Fix handler crashes handling

We try to send a 500 error only if we didn't send the response
headers yet. If they were, then we have no way to be sure the
response was fully sent, nor should we assume anything about
how this will be handled client-side, so we do nothing more
and in both cases close the connection.

include/http.hrl

@@ -46,6 +46,7 @@
 	connection = keepalive :: keepalive | close,
 
 	%% Request.
+	pid        = undefined :: pid(),
 	method     = 'GET'     :: http_method(),
 	version    = {1, 1}    :: http_version(),
 	peer       = undefined :: undefined | {inet:ip_address(), inet:ip_port()},

src/cowboy_http_protocol.erl

@@ -120,13 +120,13 @@ request({http_request, Method, {abs_path, AbsPath}, Version},
 	{Path, RawPath, Qs} = cowboy_dispatcher:split_path(AbsPath, URLDecode),
 	ConnAtom = version_to_connection(Version),
 	parse_header(#http_req{socket=Socket, transport=Transport,
-		connection=ConnAtom, method=Method, version=Version,
+		connection=ConnAtom, pid=self(), method=Method, version=Version,
 		path=Path, raw_path=RawPath, raw_qs=Qs, urldecode=URLDec}, State);
 request({http_request, Method, '*', Version},
 		State=#state{socket=Socket, transport=Transport, urldecode=URLDec}) ->
 	ConnAtom = version_to_connection(Version),
 	parse_header(#http_req{socket=Socket, transport=Transport,
-		connection=ConnAtom, method=Method, version=Version,
+		connection=ConnAtom, pid=self(), method=Method, version=Version,
 		path='*', raw_path= <<"*">>, raw_qs= <<>>, urldecode=URLDec}, State);
 request({http_request, _Method, _URI, _Version}, State) ->
 	error_terminate(501, State);
@@ -276,7 +276,7 @@ handler_handle(HandlerState, Req, State=#state{handler={Handler, Opts}}) ->
 			[Handler, Class, Reason, Opts,
 			 HandlerState, Req, erlang:get_stacktrace()]),
 		handler_terminate(HandlerState, Req, State),
-		terminate(State)
+		error_terminate(500, State)
 	end.
 
 %% We don't listen for Transport closes because that would force us
@@ -331,7 +331,9 @@ handler_call(HandlerState, Req, State=#state{handler={Handler, Opts}},
 			"** Options were ~p~n** Handler state was ~p~n"
 			"** Request was ~p~n** Stacktrace: ~p~n~n",
 			[Handler, Class, Reason, Opts,
-			 HandlerState, Req, erlang:get_stacktrace()])
+			 HandlerState, Req, erlang:get_stacktrace()]),
+		handler_terminate(HandlerState, Req, State),
+		error_terminate(500, State)
 	end.
 
 -spec handler_terminate(any(), #http_req{}, #state{}) -> ok.
@@ -359,6 +361,8 @@ next_request(Req=#http_req{connection=Conn, buffer=Buffer},
 		HandlerRes) ->
 	RespRes = ensure_response(Req),
 	BodyRes = ensure_body_processed(Req),
+	%% Flush the resp_sent message before moving on.
+	receive {cowboy_http_req, resp_sent} -> ok after 0 -> ok end,
 	case {HandlerRes, BodyRes, RespRes, Conn} of
 		{ok, ok, ok, keepalive} when Keepalive < MaxKeepalive ->
 			?MODULE:parse_request(State#state{
@@ -395,11 +399,17 @@ ensure_response(#http_req{socket=Socket, transport=Transport,
 	Transport:send(Socket, <<"0\r\n\r\n">>),
 	close.
 
+%% Only send an error reply if there is no resp_sent message.
 -spec error_terminate(http_status(), #state{}) -> ok.
 error_terminate(Code, State=#state{socket=Socket, transport=Transport}) ->
-	_ = cowboy_http_req:reply(Code, [], [], #http_req{
+	receive
+		{cowboy_http_req, resp_sent} -> ok
+	after 0 ->
+		_ = cowboy_http_req:reply(Code, #http_req{
 			socket=Socket, transport=Transport,
-		connection=close, resp_state=waiting}),
+			connection=close, pid=self(), resp_state=waiting}),
+		ok
+	end,
 	terminate(State).
 
