fix: Replace unreleased InitialSubscribeRequest initial_cursor field …

…with initial_location (#150)

google/cloud/pubsublite_v1/types/subscriber.py

@@ -50,18 +50,16 @@ class InitialSubscribeRequest(proto.Message):
             The partition from which to receive messages. Partitions are
             zero indexed, so ``partition`` must be in the range [0,
             topic.num_partitions).
-        initial_cursor (google.cloud.pubsublite_v1.types.Cursor):
-            Optional. Initial stream delivery cursor,
-            pointing to anywhere in the topic partition.
-            Cursors past head result in stream breakage. If
-            not set, messages will be delivered from the
-            commit cursor for the given subscription and
-            partition.
+        initial_location (google.cloud.pubsublite_v1.types.SeekRequest):
+            Optional. Initial target location within the
+            message backlog. If not set, messages will be
+            delivered from the commit cursor for the given
+            subscription and partition.
     """
 
     subscription = proto.Field(proto.STRING, number=1,)
     partition = proto.Field(proto.INT64, number=2,)
-    initial_cursor = proto.Field(proto.MESSAGE, number=3, message=common.Cursor,)
+    initial_location = proto.Field(proto.MESSAGE, number=4, message="SeekRequest",)
 
 
 class InitialSubscribeResponse(proto.Message):
@@ -79,9 +77,11 @@ class InitialSubscribeResponse(proto.Message):
 class SeekRequest(proto.Message):
     r"""Request to update the stream's delivery cursor based on the
     given target. Resets the server available tokens to 0.
+    SeekRequests past head result in stream breakage.
+
     SeekRequests may not be sent while another SeekRequest is
     outstanding (i.e., has not received a SeekResponse) on the same
-    stream. SeekRequests past head result in stream breakage.
+    stream.
 
     Attributes:
         named_target (google.cloud.pubsublite_v1.types.SeekRequest.NamedTarget):