Lua - Get data from buffer when packet size varies

edit

Say i'm using the buffer(offset,len) method to view the 5th hex value (4,1)

first packet:

00 11 22 33 44 55

buffer would return '44'.

second packet:

00 11 AA 22 33 44 55

buffer would now return '33' where I actually wanted '44'.

Does this help to clarify? I would not be able to base the buffer off a previous field as the extra byte appears between fields.

Well, you need to track the offset then. Somehow you have to know that the AA was inserted and if so, increment your offset accordingly. For example:

offset = 0
tree:add(p_foo.field_00_11, buffer(offset, 2))
offset = offset + 2
if <some test condition> then
    tree:add(p_foo.field_AA, buffer(offset, 1))
    offset = offset + 1
end

tree:add(p_foo.field_22_33, buffer(offset, 2))
offset = offset + 2
tree:add(p_foo.field_44, buffer(offset, 1))
offset = offset + 1
tree:add(p_foo.field_55, buffer(offset, 1))
offset = offset + 1
...

I have no idea what your test condition would be because I don't know anything about your protocol, so you'll have to make that determination.

Hi, I can't figure out the test condition. I've tried the below but the script doesn't apply the offset.

if buffer(offset,1) == 'AA' then 
offset = offset + 1
end

What am i doing wrong?

If I interpret your code correctly, it would appear that you're trying to compare the value of 1 byte in the buffer at offset offset to the hexadecimal value of 0xAA or decimal value 170. If that's the case, then try this:

if buffer(offset,1):uint() == 170 then
    offset = offset + 1
end

thank you for your help!