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Add a textStream() method to the Body mixin #1862

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Add a textStream() method to the Body mixin #1862

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18 changes: 18 additions & 0 deletions fetch.bs
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Original file line number Diff line number Diff line change
Expand Up @@ -8032,6 +8032,7 @@ interface mixin Body {
[NewObject] Promise<FormData> formData();
[NewObject] Promise<any> json();
[NewObject] Promise<USVString> text();
[NewObject] ReadableStream textStream();
};</pre>

<p class=note>Formats you would not want a network layer to be dependent upon, such as
Expand Down Expand Up @@ -8073,6 +8074,9 @@ due course.

<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 a {{ReadableStream}} with <var>requestOrResponse</var>'s body as string chunks.
</dl>

<hr>
Expand Down Expand Up @@ -8246,6 +8250,20 @@ of running <a for=Body>consume body</a> with <a>this</a> and <a>parse JSON from
of running <a for=Body>consume body</a> with <a>this</a> and <a>UTF-8 decode</a>.
</div>

<div algorithm>
<p>The <dfn method for=Body><code>textStream()</code></dfn> method steps are:</p>
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I think for the null case it'd be nicer to return an empty stream, similar to what text() does.

Another thing that's not entirely clear to me is whether piping ends up making the underlying stream unusable so that you can't invoke text() after textStream() for instance. (That's a property we want.)

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Ah, I didn't realize what text() does if this.body is null. I agree an empty stream would be better, code that doesn't consider this case would likely just work.

I thought this should behave like when you try to use both blob() and bytes(), or indeed call one of those twice. That throws a TypeError in the first step of https://fetch.spec.whatwg.org/#concept-body-consume-body.

Since it's not possible to call text() twice, should it really be possible to call text() after textStream()?

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It should not be possible.

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Good, that should be easy to achieve, even though the current spec text doesn't make clear what happens.


<ol>
<li><p>If <span>this</span>'s <a for=Body>body</a> is null, throw a {{TypeError}}.

<li><p>Let <var>stream</var> be <a>this</a>'s <a for=Body>body</a>'s <a for=body>stream</a>.

<li><p>Let <var>decoder</var> be a new {{TextDecoderStream}} object.
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This and the next step would need improving if there's interest in this method.

The constructor steps for TextDecoderStream aren't implicitly run by just saying "new object", but what I'm after is an UTF-8 decoder with the default settings.

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@MattiasBuelens or @ricea might have thoughts, but ideally we don't use public API for internal algorithms.

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We should probably expose an algorithm to create a TextDecoderStream from other specifications, like we do for Streams.


<li><p>Return the result of piping <var>stream</var> through <var>decoder</var>.
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Here "pipe through" would need to link to something. I'm not sure if there are other APIs that internally do something similar that I could copy?

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@MattiasBuelens MattiasBuelens Oct 2, 2025 •
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You should be able to use the pipe through algorithm exposed for other specifications. [=piping through=] should work. 😉

</ol>
</div>


<h3 id=request-class>Request class</h3>

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