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Thanks for investigating and for the reproducer.
When I run the code you shared, I have everything green:
✅ HTTP/1 default behavior
✅ HTTP/2 default behavior
✅ HTTP/1 suppressed header
✅ HTTP/2 suppressed header

Could this be related to some curl bug? Which exact version of curl and php do you have ? (php --ri curl && php -v)

Mine:

• curl 7.81.0
• php 8.3.4

Hey Nicolas, that's interesting!

• curl: 8.7.1
• PHP: 8.3.4

I checked the curl issues and found some posts that may be related:

• chunked POST via callback regression in 8.7.X curl/curl#13229
• chunked POST forced, disable length check on read callback curl/curl#13257

While I'm not sure this is the bug I'm experiencing, there is a relevant quote:

Applications are encouraged to not force "chunked", but rather set length information for a POST. By setting -1, curl will auto-select chunked on HTTP/1.1 and work properly on other HTTP versions.

That is the behavior this pull request would address.

I just checked the servers where I first experienced #54491 and they are also on curl 8.7.1.

Thank you @michaelhue.

Since this patch, our HTTP client does not add transfer-encoding: chunked header when specifying the body as a callable

We have to force the header to make it work, is this a problem between curl version and this patch ?

FYI :

php version : 8.3.6
curl: 7.64.0

I've to apply also the "Transfer-encoding: chunked" header to make my request (see code snipped) work again after this patch:

$formData = new FormDataPart([
    'degree' => '90',
    'file' => new DataPart(
        $fileResource, // a resource not a string
        'image.jpg',
        'image/jpeg'
    )
]);

$response = $client->request('POST', '/api/image/rotate/', [
    'headers' => [
        ...$formData->getPreparedHeaders()->toArray(),
        'Transfer-encoding: chunked' // with this header the patch works, without it does not send the data
    ],
    'body' => $formData->bodyToIterable(),
]);

PHP Version: 7.4.33
Curl: 7.61.1

Do we know from which Curl version we should apply the following behavior?

Applications are encouraged to not force "chunked", but rather set length information for a POST. By setting -1, curl will auto-select chunked on HTTP/1.1 and work properly on other HTTP versions.

Since Symfony 5.4 is supported also for PHP >=7.2.5, which often runs on systems where these dependencies are not necessarily updatable, I wonder if it was right to backport this patch to this version?

Closed issues cannot be tracked so please open one to describe the bug

@ddegasperi this solution might break once we fix the bug

FYI updating to curl 8.8 fixed this issue for me

FYI I think we should revert this, see #57569