Parsing Proxy Auto-Config files

One thing I’ve always been wanting to be able to do was parse a proxy auto-config file from the command line.

I only recently found the pacparser library but found it limiting because it isn’t easy to install and use. So I decided to write a rubygem that would parse a pac file.

I started using the execjs gem but one thing I quickly figured out is that you cannot implement all of the pac functions in pure JavaScript. Most notably is the dnsResolve(host) function which you cannot write in JavaScript because it lacks a way to make DNS queries.

So I took the code from execjs that deals with the four native runtimes and modified it to make ruby methods available in the JavaScript runtime. And now it’s available in the pac gem.

You will need a JavaScript runtime installed to be able to use the pac gem, I recommend therubyracer gem for ruby and therubyrhino for jruby. johnson only works with ruby 1.8 and mustang requires the v8 library to be installed.

gem install therubyracer pac

And now you can use the parsepac executable.

parsepac http://cloud.github.com/downloads/samuelkadolph/ruby-pac/sample.pac http://samuel.kadolph.com

Or in ruby.

require "rubygems"
require "pac"

pac = PAC.load("http://cloud.github.com/downloads/samuelkadolph/ruby-pac/sample.pac")
pac.find("http://samuel.kadolph.com") # => "DIRECT"

pac = PAC.read("sample.pac")

pac = PAC.source <<-JS
  function FindProxyForURL(url, host) {
    return "DIRECT";
  }
JS

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