Optionally reset the idle timeout when sending data

A new option reset_idle_timeout_on_send has been added.
When set to 'true', the idle timeout is reset not only
when data is received, but also when data is sent.

This allows sending large responses without having to
worry about timeouts triggering.

The default is currently unchanged but might change in
a future release.

LH: Greatly reworked the implementation so that the
    timeout gets reset on almost all socket writes.
	This essentially completely supersets the original
	work. Tests are mostly the same although I
	refactored a bit to avoid test code duplication.

This commit also changes HTTP/2 behavior a little when
data is received: Cowboy will not attempt to update the
window before running stream handler commands to avoid
sending WINDOW_UPDATE frames twice. Now it has some
small heuristic to ensure they can only be sent once
at most.

1 files changed, 32 insertions, 13 deletions

diff --git a/src/cowboy_http.erl b/src/cowboy_http.erl
index abaab06..bba2108 100644
--- a/src/cowboy_http.erl
+++ b/src/cowboy_http.erl
@@ -47,6 +47,7 @@
 	middlewares => [module()],
 	proxy_header => boolean(),
 	request_timeout => timeout(),
+	reset_idle_timeout_on_send => boolean(),
 	sendfile => boolean(),
 	shutdown_timeout => timeout(),
 	stream_handlers => [module()],
@@ -294,6 +295,14 @@ set_timeout(State0=#state{opts=Opts, overriden_opts=Override}, Name) ->
 	end,
 	State#state{timer=TimerRef}.
 
