Better backpressure management. #352
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artemredkin
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Motivation: Users of the HTTPClientResponseDelegate expect that the event loop futures returned from didReceiveHead and didReceiveBodyPart can be used to exert backpressure. To be fair to them, they somewhat can. However, the TaskHandler has a bit of a misunderstanding about how NIO backpressure works, and does not correctly manage the buffer of inbound data. The result of this misunderstanding is that multiple calls to didReceiveBodyPart and didReceiveHead can be outstanding at once. This would likely lead to severe bugs in most delegates, as they do not expect it. We should make things work the way delegate implementers believe it works. Modifications: - Added a buffer to the TaskHandler to avoid delivering data that the delegate is not ready for. - Added a new "pending close" state that keeps track of a state where the TaskHandler has received .end but not yet delivered it to the delegate. This allows better error management. - Added some more tests. - Documented our backpressure commitments. Result: Better respect for backpressure. Resolves swift-server#348
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Motivation:
Users of the HTTPClientResponseDelegate expect that the event loop
futures returned from didReceiveHead and didReceiveBodyPart can be used
to exert backpressure. To be fair to them, they somewhat can. However,
the TaskHandler has a bit of a misunderstanding about how NIO
backpressure works, and does not correctly manage the buffer of inbound
data.
The result of this misunderstanding is that multiple calls to
didReceiveBodyPart and didReceiveHead can be outstanding at once. This
would likely lead to severe bugs in most delegates, as they do not
expect it.
We should make things work the way delegate implementers believe it
works.
Modifications:
delegate is not ready for.
the TaskHandler has received .end but not yet delivered it to the
delegate. This allows better error management.
Result:
Better respect for backpressure.
Resolves #348