Implement forgetting about rooms (#1572)

* Add basic storage methods

* Add internal api handler

* Add check for forgotten room

* Add /rooms/{roomID}/forget endpoint

* Add missing rsAPI method

* Remove unused parameters

* Add passing tests

Signed-off-by: Till Faelligen <tfaelligen@gmail.com>

* Add missing file

* Add postgres migration

* Add sqlite migration

* Use Forgetter to forget room

* Remove empty line

* Update HTTP status codes

It looks like the spec calls for these to be 400, rather than 403: https://matrix.org/docs/spec/client_server/r0.6.1#post-matrix-client-r0-rooms-roomid-forget

Co-authored-by: Neil Alexander <neilalexander@users.noreply.github.com>

syncapi/routing/messages.go

@@ -59,6 +59,7 @@ const defaultMessagesLimit = 10
 // OnIncomingMessagesRequest implements the /messages endpoint from the
 // client-server API.
 // See: https://matrix.org/docs/spec/client_server/latest.html#get-matrix-client-r0-rooms-roomid-messages
+// nolint:gocyclo
 func OnIncomingMessagesRequest(
 	req *http.Request, db storage.Database, roomID string, device *userapi.Device,
 	federation *gomatrixserverlib.FederationClient,
@@ -67,6 +68,19 @@ func OnIncomingMessagesRequest(
 ) util.JSONResponse {
 	var err error
 
+	// check if the user has already forgotten about this room
+	isForgotten, err := checkIsRoomForgotten(req.Context(), roomID, device.UserID, rsAPI)
+	if err != nil {
+		return jsonerror.InternalServerError()
+	}
+
+	if isForgotten {
+		return util.JSONResponse{
+			Code: http.StatusForbidden,
+			JSON: jsonerror.Forbidden("user already forgot about this room"),
+		}
+	}
+
 	// Extract parameters from the request's URL.
 	// Pagination tokens.
 	var fromStream *types.StreamingToken
@@ -182,6 +196,19 @@ func OnIncomingMessagesRequest(
 	}
 }
 
+func checkIsRoomForgotten(ctx context.Context, roomID, userID string, rsAPI api.RoomserverInternalAPI) (bool, error) {
+	req := api.QueryMembershipForUserRequest{
+		RoomID: roomID,
+		UserID: userID,
+	}
+	resp := api.QueryMembershipForUserResponse{}
+	if err := rsAPI.QueryMembershipForUser(ctx, &req, &resp); err != nil {
+		return false, err
+	}
+
+	return resp.IsRoomForgotten, nil
+}
+
 // retrieveEvents retrieves events from the local database for a request on
 // /messages. If there's not enough events to retrieve, it asks another
 // homeserver in the room for older events.