RFC 7540 does not enforce any limit on the number of incoming reserved
streams (in RFC 7540 terms, streams in reserved (remote) state). This
only affects client side, since only server can push streams.
Malicious server can push arbitrary number of streams, and make
client's memory exhausted. The new option,
nghttp2_set_max_reserved_remote_streams, can set the maximum number of
such incoming streams to avoid possible memory exhaustion. If this
option is set, and pushed streams are automatically closed on
reception, without calling user provided callback, if they exceed the
given limit. The default value is 200. If session is configured as
server side, this option has no effect. Server can control the number
of streams to push.
The intention of this stream API is give server application about
stream dependency information, so that it can utilize it for better
scheduling of stream processing. We have no plan to add object
oriented API based on stream object.
We now use priority queue per stream, which contains the stream which
has ready to send a frame, or one of its descendants have a frame to
send. We maintain invariant that if a stream is queued, then its
ancestors are also queued (except for root). When we re-schedule
stream after transmission, we re-schedule all ancestors, so that
streams on the other path can get a chance to send. This is basically
the same mechanism h2o project uses, but there are differences in the
details.
Previously, the number of stream in one dependency tree (not including
root) is limited to 120. This is due to the fact that we use
recursive calls to traverse trees. Now we replaced recursive calls
with loop, we can remove this limitation. Also now all streams are
descendant of root stream, rather than linked list of individual
subtree root.
This commit fixes the bug that DATA is not consumed if
nghttp2_http_on_data_chunk is failed. It also simplify the handling
of missing stream in NGHTTP2_IB_READ_DATA state.
This commit documents NGHTTP2_ERR_DATA_EXIST also occurs if HEADERS
has been already attached to stream too. This commit also fixes
possible assertion error, and now nghttp2_submit_headers() and
nghttp2_submit_response() may return NGHTTP2_ERR_DATA_EXIST. But we
recommend to use nghttp2_submit_request() and
nghttp2_submit_response(), and using them will avoid this error.
Previously, we did not handle PRIORITY frame which depends on itself
and for idle stream. As a result, nghttp2_session_mem_recv (or
nghttp2_session_recv) returne NGHTTP2_ERR_NOMEM. The error code was
still misleading. It was not out of memory, and we failed to insert
hash map because of duplicated key, which was treated as out of
memory. This commit fixes this issue, by explicitly checking
dependency for incoming PRIORITY for all cases.
When we know that stream is closed at time we read DATA frame header,
we use NGHTTP2_IB_IGN_DATA, and consume data for connection if
nghttp2_option_set_no_auto_window_update() is used. However, if
stream is closed while we are in NGHTTP2_IB_READ_DATA, those bytes are
not consumed for connection, nor notified to application via callback,
so it eventually fills up connection window and connection will
freeze. This commit fixes this issue by consuming these data for
connection when stream is closed or does not exist.
The private global variable nghttp2_enable_strict_preface is also
marked as NGHTTP2_EXTERN, but it is test purpose only (test with
.dll), and not part of public API. It could be removed in the future
release.
After reviewing codebase, only queue for DATA frames requires
priorities. Other frames can be replaced multiple linear queues.
Replacing priority queue with linear queue allows us to simplify
codebase a bit; for example, now nghttp2_session.next_seq is gone.
Since application most likely allocates the stream object in
nghttp2_on_begin_headers_callback, it is desirable to handle its
failure as stream error. But previously it only signals success or
fatal error. Submitting RST_STREAM does not prevent
nghttp2_on_header_callback from being invoked. This commit improves
this situation by allowing NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE from
nghttp2_on_begin_headers_callback. If that value is returned, library
submits RST_STREAM with error code INTERNAL_ERROR, and
nghttp2_on_header_callback and nghttp2_on_frame_recv_callback for that
frame are not invoked. Note that for PUSH_PROMISE frame, the stream
to be reset is promised stream.
We rewrite static header table handling in nghttp2_hd.c. We expand
nghttp2_token to include all static header table entries, and fully
use them in header compression and decompression. The lookup function
is now located in nghttp2_hd.c. We add new nghttp2_hd_inflate_hd2()
function to export token value for header name, then we pass it to
nghttp2_http_on_header function, so that we don't have to look up
token there. We carefully set enum value of token to static table
index, so looking up static table is now O(1), assuming we have token.
