Better handle socket closing with loop handlers

We now read from the socket to be able to detect errors or TCP close
events, and buffer the data if any. Once the data receive goes over
a certain limit, which defaults to 5000 bytes, we simply close the
connection with an {error, overflow} reason.

src/cowboy_req.erl

@@ -104,6 +104,7 @@
 -export([ensure_response/2]).
 
 %% Private setter/getter API.
+-export([append_buffer/2]).
 -export([get/2]).
 -export([set/2]).
 -export([set_bindings/4]).
@@ -1065,6 +1066,11 @@ ensure_response(#http_req{socket=Socket, transport=Transport,
 
 %% Private setter/getter API.
 
+%% @private
+-spec append_buffer(binary(), Req) -> Req when Req::req().
+append_buffer(Suffix, Req=#http_req{buffer=Buffer}) ->
+	Req#http_req{buffer= << Buffer/binary, Suffix/binary >>}.
+
 %% @private
 -spec get(atom(), req()) -> any(); ([atom()], req()) -> any().
 get(List, Req) when is_list(List) ->