how to use Lua to write multi protocol dissector plugin

Question

I am writing an XLES protocol dissector, but this protocol is in the payload of LAPV5, so I have to write the LAPV5 dissector first. How do I connect the two protocols?

I wrote something like this:

udp_encap_table = DissectorTable.get("udp.port")
udp_encap_table:add(49152,lapV5Proto)
lapV5DessectorTable = DissectorTable.new("lapv5.data", "lapv5 dissector table",ftypes.STRING,base.none)
lapv5_encap_table = DissectorTable.get("lapv5.data")
lapv5_encap_table:add(".",xlesProto)

But it doesn’t work. XLES only exists when LAPV5 has a payload. Does the pattern argument in DissectorTable.add(pattern,dissector) only support a full match?

Accepted Answer

In your case, you would daisy-chain the dissectors. That is, call your XLES dissector directly from your LAPV5 dissector. Try this Lua:

-- ############# 
-- # XLES
-- #############
local proto_xles = Proto("xles", "XLES Protocol")
function proto_xles.dissector(buf, pinfo, tree)
print('XLES', tostring(buf))
end
– #############
– # LAPV5
– #############
local proto_lap5 = Proto("lapv5", "LAPV5 Protocol")
– assume data (i.e., the body) is present only if the packet is
– longer than the header
local HEADER_LEN = 5
function proto_lap5.dissector(buf, pinfo, tree)
if buf:len() &gt; HEADER_LEN then
    -- create a new buffer containing only the XLES data,
    -- and pass it to the XLES dissector
    Dissector.get(&quot;xles&quot;):call(buf(HEADER_LEN):tvb(),  pinfo, tree)
end

end
– install LAPV5 dissector at UDP port 49152
DissectorTable.get("udp.port"):add(49152, proto_lap5)