how to convert to host byte order using lua in wireshark

Question

I am getting no luck searching for a standard function to do byte-order conversion to write a lua plug-in for wireshark.

struct.pack doesn't seem to work, at least when doing "require 'struct'", wireshark throws an error.

You can call tvb functions to get an explicit (that's what I am doing now so it's not portable :((( ) conversion to either big endian or little endian, but nothing to the host endian byte order.

I searched and searched online but nothing came up so I am hoping someone can offer a solution.

Thanks!

Answer 1

Is it enough if you can determine the endianness of the system you are running on?

In Lua 5.1 and 5.2 at least, the 7th byte of the bytecode header is 1 for little endian systems and 0 for big endian systems. You can obtain this byte from any Lua script this way:

string.dump(function() end):byte(7)

If you use LuaJIT you can just check the value of:

ffi.abi("le")

Finding this out should be enough to let you write portable code.

Answer 2

Wireshark is close to supporting struct.unpack way of doing things. It's not out on a stable release yet.

http://ask.wireshark.org/questions/32715/no-struct-support-in-wireshark-1107s-lua-interpreter