Fix a bug where dupe headers were sent in cowboy_http_req:reply/4.

Now the server defines default headers that can be overwritten by the
handler simply by passing them to the reply/4 function. Default headers
include, for now, Connection and Content-Length headers. Note that it isn't
enough to change the Connection header to close a keep-alive connection
server-side.

test/http_handler.erl

@@ -4,11 +4,15 @@
 -behaviour(cowboy_http_handler).
 -export([init/3, handle/2, terminate/2]).
 
-init({_Transport, http}, Req, _Opts) ->
-	{ok, Req, undefined}.
+-record(state, {headers, body}).
 
-handle(Req, State) ->
-	{ok, Req2} = cowboy_http_req:reply(200, [], "http_handler", Req),
+init({_Transport, http}, Req, Opts) ->
+	Headers = proplists:get_value(headers, Opts, []),
+	Body = proplists:get_value(body, Opts, "http_handler"),
+	{ok, Req, #state{headers=Headers, body=Body}}.
+
+handle(Req, State=#state{headers=Headers, body=Body}) ->
+	{ok, Req2} = cowboy_http_req:reply(200, Headers, Body, Req),
 	{ok, Req2, State}.
 
 terminate(_Req, _State) ->