Implement the redecryption logic in the event cache #5746

poljar · 2025-10-03T14:34:59Z

This is very much a WIP PR. Eventually it will get split into different smaller PRs.

Things that still need to be addressed:

Don't load all events for a certain room when attempting to redecrypt events.
Decide what to do when the room key stream has lagged.
Handle the room key withheld stream as well.
Connect the UTD hook to the new redecryptor.
Port the timeline redecryption tests.
Completely remove the timeline redecryption logic. (this has been pushed to a separate PR).

codspeed-hq · 2025-10-03T14:54:18Z

CodSpeed Performance Report

Merging #5746 will not alter performance

_{Comparing poljar/event-cache/redecryptor (9508675) with main (f702364)}

Summary

✅ 50 untouched

codecov · 2025-11-07T14:29:15Z

Codecov Report

❌ Patch coverage is 84.30493% with 70 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.59%. Comparing base (c064ca8) to head (9508675).
⚠️ Report is 59 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
crates/matrix-sdk/src/event_cache/redecryptor.rs	83.60%	57 Missing and 13 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5746      +/-   ##
==========================================
- Coverage   88.61%   88.59%   -0.03%     
==========================================
  Files         361      362       +1     
  Lines      102160   102604     +444     
  Branches   102160   102604     +444     
==========================================
+ Hits        90532    90903     +371     
- Misses       7410     7469      +59     
- Partials     4218     4232      +14

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… stream

…dates

This allows us to properly calculate the push actions.

This is necessary because both the timeline and the event cache attempt to redecrypt events currently. This will change once only the event cache handles this task.

Hywan

Wow. That was an impressive set of patches.

How a simple problem gently piles more and more complexity. The resulting code is not complex however, and that's really great. Thank you for the great documentation, including inline documentation!

I've left a couple of feedback, but nothing requiring a huge change.

crates/matrix-sdk/src/event_cache/room/mod.rs

crates/matrix-sdk/src/event_cache/redecryptor.rs

Hywan · 2025-11-11T07:16:48Z

crates/matrix-sdk/src/event_cache/redecryptor.rs

+        let (room_cache, _drop_handles) = self.for_room(room_id).await?;
+        let mut state = room_cache.inner.state.write().await;
+
+        let event_ids: Vec<_> = events.iter().map(|(event_id, _)| event_id).collect();


Can we compute event_ids if and only if trace! is enabled? Maybe with tracing::enabled!?

Alternatively, I confess it's a bit more logs but, I would put the trace! inside the loop, closer to replace_event_at, because it's where we are really replacing the event. Thoughts?

Can we compute event_ids if and only if trace! is enabled? Maybe with tracing::enabled!?

Sadly we can't, as the event IDs are sent out as part of the RedecryptorReport, that's also the reason why we're cloning it in later parts of this patchset:

a2f89e8#diff-5c3b83b7260e87e30c1b6b3bfad8b5be005c31d142b825e75ff0e047680c2923R201

Alternatively, I confess it's a bit more logs but, I would put the trace! inside the loop, closer to replace_event_at, because it's where we are really replacing the event. Thoughts?

Hmm, I'm really worried about log spam here. If you're suggesting this because you want to avoid the building of the BTreeSet then I would say that this comment resolved itself since the BTreeSet is necessary for the RedecryptorReport.

crates/matrix-sdk/src/event_cache/redecryptor.rs

crates/matrix-sdk/src/event_cache/room/mod.rs

crates/matrix-sdk/src/event_cache/redecryptor.rs

… better

… fetching events

… task

…n the r2d2 docs

…uples

poljar · 2025-11-13T11:05:07Z

I'm going to merge this since you approved it. If you feel like there's more to do here please shout and I'll handle it in a separate PR.

poljar force-pushed the poljar/event-cache/redecryptor branch from 54f3b5f to 0f4bbe5 Compare November 7, 2025 14:06

poljar marked this pull request as ready for review November 7, 2025 14:10

poljar requested a review from a team as a code owner November 7, 2025 14:10

poljar requested review from stefanceriu and removed request for a team November 7, 2025 14:10

poljar closed this Nov 7, 2025

poljar reopened this Nov 7, 2025

feat(event cache): Add a method to access the linked chunk mutably

d3c839a

poljar force-pushed the poljar/event-cache/redecryptor branch from 0f4bbe5 to 9f1aff6 Compare November 7, 2025 14:14

feat(event cache): Create the redecryptor

8103b9c

poljar force-pushed the poljar/event-cache/redecryptor branch from 9f1aff6 to c21daed Compare November 7, 2025 14:35

poljar added 12 commits November 7, 2025 15:38

test(redecryptor): Add a test to show that the redecryptor works

f2cc6c6

feat(redecryptor): Rejigger things so we can relisten to the room key…

e934235

… stream

doc(event cache): Document the redecryptor

5c3bca8

feat(event cache): Enable the redecryptor in the event cache

4ed2393

feat: Redecryptor start to send out redecryptor reports

a2f89e8

feat(redecryptor): Let the redecryptor listen to room key withheld up…

621d936

…dates

feat(redecryptor): Use the room to redecrypt events

3a0a5b9

This allows us to properly calculate the push actions.

feat(redecryptor): More precise logs for the redecryption attempts

7e98858

feat(redecryptor): Post-process the events once they are replaced

4109fdd

test(redecryptor): More tests for the redecryptor

4a519bd

test(timeline): Workarounds to get the timeline tests passing

4c4cd41

This is necessary because both the timeline and the event cache attempt to redecrypt events currently. This will change once only the event cache handles this task.

docs(redecryptor): Document the redecryptor a bit more

d7d4730

poljar force-pushed the poljar/event-cache/redecryptor branch from c21daed to d7d4730 Compare November 7, 2025 14:38

stefanceriu requested review from Hywan and removed request for stefanceriu November 10, 2025 09:51

Hywan approved these changes Nov 11, 2025

View reviewed changes

fix(event-cache): Limit the visibility of room_linked_chunk_mut a bit…

d2eab60

… better

poljar added 7 commits November 12, 2025 12:54

fix(event-cache): Don't hold on to the event cache locks as long when…

84a21a4

… fetching events

chore(redecryptor): Use relative imports more often

3ad7062

docs(redecryptor): Add some docs to the Redecryptor struct itself

717f016

chore(redecryptor): Time how long it takes to replace UTDs

952c5af

refactor(redecryptor): Use an abort handle to manage the redecryption…

f9c23b3

… task

chore(event-cache): Limit the visibility of post_process_new_events

38df621

chore(redecryptor): Ensure the upgrade_event_cache method is inlined

2e9e9ae

poljar requested a review from Hywan November 12, 2025 12:45

poljar added 3 commits November 13, 2025 11:59

docs(redecryptor): Clarify that we're talking about the UI timeline i…

913ebe9

…n the r2d2 docs

refactor(redecryptor): Add some type aliases for the event ID/event t…

0d08ed0

…uples

fix(redecryptor): Early return if we don't have any events to process

9508675

poljar force-pushed the poljar/event-cache/redecryptor branch from c3fb01d to 9508675 Compare November 13, 2025 11:05

poljar enabled auto-merge November 13, 2025 11:05

poljar merged commit 4fbc83a into main Nov 13, 2025
51 checks passed

poljar deleted the poljar/event-cache/redecryptor branch November 13, 2025 11:19

poljar mentioned this pull request Nov 14, 2025

Remove the redecryption logic in the timeline #5869

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