Library bin

A problem script authors often face is the necessity of encoding valuesinto binary data. For example after analyzing a protocol the startingpoint to write a script could be a hex dump, which serves as a preambleto every sent packet. Although it is possible to work with thefunctionality Lua provides, it's not very convenient. Therefore NSE includesBinlib, 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 binarydata. Packing and unpacking are controlled by the following operatorcharacters:

• 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 thecharacters 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 operatorsstand 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 currentlyresults 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 unpackingstopped. This can be used as theinit value for subsequentcalls. The following return values are the values according to the formatstring. Numerical values in the format string are interpreted as repetitionslike inpack, except if used withA,B, orH, in which cases the number tellsunpack how many bytes to read.unpack stops ifeither 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.