HTTP/3 server push: handling of lost PUSH_PROMISE

[Tatsuhiro Tsujikawa <[e-mail]>]

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