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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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50
test/rfc7540_SUITE.erl
View file

@ -3117,56 +3117,6 @@ data_reject_overflow_stream(Config0) ->
cowboy:stop_listener(?FUNCTION_NAME)
end.
lingering_data_counts_toward_connection_window(Config0) ->
doc("DATA frames received after sending RST_STREAM must be counted "
"toward the connection flow-control window. (RFC7540 5.1)"),
Config = cowboy_test:init_http(?FUNCTION_NAME, #{
env => #{dispatch => cowboy_router:compile(init_routes(Config0))},
initial_connection_window_size => 100000
}, Config0),
try
%% We need to do the handshake manually because a WINDOW_UPDATE
%% frame will be sent to update the connection window.
{ok, Socket} = gen_tcp:connect("localhost", config(port, Config), [binary, {active, false}]),
%% Send a valid preface.
ok = gen_tcp:send(Socket, ["PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n", cow_http2:settings(#{})]),
%% Receive the server preface.
{ok, << Len1:24 >>} = gen_tcp:recv(Socket, 3, 1000),
{ok, << 4:8, 0:40, _:Len1/binary >>} = gen_tcp:recv(Socket, 6 + Len1, 1000),
%% Send the SETTINGS ack.
ok = gen_tcp:send(Socket, cow_http2:settings_ack()),
%% Receive the WINDOW_UPDATE for the connection.
{ok, << 4:24, 8:8, 0:40, _:32 >>} = gen_tcp:recv(Socket, 13, 1000),
%% Receive the SETTINGS ack.
{ok, << 0:24, 4:8, 1:8, 0:32 >>} = gen_tcp:recv(Socket, 9, 1000),
Headers = [
{<<":method">>, <<"POST">>},
{<<":scheme">>, <<"http">>},
{<<":authority">>, <<"localhost">>}, %% @todo Correct port number.
{<<":path">>, <<"/loop_handler_abort">>}
],
{HeadersBlock, _} = cow_hpack:encode(Headers),
ok = gen_tcp:send(Socket, [
cow_http2:headers(1, nofin, HeadersBlock),
cow_http2:data(1, nofin, <<0:1000/unit:8>>)
]),
% Make sure server send RST_STREAM.
timer:sleep(100),
ok = gen_tcp:send(Socket, [
cow_http2:data(1, nofin, <<0:0/unit:8>>),
cow_http2:data(1, fin, <<0:1000/unit:8>>)
]),
{ok, << SkipLen:24, 1:8, _:8, 1:32 >>} = gen_tcp:recv(Socket, 9, 1000),
% Skip the header.
{ok, _} = gen_tcp:recv(Socket, SkipLen, 1000),
% Skip RST_STREAM.
{ok, << 4:24, 3:8, 1:40, _:32 >>} = gen_tcp:recv(Socket, 13, 1000),
% Received a WINDOW_UPDATE frame after we got RST_STREAM.
{ok, << 4:24, 8:8, 0:40, 1000:32 >>} = gen_tcp:recv(Socket, 13, 1000)
after
cowboy:stop_listener(?FUNCTION_NAME)
end.
%% (RFC7540 6.9.1)
% Frames with zero length with the END_STREAM flag set (that
% is, an empty DATA frame) MAY be sent if there is no available space

5
test/rfc8441_SUITE.erl
View file

@ -389,15 +389,10 @@ accept_handshake_when_enabled(Config) ->
{RespHeaders, _} = cow_hpack:decode(RespHeadersBlock),
{_, <<"200">>} = lists:keyfind(<<":status">>, 1, RespHeaders),
%% Masked text hello echoed back clear by the server.
%%
%% We receive WINDOW_UPDATE frames before the actual data
%% due to flow control updates every time a data frame is received.
Mask = 16#37fa213d,
MaskedHello = ws_SUITE:do_mask(<<"Hello">>, Mask, <<>>),
ok = gen_tcp:send(Socket, cow_http2:data(1, nofin,
<<1:1, 0:3, 1:4, 1:1, 5:7, Mask:32, MaskedHello/binary>>)),
{ok, <<4:24, 8:8, _:72>>} = gen_tcp:recv(Socket, 13, 1000),
{ok, <<4:24, 8:8, _:72>>} = gen_tcp:recv(Socket, 13, 1000),
{ok, <<Len2:24, _:8, _:8, _:32>>} = gen_tcp:recv(Socket, 9, 1000),
{ok, <<1:1, 0:3, 1:4, 0:1, 5:7, "Hello">>} = gen_tcp:recv(Socket, Len2, 1000),
ok.