Previously we did not handle the situation where RST_STREAM is
submitted against a stream while requet HEADERS which opens that
stream is still in queue. Due to max concurrent streams limit,
RST_STREAM is sent first, and then request HEADERS, which effectively
voids RST_STREAM.
In this commit, we checks RST_STREAM against currently pending request
HEADERS in queue and if stream ID matches, we mark that HEADERS as
canceled and RST_STREAM is not sent in this case. The library will
call on_frame_not_sent_callback for the canceled HEADERS with error
code from RST_STREAM.
Previously we use 16K - 9 bytes (frame header) as frame payload size
so that whole frame fits in 1 TLS record size (16K). But it turns out
that in proxy use case, we will receive 16K payload from backend and
we have to split it into 2 odd looking frames (16K - 9 and 9), and
latter is highly inefficient. To avoid this situation, we decided to
use min frame payload size to 16K. Since we operates on TLS as stream
of data, we are not so much restricted in its record size.
Previously we treat stream in NGHTTP2_STREAM_RESERVED state specially,
that is we don't increment or decrement streams counts if stream is in
that state. Because of this, we don't change the stream state to
NGHTTP2_STREAM_CLOSING if stream is in NGHTTP2_STREAM_RESERVED. But
it turns out that it causes a problem. If client canceled pushed
stream before push response HEADERS, stream is still in
NGHTTP2_STREAM_RESERVED state. If push response HEADERS arrived in
this state, library happily accepts it and passed to application.
With this commit, this bug was corrected. We now change stream state
to NGHTTP2_STREAM_CLOSING even if it was in NGHTTP2_STREAM_RESERVED
state. We now use NGHTTP2_STREAM_FLAG_PUSH to determine whether we
have to increase/decrase stream count.
nghttp2_submit_shutdown_notice() is used to notify the client that
graceful shutdown is started. We expect that after this call, the
server application should send another GOAWAY using
nghttp2_submit_goaway() with appropriate last_stream_id. In this
commit, we also added nghttp2_session_get_last_proc_stream_id(), which
can be used as last_stream_id parameter.
This commit implements graceful shutdown in nghttpx. The integration
test for graceful shutdown is also added.
This change makes sure that GOAWAY which terminates session is
immediately sent without blocked by other frames.
NGHTTP2_ERR_SESSION_CLOSING library error code was added to indicate
this situation to callback.
Initially, we use nghttp2_stream.data_item to refer only item with
DATA frame. But recently we use it to refer HEADERS frame as well.
So it is better to call just item rather than data_item. This applies
to all related functions.
Previously session_after_frame_sent is called after we detected all
data is sent. In nghttp2_session_mem_send, we only detect it in the
next call of the function. It means that if a frame data bearing
END_STREAM is on flight to the peer as a result of
nghttp2_session_mem_send, peer may get that data and knows the stream
closure and issues new stream. We may receive this new stream before
the next nghttp2_session_mem_send call, which means that we may
incorrectly assumes that peer violates maximum concurrent stream
limit. To fix this issue, we separate session_after_frame_sent into 2
functions: session_after_frame_sent1 and session_after_frame_sent2.
session_after_frame_sent1 handles on_frame_send_callback and stream
closure and we call this early in nghttp2_session_mem_send. This
makes number of streams are synchronized correctly with peer.
Previously we handle idle streams as closed streams. We only keeps
sum of closed streams and active streams under max concurrent streams
limit, idle streams gets deleted earlier than client expects.
In this change, idle streams are kept in separate list and not handled
as closed streams. To mitigate possible attack vector to make
unlimited idle streams, we cap the number of idle streams in a half of
max concurrent streams. This is arbitrary choice. It may be adjusted
in the future when we have interop experience.
nghttp2_mem structure is introduced to hold custom memory allocator
functions and user supplied pointer. nghttp2_mem object can be passed
to nghttp2_session_client_new3(), nghttp2_session_server_new3(),
nghttp2_hd_deflate_new2() and nghttp2_hd_inflate_new2() to replace
standard malloc(), free(), calloc() and realloc(). nghttp2_mem
structure has user supplied pointer mem_user_data which can be used as
per session/object memory pool.
This change will utilize last_stream_id in GOAWAY extensively. When
GOAWAY is received with a last_stream_id, library closes all outgoing
streams whose stream_id > received last_stream_id.
nghttp2_on_stream_callback is called for each stream to be closed.
When GOAWAY is sent with a last_stream_id, library closes all incoming
streams whose stream_id > sent last_stream_id.
nghttp2_on_stream_callback is called for each stream to be closed.
If stream ID is not idle, it might be valid HEADERS. If stream ID is
idle, it is invalid regardless stream ID is even or odd, since client
is not expected to recieve request from server. nghttp2 library
historically allows this, but now we forbids this.
Tatsuhiro Tsujikawa
Alexis La Goutte