class StructFu::IntString

Provides a primitive for creating strings, preceeded by an Int type of length. By default, a string of length zero with a one-byte length is presumed.

Note that IntStrings aren’t used for much, but it seemed like a good idea at the time.

Public Class Methods

new(string='',int=Int8,mode=nil) click to toggle source
Calls superclass method
# File lib/packetfu/structfu.rb, line 211
def initialize(string='',int=Int8,mode=nil)
  if int < Int
    super(int.new,string,mode)
    calc
  else
    raise "IntStrings need a StructFu::Int for a length."
  end
end

Public Instance Methods

calc() click to toggle source

Calculates the size of a string, and sets it as the value.

# File lib/packetfu/structfu.rb, line 221
def calc
  int.v = string.to_s.size
  self.to_s
end
len() click to toggle source

Shorthand for querying a length. Note that the usual “length” and “size” refer to the number of elements of this struct.

# File lib/packetfu/structfu.rb, line 252
def len
  self[:int].value
end
len=(i) click to toggle source

Override the size, if you must.

# File lib/packetfu/structfu.rb, line 257
def len=(i)
  self[:int].value=i
end
parse(s) click to toggle source

parse() is like read(), except that it interprets the string, either based on the declared length, or the actual length. Which strategy is used is dependant on which :mode is set (with self.mode).

:parse : Read the length, and then read in that many bytes of the string. The string may be truncated or padded out with nulls, as dictated by the value.

:fix : Skip the length, read the rest of the string, then set the length to what it ought to be.

else : If neither of these modes are set, just perfom a normal read(). This is the default.

# File lib/packetfu/structfu.rb, line 287
def parse(s)
  unless s[0,int.width].size == int.width
    raise StandardError, "String is too short for type #{int.class}"
  else
    case mode
    when :parse
      int.read(s[0,int.width])
      self[:string] = s[int.width,int.value]
      if string.size < int.value
        self[:string] += ("\x00" * (int.value - self[:string].size))
      end
    when :fix
      self.string = s[int.width,s.size]
    else
      return read(s)
    end
  end
  self.to_s
end
read(s) click to toggle source

Read takes a string, assumes an int width as previously defined upon initialization, but makes no guarantees the int value isn’t lying. You’re on your own to test for that (or use parse() with a :mode set).

# File lib/packetfu/structfu.rb, line 265
def read(s)
  unless s[0,int.width].size == int.width
    raise StandardError, "String is too short for type #{int.class}"
  else
    int.read(s[0,int.width])
    self[:string] = s[int.width,s.size]
  end
  self.to_s
end
string=(s) click to toggle source

By redefining string=, we can ensure the correct value is calculated upon assignment. If you’d prefer to have an incorrect value, use the syntax, obj=“value” instead. Note, by using the alternate form, you must calc before you can trust the int’s value. Think of the = assignment as “set to equal,” while the []= assignment as “boxing in” the value. Maybe.

# File lib/packetfu/structfu.rb, line 245
def string=(s)
  self[:string] = s
  calc
end
to_s() click to toggle source

Returns the object as a string, depending on the mode set upon object creation.

# File lib/packetfu/structfu.rb, line 227
def to_s
  if mode == :parse
    "#{int}" + [string].pack("a#{len}")
  elsif mode == :fix
    self.int.v = string.size
    "#{int}#{string}"
  else
    "#{int}#{string}"
  end
end