Lua error: “Tvbs can only be created and used in dissectors”

I am trying to use lua to dissect my protocol stack.

The one problem I cannot solve is this:

I can get several messages that are completed in the same packet.

I would then like to make tvbs for each of the completed messages and hand them over to a dissector. But if I get more than one extra tvb - and a dissector that is not the generic data-dissector - I get this fault message:

"Tvbs can only be created and used in dissectors"

What am I doing wrong?

This is smallest lua file that can reproduce the problem:

------------- lua dissector
local data_dis = Dissector.get ("data")
– mini dissector I would like to use on reassembled messages
local p_foo = Proto ("foo", "foo proto")
local f_foo_first_byte = ProtoField.uint8 ("foo.ind", "Index")
p_foo.fields = {f_foo_first_byte}
function p_foo.dissector(tvb, pinfo, tree)
local subtree = tree:add (p_foo, tvb())
subtree:add (f_foo_first_byte, tvb(0,1))
end
– the dissector for the udp packets on port 2800
local p_bar = Proto ("bar", "bar proto")
local f_bar_ind = ProtoField.uint8 ("bar.ind", "Index")
p_bar.fields = {f_bar_ind}
function p_bar.dissector (tvb, pinfo, tree)
local subtree = tree:add (p_bar, tvb())
subtree:add (f_bar_ind, tvb(0,1))
data_dis:call(tvb, pinfo, tree)
local dissector
local alt = 0
– alt = 1 – uncomment to see that it does not works with the foo-dissector
if alt == 0 then
dissector = Dissector.get ("data")
else
dissector = Dissector.get ("foo")
end
– The following is just done to fake reassembly
local range = tvb(0,tvb:len())
bytes = range:bytes()
newTvb = ByteArray.tvb(bytes, "first")
dissector:call(newTvb, pinfo, tree)
newTvb1 = ByteArray.tvb(bytes, "second")
dissector:call(newTvb1, pinfo, tree)
end
local udp_encap_table = DissectorTable.get("udp.port")
udp_encap_table:add(2800,p_bar)

And here a script that generates a packet to dissect

#!/bin/bash

port=2800
messageIndex="00"
data="00010203040506070809"
packetSender() {
sudo nping 4.3.2.1 –udp -c 1 –source-ip 1.2.3.4 –source-port $port –dest-port $port –data "$messageIndex$data"
}
packetSender