description = [[
Discovers servers running the X Display Manager Control Protocol (XDMCP) by
sending a XDMCP broadcast request to the LAN. Display managers allowing access
are marked using the keyword Willing in the result.
]]

---
-- @usage
-- nmap --script broadcast-xdmcp-discover
--
-- @output
-- Pre-scan script results:
-- | broadcast-xdmcp-discover: 
-- |_  192.168.2.162 - Willing
--
-- @arg broadcast-xdmcp-discover.timeout socket timeout in seconds (default: 5)

author = "Patrik Karlsson"
license = "Same as Nmap--See http://nmap.org/book/man-legal.html"
categories = {"broadcast", "safe"}

require 'xdmcp'

prerule = function() return true end

local arg_timeout = stdnse.get_script_args(SCRIPT_NAME .. ".timeout")

action = function()

	local host, port = { ip = "255.255.255.255" }, { number = 177, protocol = "udp" }
	local options = { timeout = 1 }	
	local helper = xdmcp.Helper:new(host, port, options)
	local status = helper:connect()
	
	local req = xdmcp.Packet[xdmcp.OpCode.BCAST_QUERY]:new(nil)
	local status, err = helper:send(req)
	if ( not(status) ) then
		return false, response
	end
	
	local timeout = arg_timeout or 5
	local start = os.time()
	local result = {}
	repeat

		local status, response = helper:recv()
		if ( not(status) and response ~= "TIMEOUT" ) then
			break
		elseif ( status ) then
			local status, _, _, rhost = helper.socket:get_info()
			if ( response.header.opcode == xdmcp.OpCode.WILLING ) then
				result[rhost] = true
			else
				result[rhost] = false
			end
		end
		
	until( os.time() - start > timeout )

	local output = {}
	for ip, res in pairs(result) do
		if ( res ) then
			table.insert(output, ("%s - Willing"):format(ip))
		else
			table.insert(output, ("%s - Unwilling"):format(ip))
		end
	end
	return stdnse.format_output(true, output)
end