Rename get_events->get_events_from_store_or_dest (#5344)

We have too many things called get_event, and it's hard to figure out what we
mean. Also remove some unused params from the signature, and add some logging.

changelog.d/5344.misc

@@ -0,0 +1 @@
+Clean up FederationClient.get_events for clarity.

synapse/federation/federation_client.py

@@ -17,7 +17,6 @@
 import copy
 import itertools
 import logging
-import random
 
 from six.moves import range
 
@@ -326,8 +325,8 @@ class FederationClient(FederationBase):
             state_event_ids = result["pdu_ids"]
             auth_event_ids = result.get("auth_chain_ids", [])
 
-            fetched_events, failed_to_fetch = yield self.get_events(
-                [destination], room_id, set(state_event_ids + auth_event_ids)
+            fetched_events, failed_to_fetch = yield self.get_events_from_store_or_dest(
+                destination, room_id, set(state_event_ids + auth_event_ids)
             )
 
             if failed_to_fetch:
@@ -397,27 +396,20 @@ class FederationClient(FederationBase):
         defer.returnValue((signed_pdus, signed_auth))
 
     @defer.inlineCallbacks
-    def get_events(self, destinations, room_id, event_ids, return_local=True):
-        """Fetch events from some remote destinations, checking if we already
-        have them.
+    def get_events_from_store_or_dest(self, destination, room_id, event_ids):
+        """Fetch events from a remote destination, checking if we already have them.
 
         Args:
-            destinations (list)
+            destination (str)
             room_id (str)
             event_ids (list)
-            return_local (bool): Whether to include events we already have in
-                the DB in the returned list of events
 
         Returns:
             Deferred: A deferred resolving to a 2-tuple where the first is a list of
             events and the second is a list of event ids that we failed to fetch.
         """
-        if return_local:
-            seen_events = yield self.store.get_events(event_ids, allow_rejected=True)
-            signed_events = list(seen_events.values())
-        else:
-            seen_events = yield self.store.have_seen_events(event_ids)
-            signed_events = []
+        seen_events = yield self.store.get_events(event_ids, allow_rejected=True)
+        signed_events = list(seen_events.values())
 
         failed_to_fetch = set()
 
@@ -428,10 +420,11 @@ class FederationClient(FederationBase):
         if not missing_events:
             defer.returnValue((signed_events, failed_to_fetch))
 
-        def random_server_list():
-            srvs = list(destinations)
-            random.shuffle(srvs)
-            return srvs
+        logger.debug(
+            "Fetching unknown state/auth events %s for room %s",
+            missing_events,
+            event_ids,
+        )
 
         room_version = yield self.store.get_room_version(room_id)
 
@@ -443,7 +436,7 @@ class FederationClient(FederationBase):
             deferreds = [
                 run_in_background(
                     self.get_pdu,
-                    destinations=random_server_list(),
+                    destinations=[destination],
                     event_id=e_id,
                     room_version=room_version,
                 )