The size of the priority field is increased by one bit in spdy/3,
and now it's a 3-bit field followed by 5 bits of unused space.
But a shift of these bits hasn't been adjusted in 39d7eef2e332
accordingly.
It simplifies the code and allows easy reuse the same queue pointer to store
streams in various queues with different requirements. Future implementation
of SPDY/3.1 will take advantage of this quality.
The "length" value better corresponds with the specification and reduces
confusion about whether frame's header is included in "size" or not.
Also this change simplifies some parts of code, since in more cases the
length of frame is more useful than its actual size, especially considering
that the size of frame header is constant.
There is no need in separate "free" pointer and like it is for ngx_chain_t
the "next" pointer can be used. But after this change successfully handled
frame should not be accessed, so the frame handling cycle was improved to
store pointer to the next frame before processing.
Also worth noting that initializing "free" pointer to NULL in the original
code was surplus.
That code was based on misunderstanding of spdy specification about
configuration applicability in the SETTINGS frames. The original
interpretation was that configuration is assigned for the whole
SPDY connection, while it is only for the endpoint.
Moreover, the strange thing is that specification forbids multiple
entries in the SETTINGS frame with the same ID even if flags are
different. As a result, Chrome sends two SETTINGS frames: one with
its own configuration, and another one with configuration stored
for a server (when the FLAG_SETTINGS_PERSIST_VALUE flags were used
by the server).
To simplify implementation we refuse to use the persistent settings
feature and thereby avoid all the complexity related with its proper
support.
The "headers" is not a good term, since it is used not only to count
name/value pairs in the HEADERS block but to count SETTINGS entries too.
Moreover, one name/value pair in HEADERS can contain multiple http headers
with the same name.
No functional changes.
While processing a DATA frame, the link to related stream is stored in spdy
connection object as part of connection state. But this stream can be closed
between receiving parts of the frame.
During the processing of input some control frames can be added to the queue.
And if there were no writing streams at the moment, these control frames might
be left unsent for a long time (or even forever).
This long delay is especially critical for PING replies since a client can
consider connection as broken and then resend exactly the same request over
a new connection, which is not safe in case of non-idempotent HTTP methods.
There is no reason to allocate it from connection pool that more like just
a bug especially since ngx_http_spdy_settings_frame_handler() already uses
sc->pool to free a chain.
The frame->stream pointer should always be initialized for control frames since
the check against it can be performed in ngx_http_spdy_filter_cleanup().
It was used to prevent destroying of request object when there are unsent
frames in queue for the stream. Since it was incremented for each frame
and is only 8 bits long, so it was not very hard to overflow the counter.
Now the stream->queued counter is checked instead.
Processing events from upstream connection can result in sending queued frames
from other streams. In this case such streams were not added to handling queue
and properly handled.
A global per connection flag was replaced by a per stream flag that indicates
currently sending stream while all other streams can be added to handling
queue.
This flag in SPDY fake write events serves the same purposes as the "ready"
flag in real events, and it must be dropped if request needs to be handled.
Otherwise, it can prevent the request from finalization if ngx_http_writer()
was set, which results in a connection leak.
Found by Xiaochen Wang.
If an error occurs in a SPDY connection, the c->error flag is set on every fake
request connection, and its read or write event handler is called, in order to
finalize it. But while waiting for request headers, it was a no-op since the
read event handler had been set to ngx_http_empty_handler().
If an error occurs in a SPDY connection, the c->error flag is set on every fake
request connection, and its read or write event handler is called, in order to
finalize it. But while waiting for a request body, it was a no-op since the
read event handler ngx_http_request_handler() calls r->read_event_handler that
had been set to ngx_http_block_reading().
They refer to the same socket descriptor as our real connection, and
deleting them will stop processing of the connection.
Events of fake connections must not be activated, and if it happened there
is nothing we can do. The whole processing should be terminated as soon as
possible, but it is not obvious how to do this safely.
A quote from SPDY draft 2 specification: "The length of each name and
value must be greater than zero. A receiver of a zero-length name or
value must send a RST_STREAM with code PROTOCOL error."
But it appears that Chrome browser allows sending requests over SPDY/2
connection using JavaScript that contain headers with empty values.
For better compatibility across SPDY clients and to be compliant with
HTTP, such headers are no longer rejected.
Also, it is worth noting that in SPDY draft 3 the statement has been
changed so that it permits empty values for headers.
It is possible to send FLAG_FIN in additional empty data frame, even if it is
known from the content-length header that request body is empty. And Firefox
actually behaves like this (see ticket #357).
To simplify code we sacrificed our microoptimization that did not work right
due to missing check in the ngx_http_spdy_state_data() function for rb->buf
set to NULL.
This is to avoid setting the TCP_NODELAY flag on SPDY socket in
ngx_http_upstream_send_response(). The latter works per request,
but in SPDY case it might affect other streams in connection.
