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. 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
