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custom LUA dissector: format display

asked 2018-12-12 14:12:18 +0000

BMWE gravatar image

updated 2019-01-30 17:18:33 +0000

cmaynard gravatar image


Lets say I'd like to have a field named ABC which will be 2 unsigned bytes: 0 to 65535 However, the actual value which is represented is -5.0 to 60.0 with linear conversion between the bits to the actual value.

I have some XML which defines the messages and their elements: the name, location, bits value (min & max), actual value (min & max), how it is stored in the database (XML is output from the database), conversion type.

I'm writing some conversion tool from the XML to LUA format. How should I write the dissector so that I'll see values between -5 to 60 ?

Thank you

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answered 2018-12-13 19:50:14 +0000

cmaynard gravatar image

updated 2018-12-13 19:50:39 +0000

The basic idea is to grab the 2-byte value and only add it to the tree after some computation is performed on it. Below is a simple Lua snippet to illustrate the idea and assumes the byte-order is big-endian (use le_uint() instead of uint() if it's little-endian):

abc = buf(offset, 2):uint()
abc_tree:add(f_abc, buf(offset, 2)):set_text(string.format("ABC: %f", -5.0 + (abc * 65.0/65535)))
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Thank you, I'll check it once I'll get my work computer. Meanwhile, can it be written in single line?

BMWE gravatar imageBMWE ( 2018-12-14 03:51:35 +0000 )edit

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Asked: 2018-12-12 14:12:18 +0000

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Last updated: Dec 13 '18