PHPLIB-327: ChangeStream::next() should not increment key for the first event

src/ChangeStream.php

@@ -38,7 +38,8 @@ class ChangeStream implements Iterator
     private $resumeToken;
     private $resumeCallable;
     private $csIt;
-    private $key;
+    private $key = 0;
+    private $hasAdvanced = false;
 
     const CURSOR_NOT_FOUND = 43;
 
@@ -53,8 +54,6 @@ class ChangeStream implements Iterator
     {
         $this->resumeCallable = $resumeCallable;
         $this->csIt = new IteratorIterator($cursor);
-
-        $this->key = 0;
     }
 
     /**
@@ -97,7 +96,10 @@ class ChangeStream implements Iterator
             $this->csIt->next();
             if ($this->valid()) {
                 $this->resumeToken = $this->extractResumeToken($this->csIt->current());
-                $this->key++;
+                if ($this->hasAdvanced) {
+                    $this->key++;
+                }
+                $this->hasAdvanced = true;
             }
         } catch (RuntimeException $e) {
             if (strpos($e->getMessage(), "not master") !== false) {
@@ -126,6 +128,7 @@ class ChangeStream implements Iterator
             $this->csIt->rewind();
             if ($this->valid()) {
                 $this->resumeToken = $this->extractResumeToken($this->csIt->current());
+                $this->hasAdvanced = true;
             }
         } catch (RuntimeException $e) {
             if (strpos($e->getMessage(), "not master") !== false) {

tests/Operation/WatchFunctionalTest.php

@@ -3,7 +3,6 @@
 namespace MongoDB\Tests\Operation;
 
 use MongoDB\ChangeStream;
-use MongoDB\Client;
 use MongoDB\Driver\Manager;
 use MongoDB\Driver\ReadPreference;
 use MongoDB\Driver\Server;
@@ -536,6 +535,23 @@ class WatchFunctionalTest extends FunctionalTestCase
         ];
     }
 
+    public function testNextAdvancesKey()
+    {
+        $operation = new Watch($this->manager, $this->getDatabaseName(), $this->getCollectionName(), [], $this->defaultOptions);
+        $changeStream = $operation->execute($this->getPrimaryServer());
+
+        $this->insertDocument(['x' => 1]);
+        $this->insertDocument(['x' => 2]);
+
+        $changeStream->next();
+
+        $this->assertSame(0, $changeStream->key());
+
+        $changeStream->next();
+
+        $this->assertSame(1, $changeStream->key());
+    }
+
     private function insertDocument($document)
     {
         $insertOne = new InsertOne($this->getDatabaseName(), $this->getCollectionName(), $document);