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# -*- coding: binary -*-
module PacketFu
# UDPHeader is a complete UDP struct, used in UDPPacket. Many Internet-critical protocols
# rely on UDP, such as DNS and World of Warcraft.
#
# For more on UDP packets, see http://www.networksorcery.com/enp/protocol/udp.htm
#
# ==== Header Definition
# Int16 :udp_src
# Int16 :udp_dst
# Int16 :udp_len Default: calculated
# Int16 :udp_sum Default: 0. Often calculated.
# String :body
class UDPHeader < Struct.new(:udp_src, :udp_dst, :udp_len, :udp_sum, :body)
include StructFu
def initialize(args={})
super(
Int16.new(args[:udp_src]),
Int16.new(args[:udp_dst]),
Int16.new(args[:udp_len] || udp_calc_len),
Int16.new(args[:udp_sum]),
StructFu::String.new.read(args[:body])
)
end
# Returns the object in string form.
def to_s
self.to_a.map {|x| x.to_s}.join
end
# Reads a string to populate the object.
def read(str)
force_binary(str)
return self if str.nil?
self[:udp_src].read(str[0,2])
self[:udp_dst].read(str[2,2])
self[:udp_len].read(str[4,2])
self[:udp_sum].read(str[6,2])
self[:body].read(str[8,str.size])
self
end
# Setter for the UDP source port.
def udp_src=(i); typecast i; end
# Getter for the UDP source port.
def udp_src; self[:udp_src].to_i; end
# Setter for the UDP destination port.
def udp_dst=(i); typecast i; end
# Getter for the UDP destination port.
def udp_dst; self[:udp_dst].to_i; end
# Setter for the length field. Usually should be recalc()'ed instead.
def udp_len=(i); typecast i; end
# Getter for the length field.
def udp_len; self[:udp_len].to_i; end
# Setter for the checksum. Usually should be recalc()'ed instad.
def udp_sum=(i); typecast i; end
# Getter for the checksum.
def udp_sum; self[:udp_sum].to_i; end
# Returns the true length of the UDP packet.
def udp_calc_len
body.to_s.size + 8
end
# Recalculates calculated fields for UDP.
def udp_recalc(arg = :all)
case arg.to_sym
when :udp_len
self.udp_len = udp_calc_len
when :all
self.udp_recalc(:udp_len)
else
raise ArgumentError, "No such field `#{arg}'"
end
end
# Equivalent to udp_src.to_i
def udp_sport
self.udp_src
end
# Equivalent to udp_src=
def udp_sport=(arg)
self.udp_src=(arg)
end
# Equivalent to udp_dst
def udp_dport
self.udp_dst
end
# Equivalent to udp_dst=
def udp_dport=(arg)
self.udp_dst=(arg)
end
# Readability aliases
def udp_sum_readable
"0x%04x" % udp_sum
end
end
end
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