Modify StoreKeyFetcher to read from server_keys_json. (#15417)

Before this change:

* `PerspectivesKeyFetcher` and `ServerKeyFetcher` write to `server_keys_json`.
* `PerspectivesKeyFetcher` also writes to `server_signature_keys`.
* `StoreKeyFetcher` reads from `server_signature_keys`.

After this change:

* `PerspectivesKeyFetcher` and `ServerKeyFetcher` write to `server_keys_json`.
* `PerspectivesKeyFetcher` also writes to `server_signature_keys`.
* `StoreKeyFetcher` reads from `server_keys_json`.

This results in `StoreKeyFetcher` now using the results from `ServerKeyFetcher`
in addition to those from `PerspectivesKeyFetcher`, i.e. keys which are directly
fetched from a server will now be pulled from the database instead of refetched.

An additional minor change is included to avoid creating a `PerspectivesKeyFetcher`
(and checking it) if no `trusted_key_servers` are configured.

The overall impact of this should be better usage of cached results:

* If a server has no trusted key servers configured then it should reduce how often keys
  are fetched.
* if a server's trusted key server does not have a requested server's keys cached then it
  should reduce how often keys are directly fetched.

1 files changed, 16 insertions, 9 deletions

diff --git a/tests/unittest.py b/tests/unittest.py

index 96ae8fca67..ee2f78ab01 100644
--- a/tests/unittest.py
+++ b/tests/unittest.py
@@ -69,7 +69,6 @@ from synapse.logging.context import (
 )
 from synapse.rest import RegisterServletsFunc
 from synapse.server import HomeServer
-from synapse.storage.keys import FetchKeyResult
 from synapse.types import JsonDict, Requester, UserID, create_requester
 from synapse.util import Clock
 from synapse.util.httpresourcetree import create_resource_tree
@@ -848,15 +847,23 @@ class FederatingHomeserverTestCase(HomeserverTestCase):
         verify_key_id = "%s:%s" % (verify_key.alg, verify_key.version)
 
         self.get_success(
-            hs.get_datastores().main.store_server_verify_keys(
+            hs.get_datastores().main.store_server_keys_json(
+                self.OTHER_SERVER_NAME,
+                verify_key_id,
                 from_server=self.OTHER_SERVER_NAME,
-                ts_added_ms=clock.time_msec(),
-                verify_keys={
-                    (self.OTHER_SERVER_NAME, verify_key_id): FetchKeyResult(
-                        verify_key=verify_key,
-                        valid_until_ts=clock.time_msec() + 10000,
-                    ),
-                },
+                ts_now_ms=clock.time_msec(),
+                ts_expires_ms=clock.time_msec() + 10000,
+                key_json_bytes=canonicaljson.encode_canonical_json(
+                    {
+                        "verify_keys": {
+                            verify_key_id: {
+                                "key": signedjson.key.encode_verify_key_base64(
+                                    verify_key
+                                )
+                            }
+                        }
+                    }
+                ),
             )
         )