require 'socket'

# one dhcp packet
class Dhcp
	MAGIC_COOKIE = 0x63825363
	OP = {
		1 => 'REQUEST', 2 => 'REPLY',
	}
	TYPE = {
		1 => 'DISCOVER', 2 => 'OFFER', 3 => 'REQUEST', 4 => 'DECLINE',
		5 => 'ACK', 6 => 'NACK', 7 => 'RELEASE', 8 => 'INFORM',
	}
	OPTION = %w[PAD SUBNETMASK TIMEOFFSET ROUTER TIMESERVER
		NAMESERVER DNS LOGSERV QUOTESSERV LPRSERV IMPSERV RESSERV
		HOSTNAME BOOTFILESIZE DUMPFILE DOMAINNAME SWAPSERV ROOTPATH
		EXTENPATH IPFORWARD SRCROUTE POLICYFILTER MAXASMSIZE IPTTL
		MTUTIMEOUT MTUTABLE MTUSIZE LOCALSUBNETS BROADCASTADDR
		DOMASKDISCOV MASKSUPPLY DOROUTEDISC ROUTERSOLICIT STATICROUTE
		TRAILERENCAP ARPTIMEOUT ETHERENCAP TCPTTL TCPKEEPALIVE
		TCPALIVEGARBAGE NISDOMAIN NISSERVERS NISTIMESERV VENDSPECIFIC
		NBNS NBDD NBTCPIP NBTCPSCOPE XFONT XDISPLAYMGR DISCOVERADDR
		LEASETIME OPTIONOVERLOAD MESSAGETYPE SERVIDENT PARAMREQUEST
		MESSAGE MAXMSGSIZE RENEWTIME REBINDTIME CLASSSID CLIENTID x x
		NISPLUSDOMAIN NISPLUSSERVERS x x MOBILEIPAGENT SMTPSERVER
		POP3SERVER NNTPSERVER WWWSERVER FINGERSERVER IRCSERVER
		STSERVER STDASERVER]

	class Option
		attr_accessor :type, :v
		def initialize(type, val)
			@type, @val = type, val
			@type = OPTION.index(@type.to_s) || @type
			if OPTION[@type] == 'MESSAGETYPE'
				@val = TYPE[@val[0]] || @val[0]
			end
		end

		def encode
			case type
			when 255: type.chr
			when OPTION.index('MESSAGETYPE'): type.chr + (TYPE.index(@val) || @val).chr
			else type.chr + @val
			end
		end

		def inspect
			"<Opt: #@type(#{OPTION[@type]})=#{@val.inspect}>"
		end
	end


	Fields = [:op, :htype, :hlen, :hops, :xid, :secs, :flags, :ciaddr, :yiaddr, :siaddr, :giaddr, :chaddr, :sname, :file]
	attr_accessor(*Fields)
	attr_accessor :options

	def initialize(*vals)
		Fields.each { |f| instance_variable_set("@#{f}", vals.shift) }
		[@chaddr, @sname, @file].each { |s| s.sub!(/\0*$/, '') }
		if vals.shift == MAGIC_COOKIE
			@options = []
			while opt = parse_option(vals)
				@options << opt
			end
		end
	end

	def parse_option(opts)
		type = opts.shift
		case type = OPTION.index(type) || type
		when 'PAD': Option.new(type, nil)	# pad
		when 255	# end
		else
			len = opts.shift
			o = Option.new(type, opts[0, len].pack('C*'))
			opts[0, len] = []
			o
		end
	end

	class Zero
		def self.to_str ; '' end
		def self.to_int ; 0 end
	end

	def encode
		str = Fields.map { |f| instance_variable_get("@#{f}") || Zero }.pack('C4Nn2N4a16a64a128')
		str += [MAGIC_COOKIE].pack('N')
		@options.to_a.each { |op| str += op.encode }
		str
	end

	def self.decode(str)
		new(*str.unpack('C4Nn2N4a16a64a128NC*'))
	end

	def inspect
		fds = Fields + ['options']
		fds = fds.map { |f| "#{f}=#{instance_variable_get("@#{f}").inspect}" }
		"#<#{self.class}:#{'0x%08x' % object_id} #{fds.join(' ')}>"
	end
end

class Dhcpd
	def initialize(addr=0, port=67)
		@lfd = UDPSocket.open
		@lfd.bind(addr, port)
	end

	def mainloop
		loop do
			puts 'wait cx' if $VERBOSE
			nil while not IO.select([@lfd], nil, nil, 1)
			handle_newclient
		end
	end

	def handle_newclient
		packet, from = @lfd.recvfrom(516)
		p = Dhcp.decode(packet)
		@c_ip, @c_p = from[3], from[1]
		puts "#{Time.now.strftime('%H:%M:%S')} rq from #@c_ip:#@c_p - #{p.inspect}" if $VERBOSE
		# respond
		@ofd = @lfd
		# populate the arp cache with the newly assigned address, and respond using it
		arpreq = [ifindex=0, flags=0, maclen=6, ipaddr, hwaddr, pad=''].pack('LLL16C16C242C')
		@ofd.ioctl(SIOCSARP, arpreq)
		@ofd.send(resp, c_ip, c_p)
		@c_ip = @c_p = nil
	end
end

if __FILE__ == $0
	if not ARGV.delete('-c')
		# addr port
		Dhcpd.new(*ARGV).mainloop
	else
		# TODO broadcast eth
		srv = ARGV.shift
		eth = [ARGV.shift.delete(':')].pack('H*')
		rq = Dhcp.eth(eth, 'DISCOVER').add_option('PARAMREQUEST', "\001\034\002\003\017\006w\f,/\032y")

	end
end