class PacketFu::UDPPacket

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?

Attributes

eth_header[RW]
ip_header[RW]
udp_header[RW]

Public Class Methods

can_parse?(str) click to toggle source
# File lib/packetfu/protos/udp.rb, line 44
def self.can_parse?(str)
        return false unless str.size >= 28
        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={}) click to toggle source
Calls superclass method PacketFu::Packet.new
# File lib/packetfu/protos/udp.rb, line 63
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

Public Instance Methods

peek_format() click to toggle source

Peek provides summary data on packet contents.

# File lib/packetfu/protos/udp.rb, line 127
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={}) click to toggle source
Calls superclass method PacketFu::Packet#read
# File lib/packetfu/protos/udp.rb, line 52
def read(str=nil, args={})
        raise "Cannot parse `#{str}'" unless self.class.can_parse?(str)
        @eth_header.read(str)
        if args[:strip]
                udp_body_len = self.ip_len - self.ip_hlen - 8
                @udp_header.body.read(@udp_header.body.to_s[0,udp_body_len])
        end
        super(args)
        self
end
udp_calc_sum() click to toggle source

#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.

# File lib/packetfu/protos/udp.rb, line 77
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) click to toggle source

#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.
# File lib/packetfu/protos/udp.rb, line 112
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