Symfony version(s) affected

5.3

Description

Symfony HttpClient supports IDN but does not provide the right flags to the intl IDN methods (idn_to_ascii and idn_to_utf8) to be fully IDNA 2008 compliant (RFC 5891).
For example, fußball.test should be converted as xn--fuball-cta.test instead of fussball.test.

See the affected line for conversion to ASCII.

How to reproduce

$client = HttpClient::create();
$response = $client->request('GET', $url);

If $url is fußball.test it should make a query to xn--fuball-cta.test instead of fussball.test.

Possible Solution

The following flags should be provided to be the most compliant possible with IDNA 2008:
IDNA_DEFAULT | IDNA_USE_STD3_RULES | IDNA_CHECK_BIDI | IDNA_CHECK_CONTEXTJ | IDNA_NONTRANSITIONAL_TO_ASCII

Additional Context

Unicode IDNA compatibility processing