### Home Classes Methods

### In Files

- lib/packetfu/structfu.rb

### Parent

Struct.new(:int, :string, :mode)

### Methods

- ::new
- #calc
- #len
- #len=
- #parse
- #read
- #string=
- #to_s

### Files

- .document
- README.rdoc

### Class/Module Index

Quicksearch

- PacketFu
- PacketFu::ARPHeader
- PacketFu::ARPHeaderMixin
- PacketFu::ARPPacket
- PacketFu::AddrIpv6
- PacketFu::Capture
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- PacketFu::EthHeaderMixin
- PacketFu::EthMac
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- PacketFu::HSRPHeaderMixin
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- PacketFu::ICMPHeaderMixin
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- PacketFu::IPHeaderMixin
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- PacketFu::IPv6HeaderMixin
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- StructFu
- StructFu::Int
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- StructFu::Int16le
- StructFu::Int32
- StructFu::Int32be
- StructFu::Int32le
- StructFu::Int8
- StructFu::IntString
- StructFu::String
- Struct

No matching classes.

# 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

    # File lib/packetfu/structfu.rb, line 184
    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 194
    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 225
    def len
      self[:int].value
    end

len=(i) click to toggle source

Override the size, if you must.

    # File lib/packetfu/structfu.rb, line 230
    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 260
    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 238
    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 218
    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 200
    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

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