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fix(users/Profpatsch/openlab-tools): return 304 iff cache is same

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Now this is getting cool. After 5 minutes we will ask the backend
again (which takes like 3 seconds), but then we compare the old cached
result with the new result and only send it back to the client iff it
changed.

So the client will still have to wait for the roundtrip time, but
doesn’t have to pay for the content. Plus, it gets some info that
upstream hasn’t been updated.

Change-Id: I6dba40321949da5da6a16b2e799d939573c77ba7
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9811
Autosubmit: Profpatsch <mail@profpatsch.de>
Reviewed-by: Profpatsch <mail@profpatsch.de>
Tested-by: BuildkiteCI
This commit is contained in:
Profpatsch 2023-10-20 20:31:48 +02:00 committed by clbot
parent e5a44334fe
commit 7ec7f92812
1 changed files with 14 additions and 6 deletions
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20
users/Profpatsch/openlab-tools/src/OpenlabTools.hs
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@ -350,18 +350,26 @@ newCache result = do
let lastModified = until
newTVarIO $ Cache {..}
updateCache :: (NFData a) => SecondTime -> TVar (Cache a) -> a -> STM (Cache a)
updateCache :: (NFData a, Eq a) => SecondTime -> TVar (Cache a) -> a -> STM (Cache a)
updateCache now cache result' = do
-- make sure we don’t hold onto the world by deepseq-ing and evaluating to WHNF
let !result = deepseq result' result'
let until = mkSecondTime $ (5 * 60) `addUTCTime` now.unSecondTime
let lastModified = now
let !updated = Cache {..}
_ <- writeTVar cache $! updated
pure updated
!toWrite <- do
old <- readTVar cache
-- only update the lastModified time iff the content changed (this is helpful for HTTP caching with If-Modified-Since)
if old.result == result
then do
let lastModified = old.lastModified
pure $ Cache {..}
else do
let lastModified = now
pure $ Cache {..}
_ <- writeTVar cache $! toWrite
pure toWrite
-- | Run the given action iff the cache is stale, otherwise just return the item from the cache.
updateCacheIfNewer :: (MonadUnliftIO m, NFData b) => SecondTime -> TVar (Cache b) -> m b -> m (Cache b)
updateCacheIfNewer :: (MonadUnliftIO m, NFData b, Eq b) => SecondTime -> TVar (Cache b) -> m b -> m (Cache b)
updateCacheIfNewer now cache act = withRunInIO $ \runInIO -> do
old <- readTVarIO cache
if old.until < now