 -spec terminate(#state{}) -> ok.

src/cowboy_http_req.erl

@@ -473,7 +473,7 @@ reply(Status, Headers, Req=#http_req{resp_body=Body}) ->
 -spec reply(http_status(), http_headers(), iodata(), #http_req{})
 	-> {ok, #http_req{}}.
 reply(Status, Headers, Body, Req=#http_req{socket=Socket,
-		transport=Transport, connection=Connection,
+		transport=Transport, connection=Connection, pid=ReqPid,
 		method=Method, resp_state=waiting, resp_headers=RespHeaders}) ->
 	RespConn = response_connection(Headers, Connection),
 	ContentLen = case Body of {CL, _} -> CL; _ -> iolist_size(Body) end,
@@ -488,6 +488,7 @@ reply(Status, Headers, Body, Req=#http_req{socket=Socket,
 		{_, {_, StreamFun}} -> Transport:send(Socket, Head), StreamFun();
 		{_, _} -> Transport:send(Socket, [Head, Body])
 	end,
+	ReqPid ! {?MODULE, resp_sent},
 	{ok, Req#http_req{connection=RespConn, resp_state=done,
 		resp_headers=[], resp_body= <<>>}}.
 
@@ -500,8 +501,9 @@ chunked_reply(Status, Req) ->
 %% @see cowboy_http_req:chunk/2
 -spec chunked_reply(http_status(), http_headers(), #http_req{})
 	-> {ok, #http_req{}}.
-chunked_reply(Status, Headers, Req=#http_req{socket=Socket, transport=Transport,
-		connection=Connection, resp_state=waiting, resp_headers=RespHeaders}) ->
+chunked_reply(Status, Headers, Req=#http_req{socket=Socket,
+		transport=Transport, connection=Connection, pid=ReqPid,
+		resp_state=waiting, resp_headers=RespHeaders}) ->
 	RespConn = response_connection(Headers, Connection),
 	Head = response_head(Status, Headers, RespHeaders, [
 		{<<"Connection">>, atom_to_connection(Connection)},
@@ -510,6 +512,7 @@ chunked_reply(Status, Headers, Req=#http_req{socket=Socket, transport=Transport,
 		{<<"Server">>, <<"Cowboy">>}
 	]),
 	Transport:send(Socket, Head),
+	ReqPid ! {?MODULE, resp_sent},
 	{ok, Req#http_req{connection=RespConn, resp_state=chunks,
 		resp_headers=[], resp_body= <<>>}}.
 
@@ -524,14 +527,16 @@ chunk(Data, #http_req{socket=Socket, transport=Transport, resp_state=chunks}) ->
 		<<"\r\n">>, Data, <<"\r\n">>]).
 
 %% @doc Send an upgrade reply.
+%% @private
 -spec upgrade_reply(http_status(), http_headers(), #http_req{})
 	-> {ok, #http_req{}}.
 upgrade_reply(Status, Headers, Req=#http_req{socket=Socket, transport=Transport,
-		resp_state=waiting, resp_headers=RespHeaders}) ->
+		pid=ReqPid, resp_state=waiting, resp_headers=RespHeaders}) ->
 	Head = response_head(Status, Headers, RespHeaders, [
 		{<<"Connection">>, <<"Upgrade">>}
 	]),
 	Transport:send(Socket, Head),
+	ReqPid ! {?MODULE, resp_sent},
 	{ok, Req#http_req{resp_state=done, resp_headers=[], resp_body= <<>>}}.
 
 %% Misc API.

src/cowboy_http_websocket.erl

@@ -169,6 +169,8 @@ websocket_handshake(State=#state{version=0, origin=Origin,
 		 {<<"Sec-Websocket-Location">>, Location},
 		 {<<"Sec-Websocket-Origin">>, Origin}],
 		Req#http_req{resp_state=waiting}),
+	%% Flush the resp_sent message before moving on.
+	receive {cowboy_http_req, resp_sent} -> ok after 0 -> ok end,
 	%% We replied with a proper response. Proxies should be happy enough,
 	%% we can now read the 8 last bytes of the challenge keys and send
 	%% the challenge response directly to the socket.
@@ -188,6 +190,8 @@ websocket_handshake(State=#state{challenge=Challenge},
 		[{<<"Upgrade">>, <<"websocket">>},
 		 {<<"Sec-Websocket-Accept">>, Challenge}],
 		Req#http_req{resp_state=waiting}),
+	%% Flush the resp_sent message before moving on.
+	receive {cowboy_http_req, resp_sent} -> ok after 0 -> ok end,
 	handler_before_loop(State#state{messages=Transport:messages()},
 		Req2, HandlerState, <<>>).