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Implement backpressure on cowboy_req:stream_body

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This should limit the amount of memory that Cowboy is using
when a handler is sending data much faster than the network.

The new max_stream_buffer_size is a soft limit and only has
an effect when the cowboy_stream_h handler is used.
This commit is contained in:
Loïc Hoguin 2019-09-13 14:20:04 +02:00
parent 4427108b69
commit 49af57d546
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6 changed files with 91 additions and 25 deletions
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36
src/cowboy_http2.erl
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@ -45,6 +45,7 @@
max_encode_table_size => non_neg_integer(),
max_frame_size_received => 16384..16777215,
max_frame_size_sent => 16384..16777215 | infinity,
max_stream_buffer_size => non_neg_integer(),
max_stream_window_size => 0..16#7fffffff,
metrics_callback => cowboy_metrics_h:metrics_callback(),
middlewares => [module()],
@ -292,7 +293,11 @@ frame(State=#state{http2_machine=HTTP2Machine0}, Frame) ->
{ok, GoAway={goaway, _, _, _}, HTTP2Machine} ->
goaway(State#state{http2_machine=HTTP2Machine}, GoAway);
{send, SendData, HTTP2Machine} ->
send_data(maybe_ack(State#state{http2_machine=HTTP2Machine}, Frame), SendData);
%% We may need to send an alarm for each of the streams sending data.
lists:foldl(
fun({StreamID, _, _}, S) -> maybe_send_data_alarm(S, HTTP2Machine0, StreamID) end,
send_data(maybe_ack(State#state{http2_machine=HTTP2Machine}, Frame), SendData),
SendData);
{error, {stream_error, StreamID, Reason, Human}, HTTP2Machine} ->
reset_stream(State#state{http2_machine=HTTP2Machine},
StreamID, {stream_error, Reason, Human});
@ -712,7 +717,7 @@ maybe_send_data(State0=#state{http2_machine=HTTP2Machine0}, StreamID, IsFin, Dat
end,
case cow_http2_machine:send_or_queue_data(StreamID, HTTP2Machine0, IsFin, Data) of
{ok, HTTP2Machine} ->
State0#state{http2_machine=HTTP2Machine};
maybe_send_data_alarm(State0#state{http2_machine=HTTP2Machine}, HTTP2Machine0, StreamID);
{send, SendData, HTTP2Machine} ->
State = #state{http2_status=Status, streams=Streams}
= send_data(State0#state{http2_machine=HTTP2Machine}, SendData),
@ -721,7 +726,7 @@ maybe_send_data(State0=#state{http2_machine=HTTP2Machine0}, StreamID, IsFin, Dat
Status =:= closing, Streams =:= #{} ->
terminate(State, {stop, normal, 'The connection is going away.'});
true ->
State
maybe_send_data_alarm(State, HTTP2Machine0, StreamID)
end
end.
@ -759,6 +764,31 @@ send_data_frame(State=#state{socket=Socket, transport=Transport,
Transport:send(Socket, cow_http2:headers(StreamID, fin, HeaderBlock)),
State#state{http2_machine=HTTP2Machine}.
%% After we have sent or queued data we may need to set or clear an alarm.
%% We do this by comparing the HTTP2Machine buffer state before/after for
%% the relevant streams.
maybe_send_data_alarm(State=#state{opts=Opts, http2_machine=HTTP2Machine}, HTTP2Machine0, StreamID) ->
{ok, BufferSizeBefore} = cow_http2_machine:get_stream_local_buffer_size(StreamID, HTTP2Machine0),
%% When the stream ends up closed after it finished sending data,
%% we do not want to trigger an alarm. We act as if the buffer
%% size did not change.
BufferSizeAfter = case cow_http2_machine:get_stream_local_buffer_size(StreamID, HTTP2Machine) of
{ok, BSA} -> BSA;
{error, closed} -> BufferSizeBefore
end,
MaxBufferSize = maps:get(max_stream_buffer_size, Opts, 8000000),
%% I do not want to document these internal_events yet. I am not yet
%% convinced it should be {alarm, Name, on|off} and not {internal_event, E}
%% or something else entirely.
if
BufferSizeBefore >= MaxBufferSize, BufferSizeAfter < MaxBufferSize ->
info(State, StreamID, {alarm, stream_buffer_full, off});
BufferSizeBefore < MaxBufferSize, BufferSizeAfter >= MaxBufferSize ->
info(State, StreamID, {alarm, stream_buffer_full, on});
true ->
State
end.
%% Terminate a stream or the connection.
%% We may have to cancel streams even if we receive multiple