Remove support for the unstable dir flag on relations. (#14106)

From MSC3715, this was unused by clients (and there was no
way for clients to know it was supported).

Matrix 1.4 defines the stable field.

5 files changed, 31 insertions, 57 deletions

diff --git a/changelog.d/14106.removal b/changelog.d/14106.removal
new file mode 100644
index 0000000000..08fa752897
--- /dev/null
+++ b/changelog.d/14106.removal
@@ -0,0 +1 @@
+Remove the unstable identifier for [MSC3715](https://github.com/matrix-org/matrix-doc/pull/3715).
diff --git a/synapse/config/experimental.py b/synapse/config/experimental.py
index c35301207a..e00cb7096c 100644
--- a/synapse/config/experimental.py
+++ b/synapse/config/experimental.py
@@ -100,9 +100,6 @@ class ExperimentalConfig(Config):
         # MSC3773: Thread notifications
         self.msc3773_enabled: bool = experimental.get("msc3773_enabled", False)
 
-        # MSC3715: dir param on /relations.
-        self.msc3715_enabled: bool = experimental.get("msc3715_enabled", False)
-
         # MSC3848: Introduce errcodes for specific event sending failures
         self.msc3848_enabled: bool = experimental.get("msc3848_enabled", False)
 
diff --git a/synapse/handlers/relations.py b/synapse/handlers/relations.py
index 63bc6a7aa5..cc5e45c241 100644
--- a/synapse/handlers/relations.py
+++ b/synapse/handlers/relations.py
@@ -21,6 +21,7 @@ from synapse.api.errors import SynapseError
 from synapse.events import EventBase, relation_from_event
 from synapse.logging.opentracing import trace
 from synapse.storage.databases.main.relations import _RelatedEvent
+from synapse.streams.config import PaginationConfig
 from synapse.types import JsonDict, Requester, StreamToken, UserID
 from synapse.visibility import filter_events_for_client
 
@@ -72,13 +73,10 @@ class RelationsHandler:
         requester: Requester,
         event_id: str,
         room_id: str,
+        pagin_config: PaginationConfig,
+        include_original_event: bool,
         relation_type: Optional[str] = None,
         event_type: Optional[str] = None,
-        limit: int = 5,
-        direction: str = "b",
-        from_token: Optional[StreamToken] = None,
-        to_token: Optional[StreamToken] = None,
-        include_original_event: bool = False,
     ) -> JsonDict:
         """Get related events of a event, ordered by topological ordering.
 
@@ -88,14 +86,10 @@ class RelationsHandler:
             requester: The user requesting the relations.
             event_id: Fetch events that relate to this event ID.
             room_id: The room the event belongs to.
+            pagin_config: The pagination config rules to apply, if any.
+            include_original_event: Whether to include the parent event.
             relation_type: Only fetch events with this relation type, if given.
             event_type: Only fetch events with this event type, if given.
-            limit: Only fetch the most recent `limit` events.
-            direction: Whether to fetch the most recent first (`"b"`) or the
-                oldest first (`"f"`).
-            from_token: Fetch rows from the given token, or from the start if None.
-            to_token: Fetch rows up to the given token, or up to the end if None.
-            include_original_event: Whether to include the parent event.
 
         Returns:
             The pagination chunk.
@@ -114,6 +108,9 @@ class RelationsHandler:
         if event is None:
             raise SynapseError(404, "Unknown parent event.")
 
+        # TODO Update pagination config to not allow None limits.
+        assert pagin_config.limit is not None
+
         # Note that ignored users are not passed into get_relations_for_event
         # below. Ignored users are handled in filter_events_for_client (and by
         # not passing them in here we should get a better cache hit rate).
@@ -123,10 +120,10 @@ class RelationsHandler:
             room_id=room_id,
             relation_type=relation_type,
             event_type=event_type,
-            limit=limit,
-            direction=direction,
-            from_token=from_token,
-            to_token=to_token,
+            limit=pagin_config.limit,
+            direction=pagin_config.direction,
+            from_token=pagin_config.from_token,
+            to_token=pagin_config.to_token,
         )
 
         events = await self._main_store.get_events_as_list(
@@ -162,8 +159,10 @@ class RelationsHandler:
         if next_token:
             return_value["next_batch"] = await next_token.to_string(self._main_store)
 
