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Previosly the threshold was hardcoded at 10000. This value is too low for
high BDP networks. For example, if all frames are STREAM frames, and MTU
is 1500, the upper limit for congestion window would be roughly 15M
(10000 * 1500). With 100ms RTT it's just a 1.2Gbps network (15M * 10 * 8).
In reality, the limit is even lower because of other frame types. Also,
the number of frames that could be used simultaneously depends on the total
amount of data buffered in all server streams, and client flow control.
The change sets frame threshold based on max concurrent streams and stream
buffer size, the product of which is the maximum number of in-flight stream
data in all server streams at any moment. The value is divided by 2000 to
account for a typical MTU 1500 and the fact that not all frames are STREAM
frames.
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Previously the last chain field of ngx_quic_buffer_t could still reference freed
chains and buffers after calling ngx_quic_free_buffer(). While normally an
ngx_quic_buffer_t object should not be used after freeing, resetting last_chain
field would prevent a potential use-after-free.
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Currently, packets generated by ngx_quic_frame_sendto() and
ngx_quic_send_early_cc() are not logged, thus making it hard
to read logs due to gaps appearing in packet numbers sequence.
At frames level, it is handy to see immediately packet number
in which they arrived or being sent.
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Do not corrupt frame data chain pointer on ngx_quic_read_buffer() error.
The error leads to closing a QUIC connection where the frame may be used
as part of the QUIC connection tear down, which envolves writing pending
frames, including this one.
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Previously, since 3550b00d9dc8, the token was allocated on stack, to get
rid of pool usage. Now the token is allocated by ngx_quic_copy_buffer()
in QUIC buffers, also used for STREAM, CRYPTO and ACK frames.
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The function copies passed data to QUIC buffer chain and returns it.
The chain can be used in ngx_quic_frame_t data field.
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Previously, last buffer was tracked by keeping a pointer to the previous
chain link "next" field. When the previous buffer was split and then removed,
the pointer was no longer valid. Writing at this pointer resulted in broken
data chains.
Now last buffer is tracked by keeping a direct pointer to it.
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Its only call is substituted with QUIC buffer write/read pair.
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This allows to eliminate explicit trimming when handling input STREAM frame.
As a result, ngx_quic_trim_chain() is eliminated as well.
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The object is used instead of ngx_chain_t pointer for buffer operations like
ngx_quic_write_chain() and ngx_quic_read_chain(). These functions are renamed
to ngx_quic_write_buffer() and ngx_quic_read_buffer().
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Now ngx_quic_stream_t is decoupled from ngx_connection_t in a way that it
can persist after connection is closed by application. During this period,
server is expecting stream final size from client for correct flow control.
Also, buffered output is sent to client as more flow control credit is granted.
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Previously, size was calculated based on the number of input bytes processed
by the function. Now only the copied bytes are considered. This prevents
overlapping buffers from contributing twice to the overall written size.
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Previously, when input ended on a QUIC buffer boundary, input chain was not
advanced to the next buffer. As a result, ngx_quic_write_chain() returned
a chain with an empty buffer instead of NULL. This broke HTTP write filter,
preventing it from closing the HTTP request and eventually timing out.
Now input chain is always advanced to a buffer that has data, before checking
QUIC buffer boundary condition.
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The function splits a buffer at given offset. The function is now
called from ngx_quic_read_chain() and ngx_quic_write_chain(), which
simplifies both functions.
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This allows to escape calculating it before calling the function.
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Previously, ngx_quic_write_chain() treated each input buffer as a memory
buffer, which is not always the case. Special buffers were not skipped, which
is especially important when hitting the input byte limit.
The issue manifested itself with ngx_quic_write_chain() returning a non-empty
chain consisting of a special last_buf buffer when called from QUIC stream
send_chain(). In order for this to happen, input byte limit should be equal to
the chain length, and the input chain should end with an empty last_buf buffer.
An easy way to achieve this is the following:
location /empty {
return 200;
}
When this non-empty chain was returned from send_chain(), it signalled to the
caller that input was blocked, while in fact it wasn't. This prevented HTTP
request from finalization, which prevented QUIC from sending STREAM FIN to
the client. The QUIC stream was then reset after a timeout.
Now special buffers are skipped and send_chain() returns NULL in the case
above, which signals to the caller a successful operation.
Also, original byte limit is now passed to ngx_quic_write_chain() from
send_chain() instead of actual chain length to make sure it's never zero.
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Previously, buffer lists was used to track used buffers. Now reference
counter is used instead. The new implementation is simpler and faster with
many buffer clones.
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The function is unused.
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ngx_quic_alloc_buf() -> ngx_quic_alloc_chain(),
ngx_quic_free_bufs() -> ngx_quic_free_chain(),
ngx_quic_trim_bufs() -> ngx_quic_trim_chain()
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They are replaced with ngx_quic_write_chain() and ngx_quic_read_chain().
These functions represent the API to data buffering.
The first function adds data of given size at given offset to the buffer.
Now it returns the unwritten part of the chain similar to c->send_chain().
The second function returns data of given size from the beginning of the buffer.
Its second argument and return value are swapped compared to
ngx_quic_split_bufs() to better match ngx_quic_write_chain().
Added, returned and stored data are regular ngx_chain_t/ngx_buf_t chains.
Missing data is marked with b->sync flag.
The functions are now used in both send and recv data chains in QUIC streams.
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Previously, when a few bytes were send to a QUIC stream by the application, a
4K buffer was allocated for these bytes. Then a STREAM frame was created and
that entire buffer was used as data for that frame. The frame with the buffer
were in use up until the frame was acked by client. Meanwhile, when more
bytes were send to the stream, more buffers were allocated and assigned as
data to newer STREAM frames. In this scenario most buffer memory is unused.
Now the unused part of the stream output buffer is available for further
stream output while earlier parts of the buffer are waiting to be acked.
This is achieved by splitting the output buffer.
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Exceeding 10000 allocated frames is considered a flood.
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The information about the type is contained in off/len/fin bits.
Also, where possible, only the first stream type (0x08) is used for simplicity.
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Generic function ngx_quic_order_bufs() is introduced. This function creates
and maintains a chain of buffers with holes. Holes are marked with b->sync
flag. Several buffers and holes in this chain may share the same underlying
memory buffer.
When processing STREAM frames with this function, frame data is copied only
once to the right place in the stream input chain. Previously data could
be copied twice. First when buffering an out-of-order frame data, and then
when filling stream buffer from ordered frame queue. Now there's only one
data chain for both tasks.
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Previously each stream had an input buffer. Now memory is allocated as
bytes arrive. Generic buffering mechanism is used for this.
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