Fix #8518 (sync requests being cached wrongly on timeout) (#9358)

This fixes #8518 by adding a conditional check on `SyncResult` in a function when `prev_stream_token == current_stream_token`, as a sanity check. In `CachedResponse.set.<remove>()`, the result is immediately popped from the cache if the conditional function returns "false".

This prevents the caching of a timed-out `SyncResult` (that has `next_key` as the stream key that produced that `SyncResult`). The cache is prevented from returning a `SyncResult` that makes the client request the same stream key over and over again, effectively making it stuck in a loop of requesting and getting a response immediately for as long as the cache keeps those values.

Signed-off-by: Jonathan de Jong <jonathan@automatia.nl>

1 files changed, 1 insertions, 0 deletions

diff --git a/changelog.d/9358.misc b/changelog.d/9358.misc
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+Added a fix that invalidates cache for empty timed-out sync responses.
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