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EventMachine Proxy DSL for writing high-performance transparent / intercepting proxies in Ruby.

Getting started

$> gem install em-proxy
$> em-proxy
Usage: em-proxy [options]
  -l, --listen [PORT]              Port to listen on
  -d, --duplex [host:port, ...]    List of backends to duplex data to
  -r, --relay [hostname:port]      Relay endpoint: hostname:port
  -s, --socket [filename]          Relay endpoint: unix filename
  -v, --verbose                    Run in debug mode

$> em-proxy -l 8080 -r localhost:8081 -d localhost:8082,localhost:8083 -v

The above will start em-proxy on port 8080, relay and respond with data from port 8081, and also (optional) duplicate all traffic to ports 8082 and 8083 (and discard their responses).

Simple port forwarding proxy

Proxy.start(:host => "", :port => 80, :debug => true) do |conn|
  conn.server :srv, :host => "", :port => 81

  # modify / process request stream
  conn.on_data do |data|
    p [:on_data, data]

  # modify / process response stream
  conn.on_response do |backend, resp|
    p [:on_response, backend, resp]

  # termination logic
  conn.on_finish do |backend, name|
    p [:on_finish, name]

    # terminate connection (in duplex mode, you can terminate when prod is done)
    unbind if backend == :srv

For more examples see the /examples directory.

  • SMTP Spam Filtering
  • Duplicating traffic
  • Selective forwarding
  • Beanstalkd interceptor
  • etc.

A schema-free MySQL proof of concept, via an EM-Proxy server:


The MIT License - Copyright (c) 2010 Ilya Grigorik