+maybe_reset_idle_timeout(State=#state{opts=Opts}) ->
+	case maps:get(reset_idle_timeout_on_send, Opts, false) of
+		true ->
+			set_timeout(State, idle_timeout);
+		false ->
+			State
+	end.
+
 cancel_timeout(State=#state{timer=TimerRef}) ->
 	ok = case TimerRef of
 		undefined ->
@@ -366,6 +375,11 @@ after_parse({request, Req=#{streamid := StreamID, method := Method,
 		cowboy:log(cowboy_stream:make_error_log(init,
 			[StreamID, Req, Opts],
 			Class, Exception, Stacktrace), Opts),
+		%% We do not reset the idle timeout on send here
+		%% because an error occurred in the application. While we
+		%% are keeping the connection open for further requests we
+		%% do not want to keep the connection up too long if no
+		%% additional requests come in.
 		early_error(500, State0, {internal_error, {Class, Exception},
 			'Unhandled exception in cowboy_stream:init/3.'}, Req),
 		parse(Buffer, State0)
@@ -1012,19 +1026,20 @@ commands(State=#state{out_state=wait, out_streamid=StreamID}, StreamID,
 commands(State, StreamID, [{error_response, _, _, _}|Tail]) ->
 	commands(State, StreamID, Tail);
 %% Send an informational response.
-commands(State=#state{socket=Socket, transport=Transport, out_state=wait, streams=Streams},
+commands(State0=#state{socket=Socket, transport=Transport, out_state=wait, streams=Streams},
 		StreamID, [{inform, StatusCode, Headers}|Tail]) ->
 	%% @todo I'm pretty sure the last stream in the list is the one we want
 	%% considering all others are queued.
 	#stream{version=Version} = lists:keyfind(StreamID, #stream.id, Streams),
 	_ = case Version of
 		'HTTP/1.1' ->
-			ok = maybe_socket_error(State, Transport:send(Socket,
+			ok = maybe_socket_error(State0, Transport:send(Socket,
 				cow_http:response(StatusCode, 'HTTP/1.1', headers_to_list(Headers))));
 		%% Do not send informational responses to HTTP/1.0 clients. (RFC7231 6.2)
 		'HTTP/1.0' ->
 			ok
 	end,
+	State = maybe_reset_idle_timeout(State0),
 	commands(State, StreamID, Tail);
 %% Send a full response.
 %%
@@ -1037,17 +1052,18 @@ commands(State0=#state{socket=Socket, transport=Transport, out_state=wait, strea
 	%% considering all others are queued.
 	#stream{version=Version} = lists:keyfind(StreamID, #stream.id, Streams),
 	{State1, Headers} = connection(State0, Headers0, StreamID, Version),
-	State = State1#state{out_state=done},
+	State2 = State1#state{out_state=done},
 	%% @todo Ensure content-length is set. 204 must never have content-length set.
 	Response = cow_http:response(StatusCode, 'HTTP/1.1', headers_to_list(Headers)),
 	%% @todo 204 and 304 responses must not include a response body. (RFC7230 3.3.1, RFC7230 3.3.2)
 	case Body of
 		{sendfile, _, _, _} ->
-			ok = maybe_socket_error(State, Transport:send(Socket, Response)),
-			sendfile(State, Body);
+			ok = maybe_socket_error(State2, Transport:send(Socket, Response)),
+			sendfile(State2, Body);
 		_ ->
-			ok = maybe_socket_error(State, Transport:send(Socket, [Response, Body]))
+			ok = maybe_socket_error(State2, Transport:send(Socket, [Response, Body]))
 	end,
+	State = maybe_reset_idle_timeout(State2),
 	commands(State, StreamID, Tail);
 %% Send response headers and initiate chunked encoding or streaming.
 commands(State0=#state{socket=Socket, transport=Transport,
@@ -1084,9 +1100,10 @@ commands(State0=#state{socket=Socket, transport=Transport,
 		trailers -> Headers1;
 		_ -> maps:remove(<<"trailer">>, Headers1)
 	end,
-	{State, Headers} = connection(State1, Headers2, StreamID, Version),
-	ok = maybe_socket_error(State, Transport:send(Socket,
+	{State2, Headers} = connection(State1, Headers2, StreamID, Version),
+	ok = maybe_socket_error(State2, Transport:send(Socket,
 		cow_http:response(StatusCode, 'HTTP/1.1', headers_to_list(Headers)))),
+	State = maybe_reset_idle_timeout(State2),
 	commands(State, StreamID, Tail);
 %% Send a response body chunk.
 %% @todo We need to kill the stream if it tries to send data before headers.
@@ -1147,17 +1164,18 @@ commands(State0=#state{socket=Socket, transport=Transport, streams=Streams0, out
 			end,
 			Stream0#stream{local_sent_size=SentSize}
 	end,
-	State = case IsFin of
+	State1 = case IsFin of
 		fin -> State0#state{out_state=done};
 		nofin -> State0
 	end,
+	State = maybe_reset_idle_timeout(State1),
 	Streams = lists:keyreplace(StreamID, #stream.id, Streams0, Stream),
 	commands(State#state{streams=Streams}, StreamID, Tail);
-commands(State=#state{socket=Socket, transport=Transport, streams=Streams, out_state=OutState},
+commands(State0=#state{socket=Socket, transport=Transport, streams=Streams, out_state=OutState},
 		StreamID, [{trailers, Trailers}|Tail]) ->
 	case stream_te(OutState, lists:keyfind(StreamID, #stream.id, Streams)) of
 		trailers ->
-			ok = maybe_socket_error(State,
+			ok = maybe_socket_error(State0,
 				Transport:send(Socket, [
 					<<"0\r\n">>,
 					cow_http:headers(maps:to_list(Trailers)),
@@ -1165,12 +1183,13 @@ commands(State=#state{socket=Socket, transport=Transport, streams=Streams, out_s
 				])
 			);
 		no_trailers ->
-			ok = maybe_socket_error(State,
+			ok = maybe_socket_error(State0,
 				Transport:send(Socket, <<"0\r\n\r\n">>));
 		not_chunked ->
 			ok
 	end,
-	commands(State#state{out_state=done}, StreamID, Tail);
+	State = maybe_reset_idle_timeout(State0#state{out_state=done}),
+	commands(State, StreamID, Tail);
 %% Protocol takeover.
 commands(State0=#state{ref=Ref, parent=Parent, socket=Socket, transport=Transport,
 		out_state=OutState, opts=Opts, buffer=Buffer, children=Children}, StreamID,