UDPPacket is used to construct UDP Packets. They contain an EthHeader, an IPHeader, and a UDPHeader.

Example

  udp_pkt = PacketFu::UDPPacket.new
  udp_pkt.udp_src=rand(0xffff-1024) + 1024
  udp_pkt.udp_dst=53

  udp_pkt.ip_saddr="1.2.3.4"
  udp_pkt.ip_daddr="10.20.30.40"

  udp_pkt.recalc
  udp_pkt.to_f('/tmp/udp.pcap')

Parameters

 :eth
   A pre-generated EthHeader object.
 :ip
   A pre-generated IPHeader object.
 :flavor
   TODO: Sets the "flavor" of the UDP packet. UDP packets don't tend have a lot of
   flavor, but their underlying ip headers do.
 :config
  A hash of return address details, often the output of Utils.whoami?
Methods
C
N
P
R
U
Attributes
[RW] eth_header
[RW] ip_header
[RW] udp_header
Class Public methods
can_parse?(str)

Source: show 

# File lib/packetfu/protos/udp.rb, line 137
                def self.can_parse?(str)
                        return false unless str.size >= 54
                        return false unless EthPacket.can_parse? str
                        return false unless IPPacket.can_parse? str
                        return false unless str[23,1] == "\x11"
                        return true
                end
new(args={})

Source: show 

# File lib/packetfu/protos/udp.rb, line 161
                def initialize(args={})
                        @eth_header = EthHeader.new(args).read(args[:eth])
                        @ip_header = IPHeader.new(args).read(args[:ip])
                        @ip_header.ip_proto=0x11
                        @udp_header = UDPHeader.new(args).read(args[:icmp])
                        @ip_header.body = @udp_header
                        @eth_header.body = @ip_header
                        @headers = [@eth_header, @ip_header, @udp_header]
                        super
                        udp_calc_sum
                end
Instance Public methods
peek_format()

Peek provides summary data on packet contents.

Source: show 

# File lib/packetfu/protos/udp.rb, line 225
                def peek_format
                        peek_data = ["U  "]
                        peek_data << "%-5d" % self.to_s.size
                        peek_data << "%-21s" % "#{self.ip_saddr}:#{self.udp_sport}"
                        peek_data << "->"
                        peek_data << "%21s" % "#{self.ip_daddr}:#{self.udp_dport}"
                        peek_data << "%23s" % "I:"
                        peek_data << "%04x" % self.ip_id
                        peek_data.join
                end
read(str=nil, args={})

Source: show 

# File lib/packetfu/protos/udp.rb, line 145
                def read(str=nil, args={})
                        raise "Cannot parse `#{str}'" unless self.class.can_parse?(str)
                        @eth_header.read(str)
                        @ip_header.read(str[14,str.size])
                        @eth_header.body = @ip_header
                        if args[:strip]
                                udp_len = str[16,2].unpack("n")[0] - 20
                                @udp_header.read(str[14+(@ip_header.ip_hlen),udp_len])
                        else
                                @udp_header.read(str[14+(@ip_header.ip_hlen),str.size])
                        end
                        @ip_header.body = @udp_header
                        super(args)
                        self
                end
udp_calc_sum()

udp_calc_sum() computes the UDP checksum, and is called upon intialization. It usually should be called just prior to dropping packets to a file or on the wire.

Source: show 

# File lib/packetfu/protos/udp.rb, line 175
                def udp_calc_sum
                        # This is /not/ delegated down to @udp_header since we need info
                        # from the IP header, too.
                        checksum = (ip_src.to_i >> 16)
                        checksum += (ip_src.to_i & 0xffff)
                        checksum += (ip_dst.to_i >> 16)
                        checksum += (ip_dst.to_i & 0xffff)
                        checksum += 0x11
                        checksum += udp_len.to_i
                        checksum += udp_src.to_i
                        checksum += udp_dst.to_i
                        checksum += udp_len.to_i
                        if udp_len.to_i >= 8
                                # For IP trailers. This isn't very reliable. :/
                                real_udp_payload = payload.to_s[0,(udp_len.to_i-8)] 
                        else
                                # I'm not going to mess with this right now.
                                real_udp_payload = payload 
                        end
                        chk_payload = (real_udp_payload.size % 2 == 0 ? real_udp_payload : real_udp_payload + "\x00")
                        chk_payload.unpack("n*").each {|x| checksum = checksum+x}
                        checksum = checksum % 0xffff
                        checksum = 0xffff - checksum
                        checksum == 0 ? 0xffff : checksum
                        @udp_header.udp_sum = checksum
                end
udp_recalc(args=:all)

udp_recalc() recalculates various fields of the UDP packet. Valid arguments are: 

  :all
    Recomputes all calculated fields.
  :udp_sum
    Recomputes the UDP checksum.
  :udp_len
    Recomputes the UDP length.

Source: show 

# File lib/packetfu/protos/udp.rb, line 210
                def udp_recalc(args=:all)
                        case args
                        when :udp_len
                                @udp_header.udp_recalc
                        when :udp_sum
                                udp_calc_sum
                        when :all
                                @udp_header.udp_recalc
                                udp_calc_sum
                        else
                                raise ArgumentError, "No such field `#{arg}'"
                        end
                end