Fix a miscount of output flow control window for HTTP/2

The miscount occurred because of a faulty iolist split function.
The bug should now be corrected, a PropEr test has been added
and a regression test has also been added.

test/http2_SUITE.erl

@@ -18,6 +18,7 @@
 
 -import(ct_helper, [config/2]).
 -import(ct_helper, [doc/1]).
+-import(cowboy_test, [gun_open/1]).
 
 all() -> [{group, clear}].
 
@@ -25,7 +26,8 @@ groups() -> [{clear, [parallel], ct_helper:all(?MODULE)}].
 
 init_routes(_) -> [
 	{"localhost", [
-		{"/", hello_h, []}
+		{"/", hello_h, []},
+		{"/resp_iolist_body", resp_iolist_body_h, []}
 	]}
 ].
 
@@ -45,16 +47,32 @@ do_handshake(Config) ->
 
 inactivity_timeout(Config) ->
 	doc("Terminate when the inactivity timeout is reached"),
-	Ref = inactivity_timeout_listener,
 	ProtoOpts = #{
 		env => #{dispatch => cowboy_router:compile(init_routes(Config))},
 		inactivity_timeout => 1000
 	},
-	{ok, _} = cowboy:start_clear(Ref, [{port, 0}], ProtoOpts),
-	Port = ranch:get_port(Ref),
-	SocketConfig = [{type, tcp}, {protocol, http}, {port, Port}, {opts, []}|Config],
-	{ok, Socket} = do_handshake(SocketConfig),
+	{ok, _} = cowboy:start_clear(inactivity_timeout, [{port, 0}], ProtoOpts),
+	Port = ranch:get_port(inactivity_timeout),
+	{ok, Socket} = do_handshake([{port, Port}|Config]),
 	receive after 1000 -> ok end,
 	%% Receive a GOAWAY frame back with an INTERNAL_ERROR.
 	{ok, << _:24, 7:8, _:72, 2:32 >>} = gen_tcp:recv(Socket, 17, 1000),
 	ok.
+
+resp_iolist_body(Config) ->
+	doc("Regression test when response bodies are iolists that "
+		"include improper lists, empty lists and empty binaries. "
+		"The original issue failed to split the body into frames properly."),
+	ProtoOpts = #{
+		env => #{dispatch => cowboy_router:compile(init_routes(Config))}
+	},
+	{ok, _} = cowboy:start_clear(resp_iolist_body, [{port, 0}], ProtoOpts),
+	Port = ranch:get_port(resp_iolist_body),
+	ConnPid = gun_open([{type, tcp}, {protocol, http2}, {port, Port}|Config]),
+	Ref = gun:get(ConnPid, "/resp_iolist_body"),
+	{response, nofin, 200, RespHeaders} = gun:await(ConnPid, Ref),
+	{_, BinLen} = lists:keyfind(<<"content-length">>, 1, RespHeaders),
+	Len = binary_to_integer(BinLen),
+	{ok, RespBody} = gun:await_body(ConnPid, Ref),
+	Len = iolist_size(RespBody),
+	gun:close(ConnPid).