2021年7月28日(水) 11:53 Tatsuhiro Tsujikawa <[email protected]>:
> 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. > Thank you for checking. I've opened https://github.com/quicwg/base-drafts/issues/4930. As stated on the issue, I think that lack of delivery guarantee is not only a problem for PUSH_PROMISE, but also for Push Stream Header. > 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 >> > -- Kazuho Oku
