ext/curl: curl_error using curl_easy_strerror if CURLOPT_ERRORBUFFER

[devnexen]

did not fill the error buffer.

[devnexen]

Linked to GH-14915. IMHO the analysis nearly got it right (about the solution). I took it as feature request rather than bug though cc @adoy.

[adoy]

I think it's ok to treat this as a new feature. Someone could easily call
curl_strerror(curl_errno()) if string is empty and code will still work later when upgraded to PHP8.4+.

[Ayesh]

I also read the issue and was trying a fix like this. Pleasant surprise to see this PR!

I'd argue that this is in fact a bug fix.

// curl_exec($ch);
if (curl_error($ch)) {
  throw new \RuntimeException();
}

Snippets like this expect curl_error to return a truthy value (which "" is not), so unless Curl has a custom error message (like "Unable to resolve hostname: abcde") unrecognized errors do not trigger the exception; This is likely unexpected behavior.

[devnexen]

As mentioned above, it can be circumvented and this error occurs only on rare occasion and if the curl backend does not set the error (ie failf) for the defined case. Pretty difficult to be tested ("unfortunately" error buffer is handled internally :)) but I ll ask @Girgias if I should consider it as bug instead.

[Girgias]

I think this is indeed more of a bugfix than a feature.

It is quite weird that an empty string may be returned when an error has indeed occurred.