local bin = require "bin"
local bit = require "bit"
local nmap = require "nmap"
local os = require "os"
local stdnse = require "stdnse"
local table = require "table"

description = [[
Discovers Sybase Anywhere servers on the LAN by sending broadcast discovery messages.
]]

---
-- @usage
-- nmap --script broadcast-sybase-asa-discover
--
-- @output
-- Pre-scan script results:
-- | broadcast-sybase-asa-discover: 
-- |   ip=192.168.0.1; name=mysqlanywhere1; port=2638
-- |_  ip=192.168.0.2; name=mysqlanywhere2; port=49152
--

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

prerule = function() return ( nmap.address_family() == "inet") end

--
-- The following code is a bit overkill and is ment to go into a library once
-- more scripts that make use of it are developed.
--
Ping = {
	
	-- The PING request class
	Request = {

		-- Creates a new Ping request
		new = function(self)
			local o = {}
			setmetatable(o, self)
	        self.__index = self
			return o
		end,

		-- returns the ping request as a string
		__tostring = function(self)
			return bin.pack("HAH", "1b00003d0000000012", "CONNECTIONLESS_TDS",
				"000000010000040005000500000102000003010104080000000000000000070204b1")
		end
	},
	
	-- The Ping Response class
	Response = {
		-- Creates a new response
		-- @param data string containing the raw data as received over the socket
		-- @return o instance of Response
		new = function(self, data)
			local o = { data = data }
			setmetatable(o, self)
	        self.__index = self
			o:parse()
			if ( o.dbinstance ) then
				return o
			end
		end,

		-- Parses the raw response and populates the
		-- <code>dbinstance.name</code> and <code>dbinstance.port</code> fields
		parse = function(self)
			-- do a very basic length check
			local pos, len = bin.unpack(">I", self.data)
			len = bit.band(len, 0x0000FFFF)

			if ( len ~= #self.data ) then
				stdnse.print_debug(2, "The packet length was reported as %d, expected %d", len, #self.data)
				return
			end

			local connectionless_tds
			pos, connectionless_tds = bin.unpack("p", self.data, 9)
			if ( connectionless_tds ~= "CONNECTIONLESS_TDS" ) then
				stdnse.print_debug(2, "Did not find the expected CONNECTIONLESS_TDS header")
				return
			end

			self.dbinstance = {}
			pos, self.dbinstance.name = bin.unpack("p", self.data, 40)
			pos = pos + 2
			pos, self.dbinstance.port = bin.unpack(">S", self.data, pos)
		end,
	}

}

-- Main script interface
Helper = {
	
	-- Creates a new helper instance
	-- @param host table as received by the action method
	-- @param port table as received by the action method
	-- @param options table containing:
	-- 	<code>timeout</code> - the amount of time to listen for responses
	-- @return o instance of Helper
	new = function(self, host, port, options)
		local o = {
			host = host,
			port = port,
			options = options or {}
		}
		setmetatable(o, self)
        self.__index = self
		return o
	end,
	
	-- Sends a ping request to the service and processes the response
	-- @return status true on success, false on failure
	-- @return instances table of instance tables containing
	-- 	<code>name</code> - the instance name
	--	<code>ip</code> - the instance ip
	--	<code>port</code> - the instance port
	--         err string containing error message on failure
	ping = function(self)
		local socket = nmap.new_socket("udp")
		socket:set_timeout(1000)
		
		-- send 2 packets just in case
		for i=1, 2 do
			local ping_req = Ping.Request:new()
			local status, err = socket:sendto(self.host, self.port, tostring(ping_req))
			if ( not(status) ) then
				return false, "Failed to send broadcast packet"
			end
		end

		local stime = os.time()
		local instances = {}
		local timeout = self.options.timeout or ( 20 / ( nmap.timing_level() + 1 ) )

		repeat
			local status, data = socket:receive()
			if ( status ) then
				local response = Ping.Response:new(data)
				if ( response ) then
					local status, _, _, rhost, _ = socket:get_info()
					if ( not(status) ) then
						socket:close()
						return false, "Failed to get socket information"
					end
					response.dbinstance.ip = rhost
					-- avoid duplicates
					instances[response.dbinstance.name] = response.dbinstance
				end
			end
		until( os.time() - stime > timeout )
		socket:close()
		
		return true, instances
	end,
	
	
}

action = function()
		
	local timeout = ( 20 / ( nmap.timing_level() + 1 ) )
	local host = { ip = "255.255.255.255" }
	local port = { number = 2638, protocol = "udp" }
		
	local helper = Helper:new(host, port)
	local status, instances = helper:ping()
	
	if ( not(status) ) then
		return ("\n  ERROR: %s"):format(instances)
	end
		
	-- if we don't have any instances, silently abort
	if ( next(instances) == nil ) then
		return
	end

	local result = {}
	for _, instance in pairs(instances) do
		table.insert(result, ("ip=%s; name=%s; port=%d"):format(instance.ip, instance.name, instance.port))
	end
	table.sort(result)
	return stdnse.format_output(true, result)
end
