Adds messaging sendMulticast function

Author: ZachOrr

firebase_admin/messaging.py

@@ -47,6 +47,7 @@
 
     'send',
     'sendAll',
+    'sendMulticast',
     'subscribe_to_topic',
     'unsubscribe_from_topic',
 ]
@@ -110,6 +111,35 @@ def sendAll(messages, dry_run=False, app=None):
     """
     return _get_messaging_service(app).sendAll(messages, dry_run)
 
+def sendMulticast(tokens, message, dry_run=False, app=None):
+    """Batch sends the given message to the specified via Firebase Cloud Messaging (FCM).
+
+    If the ``dry_run`` mode is enabled, the message will not be actually delivered to the
+    recipients. Instead FCM performs all the usual validations, and emulates the send operation.
+
+    Args:
+        tokens: A list of token strings.
+        message: An instance of ``messaging.Message``.
+        dry_run: A boolean indicating whether to run the operation in dry run mode (optional).
+        app: An App instance (optional).
+
+    Returns:
+        list: A list of message ID string that uniquely identifies the sent the messages.
+
+    Raises:
+        ApiCallError: If an error occurs while sending the message to FCM service.
+        ValueError: If the input arguments are invalid.
+    """
+    messages = map(lambda token: Message(
+        data=message.data,
+        notification=message.notification,
+        android=message.android,
+        webpush=message.webpush,
+        apns=message.apns,
+        token=token
+    ), tokens)
+    return _get_messaging_service(app).sendAll(messages, dry_run)
+
 def subscribe_to_topic(tokens, topic, app=None):
     """Subscribes a list of registration tokens to an FCM topic.
 
@@ -272,8 +302,6 @@ def encode_message(cls, message):
             raise ValueError('Message must be an instance of messaging.Message class.')
         return cls.JSON_ENCODER.default(message)
 
-    # TODO: sendMulticast
-
     def send(self, message, dry_run=False):
         data = self._message_data(message, dry_run)
         try: