fix: supprot protocol-relative links

Author: kenjis

system/HTTP/SiteURI.php

@@ -381,8 +381,13 @@ public function baseUrl($relativePath = '', ?string $scheme = null): string
 
         $uri = new self($config, $relativePath, $host, $scheme);
 
+        // For protocol-relative links
+        if ($scheme !== '') {
+            $scheme = $uri->getScheme();
+        }
+
         return URI::createURIString(
-            $uri->getScheme(),
+            $scheme,
             $uri->getAuthority(),
             $uri->getPath(),
             $uri->getQuery(),
@@ -420,8 +425,13 @@ public function siteUrl($relativePath = '', ?string $scheme = null, ?App $config
 
         $uri = new self($config, $relativePath, $host, $scheme);
 
+        // For protocol-relative links
+        if ($scheme !== '') {
+            $scheme = $uri->getScheme();
+        }
+
         return URI::createURIString(
-            $uri->getScheme(),
+            $scheme,
             $uri->getAuthority(),
             $uri->getPath(),
             $uri->getQuery(),

system/HTTP/URI.php

@@ -147,7 +147,8 @@ class URI
     /**
      * Builds a representation of the string from the component parts.
      *
-     * @param string|null $scheme URI scheme. E.g., http, ftp
+     * @param string|null $scheme URI scheme. E.g., http, ftp. Empty string creates
+     *                            protocol-relative URI.
      *
      * @return string URI string with only passed parts. Maybe incomplete as a URI.
      */
@@ -159,9 +160,14 @@ public static function createURIString(
         ?string $fragment = null
     ): string {
         $uri = '';
+
         if (! empty($scheme)) {
             $uri .= $scheme . '://';
         }
+        // For protocol-relative links
+        elseif ($scheme === '') {
+            $uri .= '//';
+        }
 
         if (! empty($authority)) {
             $uri .= $authority;

system/Helpers/url_helper.php

@@ -33,7 +33,6 @@ function site_url($relativePath = '', ?string $scheme = null, ?App $config = nul
 
         assert($currentURI instanceof SiteURI);
 
-        // @TODO supprot protocol-relative links
         return $currentURI->siteUrl($relativePath, $scheme, $config);
     }
 }