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Fix and optimize sending of WINDOW_UPDATE frames

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For long-running connections it was possible for the connection
window to become larger than allowed by the protocol because the
window increases claimed by stream handlers were never reclaimed
even if no data was consumed.

The new code applies heuristics to fix this and reduce the number
of WINDOW_UPDATE frames that are sent. It includes six new options
to control that behavior: margin, max and threshold for both the
connection and stream windows. The margin is some extra space
added on top of the requested read size. The max is the maximum
window size at any given time. The threshold is a minimum window
size that must be reached before we even consider sending more
WINDOW_UPDATE frames. We also avoid sending WINDOW_UPDATE frames
when there is already enough space in the window, or when the
read size is 0.

Cowlib is set to master until a new tag is done.
This commit is contained in:
Loïc Hoguin 2019-09-02 14:48:28 +02:00
parent aedf6379cc
commit 48f417ac8f
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GPG key ID: 8A9DF795F6FED764
6 changed files with 136 additions and 93 deletions
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52
doc/src/manual/cowboy_http2.asciidoc
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@ -18,21 +18,27 @@ as a Ranch protocol.
----
opts() :: #{
connection_type => worker | supervisor,
connection_window_margin_size => 0..16#7fffffff,
connection_window_update_threshold => 0..16#7fffffff,
enable_connect_protocol => boolean(),
idle_timeout => timeout(),
inactivity_timeout => timeout(),
initial_connection_window_size => 65535..16#7fffffff,
initial_stream_window_size => 0..16#7fffffff,
max_concurrent_streams => non_neg_integer() | infinity,
max_connection_window_size => 0..16#7fffffff,
max_decode_table_size => non_neg_integer(),
max_encode_table_size => non_neg_integer(),
max_frame_size_received => 16384..16777215,
max_frame_size_sent => 16384..16777215 | infinity,
max_stream_window_size => 0..16#7fffffff,
preface_timeout => timeout(),
proxy_header => boolean(),
sendfile => boolean(),
settings_timeout => timeout(),
stream_handlers => [module()]
stream_handlers => [module()],
stream_window_margin_size => 0..16#7fffffff,
stream_window_update_threshold => 0..16#7fffffff
}
----
@ -51,6 +57,19 @@ connection_type (supervisor)::
Whether the connection process also acts as a supervisor.
connection_window_margin_size (65535)::
Extra amount to be added to the window size when
updating the connection window. This is used to
ensure that there is always some space available in
the window.
connection_window_update_threshold (163840)::
The connection window will only get updated when its size
becomes lower than this threshold. This is to avoid sending
too many `WINDOW_UPDATE` frames.
enable_connect_protocol (false)::
Whether to enable the extended CONNECT method to allow
@ -84,6 +103,12 @@ max_concurrent_streams (infinity)::
Maximum number of concurrent streams allowed on the connection.
max_connection_window_size (16#7fffffff)::
Maximum connection window size. This is used as an upper bound
when calculating the window size, either when reading the request
body or receiving said body.
max_decode_table_size (4096)::
Maximum header table size used by the decoder. This is the value advertised
@ -111,6 +136,12 @@ following the client's advertised maximum.
Note that actual frame sizes may be lower than the limit when
there is not enough space left in the flow control window.
max_stream_window_size (16#7fffffff)::
Maximum stream window size. This is used as an upper bound
when calculating the window size, either when reading the request
body or receiving said body.
preface_timeout (5000)::
Time in ms Cowboy is willing to wait for the connection preface.
@ -135,8 +166,27 @@ stream_handlers ([cowboy_stream_h])::
Ordered list of stream handlers that will handle all stream events.
stream_window_margin_size (65535)::
Extra amount to be added to the window size when
updating a stream's window. This is used to
ensure that there is always some space available in
the window.
stream_window_update_threshold (163840)::
A stream's window will only get updated when its size
becomes lower than this threshold. This is to avoid sending
too many `WINDOW_UPDATE` frames.
== Changelog
* *2.7*: Add the options `connection_window_margin_size`,
`connection_window_update_threshold`,
`max_connection_window_size`, `max_stream_window_size`,
`stream_window_margin_size` and
`stream_window_update_threshold` to configure
behavior on sending WINDOW_UPDATE frames.
* *2.6*: The `proxy_header` and `sendfile` options were added.
* *2.4*: Add the options `initial_connection_window_size`,
`initial_stream_window_size`, `max_concurrent_streams`,