Normalize host to lowercase

Author: nyamsprod

Diff for: interfaces/UriString.php

@@ -296,20 +296,22 @@ public static function parseNormalized(Stringable|string $uri): array
         static $isSupported = null;
         $isSupported ??= (function_exists('\idn_to_ascii') && defined('\INTL_IDNA_VARIANT_UTS46'));
 
-        if (null !== $components['host'] &&
-            false === filter_var($components['host'], FILTER_VALIDATE_IP, FILTER_FLAG_IPV4) &&
-            !IPv6Converter::isIpv6($components['host'])
-        ) {
-            $decodedHost = rawurldecode($components['host']);
-            $components['host'] = (string) preg_replace_callback(
-                '/%[0-9A-F]{2}/i',
-                fn (array $matches): string => strtoupper($matches[0]),
-                strtolower($components['host'])
-            );
-            if ($isSupported) {
-                $host = IdnaConverter::toAscii($decodedHost);
-                if (!$host->hasErrors()) {
-                    $components['host'] = $host->domain();
+        if (null !== $components['host'] && false === filter_var($components['host'], FILTER_VALIDATE_IP, FILTER_FLAG_IPV4)) {
+            // if host is IPv6 it should be lowercased according to
+            // https://www.rfc-editor.org/rfc/rfc5952#section-4.3
+            $components['host'] = strtolower($components['host']);
+            if (!IPv6Converter::isIpv6($components['host'])) {
+                $decodedHost = rawurldecode($components['host']);
+                $components['host'] = (string) preg_replace_callback(
+                    '/%[0-9A-F]{2}/i',
+                    fn (array $matches): string => strtoupper($matches[0]),
+                    $components['host']
+                );
+                if ($isSupported) {
+                    $host = IdnaConverter::toAscii($decodedHost);
+                    if (!$host->hasErrors()) {
+                        $components['host'] = $host->domain();
+                    }
                 }
             }
         }