A request/response rewriting HTTP proxy. A Rack app.
Ruby
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ncr Merge pull request #73 from voikya/master
Fix incorrect header serialization in streamed responses
Latest commit 8056fb7 Mar 26, 2018

README.md

A request/response rewriting HTTP proxy. A Rack app. Subclass Rack::Proxy and provide your rewrite_env and rewrite_response methods.

Installation

Add the following to your Gemfile:

gem 'rack-proxy', '~> 0.6.4'

Or install:

gem install rack-proxy

Use Cases

Below are some examples of real world use cases for Rack-Proxy, done something interesting add the list below and send a PR.

  • Allowing one app to act as central trust authority
    • handle accepting self-sign certificates for internal apps
    • authentication / authorization prior to proxying requests to a blindly trusting backend
    • avoiding CORs complications by proxying from same domain to another backend
  • subdomain based pass-through to multiple apps
  • Complex redirect rules
    • redirect pages with different extensions (ex: .php) to another app
    • useful for handling awkward redirection rules for moved pages
  • fan Parallel Requests: turning a single API request to multiple concurrent backend requests & merging results.
  • inserting or stripping headers required or problematic for certain clients

Options

Options can be set when initializing the middleware or overriding a method.

  • :streaming - defaults to true, but does not work on all Ruby versions, recommend to set to false
  • :ssl_verify_none - tell Net::HTTP to not validate certs
  • :ssl_version - tell Net::HTTP to set a specific ssl_version
  • :backend - the URI parseable format of host and port of the target proxy backend. If not set it will assume the backend target is the same as the source.
  • :read_timeout - set proxy timeout it defaults to 60 seconds

To pass in options, when you configure your middleware you can pass them in as an optional hash.

Rails.application.config.middleware.use ExampleServiceProxy, backend: 'http://guides.rubyonrails.org', streaming: false

Examples

See and run the examples below from lib/rack_proxy_examples/. To mount any example into an existing Rails app:

  1. create config/initializers/proxy.rb
  2. modify the file to require the example file
require 'rack_proxy_examples/forward_host'

Forward request to Host and Insert Header

Test with require 'rack_proxy_examples/forward_host'

class ForwardHost < Rack::Proxy

  def rewrite_env(env)
    env["HTTP_HOST"] = "example.com"
    env
  end

  def rewrite_response(triplet)
    status, headers, body = triplet

    # example of inserting an additional header
    headers["X-Foo"] = "Bar"
    
    # if you rewrite env, it appears that content-length isn't calculated correctly
    # resulting in only partial responses being sent to users
    # you can remove it or recalculate it here
    headers["content-length"] = nil

    triplet
  end

end

Disable SSL session verification when proxying a server with e.g. self-signed SSL certs

Test with require 'rack_proxy_examples/trusting_proxy'

class TrustingProxy < Rack::Proxy

  def rewrite_env(env)
    env["HTTP_HOST"] = "self-signed.badssl.com"

    # We are going to trust the self-signed SSL 
    env["rack.ssl_verify_none"] = true
    env
  end

  def rewrite_response(triplet)
    status, headers, body = triplet
    
    # if you rewrite env, it appears that content-length isn't calculated correctly
    # resulting in only partial responses being sent to users
    # you can remove it or recalculate it here
    headers["content-length"] = nil

    triplet
  end

end

The same can be achieved for all requests going through the Rack::Proxy instance by using

Rack::Proxy.new(ssl_verify_none: true)

Rails middleware example

Test with require 'rack_proxy_examples/example_service_proxy'

###
# This is an example of how to use Rack-Proxy in a Rails application.
#  
# Setup:
# 1. rails new test_app 
# 2. cd test_app
# 3. install Rack-Proxy in `Gemfile`
#    a. `gem 'rack-proxy', '~> 0.6.3'`
# 4. install gem: `bundle install`
# 5. create `config/initializers/proxy.rb` adding this line `require 'rack_proxy_examples/example_service_proxy'`
# 6. run: `SERVICE_URL=http://guides.rubyonrails.org rails server`
# 7. open in browser: `http://localhost:3000/example_service`
#
###
ENV['SERVICE_URL'] ||= 'http://guides.rubyonrails.org'

class ExampleServiceProxy < Rack::Proxy
  def perform_request(env)
    request = Rack::Request.new(env)

    # use rack proxy for anything hitting our host app at /example_service
    if request.path =~ %r{^/example_service}
        backend = URI(ENV['SERVICE_URL'])
        # most backends required host set properly, but rack-proxy doesn't set this for you automatically
        # even when a backend host is passed in via the options
        env["HTTP_HOST"] = backend.host

        # This is the only path that needs to be set currently on Rails 5 & greater
        env['PATH_INFO'] = ENV['SERVICE_PATH'] || '/configuring.html'
        
        # don't send your sites cookies to target service, unless it is a trusted internal service that can parse all your cookies
        env['HTTP_COOKIE'] = ''
        super(env)
    else
      @app.call(env)
    end
  end
end

Using as middleware to forward only some extensions to another Application

Test with require 'rack_proxy_examples/rack_php_proxy'

Example: Proxying only requests that end with ".php" could be done like this:

###
# Open http://localhost:3000/test.php to trigger proxy
###
class RackPhpProxy < Rack::Proxy

  def perform_request(env)
    request = Rack::Request.new(env)
    if request.path =~ %r{\.php}
      env["HTTP_HOST"] = ENV["HTTP_HOST"] ? URI(ENV["HTTP_HOST"]).host : "localhost"
      ENV["PHP_PATH"] ||= '/manual/en/tutorial.firstpage.php'
       
      # Rails 3 & 4
      env["REQUEST_PATH"] = ENV["PHP_PATH"] || "/php/#{request.fullpath}"
      # Rails 5 and above
      env['PATH_INFO'] = ENV["PHP_PATH"] || "/php/#{request.fullpath}"

      env['content-length'] = nil
      
      super(env)
    else
      @app.call(env)
    end
  end

  def rewrite_response(triplet)
    status, headers, body = triplet
    
    # if you proxy depending on the backend, it appears that content-length isn't calculated correctly
    # resulting in only partial responses being sent to users
    # you can remove it or recalculate it here
    headers["content-length"] = nil

    triplet
  end
end

To use the middleware, please consider the following:

  1. For Rails we could add a configuration in config/application.rb
  config.middleware.use RackPhpProxy, {ssl_verify_none: true}
  1. For Sinatra or any Rack-based application:
class MyAwesomeSinatra < Sinatra::Base
   use  RackPhpProxy, {ssl_verify_none: true}
end

This will allow to run the other requests through the application and only proxy the requests that match the condition from the middleware.

See tests for more examples.

WARNING

Doesn't work with fakeweb/webmock. Both libraries monkey-patch net/http code.

Todos

  • Make the docs up to date with the current use case for this code: everything except streaming which involved a rather ugly monkey patch and only worked in 1.8, but does not work now.
  • Improve and validate requirements for Host and Path rewrite rules
  • Ability to inject logger and set log level