[Work in Progress] 3rd-party API: ETag for faster synchronization

controller/notesapicontroller.php

@@ -64,6 +64,17 @@ private function excludeFields(Note $note, array $exclude) {
     }
 
 
+    private function excludeIfNotModified(Note $note, array $etags) {
+        $etag = $note->getEtag();
+        if($etag!==null && in_array($etag, $etags)) {
+            $vars = get_object_vars($note);
+            unset($vars['id']);
+            $this->excludeFields($note, array_keys($vars));
+        }
+        return $note;
+    }
+
+
     /**
      * @NoAdminRequired
      * @CORS
@@ -74,11 +85,14 @@ private function excludeFields(Note $note, array $exclude) {
      */
     public function index($exclude='') {
         $exclude = explode(',', $exclude);
+        $etags = array_key_exists('HTTP_X_NOTES_ETAGS', $_SERVER) ? $_SERVER['HTTP_X_NOTES_ETAGS'] : '';
+        $etags = str_split($etags, 20);
         $notes = $this->service->getAll($this->userId);
         foreach ($notes as $note) {
             $note = $this->excludeFields($note, $exclude);
+            $note = $this->excludeIfNotModified($note, $etags);
         }
-        return new DataResponse($notes);
+        return (new DataResponse($notes))->addHeader('Vary', 'X-Notes-Etags');
     }
 
 

db/note.php

@@ -19,6 +19,8 @@
  * Class Note
  * @method integer getId()
  * @method void setId(integer $value)
+ * @method string getEtag()
+ * @method void setEtag(string $value)
  * @method integer getModified()
  * @method void setModified(integer $value)
  * @method string getTitle()
@@ -33,6 +35,7 @@
  */
 class Note extends Entity {
 
+    public $etag;
     public $modified;
     public $title;
     public $category;
@@ -60,8 +63,34 @@ public static function fromFile(File $file, Folder $notesFolder, $tags=[]){
             $note->setFavorite(true);
             //unset($tags[array_search(\OC\Tags::TAG_FAVORITE, $tags)]);
         }
+        $note->updateETag();
         $note->resetUpdatedFields();
         return $note;
     }
 
+    private function updateETag() {
+        $etag = '';
+        // collect all relevant attributes
+        $data = '';
+        foreach(get_object_vars($this) as $key => $val) {
+            if($key!=='etag') {
+                $data .= $val;
+            }
+        }
+        // create binary checksum
+        $md5 = md5($data, true);
+        // binary-to-text using a base85 derivate:
+        // - only 25% larger than binary data
+        // - replace problematic characters by not-used ones (no escaping necessary in JSON or HTTP-header)
+        // - the result has always the same length (20 characters for 16byte md5-checksum)
+        foreach(unpack('N*', $md5) as $chunk) {
+            for ($a = 0; $a < 5; $a++) {
+                $b = intval($chunk / (pow(85,4 - $a)));
+                $chr = str_replace(array('\\', '/', '<', '>'), array('z', '|', '{', '}'), chr($b + 35));
+                $etag .= $chr;
+                $chunk -= $b * pow(85,4 - $a);
+            }
+        }
+        $this->setEtag($etag);
+    }
 }

tests/unit/controller/NotesApiControllerTest.php

@@ -87,12 +87,14 @@ public function testGetAllHide(){
 
         $this->assertEquals(json_encode([
             [
+                'etag' => null,
                 'modified' => 123,
                 'category' => null,
                 'favorite' => false,
                 'id' => 3,
             ],
             [
+                'etag' => null,
                 'modified' => 111,
                 'category' => null,
                 'favorite' => false,
@@ -139,6 +141,7 @@ public function testGetHide(){
         $response = $this->controller->get(3, 'title,content');
 
         $this->assertEquals(json_encode([
+            'etag' => null,
             'modified' => 123,
             'category' => null,
             'favorite' => false,