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, 15 insertions, 15 deletions

diff --git a/synapse/crypto/keyring.py b/synapse/crypto/keyring.py
index d2f99dc2ac..afdf6863d6 100644
--- a/synapse/crypto/keyring.py
+++ b/synapse/crypto/keyring.py
@@ -150,18 +150,19 @@ class Keyring:
     def __init__(
         self, hs: "HomeServer", key_fetchers: "Optional[Iterable[KeyFetcher]]" = None
     ):
-        self.clock = hs.get_clock()
-
         if key_fetchers is None:
-            key_fetchers = (
-                # Fetch keys from the database.
-                StoreKeyFetcher(hs),
-                # Fetch keys from a configured Perspectives server.
-                PerspectivesKeyFetcher(hs),
-                # Fetch keys from the origin server directly.
-                ServerKeyFetcher(hs),
-            )
-        self._key_fetchers = key_fetchers
+            # Always fetch keys from the database.
+            mutable_key_fetchers: List[KeyFetcher] = [StoreKeyFetcher(hs)]
+            # Fetch keys from configured trusted key servers, if any exist.
+            key_servers = hs.config.key.key_servers
+            if key_servers:
+                mutable_key_fetchers.append(PerspectivesKeyFetcher(hs))
+            # Finally, fetch keys from the origin server directly.
+            mutable_key_fetchers.append(ServerKeyFetcher(hs))
+
+            self._key_fetchers: Iterable[KeyFetcher] = tuple(mutable_key_fetchers)
+        else:
+            self._key_fetchers = key_fetchers
 
         self._fetch_keys_queue: BatchingQueue[
             _FetchKeyRequest, Dict[str, Dict[str, FetchKeyResult]]
@@ -510,7 +511,7 @@ class StoreKeyFetcher(KeyFetcher):
             for key_id in queue_value.key_ids
         )
 
-        res = await self.store.get_server_verify_keys(key_ids_to_fetch)
+        res = await self.store.get_server_keys_json(key_ids_to_fetch)
         keys: Dict[str, Dict[str, FetchKeyResult]] = {}
         for (server_name, key_id), key in res.items():
             keys.setdefault(server_name, {})[key_id] = key
@@ -522,7 +523,6 @@ class BaseV2KeyFetcher(KeyFetcher):
         super().__init__(hs)
 
         self.store = hs.get_datastores().main
-        self.config = hs.config
 
     async def process_v2_response(
         self, from_server: str, response_json: JsonDict, time_added_ms: int
@@ -626,7 +626,7 @@ class PerspectivesKeyFetcher(BaseV2KeyFetcher):
         super().__init__(hs)
         self.clock = hs.get_clock()
         self.client = hs.get_federation_http_client()
-        self.key_servers = self.config.key.key_servers
+        self.key_servers = hs.config.key.key_servers
 
     async def _fetch_keys(
         self, keys_to_fetch: List[_FetchKeyRequest]
@@ -775,7 +775,7 @@ class PerspectivesKeyFetcher(BaseV2KeyFetcher):
 
             keys.setdefault(server_name, {}).update(processed_response)
 
-        await self.store.store_server_verify_keys(
+        await self.store.store_server_signature_keys(
             perspective_name, time_now_ms, added_keys
         )