--------------------------------------------------------------------------------
-- Title:               Ident.lua
-- Description:         Like a square peg in a round hole
-- Author:              Raphaël Szwarc http://alt.textdrive.com/lua/
-- Creation Date:       September 21, 2008
-- Legal:               Copyright (C) 2008 Raphaël Szwarc
--                      Under the terms of the MIT License
--                      http://www.opensource.org/licenses/mit-license.html
--------------------------------------------------------------------------------

-- import dependencies
local socket = require( 'socket' )

local assert = assert
local getmetatable = getmetatable
local ipairs = ipairs
local setmetatable = setmetatable
local tonumber = tonumber
local tostring = tostring

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-- Ident
--------------------------------------------------------------------------------

module( 'Ident' )
_VERSION = '1.0'

local self = setmetatable( _M, {} )
local meta = getmetatable( self )

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-- Utilities
--------------------------------------------------------------------------------

local IPRange =
{
    { 167772160, 184549375 },   -- 10.0.0.0 to 10.255.255.255
    { 2130706433, 2130706433 }, -- 127.0.0.1 to 127.0.0.1
    { 2886729728, 2887778303 }, -- 172.16.0.0 to 172.31.255.255
    { 3232235520, 3232301055 }  -- 192.168.0.0 to 192.168.255.255
}

local function IPNumber( anAddress )
    local anAddress = anAddress or '0.0.0.0'
    local aNumber = 0

	for anOctet in anAddress:gmatch( '%d+' ) do
		aNumber = ( aNumber * 256 ) + ( tonumber( anOctet ) or 0 )
	end
    
    return aNumber  
end

local function Accept( anAddress )
    local aNumber = IPNumber( anAddress )
    
    for anIndex, aRange in ipairs( IPRange ) do
        if aNumber >= aRange[ 1 ] and aNumber <= aRange[ 2 ] then
            return true
        end
    end
    
    return false
end

local function Connection( anAddress, aPort )
    local aPort = aPort or 113
    local aConnection = socket.tcp()
    
    if aConnection then
        aConnection:settimeout( 0.1 )
        aConnection:connect( anAddress, aPort )
        
        return aConnection
    end
end

local function Ident( aRemoteAddress, aRemotePort, aLocalPort )
    local aConnection = Connection( aRemoteAddress )
    
    if aConnection then
        local aRequest = ( '%d,%d\r\n' ):format( aRemotePort, aLocalPort )
              aConnection:send( aRequest )
        local aResponse = aConnection:receive( '*l' ) or ''
        local aServerPort, aClientPort, aType, anOS, anIdent = aResponse:match( '(%d+)%s*,%s*(%d+)%s*:%s*(.-)%s*:%s*(.-)%s*:%s*(.+)' )
        
        aConnection:close()
        
        if aServerPort and aClientPort and aType and anOS and anIdent then
            return anIdent
        end
    end
end

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-- Metamethods
--------------------------------------------------------------------------------

local cache = setmetatable( {}, { __mode = 'k' } )

function meta:__call( aRemoteAddress, aRemotePort, aLocalPort )
    if aRemoteAddress then
        local aRemoteAddress = socket.dns.toip( aRemoteAddress ) or '0.0.0.0'
        local aRemotePort = aRemotePort or 0
        local aLocalPort = aLocalPort or 0
        local aKey = ( '%s:%d,%d' ):format( aRemoteAddress, aRemotePort, aLocalPort )
        local anIndent = cache[ aKey ]
        
        if anIndent == nil and Accept( aRemoteAddress ) then    
            anIdent = Ident( aRemoteAddress, aRemotePort, aLocalPort )
            cache[ aKey ] = anIdent or false
        end
        
        if anIdent then
            return anIdent
        end
    end
end

function meta:__concat( aValue )
    return tostring( self ) .. tostring( aValue )
end

function meta:__tostring()
    return ( '%s/%s' ):format( self._NAME, self._VERSION )
end