Make token serializing/deserializing async (#8427)

The idea is that in future tokens will encode a mapping of instance to position. However, we don't want to include the full instance name in the string representation, so instead we'll have a mapping between instance name and an immutable integer ID in the DB that we can use instead. We'll then do the lookup when we serialize/deserialize the token (we could alternatively pass around an `Instance` type that includes both the name and ID, but that turns out to be a lot more invasive).

synapse/streams/config.py

@@ -12,7 +12,6 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-
 import logging
 from typing import Optional
 
@@ -21,6 +20,7 @@ import attr
 from synapse.api.errors import SynapseError
 from synapse.http.servlet import parse_integer, parse_string
 from synapse.http.site import SynapseRequest
+from synapse.storage.databases.main import DataStore
 from synapse.types import StreamToken
 
 logger = logging.getLogger(__name__)
@@ -39,8 +39,9 @@ class PaginationConfig:
     limit = attr.ib(type=Optional[int])
 
     @classmethod
-    def from_request(
+    async def from_request(
         cls,
+        store: "DataStore",
         request: SynapseRequest,
         raise_invalid_params: bool = True,
         default_limit: Optional[int] = None,
@@ -54,13 +55,13 @@ class PaginationConfig:
             if from_tok == "END":
                 from_tok = None  # For backwards compat.
             elif from_tok:
-                from_tok = StreamToken.from_string(from_tok)
+                from_tok = await StreamToken.from_string(store, from_tok)
         except Exception:
             raise SynapseError(400, "'from' parameter is invalid")
 
         try:
             if to_tok:
-                to_tok = StreamToken.from_string(to_tok)
+                to_tok = await StreamToken.from_string(store, to_tok)
         except Exception:
             raise SynapseError(400, "'to' parameter is invalid")