Updating state in Cowboy Websocket handler crashes or ignores silently - websocket

Question

I have a ws_handler which receives a websocket connection.
This process waits for input starting with <<"h to login.
It then saves the default Websocket state, a Player process ID (which is spawned with a reference to the current PID), and an outbox message, `<<"turn1">>
websocket_handle({text, <<"h", Name/binary>>}, State) ->
{ok, PID} = player:go(self(), <<"profiledata", Name/binary>>),
erlang:start_timer(1000, self(), <<"Hello!">>),
{reply, {text, <<"You joined, ", Name/binary>>}, {State, PID, <<"turn1">>}};
I want to control data flow from this seperate player process, then have my websocket handler retrieve messages and pass them on to its client via the Outbox element.
So I add this in to manually trigger a message:
websocket_handle({text, <<"myscreen">>}, S = {_, P, _}) ->
gen_server:call(P, myscreen),
{ok, S};
and in player.erl,
handle_call(myscreen, _, {WS, Profile, Cab}) ->
gen_server:cast(WS, myscreenupdate),
{reply, ok, {WS, Profile, Cab}};
Back in ws_handler I expect this to get called:
websocket_info(myscreenupdate, State = {St,P, _}) ->
{reply, {text, <<"My screen update">>}, {St, P, <<"turn2">>}};
But the websocket output in my browser continuously prints turn1, instead of turn2.
I tried gen_server:call in player.erl and I get a timeout crash. I think this is because the {reply tuple of websocket_handle in ws_handler is supposed to be replying to the websocket.. but if that were true, then I'd expect the data to be updated:
websocket_info(myscreenupdate, State = {St,P, _}) ->
{reply, {text, <<"My screen update">>}, {St, P, <<"turn2">>}};
So I'm uncertain what's happening here.
How do I update state from a Player process then have my websocket handler retrieve that State and send it out to its connection?
ws_handler.erl:
-module(ws_handler).
-export([init/2]).
-export([websocket_init/1]).
-export([websocket_handle/2]).
-export([websocket_info/2]).
init(Req, Opts) ->
{cowboy_websocket, Req, Opts}.
websocket_init(State) ->
{ok, State}.
websocket_handle({text, <<"h", Name/binary>>}, State) ->
{ok, PID} = player:go(self(), <<"profiledata", Name/binary>>),
erlang:start_timer(1000, self(), <<"Hello!">>),
{reply, {text, <<"You joined, ", Name/binary>>}, {State, PID, <<"turn1">>}};
websocket_handle({text, <<"myscreen">>}, S = {_, P, _}) ->
gen_server:call(P, myscreen),
{ok, S};
websocket_handle({text, <<"auth", Auth/binary>>}, S = {_St, P, _}) ->
case s:s(P, Auth) of
{ok, Valid} -> {reply, {text, << "Authorized">>}, S};
_ -> {reply, {text, <<"Error">>}, S}
end;
websocket_handle({text, Msg}, S = {_St, P, Outbox}) ->
{reply, {text, Outbox}, S};
websocket_handle(_Data, State) ->
{ok, State}.
websocket_info(myscreenupdate, State = {St,P, _}) ->
{reply, {text, <<"My screen update">>}, {St, P, <<"turn2">>}};
websocket_info({timeout, _Ref, _Ignored}, State = {_, P, Outbox}) ->
erlang:start_timer(1000, self(), <<"This is ignored">>),
Msg = Outbox,
{reply, {text, Msg}, State};
websocket_info(_Info, State) ->
{ok, State}.
player.erl:
-module(player).
-compile(export_all).
handle_call(myscreen, _, {WS, Profile, Cab}) ->
gen_server:cast(WS, myscreenupdate),
{reply, ok, {WS, Profile, Cab}};
handle_call(get_profile, _, State = {_WSPID, Profile, _}) ->
{reply, Profile, State}.
init([WSPID, Profile]) ->
{ok, {WSPID, Profile, null}};
init([WSPID, Profile, CabinetPID]) ->
{ok, {WSPID, Profile, CabinetPID}}.
go(WSPID, Profile, CabinetPID) ->
gen_server:start_link(?MODULE, [WSPID, Profile, CabinetPID], []).
go(WSPID, Profile) ->
gen_server:start_link(?MODULE, [WSPID, Profile], []).

Answer 1

The problem is that cowboy's websocket_info/2 handler will only receive messages sent to the websocket process by using the erlang built-in message operator ! (or, equivalently, the erlang:send/{2,3} functions).
So you should do:
WS ! myscreenupdate
instead of
gen_server:cast(WS, myscreenupdate)
When you use gen_server:cast the message is probably discarded by the cowboy message loop since it's not a recognized message. And when you use gen_server:call you get a deadlock.