Refactor resume token extraction and invalid type exception

Author: jmikola

src/ChangeStream.php

@@ -93,7 +93,7 @@ public function next()
         try {
             $this->csIt->next();
             if ($this->valid()) {
-                $this->extractResumeToken($this->csIt->current());
+                $this->resumeToken = $this->extractResumeToken($this->csIt->current());
                 $this->key++;
             }
         } catch (RuntimeException $e) {
@@ -122,7 +122,7 @@ public function rewind()
         try {
             $this->csIt->rewind();
             if ($this->valid()) {
-                $this->extractResumeToken($this->csIt->current());
+                $this->resumeToken = $this->extractResumeToken($this->csIt->current());
             }
         } catch (RuntimeException $e) {
             if (strpos($e->getMessage(), "not master") !== false) {
@@ -152,31 +152,34 @@ public function valid()
     /**
      * Extracts the resume token (i.e. "_id" field) from the change document.
      *
+     * @param array|document $document Change document
+     * @return mixed
      * @throws InvalidArgumentException
-     * @throws ResumeTokenException if the resume token cannot be found (i.e. no _id field)
+     * @throws ResumeTokenException if the resume token is not found or invalid
      */
     private function extractResumeToken($document)
     {
         if ( ! is_array($document) && ! is_object($document)) {
             throw InvalidArgumentException::invalidType('$document', $document, 'array or object');
         }
 
-        if (is_array($document) && isset($document['_id'])) {
-            $this->resumeToken = $document['_id'];
-            return;
+        if ($document instanceof Serializable) {
+            return $this->extractResumeToken($document->bsonSerialize());
         }
 
-        if ($document instanceof Serializable) {
-            $this->extractResumeToken($document->bsonSerialize());
-            return;
+        $resumeToken = is_array($document)
+            ? (isset($document['_id']) ? $document['_id'] : null)
+            : (isset($document->_id) ? $document->_id : null);
+
+        if ( ! isset($resumeToken)) {
+            throw ResumeTokenException::notFound();
         }
 
-        if (isset($document->_id)) {
-            $this->resumeToken = $document->_id;
-            return;
+        if ( ! is_array($resumeToken) && ! is_object($resumeToken)) {
+            throw ResumeTokenException::invalidType($resumeToken);
         }
 
-        throw new ResumeTokenException("Cannot provide resume functionality when the resume token is missing");
+        return $resumeToken;
     }
 
     /**

src/Exception/ResumeTokenException.php

@@ -19,4 +19,24 @@
 
 class ResumeTokenException extends \Exception
 {
+    /**
+     * Thrown when a resume token is not found in a change document.
+     *
+     * @return self
+     */
+    public static function notFound()
+    {
+        return new static('Resume token not found in change document');
+    }
+
+    /**
+     * Thrown when a resume token has an invalid type.
+     *
+     * @param mixed $value Actual value (used to derive the type)
+     * @return self
+     */
+    public static function invalidType($value)
+    {
+        return new static(sprintf('Expected resume token to have type "array or object" but found "%s"', gettype($value)));
+    }
 }

tests/Operation/WatchFunctionalTest.php

@@ -307,8 +307,9 @@ public function testInitialCursorIsNotClosed()
 
     /**
      * @expectedException MongoDB\Exception\ResumeTokenException
+     * @expectedExceptionMessage Resume token not found in change document
      */
-    public function testNextCannotExtractResumeToken()
+    public function testNextResumeTokenNotFound()
     {
         $pipeline =  [['$project' => ['_id' => 0 ]]];
 
@@ -324,8 +325,9 @@ public function testNextCannotExtractResumeToken()
 
     /**
      * @expectedException MongoDB\Exception\ResumeTokenException
+     * @expectedExceptionMessage Resume token not found in change document
      */
-    public function testRewindCannotExtractResumeToken()
+    public function testRewindResumeTokenNotFound()
     {
         $pipeline =  [['$project' => ['_id' => 0 ]]];
 
@@ -337,6 +339,40 @@ public function testRewindCannotExtractResumeToken()
         $changeStream->rewind();
     }
 
+    /**
+     * @expectedException MongoDB\Exception\ResumeTokenException
+     * @expectedExceptionMessage Expected resume token to have type "array or object" but found "string"
+     */
+    public function testNextResumeTokenInvalidType()
+    {
+        $pipeline =  [['$project' => ['_id' => ['$literal' => 'foo']]]];
+
+        $operation = new Watch($this->manager, $this->getDatabaseName(), $this->getCollectionName(), $pipeline, ['maxAwaitTimeMS' => 100]);
+        $changeStream = $operation->execute($this->getPrimaryServer());
+
+        /* Note: we intentionally do not start iteration with rewind() to ensure
+         * that we test extraction functionality within next(). */
+        $this->insertDocument(['x' => 1]);
+
+        $changeStream->next();
+    }
+
+    /**
+     * @expectedException MongoDB\Exception\ResumeTokenException
+     * @expectedExceptionMessage Expected resume token to have type "array or object" but found "string"
+     */
+    public function testRewindResumeTokenInvalidType()
+    {
+        $pipeline =  [['$project' => ['_id' => ['$literal' => 'foo']]]];
+
+        $operation = new Watch($this->manager, $this->getDatabaseName(), $this->getCollectionName(), $pipeline, ['maxAwaitTimeMS' => 100]);
+        $changeStream = $operation->execute($this->getPrimaryServer());
+
+        $this->insertDocument(['x' => 1]);
+
+        $changeStream->rewind();
+    }
+
     public function testMaxAwaitTimeMS()
     {
         /* On average, an acknowledged write takes about 20 ms to appear in a