The existing nghttp2_session_consume() affects both connection and
stream level flow control windows. The new functions only affects
either connection or stream. There is some interesting use cases.
For example, we may want to pause a stream by not sending
WINDOW_UPDATE, meanwhile we want to continue to process other streams.
In this case, we use nghttp2_session_consume_connection() to tell
library that only connection level window is recovered. The relevant
discussion: https://code.google.com/p/chromium/issues/detail?id=473259
Previously nghttp2_session_send() and nghttp2_session_mem_send() did
not send 24 bytes client magic byte string (MAGIC). We made
nghttp2_session_recv() and nghttp2_session_mem_recv() process MAGIC by
default, so it is natural to make library send MAGIC as well. This
commit makes nghttp2_session_send() and nghttp2_session_mem_send()
send MAGIC. This commit also replace "connection preface" with
"client magic", since we call MAGIC as "connection preface" but it is
just a part of connection preface. NGHTTP2_CLIENT_CONNECTION_PREFACE
macro was replaced with NGHTTP2_CLIENT_MAGIC. The already deprecated
NGHTTP2_CLIENT_CONNECTION_HEADER macro was removed permanently.
nghttp2_option_set_no_recv_client_preface() was renamed as
nghttp2_option_set_no_recv_client_magic(). NGHTTP2_ERR_BAD_PREFACE
was renamed as NGHTTP2_ERR_BAD_CLIENT_MAGIC.
Since HTTP/2 spec requires for client to send connection preface, it
is reasonable to make this option enabled by default. It is still a
use case to disable this, so replace this option with
nghttp2_option_set_no_recv_client_preface().
To avoid buffer copy in nghttp2_data_source_read_callback, this commit
introduces NGHTTP2_DATA_FLAG_NO_COPY and nghttp2_send_data_callback.
By using NGHTTP2_DATA_FLAG_NO_COPY in
nghttp2_data_source_read_callback, application can avoid to copy
application data to given buffer. Instead, application has to
implement nghttp2_send_data_callback to send complete DATA frame by
itself. We see noticeable performance increase in nghttpd and
tiny-nghttpd using this new feature. On the other hand, nghttpx does
not show such difference, probably because buffer copy is not
bottleneck. Using nghttp2_send_data_callback adds complexity, so it
is recommended to measure the performance to see whether this extra
complexity worth it.
nghttp2_submit_request and nghttp2_submit_response will set
NGHTTP2_FLAG_END_STREAM after all given data is sent (data could be
0). This means we have no way to send trailers. In this commit, we
added NGHTTP2_DATA_FLAG_NO_END_STREAM flag. The application can set
this flag in *data_flags inside nghttp2_data_source_read_callback. If
NGHTTP2_DATA_FLAG_EOF is set, library automatically set
NGHTTP2_FLAG_END_STREAM. But if both NGHTTP2_DATA_FLAG_EOF and
NGHTTP2_DATA_FLAG_NO_END_STREAM are set, NGHTTP2_FLAG_END_STREAM will
not set by library. Then application can use new
nghttp2_submit_trailer() to send trailers. nghttp2_submit_trailer()
will set NGHTTP2_FLAG_END_STREAM and it is actually thing wrapper of
nghttp2_submit_headers().
After we sent SETTINGS including ENABLE_PUSH = 0, peer may already
issue PUSH_PROMISE before receiving our SETTINGS and react it to
SETTINGS ACK. Previously we accept this PUSH_PROMISE. In this
commit, we check the pending ENABLE_PUSH value and if it means
disabling push, we refuse PUSH_PROMISE with RST_STREAM of error
REFUSED_STREAM.
This commit only affects the library behaviour unless
nghttp2_option_set_no_http_messaging() is used.
We like strict validation against header field name and value against
RFC 7230, but we have already so much web sites and libraries in
public internet which do not obey these rules. Simply just
terminating stream because of this may break web sites and it is too
disruptive. So we decided that we should be conservative here so
those header fields containing illegal characters are just ignored.
But we are conservative only for regular headers. We are strict for
pseudo headers since it is new to HTTP/2 and new implementations
should know the rules better.
Tatsuhiro Tsujikawa