Object Buffer

Represents a sequence of raw bytes. Many of your LUA scripts will get this object when dealing with packet contents.

Functions

A summary of the functions available in this object.

Name	In	Out	Description
size		number	size of the buffer containing the raw bytes
length		number	same as size
hexdump	offset, size (both optional)	string	string with hexdump of the buffer in canonical format. Specify offset, size to dump a subset
hval_8	offset	number	returns the byte at buffer+offset
hval_16	offset	number	same as ntohs( ) on the 2 bytes at buffer+offset
hval_24	offset	number	The 3 byte (24 bit) number at buffer_offset
hval_32	offset	number	same as ntohl( ) on the 4 bytes at buffer+offset
tostring	offset, size (both optional)	string	tostring() returns the full string to LUA tostring(offset,size) returns the substring of size bytes starting and including offset
appendtofile	filename	string	append the contents of the buffer to the filename specified
writetofile	filename, offset	string, number	write the contents of the buffer to the filename specified at the offset

Function reference

Function hexdump

Adds a single metric to the Trisul framework.

Purpose

Dump the buffer in canonical hex dump format and return a string. Very useful while developing packet dissectors.

Parameters

Note : The offset starts at 0. Watch out for this because LUA strings start at 1.

Parameter	optional	Info
offset	optional : default 0	offset from start of buffer. NOTE: Offset start from 0 , unlike the normal LUA array of 1
size	optional: default buffer:size()	Number of bytes to dump in hex

Return value

Parameter	Info
string	Hexdump of requested string

Usage

Some sample uses

..

 print(buff:hexdump())

00000000   0d ec bf b3 91 ab 42 d9 39 51 30 33 35 01 6e f4    ......B.9Q035.n.
00000010   b3 1d 11 42 9d f3 41 98 0a 55 a0 01 00 04 43 48    ...B..A..U....CH
00000020   4c 4f 1d 00 00 00 50 41 44 00 d4 00 00 00 53 4e    LO....PAD.....SN
00000030   49 00 e3 00 00 00 53 54 4b 00 6b 01 00 00 56 45    I.....STK.k...VE
00000040   52 00 6f 01 00 00 43 43 53 00 7f 01 00 00 4e 4f    R.o...CCS.....NO
00000050   4e 43 9f 01 00 00 4d 53 50 43 a3 01 00 00 41 45    NC....MSPC....AE
00000060   41 44 a7 01 00 00 55 41 49 44 c8 01 00 00 53 43    AD....UAID....SC
00000070   49 44 d8 01 00 00 54 43 49 44 dc 01 00 00 50 44    ID....TCID....PD
00000080   4d 44 e0 01 00 00 53 52 42 46 e4 01 00 00 53 4d    MD....SRBF....SM
00000090   48 4c e8 01 00 00 49 43 53 4c ec 01 00 00 43 54    HL....ICSL....CT


 print(buff:hexdump(32,16))

00000000   4c 4f 1d 00 00 00 50 41 44 00 d4 00 00 00 53 4e    LO....PAD.....SN

Function tostring

Gets buffer contents into a LUA string

Purpose

Gets the buffer into a LUA string for further processing. You can get the full buffer or Parts of the buffer.

Parameters

note

The offset starts at 0. Watch out for this because LUA strings start at 1.

Parameter	Optional	Info
offset	optional : default 0	offset from start of buffer. NOTE: Offset start from 0 , unlike the normal LUA array of 1
size	optional: default buffer:size()	Number of bytes to retrieve

Return value

parameter	info
string	LUA string bytes

Usage

Function appendtofile

Append the contents of the buffer to a file.

Purpose

This is typically used by scripts for extracting contents to a disk file.

Parameters

Name	Type	Info
filename	string	The file where you want to append to. If file does not exit, it is created.

Return value

None

Usage

Function writetofile

Write contents of the buffer to a file at the specified offset.

Purpose

Typically used by scripts that do reassembly that need to write at particular offset.

Parameters

Name	Type	Info
filename	string	The file where you want to append to. If file does not exit, it is created.
offset	number	The seek position of the file. NOTE: Offset is 0 based unlike LUA arrays which are 1 based. Essentially this method from the C side does lseek(..) followed by write(..)

Return value

None