feat: add exactly once delivery flag

Google APIs · copybara-github · commit f02f4392673e · 2022-02-04T07:45:49.000-08:00
PiperOrigin-RevId: 426401315
diff --git a/google/pubsub/v1/pubsub.proto b/google/pubsub/v1/pubsub.proto
@@ -752,6 +752,19 @@ message Subscription {
   // the endpoint will not be made.
   bool detached = 15;
 
+  // If true, Pub/Sub provides the following guarantees for the delivery of
+  // a message with a given value of `message_id` on this subscription:
+  //
+  // * The message sent to a subscriber is guaranteed not to be resent
+  // before the message's acknowledgement deadline expires.
+  // * An acknowledged message will not be resent to a subscriber.
+  //
+  // Note that subscribers may still receive multiple copies of a message
+  // when `enable_exactly_once_delivery` is true if the message was published
+  // multiple times by a publisher client. These copies are  considered distinct
+  // by Pub/Sub and have distinct `message_id` values.
+  bool enable_exactly_once_delivery = 16;
+
   // Output only. Indicates the minimum duration for which a message is retained
   // after it is published to the subscription's topic. If this field is set,
   // messages published to the subscription's topic in the last
