https://bugs.webkit.org/show_bug.cgi?id=316191
- Deno (not for CORS changes): Blob/Body textStream() denoland/deno#34792
MDN issue is filed: this is done by chromium release process.
The top of this comment includes a clear commit message to use.

(See WHATWG Working Mode: Changes for more details.)

Preview | Diff

noamr · 2026-05-17T19:17:37Z

See corresponding FileAPI PR: w3c/FileAPI#221

reillyeon · 2026-05-19T21:09:24Z

If an HTTP response includes a Content-Type header with charset to something other than utf-8 should this method use that when decoding the byte stream to a text stream? It seems like in some other places we explicitly say that charset is ignored and the data is decoded as UTF-8 so we probably need something similar here to disambiguate.

noamr · 2026-05-19T21:17:18Z

If an HTTP response includes a Content-Type header with charset to something other than utf-8 should this method use that when decoding the byte stream to a text stream? It seems like in some other places we explicitly say that charset is ignored and the data is decoded as UTF-8 so we probably need something similar here to disambiguate.

Yes, this is discussed on the issue (#1861)

reillyeon · 2026-05-19T21:52:36Z

Ack, I just don't see any mention of it in the text added by the PR, while other methods like text() and formData() are explicit about it.

annevk · 2026-05-20T06:09:10Z

A note similar to what we have for formData() would probably be good.

Fixes #1861.

One (the constructor) for use by JS and one (the set up steps) for use by other specifications. See whatwg/fetch#1862 (review).

noamr · 2026-05-21T10:28:23Z

A note similar to what we have for formData() would probably be good.

Done

noamr

Using the new "set up" algo and also resolved some other comments.

annevk · 2026-05-21T10:56:51Z

 <dt><code><var>requestOrResponse</var> . <a method for=Body>text</a>()</code>
 <dd><p>Returns a promise fulfilled with <var>requestOrResponse</var>'s body as string.
+
+ <dt><code><var>requestOrResponse</var> . <a method for=Body>textStream</a>()</code> <dd><p>Returns


Is this another specfmt bug?

Yes. I double checked the formatting and then ran specfmt, should do it in reverse order next time. Anyway, fixed

I'd recommend committing, then running specfmt and reviewing the diff.

annevk

The emptyStream thing is both correct and annoying.

annevk · 2026-05-21T13:59:56Z

+
+ <li>
+  <p><a data-lt="set up a text decoder stream">Set up</a> <var>decoder</var> with <a
+  for=/>UTF-8</a>.


no newline inside phrasing

This is a convenience method to pipe a byte stream through a TextDecoderStream. - Extracted the "Transformer" internals from TextDecoderStream into core/ - Call it from both the TextDecoderStream constructor and Body.textStream() Still TODO: implement this for Blob. See https://chromestatus.com/feature/5146752165478400 and whatwg/fetch#1862 Bug: 514448226 Change-Id: Ibf29c2780cfc5fe8b438de94fd6be342997c975c Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7864305 Commit-Queue: Noam Rosenthal <nrosenthal@google.com> Reviewed-by: Philip Jägenstedt <foolip@chromium.org> Cr-Commit-Position: refs/heads/main@{#1637750}

…a flag, a=testonly Automatic update from web-platform-tests Implement BodyMixin.textStream() behind a flag This is a convenience method to pipe a byte stream through a TextDecoderStream. - Extracted the "Transformer" internals from TextDecoderStream into core/ - Call it from both the TextDecoderStream constructor and Body.textStream() Still TODO: implement this for Blob. See https://chromestatus.com/feature/5146752165478400 and whatwg/fetch#1862 Bug: 514448226 Change-Id: Ibf29c2780cfc5fe8b438de94fd6be342997c975c Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7864305 Commit-Queue: Noam Rosenthal <nrosenthal@google.com> Reviewed-by: Philip Jägenstedt <foolip@chromium.org> Cr-Commit-Position: refs/heads/main@{#1637750} -- wpt-commits: cc98dd90af1747562bcdb1af6c6fda329e8a6b01 wpt-pr: 60237

Co-authored-by: Anne van Kesteren <annevk@annevk.nl>

noamr · 2026-06-03T11:24:31Z

I've ticked all the checkboxes, apart from implementer support. Do we need a whole "Standards position" for this @annevk @zcorpan ?

annevk · 2026-06-04T14:08:13Z

You can consider WebKit supportive. I left one nit on the test coverage. Thanks by the way for making those tentative PRs easily reviewable on WPT, that's really nice and maybe we should just enshrine that somewhere so that everyone starts doing that.

Once the tests are done feel free to land them and the specification changes, but please be careful to follow the commit message guidelines (ask me if you're unsure).

noamr · 2026-06-04T15:05:52Z

You can consider WebKit supportive. I left one nit on the test coverage. Thanks by the way for making those tentative PRs easily reviewable on WPT, that's really nice and maybe we should just enshrine that somewhere so that everyone starts doing that.

I thought it was the standard way of doing this? It's at least on the WHATWG PR template

annevk · 2026-06-04T15:10:36Z

It's supposed to be, yes. But people don't always do it well and then you have to dig through Mozilla or Chromium changelogs to find what you want.

noamr · 2026-06-04T15:13:00Z

Once the tests are done feel free to land them and the specification changes, but please be careful to follow the commit message guidelines (ask me if you're unsure).

I don't have permissions to land the spec changes.

* Un-tentative textStream() tests See w3c/FileAPI#221 and whatwg/fetch#1862 * Added some tests for null body

…Blob` and `Body`), a=testonly Automatic update from web-platform-tests Un-tentative `textStream()` tests (for `Blob` and `Body`) (#60356) * Un-tentative textStream() tests See w3c/FileAPI#221 and whatwg/fetch#1862 * Added some tests for null body -- wpt-commits: 15694f7be1515a179dff1cdc7ba42189d795d9d4 wpt-pr: 60356

foolip mentioned this pull request Oct 2, 2025

Convenience method to stream a response as text #1861

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foolip commented Oct 2, 2025

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foolip mentioned this pull request Oct 9, 2025

Streaming support w3c/trusted-types#594

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noamr mentioned this pull request May 17, 2026

Add textStream() method to Blob interface w3c/FileAPI#221

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noamr mentioned this pull request May 19, 2026

Editorial: separate TextDecoderStream constructor to two algos whatwg/encoding#364

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Add a textStream() method to the Body mixin

8a5f957

Fixes #1861.

annevk pushed a commit to whatwg/encoding that referenced this pull request May 21, 2026

Editorial: separate TextDecoderStream constructor to two algorithms

a985b62

One (the constructor) for use by JS and one (the set up steps) for use by other specifications. See whatwg/fetch#1862 (review).

Use the new 'set up a text decoder stream'

b7d8c9d

noamr force-pushed the foolip/textStream branch from 0150222 to b7d8c9d Compare May 21, 2026 09:52

Return an empty stream for null body

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annevk reviewed May 21, 2026

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unspecfmt

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annevk approved these changes May 21, 2026

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chromium-wpt-export-bot mentioned this pull request May 28, 2026

Implement BodyMixin.textStream() behind a flag web-platform-tests/wpt#60237

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noamr mentioned this pull request Jun 3, 2026

Un-tentative textStream() tests (for Blob and Body) web-platform-tests/wpt#60356

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Co-authored-by: Anne van Kesteren <annevk@annevk.nl>

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noamr mentioned this pull request Jun 3, 2026

Blob/Body textStream() denoland/deno#34792

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noamr mentioned this pull request Jun 4, 2026

textStream() for request/response/blob web-platform-dx/web-features#4094

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noamr added a commit to web-platform-tests/wpt that referenced this pull request Jun 4, 2026

Un-tentative textStream() tests (for Blob and Body) (#60356)

15694f7

* Un-tentative textStream() tests See w3c/FileAPI#221 and whatwg/fetch#1862 * Added some tests for null body

annevk merged commit 30140d0 into main Jun 5, 2026
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annevk deleted the foolip/textStream branch June 5, 2026 07:47

noamr mentioned this pull request Jun 9, 2026

Other Spec Review: textStream() for Blob and Body w3ctag/design-reviews#1236

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