erlang - cowboy debugging helper request/response

cowboy_debug.erl

%% See LICENSE for licensing information.
-module(cowboy_debug).

-export([onrequest_hook/1]).
-export([onresponse_hook/4]).

onrequest_hook(Req) ->
    Method = to_string(extract(cowboy_req:method(Req))),
    Path   = to_string(extract(cowboy_req:path(Req))),
    Params = params_to_string(extract(cowboy_req:qs_vals(Req))),
    Host   = to_string(extract(cowboy_req:host(Req))),
    Port   = port_to_string(extract(cowboy_req:port(Req))),
    lager:debug("~n~nStarted " ++ Method ++ " " ++ Path ++ Params ++ " for " ++ Host ++ Port ++ "~n"
                "  qs_vals  : " ++ to_native_string(extract(cowboy_req:qs_vals(Req))) ++ "~n"
                "  raw_qs   : " ++ to_native_string(extract(cowboy_req:qs(Req))) ++ "~n"
                "  bindings : " ++ to_native_string(extract(cowboy_req:bindings(Req))) ++ "~n"
                "  cookies  : " ++ to_native_string(extract(cowboy_req:cookies(Req))) ++ "~n"
                "  headers  : " ++ to_native_string(extract(cowboy_req:headers(Req))) ++ "~n"),
    Req.

onresponse_hook(Code, Headers, Response, Req) ->
    Method = to_string(extract(cowboy_req:method(Req))),
    Path   = to_string(extract(cowboy_req:path(Req))),
    Params = params_to_string(extract(cowboy_req:qs_vals(Req))),
    Host   = to_string(extract(cowboy_req:host(Req))),
    Port   = port_to_string(extract(cowboy_req:port(Req))),
    lager:debug(
      "~n~nCompleted " ++ to_string(Code) ++ " " ++ Method ++ " " ++ Path ++ Params ++ " for " ++ Host ++ Port ++ "~n"
      "  cookies  : " ++ to_native_string(extract(cowboy_req:cookies(Req))) ++ "~n"
      "  headers  : " ++ to_native_string(Headers) ++ "~n"
      "  response : " ++ to_native_string(Response)),
    Req.

extract({Value, _Req}) ->
    Value.

params_to_string(Params) ->
    case to_string(Params) of
        "" ->
            "";
        OtherParams -> "?" ++ OtherParams
    end.

port_to_string(Port) ->    case to_string(Port) of
                               "80" -> "";
                               OtherPort -> ":" ++ OtherPort
                           end.

%% print value as standard format
to_native_string(Value) ->
    io_lib:format("~p", [Value]).

%% convert everything to string
to_string(undefined) ->
    "";
to_string(Atom) when is_atom(Atom) ->
    atom_to_list(Atom);
to_string(Binary) when is_binary(Binary) ->
    binary_to_list(Binary);
to_string(Integer) when is_integer(Integer) ->
    integer_to_list(Integer);
to_string([])
-> "";
to_string(List) when is_list(List) ->
    to_string(List, "").

%% convert lists to string
to_string(Binary, Separator) when is_binary(Binary) ->
    to_string(binary_to_list(Binary), Separator);
to_string(List, Separator) when is_list(List) ->
    string:join(list_to_string(List, []), Separator).

list_to_string([], Result) ->
    lists:reverse(Result);
list_to_string([Head| Rest], Result) ->
    list_to_string(Rest, [to_string(Head)|Result]).

example_output.txt

Started GET /sdk/src/tab/Tab.js for localhost:8080
  qs_vals  : undefined
  raw_qs   : <<"_dc=1347397546129">>
  bindings : undefined
  cookies  : undefined
  headers  : [{'Connection',<<"keep-alive">>},
 {'Cookie',<<"__utma=111872281.400915425.1346312146.1346322221.1346410278.3; __utmz=111872281.1346312146.1.1.utmcsr=(direct)|utmccn=(direct)|utmcmd=(none); SnapABugHistory=83#">>},
 {'Accept-Encoding',<<"gzip, deflate">>},
 {'Accept-Language',<<"en-us">>},
 {'Referer',<<"http://localhost:8080/">>},
 {'Accept',<<"*/*">>},
 {'User-Agent',<<"Mozilla/5.0 (Macintosh; Intel Mac OS X 10_8_1) AppleWebKit/536.25 (KHTML, like Gecko) Version/6.0 Safari/536.25">>},
 {'Host',<<"localhost:8080">>}]
23:05:46.133 [info] 

Completed 200 GET /sdk/src/tab/Tab.js for localhost:8080
  cookies  : undefined
  headers  : [{<<"Last-Modified">>,"Tue, 11 Sep 2012 17:35:50 GMT"},
 {<<"Content-Type">>,[<<"application">>,<<"/">>,<<"javascript">>,<<>>]},
 {<<"Content-Length">>,"3073"},
 {<<"Date">>,<<"Tue, 11 Sep 2012 21:05:45 GMT">>},
 {<<"Server">>,<<"Cowboy">>},
 {<<"Connection">>,<<"keep-alive">>}]
  response : <<"{}">>

online_app.erl

...
    {ok, _} = cowboy:start_http(http, 100,
                                [{port, 8080}], [
                                                                      {env, [{dispatch, Dispatch}]},
                                                                      {onrequest, fun cowboy_debug:onrequest_hook/1},
                                                                      {onresponse, fun cowboy_debug:onresponse_hook/4}
                                                                     ]),
...

I was trying this out, and had to add a line to your code to make it work.

to_string('undefined', _Seperator) ->
"undefined".

because it seems the host was undefined as you can see in the Completed 101 GET below.

Started GET / for my.domain.com:7004
qs_vals : undefined
raw_qs : <<"ts=1382971249858">>
bindings : undefined
cookies : undefined
headers : [{'Cookie',<<"fbm_xxxxx=base_domain=.domain.com; _smsg_xxxxxx=true; fbm_xxxxxxxxx=base_domain=.domain.com; fbm_xxxxxxxxxxxxx=base_domain=.domain.com">>},
{'User-Agent',<<"Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/30.0.1599.101 Safari/537.36">>},
{<<"Sec-Websocket-Extensions">>,<<"x-webkit-deflate-frame">>},
{<<"Sec-Websocket-Version">>,<<"13">>},
{<<"Sec-Websocket-Key">>,<<"aaaaaaaaaaaaaaaaaaaaaaaaaa">>},
{'Cache-Control',<<"no-cache">>},
{'Pragma',<<"no-cache">>},
{<<"Origin">>,<<"https://test.com:1008">>},
{'Host',<<"my.domain.com:7004">>},
{'Connection',<<"Upgrade">>},
{'Upgrade',<<"websocket">>}]
2013-10-28 07:40:50.276 [info] <0.1466.0>@cowboy_debug:onresponse_hook:33

Completed 101 GET / for undefined:7004
cookies : []
headers : [{<<"Upgrade">>,<<"websocket">>},
{<<"Sec-Websocket-Accept">>,<<"bbbbbbbbbbbbbbbbbbbbbbbbbbbb">>},
{<<"Connection">>,<<"Upgrade">>}]

Do you think this reflects a problem in my code?

Thanks

updated for latest cowboy api.