Understanding an "attempt to index global 'ftypes' (a nil value)" Lua error

Question

I was attempting to use the ZMTP Wireshark Dissector with my current copy of Wireshark (v4.0.6) which uses Lua 5.2.4 on my Ubuntu 20.04 machine to dissect zeromq.

I put the lua file in the proper place for Wireshark, and when I start wireshark it obviously sees it, but it throws an "attempt to index global 'ftypes' (a nil value)" error.

screenshot of error

To me, this means that the Lua dissector was not happy with the code itself (so not a Wireshark problem per say, but a Lua one). The repo this dissector came from was last updated in 2020, so I am guessing that something small has been updated on the Lua side and has caused the code to not keep pace.

I believe there are only a handful of lines that matter for this error, and they are:

-- zmq protocol example
-- declare our protocol
local zmtp_proto = Proto("zmtp", "ZMTP", "ZeroMQ Message Transport Protocol")

-- setup protocol fields.

vs_stype = {
    [0] = "pair",
    [1] = "publish",
    [2] = "subscribe",
    [3] = "request",
    [4] = "reply",
    [5] = "dealer",
    [6] = "router",
    [7] = "pull",
    [8] = "push"
}

zmtp_proto.fields = {}
local fds = zmtp_proto.fields
fds.greeting = ProtoField.new("Signature", "zmtp.greeting", ftypes.BYTES)

With that last line being like 41 that was referenced in the error message. Is there some way that these Lua proto fields should be setup differently?

I have tried making the suspect line a local and taking away the fds, but that seemed to not help any.

Answer 1

The ftypes table is defined in the init.lua file, which should be installed in the Wireshark "global installation directory".

Does your system have that file?