[HttpClient] cURL handles are not resources in php8

[derrabus]

Symfony version(s) affected: 5.1.2

Description
A console tool that I'm building uses the HttpClient component to query an API. It works perfectly fine of php 7.4, but if I run it on php 8 with ext-curl, I get the following error:

TypeError {#81
  #message: "curl_setopt(): Argument #1 ($handle) must be of type CurlHandle, null given"
  #code: 0
  #file: "./vendor/symfony/http-client/Response/CurlResponse.php"
  #line: 72
  trace: {
    ./vendor/symfony/http-client/Response/CurlResponse.php:72 { …}
    ./vendor/symfony/http-client/CurlHttpClient.php:311 { …}
    ./path/to/my/code { …}
  }
}

How to reproduce
The problem is apparently, that the code assumes that "curl handles" returned by curl_init() and curl_multi_init() are resources. However, in php 8 they're objects of type CurlHandle.

Possible Solution
Adjust CurlHttpClient and related classes to the new type of curl handles. I could work on a patch.

Additional Context
is_resource() is called on a handle:

symfony/src/Symfony/Component/HttpClient/Response/CurlResponse.php

Line 46 in 2c9e9cd

if (\is_resource($ch)) {

A handle is cast to an int which does not work on objects:

symfony/src/Symfony/Component/HttpClient/Response/CurlResponse.php

Line 60 in 2c9e9cd

$this->id = $id = (int) $ch;

[nicolas-grekas]

PR welcome :)
See php/php-src#5743 for some recent related progress.

[nicolas-grekas]

Oh, and if you're up to, we might want a VarDumper Caster for the new objects btw.

[derrabus]

See #37379 and php/php-src@26171c3

Thanks for the quick support, @nikic.