Resources to be pushed are configured with the "http2_push" directive.
Also, preload links from the Link response headers, as described in
https://www.w3.org/TR/preload/#server-push-http-2, can be pushed, if
enabled with the "http2_push_preload" directive.
Only relative URIs with absolute paths can be pushed.
The number of concurrent pushes is normally limited by a client, but
cannot exceed a hard limit set by the "http2_max_concurrent_pushes"
directive.
This change lets NGINX talk to clients with SETTINGS_HEADER_TABLE_SIZE
smaller than the default 4KB. Previously, NGINX would ACK the SETTINGS
frame with a small dynamic table size, but it would never send dynamic
table size update, leading to a connection-level COMPRESSION_ERROR.
Also, it allows clients to release 4KB of memory per connection, since
NGINX doesn't use HPACK's dynamic table when encoding headers, however
clients had to maintain it, since NGINX never signaled that it doesn't
use it.
Signed-off-by: Piotr Sikora <piotrsikora@google.com>
Previously, SETTINGS ACK was sent immediately upon receipt of SETTINGS
frame, before already queued DATA frames created using old SETTINGS.
This incorrect behavior was source of interoperability issues, because
peers rely on the fact that new SETTINGS are in effect after receiving
SETTINGS ACK.
Reported by Feng Li.
Signed-off-by: Piotr Sikora <piotrsikora@google.com>
A bug was introduced by 82efcedb310b that could lead to timing out of
responses or segmentation fault, when accept_mutex was enabled.
The output queue in HTTP/2 can contain frames from different streams.
When the queue is sent, all related write handlers need to be called.
In order to do so, the streams were added to the h2c->posted queue
after handling sent frames. Then this queue was processed in
ngx_http_v2_write_handler().
If accept_mutex is enabled, the event's "ready" flag is set but its
handler is not called immediately. Instead, the event is added to
the ngx_posted_events queue. At the same time in this queue can be
events from upstream connections. Such events can result in sending
output queue before ngx_http_v2_write_handler() is triggered. And
at the time ngx_http_v2_write_handler() is called, the output queue
can be already empty with some streams added to h2c->posted.
But after 82efcedb310b, these streams weren't processed if all frames
have already been sent and the output queue was empty. This might lead
to a situation when a number of streams were get stuck in h2c->posted
queue for a long time. Eventually these streams might get closed by
the send timeout.
In the worst case this might also lead to a segmentation fault, if
already freed stream was left in the h2c->posted queue. This could
happen if one of the streams was terminated but wasn't closed, due to
the HEADERS frame or a partially sent DATA frame left in the output
queue. If this happened the ngx_http_v2_filter_cleanup() handler
removed the stream from the h2c->waiting or h2c->posted queue on
termination stage, before the frame has been sent, and the stream
was again added to the h2c->posted queue after the frame was sent.
In order to fix all these problems and simplify the code, write
events of fake stream connections are now added to ngx_posted_events
instead of using a custom h2c->posted queue.
Previously, while shutting down gracefully, the HTTP/2 connections were
closed in transition to idle state after all active streams have been
processed. That might never happen if the client continued opening new
streams.
Now, nginx sends GOAWAY to all HTTP/2 connections and ignores further
attempts to open new streams. A worker process will quit as soon as
processing of already opened streams is finished.
On non-aligned platforms, properly cast argument before left-shifting it in
ngx_http_v2_parse_uint32 that is used with u_char. Otherwise it propagates
to int to hold the value and can step over the sign bit. Usually, on known
compilers, this results in negation. Furthermore, a subsequent store into a
wider type, that is ngx_uint_t on 64-bit platforms, results in sign-extension.
In practice, this can be observed in debug log as a very large exclusive bit
value, when client sent PRIORITY frame with exclusive bit set:
: *14 http2 PRIORITY frame sid:5 on 1 excl:8589934591 weight:17
Found with UndefinedBehaviorSanitizer.
Previously, the stream's window was kept zero in order to prevent a client
from sending the request body before it was requested (see 887cca40ba6a for
details). Until such initial window was acknowledged all requests with
data were rejected (see 0aa07850922f for details).
That approach revealed a number of problems:
1. Some clients (notably MS IE/Edge, Safari, iOS applications) show an error
or even crash if a stream is rejected;
2. This requires at least one RTT for every request with body before the
client receives window update and able to send data.
To overcome these problems the new directive "http2_body_preread_size" is
introduced. It sets the initial window and configures a special per stream
preread buffer that is used to save all incoming data before the body is
requested and processed.
If the directive's value is lower than the default initial window (65535),
as previously, all streams with data will be rejected until the new window
is acknowledged. Otherwise, no special processing is used and all requests
with data are welcome right from the connection start.
The default value is chosen to be 64k, which is bigger than the default
initial window. Setting it to zero is fully complaint to the previous
behavior.
A client is allowed to send requests before receiving and acknowledging
the SETTINGS frame. Such a client having a wrong idea about the stream's
could send the request body that nginx isn't ready to process.
The previous behavior was to send RST_STREAM with FLOW_CONTROL_ERROR in
such case, but it didn't allow retrying requests that have been rejected.
There are two improvements:
1. Support for request body filters;
2. Receiving of request body is started only after
the ngx_http_read_client_request_body() call.
The last one fixes the problem when the client_max_body_size value might not be
respected from the right location if the location was changed either during the
process of receiving body or after the whole body had been received.
RFC 7540 states that "A server can send a complete response prior to the client
sending an entire request if the response does not depend on any portion of the
request that has not been sent and received. When this is true, a server MAY
request that the client abort transmission of a request without error by sending
a RST_STREAM with an error code of NO_ERROR after sending a complete response
(i.e., a frame with the END_STREAM flag)."
This should prevent a client from blocking on the stream window, since it isn't
maintained for closed streams. Currently, quite big initial stream windows are
used, so such blocking is very unlikly, but that will be changed in the further
patches.
This is required for implementing per request timeouts.
Previously, the temporary pool was used only during skipping of
headers and the request pool was used otherwise. That required
switching of pools if the request was closed while parsing.
It wasn't a problem since the request could be closed only after
the validation of the fully parsed header. With the per request
timeouts, the request can be closed at any moment, and switching
of pools in the middle of parsing header name or value becomes a
problem.
To overcome this, the temporary pool is now always created and
used. Special checks are added to keep it when either the stream
is being processed or until header block is fully parsed.
Now it limits only the maximum length of literal string (either raw or
compressed) in HPACK request header fields. It's easier to understand
and to describe in the documentation.
