Decode and visualize Protobuf messages over TCP

I wrote a socket interface C++ code, between two processes with Protobuf over TCP protocol. The interface works fine, I can decode and send messages over the interface. However I also want to visualize the messages between two processes.

Wireshark is a good tool for listening socket messages. I can store the pcap with tcpdump and open it on wireshark. However it seems I could not make a visual from pcap.

I added protofile folder for wireshark:

Added a Lua file inside plugins folder:

do
local protobuf_dissector = Dissector.get("protobuf")

-- Create protobuf dissector based on UDP or TCP.
-- The UDP dissector will take the whole tvb as a message.
-- The TCP dissector will parse tvb as format:
--         [4bytes length][a message][4bytes length][a message]...
-- @param name  The name of the new dissector.
-- @param desc  The description of the new dissector.
-- @param for_udp  Register the new dissector to UDP table.(Enable 'Decode as')
-- @param for_tcp  Register the new dissector to TCP table.(Enable 'Decode as')
-- @param msgtype  Message type. This must be the root message defined in your .proto file.
local function create_protobuf_dissector(name, desc, for_udp, for_tcp, msgtype)
    local proto = Proto(name, desc)
    local f_length = ProtoField.uint32(name .. ".length", "Length", base.DEC)
    proto.fields = { f_length }

    proto.dissector = function(tvb, pinfo, tree)
        local subtree = tree:add(proto, tvb())
        if for_udp and pinfo.port_type == 3 then -- UDP
            if msgtype ~= nil then
                pinfo.private["pb_msg_type"] = "message," .. msgtype
            end
            pcall(Dissector.call, protobuf_dissector, tvb, pinfo, subtree)
        elseif for_tcp and pinfo.port_type == 2 then -- TCP
            local offset = 0
            local remaining_len = tvb:len()
            while remaining_len > 0 do
                if remaining_len < 4 then -- head not enough
                    pinfo.desegment_offset = offset
                    pinfo.desegment_len = DESEGMENT_ONE_MORE_SEGMENT
                    return -1
                end

                local data_len = tvb(offset, 4):uint()

                if remaining_len - 4 < data_len then -- data not enough
                    pinfo.desegment_offset = offset
                    pinfo.desegment_len = data_len - (remaining_len - 4)
                    return -1
                end
                subtree:add(f_length, tvb(offset, 4))

                if msgtype ~= nil then
                    pinfo.private["pb_msg_type"] = "message," .. msgtype
                end
                pcall(Dissector.call, protobuf_dissector, 
                       tvb(offset + 4, data_len):tvb(), pinfo, subtree)

                offset = offset + 4 + data_len
                remaining_len = remaining_len - 4 - data_len
            end
        end
        pinfo.columns.protocol:set(name)
    end

    if for_udp then DissectorTable.get("udp.port"):add(0, proto) end
    if for_tcp then DissectorTable.get("tcp.port"):add(0, proto) end
    return proto
end

-- default pure protobuf udp and tcp dissector without message type
create_protobuf_dissector("protobuf_udp", "Protobuf UDP")
create_protobuf_dissector("protobuf_tcp", "Protobuf TCP")
-- add more protobuf dissectors with message types
create_protobuf_dissector("Oamc", "OamcPacketProto",
                          false, true, "OamcPacketProto")

end

And when I try to decode as below:

TCP messages appears but no protobuf payload appears in the wireshark as in this Tutorial Wireshark tutorial?

Am I missing something? My proto file looks something like below:

message OamcPacketProto {
  oneof packet {
    .....
  }
}