Whireshark Lua解析器不显示树形结构

我有一个包，包含了尾随数据，例如ixia时间戳尾随器。我尝试编写一个与ixia-packet_trailer插件类似的Wireshark解析器。https://raw.githubusercontent.com/boundary/wireshark/master/epan/dissectors/packet-ixiatrailer.c

但我想用Lua编写，因为它最容易更改。

我将Lua编写为启发式函数，使用函数is_my_trailer(如Wireshark Lua解析器插件表错误中建议的)，现在它停止在以太网树中显示尾随器，所以我相信它能够识别模式0xae12，但它不显示我的"my trailer"树形结构

-- 声明我们的协议
local my_trailer_proto = Proto("my_trailer","my Trailer")

-- 头字段
local timestamp  = ProtoField.uint64 ("my_trailer_proto.timestamp", "timestamp", base.HEX)
local proto_flag  = ProtoField.uint8 ("my_trailer_proto.proto_flag", "protoFlag", base.HEX)
local msg_id     = ProtoField.uint16("my_trailer_proto.msg_id"    , "msdId"    , base.HEX)

my_trailer_proto.fields = { timestamp, proto_flag, msg_id }

-- 此数据包是否包含尾随器
local function is_my_trailer(buffer,pinfo,tree)
    local length = buffer:len()
    if length < 12 then return 1 end
    local type = buffer(length-12, 2):uint()

    if type == 0xae12 then  return true end
    return false
end

function my_trailer_proto.dissector(buffer, pinfo, tree)
    length = buffer:len()
    if length == 0 then return end

    local subtree = tree:add(my_trailer_proto, buffer(), "my trailer")

    -- Header
    subtree:add(timestamp, buffer(length-10,8))
    subtree:add(proto_flag, buffer(length-3,1))
    subtree:add(msg_id, buffer(length-2,2))

    pinfo.cols.protocol = my_trailer_proto.name
    pinfo.cols.protocol:set("proto_flag")
    pinfo.cols.info:set("proto_flag: " .. proto_flag)
end

my_trailer_proto:register_heuristic("eth.trailer", is_my_trailer)

这里有一个带尾随器的pcap文件示例https://transfernow.net/87kwt2k0dne7