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Pack and unpack binary data.

A problem script authors often face is the necessity of encoding values into binary data. For example after analyzing a protocol the starting point to write a script could be a hex dump, which serves as a preamble to every sent packet. Although it is possible to work with the functionality Lua provides, it's not very convenient. Therefore NSE includes Binlib, based on lpack (http://www.tecgraf.puc-rio.br/~lhf/ftp/lua/) by Luiz Henrique de Figueiredo.

The Binlib functions take a format string to encode and decode binary data. Packing and unpacking are controlled by the following operator characters:

  • H hex string
  • B bit string
  • x null byte
  • z zero-terminated string
  • p string preceded by 1-byte integer length
  • P string preceded by 2-byte integer length
  • a string preceded by 4-byte integer length
  • A string
  • f float
  • d double
  • n Lua number
  • c char (1-byte integer)
  • C byte = unsigned char (1-byte unsigned integer)
  • s short (2-byte integer)
  • S unsigned short (2-byte unsigned integer)
  • i int (4-byte integer)
  • I unsigned int (4-byte unsigned integer)
  • l long (8-byte integer)
  • L unsigned long (8-byte unsigned integer)
  • < little endian modifier
  • > big endian modifier
  • = native endian modifier

Note that the endian operators work as modifiers to all the characters following them in the format string.

Functions

pack (format, ...)

Returns a binary packed string.

unpack (format, data, init)

Returns values read from the binary packed data string.



Functions

pack (format, ...)

Returns a binary packed string.

The format string describes how the parameters (p1, ...) will be interpreted. Numerical values following operators stand for operator repetitions and need an according amount of parameters. Operators expect appropriate parameter types.

Note: on Windows packing of 64-bit values > 2^63 currently results in packing exactly 2^63.

Parameters

  • format: Format string, used to pack following arguments.
  • ...: The values to pack.

Return value:

String containing packed data.
unpack (format, data, init)

Returns values read from the binary packed data string.

The first return value of this function is the position at which unpacking stopped. This can be used as the init value for subsequent calls. The following return values are the values according to the format string. Numerical values in the format string are interpreted as repetitions like in pack, except if used with A, B, or H, in which cases the number tells unpack how many bytes to read. unpack stops if either the format string or the binary data string are exhausted.

Parameters

  • format: Format string, used to unpack values out of data string.
  • data: String containing packed data.
  • init: Optional starting position within the string.

Return values:

  1. Position in the data string where unpacking stopped.
  2. All unpacked values.

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