Add the response_start event

Thought it needed cow_http2_machine changes but everything
was available. For HTTP/1.1 it is triggered when receiving
data while expecting headers. For HTTP/2 it is triggered
after we have received a HEADERS frame for streams in idle
state.

5 files changed, 64 insertions, 4 deletions

diff --git a/src/gun_default_event_h.erl b/src/gun_default_event_h.erl
index 4156ed7..cd48fc2 100644
--- a/src/gun_default_event_h.erl
+++ b/src/gun_default_event_h.erl
@@ -21,6 +21,7 @@
 -export([request_start/2]).
 -export([request_headers/2]).
 -export([request_end/2]).
+-export([response_start/2]).
 -export([response_inform/2]).
 -export([response_headers/2]).
 -export([response_end/2]).
@@ -45,6 +46,9 @@ request_headers(_EventData, State) ->
 request_end(_EventData, State) ->
 	State.
 
+response_start(_EventData, State) ->
+	State.
+
 response_inform(_EventData, State) ->
 	State.
 
diff --git a/src/gun_event.erl b/src/gun_event.erl
index 8e66400..2a742a1 100644
--- a/src/gun_event.erl
+++ b/src/gun_event.erl
@@ -68,6 +68,15 @@
 
 -callback request_end(request_end_event(), State) -> State.
 
+%% response_start.
+
+-type response_start_event() :: #{
+	stream_ref := reference(),
+	reply_to := pid()
+}.
+
+-callback response_start(response_start_event(), State) -> State.
+
 %% response_inform/response_headers.
 
 -type response_headers_event() :: #{
@@ -113,8 +122,7 @@
 %% @todo origin_changed
 %% @todo transport_changed
 %% @todo protocol_changed
-%% @todo response_start (needs changes in cow_http2_machine to have an event before decoding headers)
-%% @todo response_trailers (same)
+%% @todo response_trailers
 %% @todo push_promise_start
 %% @todo push_promise_end
 %% @todo cancel_start
diff --git a/src/gun_http.erl b/src/gun_http.erl
index 7edaf14..b7c5bc1 100644
--- a/src/gun_http.erl
+++ b/src/gun_http.erl
@@ -100,7 +100,19 @@ handle(<<>>, State, _, EvHandlerState) ->
 handle(_, #http_state{streams=[]}, _, EvHandlerState) ->
 	{close, EvHandlerState};
 %% Wait for the full response headers before trying to parse them.
-handle(Data, State=#http_state{in=head, buffer=Buffer}, EvHandler, EvHandlerState) ->
+handle(Data, State=#http_state{in=head, buffer=Buffer,
+		streams=[#stream{ref=StreamRef, reply_to=ReplyTo}|_]}, EvHandler, EvHandlerState0) ->
+	%% Send the event only if there was no data in the buffer.
+	%% If there is data in the buffer then we already sent the event.
+	EvHandlerState = case Buffer of
+		<<>> ->
+			EvHandler:response_start(#{
+				stream_ref => StreamRef,
+				reply_to => ReplyTo
+			}, EvHandlerState0);
+		_ ->
+			EvHandlerState0
+	end,
 	Data2 = << Buffer/binary, Data/binary >>,
 	case binary:match(Data2, <<"\r\n\r\n">>) of
 		nomatch -> {{state, State#http_state{buffer=Data2}}, EvHandlerState};
diff --git a/src/gun_http2.erl b/src/gun_http2.erl
index 17bedde..4814818 100644
--- a/src/gun_http2.erl
+++ b/src/gun_http2.erl
@@ -113,7 +113,27 @@ parse(Data, State0=#http2_state{http2_machine=HTTP2Machine}, EvHandler, EvHandle
 
 %% Frames received.
 
-frame(State=#http2_state{http2_machine=HTTP2Machine0}, Frame, EvHandler, EvHandlerState) ->
+frame(State=#http2_state{http2_machine=HTTP2Machine0}, Frame, EvHandler, EvHandlerState0) ->
+	EvHandlerState = if
+		is_tuple(Frame) andalso element(1, Frame) =:= headers ->
+			EvStreamID = element(2, Frame),
+			case cow_http2_machine:get_stream_remote_state(EvStreamID, HTTP2Machine0) of
+				{ok, idle} ->
+					#stream{ref=StreamRef, reply_to=ReplyTo} = get_stream_by_id(State, EvStreamID),
+					EvHandler:response_start(#{
+						stream_ref => StreamRef,
+						reply_to => ReplyTo
+					}, EvHandlerState0);
+				{ok, nofin} ->
+					%% @todo response_trailers.
+					EvHandlerState0;
+				%% This is an invalid headers frame.
+				_ ->
+					EvHandlerState0
+			end;
+		true ->
+			EvHandlerState0
+	end,
 	case cow_http2_machine:frame(Frame, HTTP2Machine0) of
 		{ok, HTTP2Machine} ->
 			{maybe_ack(State#http2_state{http2_machine=HTTP2Machine}, Frame),
diff --git a/test/event_SUITE.erl b/test/event_SUITE.erl
index 83edca9..88f67d7 100644
--- a/test/event_SUITE.erl
+++ b/test/event_SUITE.erl
@@ -209,6 +209,18 @@ do_request_end_headers_content_length(Config, EventName) ->
 	} = do_receive_event(EventName),
 	gun:close(Pid).
 
+response_start(Config) ->
+	doc("Confirm that the request_start event callback is called."),
+	{ok, Pid, _} = do_gun_open(Config),
+	{ok, _} = gun:await_up(Pid),
+	StreamRef = gun:get(Pid, "/"),
+	ReplyTo = self(),
+	#{
+		stream_ref := StreamRef,
+		reply_to := ReplyTo
+	} = do_receive_event(?FUNCTION_NAME),
+	gun:close(Pid).
+
 response_inform(Config) ->
 	doc("Confirm that the request_inform event callback is called."),
 	{ok, Pid, _} = do_gun_open(Config),
@@ -335,6 +347,10 @@ request_end(EventData, Pid) ->
 	Pid ! {?FUNCTION_NAME, EventData},
 	Pid.
 
+response_start(EventData, Pid) ->
+	Pid ! {?FUNCTION_NAME, EventData},
+	Pid.
+
 response_inform(EventData, Pid) ->
 	Pid ! {?FUNCTION_NAME, EventData},
 	Pid.