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Allow use of the /filter Client-Server APIs on workers. #15134

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Feb 28, 2023
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Allow use of the /filter Client-Server APIs on workers. #15134

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1bdcd17
Collapse FilteringStore into FilteringWorkerStore
reivilibre Feb 22, 2023
4960619
Register /filter servlets on workers too
reivilibre Feb 22, 2023
5a84e78
Newsfile
reivilibre Feb 22, 2023
29a4ef4
Add the path to the map in the docs
reivilibre Feb 22, 2023
124c0e9
Don't forget to match /filter/<id> as well as /filter$
reivilibre Feb 22, 2023
88b9086
Add the path to the Docker Workers image
reivilibre Feb 22, 2023
3d18341
Handle the IntegrityError race
reivilibre Feb 24, 2023
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1 change: 1 addition & 0 deletions changelog.d/15134.feature
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@@ -0,0 +1 @@
Allow use of the `/filter` Client-Server APIs on workers.
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I think we also need to update:

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And yes this is annoying, see #12139.

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→ matrix-org/sytest#1331

1 change: 1 addition & 0 deletions docker/configure_workers_and_start.py
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Expand Up @@ -142,6 +142,7 @@
"^/_matrix/client/(api/v1|r0|v3|unstable/.*)/rooms/.*/aliases",
"^/_matrix/client/v1/rooms/.*/timestamp_to_event$",
"^/_matrix/client/(api/v1|r0|v3|unstable)/search",
"^/_matrix/client/(r0|v3|unstable)/user/.*/filter(/|$)",
],
"shared_extra_conf": {},
"worker_extra_conf": "",
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1 change: 1 addition & 0 deletions docs/workers.md
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Expand Up @@ -232,6 +232,7 @@ information.
^/_matrix/client/(api/v1|r0|v3|unstable)/joined_rooms$
^/_matrix/client/v1/rooms/.*/timestamp_to_event$
^/_matrix/client/(api/v1|r0|v3|unstable)/search$
^/_matrix/client/(r0|v3|unstable)/user/.*/filter(/|$)
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(Just starting a thread somewhere).

The REST servlet to add a filter:

  1. Checks the filter JSON against what's in the database and if an exact match is found it returns the same ID (i.e. you cannot have duplicate filters w/ different IDs).
  2. Otherwise it, finds the maximum current filter ID and increments by 1.
  3. Inserts the new filter.

I think this change might break step 1 -- if we have two requests to insert a filter, they can both race and return no known filter in step 1, then both insert the filter with different IDs?

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(Note the only index is UNIQUE across (user_id, filter_id).)

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You were almost right (I think) that there was a phantom write here. But funnily enough, step 1 won't be broken because step 2 will fix it. The reason I say this is:

  • we run transactions at the REPEATABLE READ isolation level by default and do not override the default for this txn
  • For your race condition to hold, Step 1 for both transactions needs to happen concurrently so neither sees the other's filter.
  • Both transactions will therefore see the same maximum filter ID in step 2 — because of REPEATABLE READ and step (1)
  • Both transactions will attempt to insert a filter with the same ID in step 3. One of them won't be able to.

When trying in psql, the second INSERT blocks until the first has committed, but then gives a unique key constraint violation. I don't think this is one of the errors we retry a transaction for, so maybe there is a problem here after all.

syn7=*> INSERT INTO user_filters (user_id, filter_id, filter_json) VALUES ('@user:syn7', 1, '{}');
ERROR:  duplicate key value violates unique constraint "user_filters_unique"
DETAIL:  Key (user_id, filter_id)=(@user:syn7, 1) already exists.

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Ah, yes good call with the isolation level we're using. 👍

I think we don't retry that, but I'm not sure. I guess using a sequence here would have been better? (Would that have solved our issues?)

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@reivilibre reivilibre Feb 24, 2023 •
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(to be fair, this exact same issue already existed if the user made two requests at once! A single worker can still run two transactions concurrently)

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Yes using a SEQUENCE or a SERIAL field would have saved this effort. I guess the original author really liked the idea of a user's filters starting at 1 and then incrementing by 1, rather than having the same space of IDs shared by all users.

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Another way of thinking of this would have been randomly generating them, like we do in a few other spots. (Incrementing IDs are usually a API smell.)

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(what's wrong with incrementing IDs?)

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(what's wrong with incrementing IDs?)

If they're scoped by user it is likely fine. If they're not then it can (potentially) leak information about other users (or your service as a whole). It also makes it easier to guess IDs.


# Encryption requests
^/_matrix/client/(r0|v3|unstable)/keys/query$
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3 changes: 1 addition & 2 deletions synapse/rest/__init__.py
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Expand Up @@ -108,8 +108,7 @@ def register_servlets(client_resource: HttpServer, hs: "HomeServer") -> None:
if is_main_process:
logout.register_servlets(hs, client_resource)
sync.register_servlets(hs, client_resource)
if is_main_process:
filter.register_servlets(hs, client_resource)
filter.register_servlets(hs, client_resource)
account.register_servlets(hs, client_resource)
register.register_servlets(hs, client_resource)
if is_main_process:
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4 changes: 2 additions & 2 deletions synapse/storage/databases/main/__init__.py
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Expand Up @@ -43,7 +43,7 @@
from .event_push_actions import EventPushActionsStore
from .events_bg_updates import EventsBackgroundUpdatesStore
from .events_forward_extremities import EventForwardExtremitiesStore
from .filtering import FilteringStore
from .filtering import FilteringWorkerStore
from .keys import KeyStore
from .lock import LockStore
from .media_repository import MediaRepositoryStore
Expand Down Expand Up @@ -99,7 +99,7 @@ class DataStore(
EventFederationStore,
MediaRepositoryStore,
RejectionsStore,
FilteringStore,
FilteringWorkerStore,
PusherStore,
PushRuleStore,
ApplicationServiceTransactionStore,
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2 changes: 0 additions & 2 deletions synapse/storage/databases/main/filtering.py
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Expand Up @@ -46,8 +46,6 @@ async def get_user_filter(

return db_to_json(def_json)


class FilteringStore(FilteringWorkerStore):
async def add_user_filter(self, user_localpart: str, user_filter: JsonDict) -> int:
def_json = encode_canonical_json(user_filter)

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