-        if from_token:
-            return_value["prev_batch"] = await from_token.to_string(self._main_store)
+        if pagin_config.from_token:
+            return_value["prev_batch"] = await pagin_config.from_token.to_string(
+                self._main_store
+            )
 
         return return_value
 
diff --git a/synapse/rest/client/relations.py b/synapse/rest/client/relations.py
index 7a25de5c85..b31ce5a0d3 100644
--- a/synapse/rest/client/relations.py
+++ b/synapse/rest/client/relations.py
@@ -16,10 +16,11 @@ import logging
 from typing import TYPE_CHECKING, Optional, Tuple
 
 from synapse.http.server import HttpServer
-from synapse.http.servlet import RestServlet, parse_integer, parse_string
+from synapse.http.servlet import RestServlet
 from synapse.http.site import SynapseRequest
 from synapse.rest.client._base import client_patterns
-from synapse.types import JsonDict, StreamToken
+from synapse.streams.config import PaginationConfig
+from synapse.types import JsonDict
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
@@ -41,9 +42,8 @@ class RelationPaginationServlet(RestServlet):
     def __init__(self, hs: "HomeServer"):
         super().__init__()
         self.auth = hs.get_auth()
-        self.store = hs.get_datastores().main
+        self._store = hs.get_datastores().main
         self._relations_handler = hs.get_relations_handler()
-        self._msc3715_enabled = hs.config.experimental.msc3715_enabled
 
     async def on_GET(
         self,
@@ -55,49 +55,24 @@ class RelationPaginationServlet(RestServlet):
     ) -> Tuple[int, JsonDict]:
         requester = await self.auth.get_user_by_req(request, allow_guest=True)
 
-        limit = parse_integer(request, "limit", default=5)
-        # Fetch the direction parameter, if provided.
-        #
-        # TODO Use PaginationConfig.from_request when the unstable parameter is
-        #      no longer needed.
-        direction = parse_string(request, "dir", allowed_values=["f", "b"])
-        if direction is None:
-            if self._msc3715_enabled:
-                direction = parse_string(
-                    request,
-                    "org.matrix.msc3715.dir",
-                    default="b",
-                    allowed_values=["f", "b"],
-                )
-            else:
-                direction = "b"
-        from_token_str = parse_string(request, "from")
-        to_token_str = parse_string(request, "to")
-
-        # Return the relations
-        from_token = None
-        if from_token_str:
-            from_token = await StreamToken.from_string(self.store, from_token_str)
-        to_token = None
-        if to_token_str:
-            to_token = await StreamToken.from_string(self.store, to_token_str)
+        pagination_config = await PaginationConfig.from_request(
+            self._store, request, default_limit=5, default_dir="b"
+        )
 
         # The unstable version of this API returns an extra field for client
         # compatibility, see https://github.com/matrix-org/synapse/issues/12930.
         assert request.path is not None
         include_original_event = request.path.startswith(b"/_matrix/client/unstable/")
 
+        # Return the relations
         result = await self._relations_handler.get_relations(
             requester=requester,
             event_id=parent_id,
             room_id=room_id,
+            pagin_config=pagination_config,
+            include_original_event=include_original_event,
             relation_type=relation_type,
             event_type=event_type,
-            limit=limit,
-            direction=direction,
-            from_token=from_token,
-            to_token=to_token,
-            include_original_event=include_original_event,
         )
 
         return 200, result
diff --git a/synapse/streams/config.py b/synapse/streams/config.py
index b52723e2b8..f6f7bf3d8b 100644
--- a/synapse/streams/config.py
+++ b/synapse/streams/config.py
@@ -42,10 +42,12 @@ class PaginationConfig:
         cls,
         store: "DataStore",
         request: SynapseRequest,
-        raise_invalid_params: bool = True,
         default_limit: Optional[int] = None,
+        default_dir: str = "f",
     ) -> "PaginationConfig":
-        direction = parse_string(request, "dir", default="f", allowed_values=["f", "b"])
+        direction = parse_string(
+            request, "dir", default=default_dir, allowed_values=["f", "b"]
+        )
 
         from_tok_str = parse_string(request, "from")
         to_tok_str = parse_string(request, "to")