Symfony version(s) affected

7.0

Description

When sending a FormData request (and possibly other chunkable body types), CurlHttpClient will set a Transfer-Encoding: chunked header:

• The HTTP/2 protocol does not support chunked transfer encoding.
• Normally curl would handle the correct format itself based on the HTTP protocol version of the server.
• But when the Transfer-Encoding header is set to chunked explicitly, curl always uses chunked transfer encoding for the body.
• This results in requests to HTTP/2 server with invalid content.

For example, given a request with FormData ['foo' => 'bar'], an HTTP/1 server receives this:

Headers {
  accept: "*/*",
  "accept-encoding": "gzip",
  "content-type": "multipart/form-data; boundary=1It362u0",
  host: "localhost:8000",
  "transfer-encoding": "chunked",
  "user-agent": "Symfony HttpClient (Curl)"
}
FormData { foo: "bar" }

While an HTTP/2 server sees this:

Headers {
  accept: "*/*",
  "accept-encoding": "gzip",
  "content-type": "multipart/form-data; boundary=Mm4P-FZG",
  "user-agent": "Symfony HttpClient (Curl)"
}
FormData { foo: "2\r\n\r\n\r\n3\r\nbar\r\n2\r\n\r\n\r\ne" }

curl does omit the transfer-encoding header, but keeps the encoding for the body.

How to reproduce

Repo for reproducing the issue:
https://github.com/michaelhue/symfony-curl-http2-chunked-issue

The test source code can be found here:
https://github.com/michaelhue/symfony-curl-http2-chunked-issue/blob/main/test.php

Possible Solution

It seems to me that the following lines can be removed completely, which will fix the issue:

However my understanding of curl and the Symfony internals is limited and I can't anticipate the potential fallout from this change.

I'd be happy to create a pull request with this solution, if deemed appropriate.

Additional Context

This problem was discovered while trying to debug this issue: #54491