udprecv-info.lua

do
    -- For each dest port we see a packet destined for, store the private "sequence #"
    -- we extracted from the UDP packet, so we can deduce which sequence number should
    -- be next
    local port_seq = {}

    -- create the dissector
    local udprecv = Proto("udprecv", "Dissector for our UDPrecv Receive Tester")

    -- Put one time initialization code here
    function udprecv.init()
    end

    -- field definitions for our protocol that tell wireshark
    -- how to parse and display the useful chunks of data
    local f = udprecv.fields
    f.seq = ProtoField.uint64("udprecv.seq", "seq")

    -- The dissector function is called for each captured packet for protocol
    -- that we subscribed
    function udprecv.dissector(buffer, pinfo, tree)

        -- Adding fields to the tree
        local subtree = tree:add(udprecv, buffer())
        -- find the chunk of buffer that holds our private "seq #", which starts at 8 bytes
        -- from the beginning of the packet, and is 8 bytes long
        local seq = buffer(8, 8)

        if not pinfo.visited then
            local port_str = tostring(pinfo.dst_port)
            if not port_seq[port_str] then
                -- we've never seen this port before, so add it to port_seq, initializing
                -- to our private "sequence number" that we've extracted from the packet
                port_seq[port_str] = seq
            else
                -- we've seen traffic to this port before, so take the last "sequence number"
                -- we saw, increment by one, and compare it with the sequence # we just
                -- extracted from the packet
                warn(port_seq[port_str])
                local expected = port_seq[port_str] + 1;

                if seq ~= expected then
                    warn("not sequential")
                    -- pinfo.cols.info = "SEQ: "..seq.." is Invalid!"
                else
                    info("it was equal")
                end
                -- Regardless of what we found, set the current sequence number received
                -- for this UDP port
                port_seq[port_str] = { seq }
            end
        end
        subtree:add(f.seq, seq)
    end

    -- subscribe for UDP packets on ports 30300-30303
    local udp_table = DissectorTable.get("udp.port")
    for i,port in ipairs{30300,30301,30302,30303} do
      udp_table:add(port,udprecv);
    end
end