bug swiftmailer#907 Fix sorting MIME children when their types are eq…

…ual (Hans Adema)

This PR was squashed before being merged into the 5.x branch (closes swiftmailer#907).

Discussion
----------

Fix sorting MIME children when their types are equal

Currently, if a message has two MIME children with the same content type, they will be added in their inverted order. In most cases, this won't matter, but for some e-mails (like X-ARF, which has two text/plain parts, one with human readable and one with YAML content), this is problematic.

This small fix ensures the original ordering is preserved when the typePrefs are identical.

Commits
-------

fe6f150 Fix sorting MIME children when their types are equal

lib/classes/Swift/Mime/SimpleMimeEntity.php

@@ -786,20 +786,23 @@ private function _sortChildren()
 
         // Sort in order of preference, if there is one
         if ($shouldSort) {
-            usort($this->_immediateChildren, array($this, '_childSortAlgorithm'));
-        }
-    }
+            // Group the messages by order of preference
+            $sorted = array();
+            foreach ($this->_immediateChildren as $child) {
+                $type = $child->getContentType();
+                $level = array_key_exists($type, $this->_alternativePartOrder) ? $this->_alternativePartOrder[$type] : max($this->_alternativePartOrder) + 1;
 
-    private function _childSortAlgorithm($a, $b)
-    {
-        $typePrefs = array();
-        $types = array(strtolower($a->getContentType()), strtolower($b->getContentType()));
+                if (empty($sorted[$level])) {
+                    $sorted[$level] = array();
+                }
 
-        foreach ($types as $type) {
-            $typePrefs[] = array_key_exists($type, $this->_alternativePartOrder) ? $this->_alternativePartOrder[$type] : max($this->_alternativePartOrder) + 1;
-        }
+                $sorted[$level][] = $child;
+            }
 
-        return $typePrefs[0] >= $typePrefs[1] ? 1 : -1;
+            ksort($sorted);
+
+            $this->_immediateChildren = array_reduce($sorted, 'array_merge', array());
+        }
     }
 
     /**

tests/unit/Swift/Mime/AbstractMimeEntityTest.php

@@ -740,6 +740,46 @@ public function testOrderingTextBeforeHtml()
             );
     }
 
+    public function testOrderingEqualContentTypesMaintainsOriginalOrdering()
+    {
+        $firstChild = new MimeEntityFixture(Swift_Mime_MimeEntity::LEVEL_ALTERNATIVE,
+            "Content-Type: text/plain\r\n".
+            "\r\n".
+            'PART 1',
+            'text/plain'
+        );
+        $secondChild = new MimeEntityFixture(Swift_Mime_MimeEntity::LEVEL_ALTERNATIVE,
+            "Content-Type: text/plain\r\n".
+            "\r\n".
+            'PART 2',
+            'text/plain'
+        );
+        $headers = $this->_createHeaderSet(array(), false);
+        $headers->shouldReceive('toString')
+            ->zeroOrMoreTimes()
+            ->andReturn("Content-Type: multipart/alternative; boundary=\"xxx\"\r\n");
+
+        $entity = $this->_createEntity($headers, $this->_createEncoder(),
+            $this->_createCache()
+        );
+        $entity->setBoundary('xxx');
+        $entity->setChildren(array($firstChild, $secondChild));
+
+        $this->assertEquals(
+            "Content-Type: multipart/alternative; boundary=\"xxx\"\r\n".
+            "\r\n\r\n--xxx\r\n".
+            "Content-Type: text/plain\r\n".
+            "\r\n".
+            'PART 1'.
+            "\r\n\r\n--xxx\r\n".
+            "Content-Type: text/plain\r\n".
+            "\r\n".
+            'PART 2'.
+            "\r\n\r\n--xxx--\r\n",
+            $entity->toString()
+        );
+    }
+
     public function testUnsettingChildrenRestoresContentType()
     {
         $cType = $this->_createHeader('Content-Type', 'text/plain', array(), false);