Hi, On Wed, Jul 28, 2021 at 9:21 AM Kazuho Oku <[email protected]> wrote:
> Tatsuhiro, thank you for raising the issue. > > I actually wonder if the example being provided is a tip of an iceberg - > is the problem related to FIN at all? > > Let's consider the following pattern: > > * client sends a request > * server starts sending response, alongside a PUSH_PROMISE > * in addition, server initiates a push stream and starts sending data > * server-sent packets carrying the PUSH_PROMISE frame are lost > * client decides to cancel the request and sends RESET_STREAM & > STOP_SENDING > * server continues sending the contents of the push stream > > I could well be missing some aspects of push, but to me, the problem looks > like the lack of delivery guarantee of PUSH_PROMISE frames. > > My initial example is intentionally nallowed down to the specific case so that client does not send STOP_SENDING, but yes, essentially, you are correct that the inherent problem is that server push design relays on the PUSH_PROMISE which can be lost. Best regards, Tatsuhiro Tsujikawa > > 2021年7月27日(火) 17:56 Tatsuhiro Tsujikawa <[email protected]>: > >> Hi, >> >> On Tue, Jul 27, 2021 at 3:31 PM Martin Thomson <[email protected]> wrote: >> >>> This is a case where QUIC processing something doesn't imply HTTP/3 >>> processing something. QUIC read the data and "processed" it. HTTP/3 >>> decided not to handle it deliberately, and the PUSH_PROMISE fell between >>> the cracks. >>> >>> One "solution" is to insist that endpoints attempt to process streams >>> for this stuff if they decide to discard responses. This is like how in >>> HTTP/2 you still have to update the HPACK table after resetting a stream. >>> It's awkward, but I think that it would work if data is available. I don't >>> think that there is any case in which data is unavailable to the client but >>> the server doesn't receive STOP_SENDING. >>> >>> >> It is indeed awkward that QUIC stack has to pass stream data all the way >> to the end of the stream (or sees RESET_STREAM or closed) to HTTP/3 client >> even after it requested stopping reading. And the HTTP/3 client has to >> process it just for PUSH_PROMISE. Does any implementation do this? >> >> Sending STOP_SENDING alone is not enough. As I wrote in the previous >> post, by the time STOP_SENDING is received by the HTTP/3 server, it has >> finished processing the pushed stream and forgets it. I imagine that if >> QUIC stack provides BSD socket-like interface and HTTP/3 server writes all >> data and can clear the memory without waiting for an acknowledgement. >> >> Best regards, >> Tatsuhiro Tsujikawa >> >> >>> On Tue, Jul 27, 2021, at 13:01, Tatsuhiro Tsujikawa wrote: >>> > Hi, >>> > >>> > It looks like in certain conditions, client is unable to process pushed >>> > stream and leaves it in unprocessable state indefinitely. >>> > >>> > Consider that client opens bidi stream and server sends PUSH_PROMISE >>> > and completes the response body which is very short (just a single >>> packet >>> > or two). For some reason, client has decided to stop reading >>> > response, but FIN is seen (data recvd state), and does not send >>> > STOP_SENDING because it is not required (RFC mentions that it has a >>> > little value to send STOP_SENDING in data recvd state and >>> > unnecessary). Client discards all stream data without handing it over >>> > to application, so PUSH_PROMISE is not processed. Client does not >>> > know the push ID. Because STOP_SENDING is not sent, server has no >>> signal >>> > which indicates PUSH_PROMISE is not processed, and opens a pushed >>> > stream. Client receives pushed stream, but unable to find the >>> > corresponding PUSH_PROMISE. It holds pushed stream until it sees >>> > PUSH_PROMISE, but it never come. This causes the pushed stream to be >>> held by >>> > client indefinitely. >>> > >>> > Even if client sends STOP_SENDING to the bidi stream, it might not >>> > work if server finishes sending stream data and a pushed stream and >>> > forgets them before receiving STOP_SENDING. >>> > >>> > Best regards, >>> > Tatsuhiro Tsujikawa >>> >>> > > -- > Kazuho Oku >
