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Wednesday, 7 September 2016


simple TCP routing proxy (layer 7) in erlang.
cowboy_revproxy is a simple TCP routing proxy (layer 7) in erlang and using Cowboy connection handling. It lets you configure the routine logic in Erlang. 
If you need to proxy connections to different backend servers depending on the contents of the transmission, then cowboy_revproxy will helps you. It's heavily inspidered from proxymachine.


You need rebar to build cowboy_revproxy:
$ rebar get-deps
$ rebar compile 


The idea is simple, once a request is coming to the proxy the data is passed to a proxy function until this function return a remote connection or tell to the proxy to close the connection. 
Valid returns values are :
  • continue or ok -> wait for next chunk
  • stop -> close the connection
  • {stop, Reply} -> send Reply to the client and close the connection
  • {http, Dispatch} -> Use the HTTP protocol of cowboy with the dispatch rules list Dispatch.
  • {remote, Remote} -> return the address of the remote connection to proxy. Remote can be one of the following:
    • {ip, port}
    • {ssl, Ip, Port, Options}, where options are ssl options (keyfile, certfile & password).
  • [{remote, Remote}, {data, Data}] -> same as above, but data passed to the proxy function is replaced by Dataand will be send to the remote connection.
  • [{remote, Remote}, {data, Data}, {reply, Reply}] -> same as above but reply Reply to the client.


Here is a simple example of function proxying the port 8080 to
-export([start/0, proxy/1]).

proxy(_Data) ->
    {remote, {"", 80}}.

start() ->
        cowboy:start_listener(http, 100,
        cowboy_tcp_transport, [{port, 8080}],
        cowboy_revproxy, [{proxy, {?MODULE, proxy}}]).
To test it do, in the source folder:
$ rebar get-deps compile
$ erl -pa ebin -pa deps/cowboy/ebin
Then in the erlang shell:
1> cowboy_revproxy_example:start().
and go on , it should display the google page.
This simple proxy function allows you to handle an HTTP request locally
proxy(Data) ->
    Dispatch = [
        %% {Host, list({Path, Handler, Opts})}
        {'_', [{'_', my_handler, []}]}
    {http, Dispatch}.
A simple "Hello World" HTTP handler:
-export([init/3, handle/2, terminate/2]).

init({tcp, http}, Req, Opts) ->
    {ok, Req, undefined_state}.

handle(Req, State) ->
    {ok, Req2} = cowboy_http_req:reply(200, [], <<"Hello World!">>, Req),
    {ok, Req2, State}.

terminate(Req, State) ->