app.rb

#!/usr/bin/env ruby

require "sinatra"
require "json"

require_relative "pactools"

get "/" do
    "Hello, world!"
end

post "/api/:browser/:format/" do
    if not ["firefox", "chrome", "safari", "ie", "edge", "opera", "all"].include? params[:browser]
        "#{params[:browser]} is not a recognized browser"
    end

    result = evaluate_pac params[:browser], params[:script]

    if params[:format] == "json"
        "#{result}"
    elsif params[:format] == "txt" or params[:format] == "text"
        "#{JSON.parse(result)['result']}"
    else
        "#{params[:format]} is not a recognized format."
    end
end

results.txt

spooky@spookypac:/var/www$ curl -sLF 'script=test' 'http://spookypac.com/api/firefox/text/' && echo
PROXY proxy.example.com:8080
spooky@spookypac:/var/www$ curl -sLF 'script=test' 'http://spookypac.com/api/firefox/txt/' && echo
PROXY proxy.example.com:8080
spooky@spookypac:/var/www$ curl -sLF 'script=test' 'http://spookypac.com/api/firefox/json/' && echo
{"browser": "firefox", "script": "test", "result": "PROXY proxy.example.com:8080"}
spooky@spookypac:/var/www$ curl -sLF 'script=test' 'http://spookypac.com/api/notabrowser/json/' && echo
{"browser": "notabrowser", "script": "test", "result": "PROXY proxy.example.com:8080"}
spooky@spookypac:/var/www$