PHPLIB-442: Ensure change stream resume token is updated after resume

This extracts common logic in next() and rewind() to a new method, which is now also called by resume() after it rewinds the internal iterator.

src/ChangeStream.php

@@ -102,22 +102,7 @@ class ChangeStream implements Iterator
     {
         try {
             $this->csIt->next();
-            if ($this->valid()) {
-                if ($this->hasAdvanced) {
-                    $this->key++;
-                }
-                $this->hasAdvanced = true;
-                $this->resumeToken = $this->extractResumeToken($this->csIt->current());
-            }
-            /* If the cursorId is 0, the server has invalidated the cursor so we
-             * will never perform another getMore. This means that we cannot
-             * resume and we can therefore unset the resumeCallable, which will
-             * free any reference to Watch. This will also free the only
-             * reference to an implicit session, since any such reference
-             * belongs to Watch. */
-            if ((string) $this->getCursorId() === '0') {
-                $this->resumeCallable = null;
-            }
+            $this->onIteration(true);
         } catch (RuntimeException $e) {
             if ($this->isResumableError($e)) {
                 $this->resume();
@@ -133,14 +118,7 @@ class ChangeStream implements Iterator
     {
         try {
             $this->csIt->rewind();
-            if ($this->valid()) {
-                $this->hasAdvanced = true;
-                $this->resumeToken = $this->extractResumeToken($this->csIt->current());
-            }
-            // As with next(), free the callable once we know it will never be used.
-            if ((string) $this->getCursorId() === '0') {
-                $this->resumeCallable = null;
-            }
+            $this->onIteration(false);
         } catch (RuntimeException $e) {
             if ($this->isResumableError($e)) {
                 $this->resume();
@@ -214,6 +192,38 @@ class ChangeStream implements Iterator
         return true;
     }
 
+    /**
+     * Perform housekeeping after an iteration event (i.e. next or rewind).
+     *
+     * @param boolean $isNext Whether the iteration event was a call to next()
+     * @throws ResumeTokenException
+     */
+    private function onIteration($isNext)
+    {
+        /* If the cursorId is 0, the server has invalidated the cursor and we
+         * will never perform another getMore nor need to resume since any
+         * remaining results (up to and including the invalidate event) will
+         * have been received in the last response. Therefore, we can unset the
+         * resumeCallable. This will free any reference to Watch as well as the
+         * only reference to any implicit session created therein. */
+        if ((string) $this->getCursorId() === '0') {
+            $this->resumeCallable = null;
+        }
+
+        if (!$this->valid()) {
+            return;
+        }
+
+        /* Increment the key if the iteration event was a call to next() and we
+         * have already advanced past the first result. */
+        if ($isNext && $this->hasAdvanced) {
+            $this->key++;
+        }
+
+        $this->hasAdvanced = true;
+        $this->resumeToken = $this->extractResumeToken($this->csIt->current());
+    }
+
     /**
      * Creates a new changeStream after a resumable server error.
      *
@@ -224,5 +234,6 @@ class ChangeStream implements Iterator
         $newChangeStream = call_user_func($this->resumeCallable, $this->resumeToken);
         $this->csIt = $newChangeStream->csIt;
         $this->csIt->rewind();
+        $this->onIteration(false);
     }
 }

tests/Operation/WatchFunctionalTest.php

@@ -322,6 +322,70 @@ class WatchFunctionalTest extends FunctionalTestCase
         $this->assertMatchesDocument($expectedResult, $changeStream->current());
     }
 
+    public function testResumeTokenIsUpdatedAfterResuming()
+    {
+        $this->insertDocument(['_id' => 1]);
+
+        $operation = new Watch($this->manager, $this->getDatabaseName(), $this->getCollectionName(), [], $this->defaultOptions);
+        $changeStream = $operation->execute($this->getPrimaryServer());
+
+        $changeStream->rewind();
+        $this->assertNull($changeStream->current());
+
+        $this->insertDocument(['_id' => 2]);
+
+        $changeStream->next();
+        $this->assertTrue($changeStream->valid());
+
+        $expectedResult = [
+            '_id' => $changeStream->current()->_id,
+            'operationType' => 'insert',
+            'fullDocument' => ['_id' => 2],
+            'ns' => ['db' => $this->getDatabaseName(), 'coll' => $this->getCollectionName()],
+            'documentKey' => ['_id' => 2],
+        ];
+
+        $this->assertMatchesDocument($expectedResult, $changeStream->current());
+
+        $this->killChangeStreamCursor($changeStream);
+
+        $this->insertDocument(['_id' => 3]);
+
+        $changeStream->next();
+        $this->assertTrue($changeStream->valid());
+
+        $expectedResult = [
+            '_id' => $changeStream->current()->_id,
+            'operationType' => 'insert',
+            'fullDocument' => ['_id' => 3],
+            'ns' => ['db' => $this->getDatabaseName(), 'coll' => $this->getCollectionName()],
+            'documentKey' => ['_id' => 3],
+        ];
+
+        $this->assertMatchesDocument($expectedResult, $changeStream->current());
+
+        /* Triggering a consecutive failure will allow us to test whether the
+         * resume token was properly updated after the last resume. If the
+         * resume token updated, the next result will be {_id: 4}; otherwise,
+         * we'll see {_id: 3} returned again. */
+        $this->killChangeStreamCursor($changeStream);
+
+        $this->insertDocument(['_id' => 4]);
+
+        $changeStream->next();
+        $this->assertTrue($changeStream->valid());
+
+        $expectedResult = [
+            '_id' => $changeStream->current()->_id,
+            'operationType' => 'insert',
+            'fullDocument' => ['_id' => 4],
+            'ns' => ['db' => $this->getDatabaseName(), 'coll' => $this->getCollectionName()],
+            'documentKey' => ['_id' => 4],
+        ];
+
+        $this->assertMatchesDocument($expectedResult, $changeStream->current());
+    }
+
     public function testKey()
     {
         $operation = new Watch($this->manager, $this->getDatabaseName(), $this->getCollectionName(), [], $this->defaultOptions);