Gracefully handle when rooms in space pagination token expires - Unable to paginate rooms in the space `/hierarchy` -> 400 `Unknown pagination token`

Steps to reproduce

1. Go to the space home
2. Scroll and paginate the rooms in the space until you get stuck
   • Maybe this matters, I was also searching/filtering for a specific room before that
3. Notice Failed to load list of rooms. message in Element and the underlying network request errors:

GET https://matrix-client.matrix.org/_matrix/client/v1/rooms/!OJBlkJuUrsKnqtNnTi%3Amatrix.org/hierarchy?suggested_only=false&from=iDciuFbCVinPIwUGYtUzQLHO&limit=20 -> ❌ 400 bad request

{"errcode":"M_INVALID_PARAM","error":"Unknown pagination token"}

---

I first created an issue in the Synapse tracker thinking the bad pagination token was being returned from the homeserver but it turns out there was just a 5 minute gap between pagination requests and Synapse only keeps track of pagination tokens within a 5 minute window.

What I think happened is this:

1. Go to the space home
2. Search/filter for a specific room
3. Wait for the spinner appearing over and over for each /hierarchy request
   • It feels like at a certain point, the app gave up on paginating the rooms for some reason even though the loading spinner was still present. So I was waiting around even though it was doing nothing and pagination token expired behind the scenes. Is there something in the logs indicating why it would stop paginating?
4. Get tired of waiting and clear the search/filter which reveals all rooms fetched so far
5. Scroll down to the bottom of the list and try to paginate more
6. Run into the Failed to load list of rooms. error and underlying network error /hierarchy ❌ 400 bad request

---

I think this is the last request Element made while I was searching/filtering even though it had a next_batch, and the spinner was still showing.

GET https://matrix-client.matrix.org/_matrix/client/v1/rooms/!OJBlkJuUrsKnqtNnTi%3Amatrix.org/hierarchy?suggested_only=false&from=rCkHRkRndYnCOIInVookuxrI&limit=20 -> ✅ 200 OK

date: Tue, 10 May 2022 19:02:38 GMT (response header)

{ "rooms": [...], "next_batch":"iDciuFbCVinPIwUGYtUzQLHO" }

Then 7 minutes later, I cleared the search/filter and tried paginating manually by scrolling to the bottom of the list:

GET https://matrix-client.matrix.org/_matrix/client/v1/rooms/!OJBlkJuUrsKnqtNnTi%3Amatrix.org/hierarchy?suggested_only=false&from=iDciuFbCVinPIwUGYtUzQLHO&limit=20 -> ❌ 400 Bad request

date: Tue, 10 May 2022 19:08:58 GMT (response header)

{"errcode":"M_INVALID_PARAM","error":"Unknown pagination token"}

Outcome

What did you expect?

1. Element keeps paginating while the loading spinner is visible when searching/filtering
2. Element gracefully fetches a new pagination token after the 5 minute expiration (we have to paginate from the beginning again)
3. All of these problems are exacerbated because searching a space is painfully slow and there is no server endpoint to do it directly.
   • https://github.com/matrix-org/synapse/issues/11694
   • https://github.com/vector-im/element-web/issues/17550

What happened instead?

• Element stopped paginating and showed an error: Failed to load list of rooms..
• Element also continuously retries the request over and over with no back-off.

Logs: https://github.com/matrix-org/element-web-rageshakes/issues/12829

Operating system

Windows 10

Browser information

Chrome Version 100.0.4896.127

URL for webapp

https://develop.element.io/

Application version

Element version: 479d4bf64d97-react-14127c777b87-js-34cfa511049e Olm version: 3.2.8

Homeserver

matrix.org

Will you send logs?

Yes -> https://github.com/matrix-org/element-web-rageshakes/issues/12829

[robintown]

Downgrading this to occasional and minor, since I don’t believe this happens super regularly, and the workaround is to reopen the space landing page and try again

[turt2live]

per https://github.com/matrix-org/synapse/issues/12697#issuecomment-1122947619 I am reopening this as a client-side problem.