domain resolver service, a very simple, fast, low heap Lua script ... i wrote this to use together with gnutella2 cache/torrent tracker who lives in google appengine and doesnt have Inet class :(

gistfile1.lua

 --[[
----------------------------------------------------------------------------
"THE BEER-WARE LICENSE" (Revision 42):
<[email protected]> wrote this file. As long as you retain this notice you
can do whatever you want with this stuff. If we meet some day, and you think
this stuff is worth it, you can buy me a beer in return
----------------------------------------------------------------------------
--]]

-- all necessery libs
local http      = require 'http'
local coroutine = require 'coroutine'
local string    = require 'string'
local table     = require 'table'
local uv        = require 'uv_native'
-- only local methods for fast addressing and low memory consumption
local gsub, find, match, format, sub, insert, each, resolve, create, resume = 
      string.gsub, string.find, string.match, string.format, string.sub, table.insert, table.foreach, uv.dnsGetAddrInfo, coroutine.create, coroutine.resume
-- clean memory
string, table, coroutine, uv = nil, nil, nil, nil

local port  = 6969

-- retrieve domain only ... avoid any weird injection
local function get_domain(domain) 
  return match(domain, "[A-Za-z0-9%.%%%+%-]+%.%w%w%w?%w?")
end

-- custom parser, luvit parse is not good
local function get_query(url)
  if find(url, '?')     == nil then return {} end
  local results         =  {}
  local parse_query     =  function(key, value)
    if find(key, "%[%]")  ~= nil then
      key          = gsub(key, '%[%]', '')
      results[key] = results[key] and results[key] or {}
      insert(results[key], value)
    else
      results[key] = value
    end
  end
  gsub(url, "%/?%??([^&=]+)=?([^&=]*)&?", parse_query)
  return results
end

-- resolve many domains it can using coroutines
local function resolve_domains_async(domains, finish_callback)
  local i, results, total_domains, coroutine = 1, {}, #domains, nil

  local callback = function(e, data, domain)
    results[domain] = (e or not data) and '' or data[1]
    total_domains = total_domains - 1
    if total_domains == 0 then
      finish_callback(results)
    end
  end
  
  for i=1, total_domains do 
    coroutine = create(resolve)
    resume(coroutine, domains[i], 2, function(err, data) callback(e, data, domains[i]) end)
  end
end

-- main, where shit happens
local function main(req, res)
  local body = ''
  local function send(code, content_type) 
    res:writeHead(code, {
      ['Content-Type']   = content_type and content_type or 'text/plain',
      ['Content-Length'] = #body
    })
    res:finish(body)
    return
  end

  local query = get_query(req.url)
  if not query.domain then
    body = [[<h2>You are not doing right</h2>
    <p>this service only respond to domain/domain[] queries, e.g. </p>
    <pre>?domain[]=google.com&domain[]=yahoo.com</pre><p>
    and responses with json formated like this:</p>
    <pre>{
  "google" : "999.999.999.999",
  "yahoo.com" : "999.999.999.999"
}</pre>]]
    send(200, 'text/html')
  else
    
    local callback = function(resolved) 
      each(resolved, function(k, v) 
          body = body .. format('"%s":"%s",', k, v) 
        end)
      body = "{".. sub(body, 1, -2) .."}"
      send(200, 'application/json')
    end
    
    if type(query.domain)=='string' then
      local t = {}
      t[1]    = query.domain
      query.domain = t
    end
    
    resolve_domains_async(query.domain, callback)
  end
end

-- horizon of events :D
http.createServer(main):listen(port)

print(format('server listening at http://localhost:%d', port))