Extract potentially multiple 'trivial' PDUs from a TCP segment

trivial_dissector.lua

-- trivial protocol example
-- inspired by http://wiki.wireshark.org/Lua/Dissectors

-- declare our protocol
trivial_proto = Proto("trivial","Trivial Protocol")
-- create a function to dissect it
function trivial_proto.dissector(buffer,pinfo,tree)
	local offset = pinfo.desegment_offset or 0
	
	local trivial_pdu_len = 4
	
	-- Enhancement: extract potentially multiple 'trivial' PDUs from buffer
	-- inspired by http://stackoverflow.com/questions/14387426/reassembling-packets-in-a-lua-wireshark-dissector
	while true do
		local nxtpdu = offset + trivial_pdu_len
		
		if nxtpdu > buffer:len() then
			pinfo.desegment_len = nxtpdu - buffer:len()
			pinfo.desegment_offset = offset
			return
		end
		
		pinfo.cols.protocol = "TRIVIAL"
		pinfo.cols.info = "Trivial Info"

		local subtree = tree:add(trivial_proto,buffer(),"Trivial Protocol Data")
		subtree:add(buffer(offset,2),"The first two bytes: " .. buffer(offset,2):uint())
		subtree = subtree:add(buffer(offset+2,2),"The next two bytes")
		subtree:add(buffer(offset+2,1),"The 3rd byte: " .. buffer(offset+2,1):uint())
		subtree:add(buffer(offset+3,1),"The 4th byte: " .. buffer(offset+3,1):uint())
		
		offset = nxtpdu
		
		if nxtpdu == buffer:len() then
			return
		end
	end
end

-- load the tcp.port table
tcp_table = DissectorTable.get("tcp.port")
-- register our protocol to handle udp port 7777
tcp_table:add(7777,trivial_proto)