275 lines
7.0 KiB
Ruby
275 lines
7.0 KiB
Ruby
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# StructFu, a nifty way to leverage Ruby's built in Struct class
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# to create meaningful binary data.
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module StructFu
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# Normally, self.size and self.length will refer to the Struct
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# size as an array. It's a hassle to redefine, so this introduces some
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# shorthand to get at the size of the resultant string.
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def sz
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self.to_s.size
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end
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alias len sz
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# Typecast is used mostly by packet header classes, such as IPHeader,
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# TCPHeader, and the like. It takes an argument, and casts it to the
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# expected type for that element.
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def typecast(i)
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c = caller[0].match(/.*`([^']+)='/)[1]
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self[c.intern].read i
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end
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# Used like typecast(), but specifically for casting Strings to StructFu::Strings.
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def body=(i)
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if i.kind_of? ::String
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typecast(i)
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elsif i.kind_of? StructFu
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self[:body] = i
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elsif i.nil?
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self[:body] = StructFu::String.new.read("")
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else
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raise ArgumentError, "Can't cram a #{i.class} into a StructFu :body"
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end
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end
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# Ints all have a value, an endianness, and a default value.
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# Note that the signedness of Int values are implicit as
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# far as the subclasses are concerned; to_i and to_f will
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# return Integer/Float versions of the input value, instead
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# of attempting to unpack the pack value. (This can be a useful
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# hint to other functions).
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#
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# ==== Header Definition
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#
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# Fixnum :value
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# Symbol :endian
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# Fixnum :width
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# Fixnum :default
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class Int < Struct.new(:value, :endian, :width, :default)
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alias :v= :value=
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alias :v :value
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alias :e= :endian=
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alias :e :endian
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alias :w= :width=
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alias :w :width
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alias :d= :default=
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alias :d :default
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# This is a parent class definition and should not be used directly.
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def to_s
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raise StandardError, "StructFu::Int#to_s accessed, must be redefined."
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end
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# Returns the Int as an Integer.
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def to_i
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(self.v || self.d).to_i
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end
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# Returns the Int as a Float.
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def to_f
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(self.v || self.d).to_f
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end
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def initialize(value=nil, endian=nil, width=nil, default=nil)
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super(value,endian,width,default=0)
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end
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# Reads either an Integer or a packed string, and populates the value accordingly.
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def read(i)
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self.v = i.kind_of?(Integer) ? i.to_i : i.to_s.unpack(@packstr).first
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self
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end
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end
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# Int8 is a one byte value.
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class Int8 < Int
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def initialize(v=nil)
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super(v,nil,w=1)
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@packstr = "C"
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end
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# Returns a one byte value as a packed string.
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def to_s
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[(self.v || self.d)].pack("C")
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end
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end
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# Int16 is a two byte value.
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class Int16 < Int
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def initialize(v=nil, e=:big)
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super(v,e,w=2)
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@packstr = (self.e == :big) ? "n" : "v"
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end
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# Returns a two byte value as a packed string.
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def to_s
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[(self.v || self.d)].pack(@packstr)
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end
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end
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# Int16be is a two byte value in big-endian format.
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class Int16be < Int16
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end
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# Int16le is a two byte value in little-endian format.
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class Int16le < Int16
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def initialize(v=nil, e=:little)
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super(v,e)
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@packstr = (self.e == :big) ? "n" : "v"
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end
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end
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# Int32 is a four byte value.
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class Int32 < Int
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def initialize(v=nil, e=:big)
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super(v,e,w=4)
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@packstr = (self.e == :big) ? "N" : "V"
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end
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# Returns a four byte value as a packed string.
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def to_s
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[(self.v || self.d)].pack(@packstr)
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end
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end
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# Int32be is a four byte value in big-endian format.
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class Int32be < Int32
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end
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# Int32le is a four byte value in little-endian format.
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class Int32le < Int32
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def initialize(v=nil, e=:little)
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super(v,e)
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end
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end
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# Strings are just like regular strings, except it comes with a read() function
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# so that it behaves like other StructFu elements.
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class String < ::String
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def read(str)
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str = str.to_s
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self.replace str
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self
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end
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end
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# Provides a primitive for creating strings, preceeded by
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# an Int type of length. By default, a string of length zero with
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# a one-byte length is presumed.
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#
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# Note that IntStrings aren't used for much, but it seemed like a good idea at the time.
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class IntString < Struct.new(:int, :string, :mode)
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def initialize(string='',int=Int8,mode=nil)
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unless int.respond_to?(:ancestors) && int.ancestors.include?(StructFu::Int)
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raise StandardError, "Invalid length (#{int.inspect}) associated with this String."
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else
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super(int.new,string,mode)
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calc
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end
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end
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# Calculates the size of a string, and sets it as the value.
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def calc
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int.v = string.to_s.size
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self.to_s
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end
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# Returns the object as a string, depending on the mode set upon object creation.
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def to_s
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if mode == :parse
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"#{int}" + [string].pack("a#{len}")
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elsif mode == :fix
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self.int.v = string.size
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"#{int}#{string}"
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else
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"#{int}#{string}"
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end
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end
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# By redefining #string=, we can ensure the correct value
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# is calculated upon assignment. If you'd prefer to have
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# an incorrect value, use the syntax, obj[:string]="value"
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# instead. Note, by using the alternate form, you must
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# #calc before you can trust the int's value. Think of the
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# = assignment as "set to equal," while the []= assignment
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# as "boxing in" the value. Maybe.
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def string=(s)
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self[:string] = s
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calc
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end
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# Shorthand for querying a length. Note that the usual "length"
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# and "size" refer to the number of elements of this struct.
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def len
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self[:int].value
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end
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# Override the size, if you must.
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def len=(i)
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self[:int].value=i
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end
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# Read takes a string, assumes an int width as previously
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# defined upon initialization, but makes no guarantees
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# the int value isn't lying. You're on your own to test
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# for that (or use parse() with a :mode set).
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def read(s)
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unless s[0,int.width].size == int.width
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raise StandardError, "String is too short for type #{int.class}"
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else
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int.read(s[0,int.width])
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self[:string] = s[int.width,s.size]
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end
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self.to_s
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end
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# parse() is like read(), except that it interprets the string, either
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# based on the declared length, or the actual length. Which strategy
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# is used is dependant on which :mode is set (with self.mode).
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#
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# :parse : Read the length, and then read in that many bytes of the string.
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# The string may be truncated or padded out with nulls, as dictated by the value.
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# :fix : Skip the length, read the rest of the string, then set the length to what it ought to be.
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# else : If neither of these modes are set, just perfom a normal read(). This is the default.
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def parse(s)
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unless s[0,int.width].size == int.width
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raise StandardError, "String is too short for type #{int.class}"
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else
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case mode
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when :parse
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int.read(s[0,int.width])
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self[:string] = s[int.width,int.value]
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if string.size < int.value
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self[:string] += ("\x00" * (int.value - self[:string].size))
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end
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when :fix
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self.string = s[int.width,s.size]
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else
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return read(s)
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end
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end
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self.to_s
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end
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end
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end
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class Struct
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# Monkeypatch for Struct to include some string safety -- anything that uses
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# Struct is going to presume binary strings anyway.
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def force_binary(str)
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str.force_encoding "binary" if str.respond_to? :force_encoding
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end
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end
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# vim: nowrap sw=2 sts=0 ts=2 ff=unix ft=ruby
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