Ensure stream terminate is called when switching protocols

doc/src/manual/cowboy_stream.asciidoc

@@ -355,7 +355,7 @@ detected.
 
 [source,erlang]
 ----
-reason() :: normal
+reason() :: normal | switch_protocol
     | {internal_error, timeout | {error | exit | throw, any()}, HumanReadable}
     | {socket_error, closed | atom(), HumanReadable}
     | {stream_error, Error, HumanReadable}

src/cowboy_http.erl

@@ -878,22 +878,17 @@ commands(State0=#state{ref=Ref, parent=Parent, socket=Socket, transport=Transpor
 	%% @todo This should be the last stream running otherwise we need to wait before switching.
 	%% @todo If there's streams opened after this one, fail instead of 101.
 	State = cancel_timeout(State0),
-	%% @todo When we actually do the upgrade, we only have the one stream left, plus
-	%% possibly some processes terminating. We need a smart strategy for handling the
-	%% children shutdown. We can start with brutal_kill and discarding the EXIT messages
-	%% received before switching to Websocket. Something better would be to let the
-	%% stream processes finish but that implies the Websocket module to know about
-	%% them and filter the messages. For now, kill them all and discard all messages
-	%% in the mailbox.
-
+	%% Send a 101 response, then terminate the stream.
+	State = #state{streams=Streams} = commands(State, StreamID, [{inform, 101, Headers}]),
+	#stream{state=StreamState} = lists:keyfind(StreamID, #stream.id, Streams),
+	%% @todo We need to shutdown processes here first.
+	stream_call_terminate(StreamID, switch_protocol, StreamState),
+	%% Terminate children processes and flush any remaining messages from the mailbox.
 	cowboy_children:terminate(Children),
-
 	flush(),
-	%% Everything good, upgrade!
-	_ = commands(State, StreamID, [{inform, 101, Headers}]),
 	%% @todo This is no good because commands return a state normally and here it doesn't
 	%% we need to let this module go entirely. Perhaps it should be handled directly in
-	%% cowboy_clear/cowboy_tls? Perhaps not. We do want that Buffer.
+	%% cowboy_clear/cowboy_tls?
 	Protocol:takeover(Parent, Ref, Socket, Transport, Opts, <<>>, InitialState);
 %% Stream shutdown.
 commands(State, StreamID, [stop|Tail]) ->

src/cowboy_stream.erl

@@ -42,7 +42,7 @@
 	| stop].
 -export_type([commands/0]).
 
--type reason() :: normal
+-type reason() :: normal | switch_protocol
 	| {internal_error, timeout | {error | exit | throw, any()}, human_reason()}
 	| {socket_error, closed | atom(), human_reason()}
 	| {stream_error, cow_http2:error(), human_reason()}

test/handlers/stream_handler_h.erl

@@ -9,6 +9,9 @@
 -export([terminate/3]).
 -export([early_error/5]).
 
+%% For switch_protocol.
+-export([takeover/7]).
+
 -record(state, {
 	pid,
 	test
@@ -43,6 +46,8 @@ init_commands(_, _, State=#state{test=shutdown_timeout_on_stream_stop}) ->
 init_commands(_, _, State=#state{test=shutdown_timeout_on_socket_close}) ->
 	Spawn = init_process(true, State),
 	[{headers, 200, #{}}, {spawn, Spawn, 2000}];
+init_commands(_, _, State=#state{test=terminate_on_switch_protocol}) ->
+	[{switch_protocol, #{}, ?MODULE, State}];
 init_commands(_, _, State=#state{test=terminate_on_stop}) ->
 	[{response, 204, #{}, <<>>}];
 init_commands(_, _, _) ->
@@ -94,3 +99,8 @@ early_error(StreamID, Reason, PartialReq, Resp, Opts) ->
 		<<"crash_in_early_error",_/bits>> -> error(crash);
 		_ -> Resp
 	end.
+
+%% @todo It would be good if we could allow this function to return normally.
+takeover(Parent, Ref, Socket, Transport, Opts, Buffer, State=#state{pid=Pid}) ->
+	Pid ! {Pid, self(), takeover, Parent, Ref, Socket, Transport, Opts, Buffer, State},
+	exit(normal).

test/stream_handler_SUITE.erl

@@ -361,3 +361,26 @@ terminate_on_stop(Config) ->
 	%% Confirm terminate/3 is called.
 	receive {Self, Pid, terminate, _, _, _} -> ok after 1000 -> error(timeout) end,
 	ok.
+
+terminate_on_switch_protocol(Config) ->
+	case config(protocol, Config) of
+		http -> do_terminate_on_switch_protocol(Config);
+		http2 -> doc("The switch_protocol command is not currently supported for HTTP/2.")
+	end.
+
+do_terminate_on_switch_protocol(Config) ->
+	doc("Confirm terminate/3 is called after switch_protocol is returned."),
+	Self = self(),
+	ConnPid = gun_open(Config),
+	Ref = gun:get(ConnPid, "/long_polling", [
+		{<<"accept-encoding">>, <<"gzip">>},
+		{<<"x-test-case">>, <<"terminate_on_switch_protocol">>},
+		{<<"x-test-pid">>, pid_to_list(Self)}
+	]),
+	%% Confirm init/3 is called and receive the response.
+	Pid = receive {Self, P, init, _, _, _} -> P after 1000 -> error(timeout) end,
+	%% Confirm terminate/3 is called.
+	receive {Self, Pid, terminate, _, _, _} -> ok after 1000 -> error(timeout) end,
+	%% Confirm takeover/7 is called.
+	receive {Self, Pid, takeover, _, _, _, _, _, _, _} -> ok after 1000 -> error(timeout) end,
+	ok.