docs: Add a link to Pub/Sub filtering language public documentation to pubsub.proto

Google APIs · copybara-github · commit a19b46e54cc5 · 2020-06-11T10:44:14.000-07:00
PiperOrigin-RevId: 315930680
diff --git a/google/pubsub/v1/pubsub.proto b/google/pubsub/v1/pubsub.proto
@@ -191,7 +191,8 @@ message PubsubMessage {
   bytes data = 1;
 
   // Attributes for this message. If this field is empty, the message must
-  // contain non-empty data.
+  // contain non-empty data. This can be used to filter messages on the
+  // subscription.
   map<string, string> attributes = 2;
 
   // ID of this message, assigned by the server when the message is published.
@@ -700,7 +701,8 @@ message Subscription {
   // value for `expiration_policy.ttl` is 1 day.
   ExpirationPolicy expiration_policy = 11;
 
-  // An expression written in the Cloud Pub/Sub filter language. If non-empty,
+  // An expression written in the Pub/Sub [filter
+  // language](https://cloud.google.com/pubsub/docs/filtering). If non-empty,
   // then only `PubsubMessage`s whose `attributes` field matches the filter are
   // delivered on this subscription. If empty, then no messages are filtered
   // out.
