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Ensure that all state event IDs are included in the added section when rewriting state (#2725)

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This should hopefully fix an entire class of problems where components
downstream from the roomserver (i.e. the sync API) could just lose a
whole bunch of state after a rewrite operation like a federated join.

The root of the bug is that we set `RewritesState` in the output event
which instructs downstream components to purge their copy of any room
state, but then didn't send the entire state snapshot in
`adds_state_event_ids` so the downstream state ends up being incomplete
as a result.
This commit is contained in:
Neil Alexander 2022-09-16 10:35:32 +01:00 committed by GitHub
parent a5f8c07184
commit fc1d8e479b
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1 changed files with 21 additions and 10 deletions
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31
roomserver/internal/input/input_latest_events.go
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@ -264,16 +264,27 @@ func (u *latestEventsUpdater) latestState() error {
return fmt.Errorf("roomState.CalculateAndStoreStateAfterEvents: %w", err)
}
// Now that we have a new state snapshot based on the latest events,
// we can compare that new snapshot to the previous one and see what
// has changed. This gives us one list of removed state events and
// another list of added ones. Replacing a value for a state-key tuple
// will result one removed (the old event) and one added (the new event).
u.removed, u.added, err = roomState.DifferenceBetweeenStateSnapshots(
ctx, u.oldStateNID, u.newStateNID,
)
if err != nil {
return fmt.Errorf("roomState.DifferenceBetweenStateSnapshots: %w", err)
// Include information about what changed in the state transition. If the
// event rewrites the state (i.e. is a federated join) then we will simply
// include the entire state snapshot as added events, as the "RewritesState"
// flag in the output event signals downstream components to purge their
// room state first. If it doesn't rewrite the state then we will work out
// what the difference is between the state snapshots and send that. In all
// cases where a state event is being replaced, the old state event will
// appear in "removed" and the replacement will appear in "added".
if u.rewritesState {
u.removed = []types.StateEntry{}
u.added, err = roomState.LoadStateAtSnapshot(ctx, u.newStateNID)
if err != nil {
return fmt.Errorf("roomState.LoadStateAtSnapshot: %w", err)
}
} else {
u.removed, u.added, err = roomState.DifferenceBetweeenStateSnapshots(
ctx, u.oldStateNID, u.newStateNID,
)
if err != nil {
return fmt.Errorf("roomState.DifferenceBetweenStateSnapshots: %w", err)
}
}
if removed := len(u.removed) - len(u.added); !u.rewritesState && removed > 0 {