+1 from me, btw wonder if a E_USER_WARNING about an unknown-ignored message would be appropriate (probably means you're running an old version of symfony)

another thing, the code above seems faulty, the loop above should be changed from

while (\CURLM_CALL_MULTI_PERFORM === curl_multi_exec($multi->handle, $active));

to something like

do{
    $err = curl_multi_exec($multi->handle, $active);
} while($err === \CURLM_CALL_MULTI_PERFORM);
if($err !== CURLM_OK){
 // handle error somehow
}

while exactly how to handle the error may be up for debate, just ignoring the error (as the current code does) is not the right approach. i've done it like

            do {
                $err = curl_multi_exec($mh, $still_running);
            } while ($err === CURLM_CALL_MULTI_PERFORM);
            if ($err !== CURLM_OK) {
                $errinfo = [
                    "multi_exec_return" => $err,
                    "curl_multi_errno" => curl_multi_errno($mh),
                    "curl_multi_strerror" => curl_multi_strerror($err)
                ];
                $errstr = "curl_multi_exec error: " . var_export($errinfo, true);
                throw new \RuntimeException($errstr);
            }

in the past, but didn't really give it much thought as to how it should really be handled. possible return values include

CURLM_CALL_MULTI_PERFORM
CURLM_OK
CURLM_BAD_HANDLE
CURLM_BAD_EASY_HANDLE
CURLM_OUT_OF_MEMORY
CURLM_INTERNAL_ERROR

btw wonder if a E_USER_WARNING about an unknown-ignored message would be appropriate (probably means you're running an old version of symfony)

Im not sure what you mean. Are you suggesting we should trigger a E_USER_WARNING if libcurl adds another value for $info['msg']?

Your other comments seams interesting. Feel free to open an new PR or issue about those. They are a bit unrelated to this PR.

Are you suggesting we should trigger a E_USER_WARNING if libcurl adds another value for $info['msg']?

maybe, after all, it means that this version Symfony received a message from libcurl that this version of Symfony doesn't understand, and because the message wasn't understood, Symfony opted to completely ignore the message. does that warrant a warning? i don't know tbh. i don't have strong feelings on it either way, just ignoring unknown messages is probably fine.

Your other comments seams interesting. Feel free to open an new PR or issue about those. They are a bit unrelated to this PR.

yeah maybe i'll do that ^^

Thank you @Nyholm.