Previously we did not check HTTP semantics and it is left out for
application. Although checking is relatively easy, but they are
scattered and error prone. We have implemented these checks in our
applications and also feel they are tedious. To make application
development a bit easier, this commit adds basic HTTP semantics
validation to library code. We do following checks:
server:
* HEADERS is either request header or trailer header. Other type of
header is disallowed.
client:
* HEADERS is either zero or more non-final response header or final
response header or trailer header. Other type of header is
disallowed.
For both:
* Check mandatory pseudo header fields.
* Make sure that content-length matches the amount of DATA we
received.
If validation fails, RST_STREAM of type PROTOCOL_ERROR is issued.
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.
We make following HEADERS under priority control:
* push response HEADERS
* HEADERS submitted by nghttp2_submit_response
Currently, HEADERS submitted by nghttp2_submit_headers is not attached
to stream. This is because it may be used as non-final response
header and application may submit final response using
nghttp2_submit_response without checking non-final response header
transmission.
Allowing PRIORITY frame at anytime so that PRIORITY frame to idle
stream can create anchor node in dependency tree. In this change, we
open stream with new NGHTTP2_STREAM_IDLE state, which is linked in
session->closed_stream_head and is treated as if it is closed stream.
One difference is that if the stream is opened, we remove it from
linked list and change the state to the appropriate one. To O(1)
removal from linked list, we change session->closed_stream_head to
doubly linked list.
This change fixes the bug that stream is out of dependency tree if the
number of nodes in a dependency tree which we add new node to is
already maximum (NGHTTP2_MAX_DEP_TREE_LENGTH) and the number of
maximum concurrent streams is more than more than
NGHTTP2_MAX_DEP_TREE_LENGTH.
* Add NGHTTP2_HTTP_1_1_REQUIRED error code
* Allow transmission of WINDOW_UPDATE on reserved (remote)
* Allow reception of WINDOW_UPDATE on reserved (local)
* Treat frame larger than MAX_FRAME_SIZE as FRAME_SIZE_ERROR
ALPN identifier is still h2-14 to continue interop, since draft-14 and
-15 are binary compatible. The new error code was added in draft-15,
but HTTP/2 allows extensions can freely add new error code, so it is
not a problem.
This also means that at least one stream whose dpri is
NGHTTP2_STREAM_DPRI_TOP exists, its siblings descendants have no
chance to send streams, even if their parent stream has
NGHTTP2_STREAM_DPRI_NODATA.
Previously when nghttp2_stream_resume_deferred_data() is called,
deferred flags in stream->flags are all cleared. This is not ideal
because if application returned NGHTTP2_ERR_DEFERRED, and also that
stream is deferred by flow control, then all flags are cleared and
read callback will be invoked again. This commit fixes this issue.
This changes error condition of nghttp2_session_resume_data().
Previously we return error if stream was deferred by flow control.
Now we don't return error in this case. We just clear
NGHTTP2_FLAG_DEFERRED_USER and if still
NGHTTP2_FLAG_DEFERRED_FLOW_CONTROL is set, just return 0.
Previously when connection level remote flow control window gets 0, we
mark the stream having DATA frame with
NGHTTP2_STREAM_FLAG_DEFERRED_FLOW_CONTROL. When connection level
WINDOW_UPDATE is received, we checks all existing streams, including
closed ones, and call nghttp2_stream_resume_deferred_data(). The
profiler shows this is expensive.
Now we prepare dedicated priority queue for DATA frames. And we don't
mark stream with NGHTTP2_STREAM_FLAG_DEFERRED_FLOW_CONTROL when DATA
cannot be sent solely due to connection level flow control. Instead,
we just queue DATA item to queue. We won't pop DATA item from queue
when connection level remote window size is 0. This way, we avoid the
expensive operation for all streams when WINDOW_UPDATE is arrived.
Previously we missed the case where stream->data_item is not deleted
and it caused leak. Now stream->data_item is properly deleted when
session is deleted. We decided not to delete data_item in
nghttp2_stream_free() since we need nghttp2_session to decide whether
data_item should be deleted or not there.
By default, nghttp2 library only handles HTTP/2 frames and does not
recognize first 24 bytes of client connection preface. This design
choice is done due to the fact that server may want to detect the
application protocol based on first few bytes on clear text
communication. But for simple servers which only speak HTTP/2, it is
easier for developers if nghttp2 library takes care of client
connection preface.
If this option is used with nonzero val, nghttp2 library checks first
24 bytes client connection preface. If it is not a valid one,
nghttp2_session_recv() and nghttp2_session_mem_recv() will return
error NGHTTP2_ERR_BAD_PREFACE, which is fatal error.
Tatsuhiro Tsujikawa
Alexis La Goutte