Question

I am using cowboy( https://github.com/extend/cowboy) for one restful web service, I need to get the params from “http://localhost:8080/?a=1&b=2&c=32”

init({tcp, http}, Req, Opts) ->
    log4erl:debug("~p~n", [Opts]),
    {ok, Req, undefined_state}.

handle(Req, State) ->
    {ok, Req2} = cowboy_http_req:reply(200, [], <<"Hello World!">>, Req),
    io:format("How to get the params from Req ? "),
    {ok, Req2, State}.

terminate(Req, State) ->
    log4erl:debug("~p~p~n", [Req, State]),
    ok.

Answer 1

You should use the cowboy_http_req:qs_val/2 function, e.g. cowboy_http_req:qs_val(<<"a">>, Req), look at https://github.com/extend/cowboy/blob/master/examples/echo_get/src/toppage_handler.erl
for an example.

You can also use cowboy_http_req:qs_vals/1 to retrieve a list of all query string values.