Rework cid: images (#8966)

* Adding CID support for HtmlHelper::image() #8877

* Move cid: checking in to UrlHelper.

While this does allow `cid:` prefixes to be used on all asset types, it
also enables other `a-z:` prefixes to be used easily as well.

Refs #8898

* Allow uppercase CID as well.

src/View/Helper/UrlHelper.php

@@ -120,7 +120,7 @@ public function assetUrl($path, array $options = [])
         if (is_array($path)) {
             return $this->build($path, !empty($options['fullBase']));
         }
-        if (strpos($path, '://') !== false) {
+        if (strpos($path, '://') !== false || preg_match('/^[a-z]+:/i', $path)) {
             return $path;
         }
         if (!array_key_exists('plugin', $options) || $options['plugin'] !== false) {

tests/TestCase/View/Helper/HtmlHelperTest.php

@@ -336,6 +336,10 @@ public function testImageTag()
         $result = $this->Html->image('/test/view/1.gif');
         $expected = ['img' => ['src' => '/test/view/1.gif', 'alt' => '']];
         $this->assertHtml($expected, $result);
+
+        $result = $this->Html->image('cid:cakephp_logo');
+        $expected = ['img' => ['src' => 'cid:cakephp_logo', 'alt' => '']];
+        $this->assertHtml($expected, $result);
     }
 
     /**

tests/TestCase/View/Helper/UrlHelperTest.php

@@ -293,6 +293,12 @@ public function testImage()
 
         $result = $this->Helper->image('dir/big+tall/image.jpg');
         $this->assertEquals('img/dir/big%2Btall/image.jpg', $result);
+
+        $result = $this->Helper->image('cid:foo.jpg');
+        $this->assertEquals('cid:foo.jpg', $result);
+
+        $result = $this->Helper->image('CID:foo.jpg');
+        $this->assertEquals('CID:foo.jpg', $result);
     }
 
     /**