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warp: fewer timer operations around streaming response bodies #1098

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warp: fewer timer operations around streaming response bodies #1098

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22 changes: 16 additions & 6 deletions warp/Network/Wai/Handler/Warp/Response.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -257,6 +257,12 @@ sendRsp conn _ th ver s hs _ maxRspBufSize _ (RspBuilder body needsChunked) = do

sendRsp conn _ th ver s hs _ _ _ (RspStream streamingBody needsChunked) = do
header <- composeHeaderBuilder ver s hs needsChunked
-- Make sure the timeout is armed for the whole streaming section,
-- so that the per-fragment 'T.tickle' below has effect. Normally
-- the handle is already active (the respond callback resumed it),
-- making this a cheap no-op; it matters for streaming responses
-- sent from an exception handler, where the handle is still paused.
T.resume th
(recv, finish) <-
newByteStringBuilderRecv $
reuseBufferStrategy $
Expand Down Expand Up @@ -408,14 +414,18 @@ sendRspFile404 conn ii th ver hs0 rspidxhdr maxRspBufSize method =
-- | Use 'connSendAll' to send this data while respecting timeout rules.
sendFragment :: Connection -> T.Handle -> ByteString -> IO ()
sendFragment Connection{connSendAll = send} th bs = do
T.resume th
T.tickle th
send bs
T.pause th

-- We pause timeouts before passing control back to user code. This ensures
-- that a timeout will only ever be executed when Warp is in control. We
-- also make sure to resume the timeout after the completion of user code
-- so that we can kill idle connections.
-- The timeout stays armed during the whole streaming section (see the
-- 'T.resume' in the RspStream case of 'sendRsp'); each fragment merely
-- tickles it, which the rate limiter in time-manager makes nearly free.
-- Compared to the previous resume/send/pause per fragment this keeps
-- slowloris protection active while the fragment is being sent. The
-- flip side is that user code producing the next fragment now runs with
-- the timeout armed, so a streaming body that emits nothing for a full
-- timeout period is killed, whereas it previously had the timeout
-- paused between fragments.

----------------------------------------------------------------

Expand Down