动态将pcap文件内容添加到Lua哈希表中

我正在尝试读取 .pcap 文件，并针对每个客户端（客户端 IP 在此处是目标地址）聚合数据包数量。例如，如果已发送 5 个数据包到 xxx.ccc.vvv.bbb，则我将以以下格式将其输出到文件中：

xxx.ccc.vvv.bbb 5

这是我编写的程序：

#!/usr/bin/lua

do
    numberofpkts = 0
    stat = {client1 = {numberofpkts = {}}}
    local file = io.open("luawrite","w")
    local function init_listener()
            local tap = Listener.new("wlan")
            local dest_addr = Field.new("wlan.da")
            local pkt_type = Field.new("wlan.fc.type")
            function tap.reset()
                    numberofpkts = 0;
            end

            function tap.packet(pinfo, tvb)
                    client = dest_addr()
                    client1 = tostring(client)
                    type = pkt_type()
                    if(tostring(type) == '2') then
                            stat.client1.numberofpkts = stat.client1.numberofpkts+1
                            file:write(tostring(client1),"\t", tostring(stat.client1.numberofpkts),"\n")
                    end
            end

    end
    init_listener()
end

这里，wlan.da 给出目标地址。wlan.fc.type 表示它是数据报文（type=2）。我正在使用 tshark 运行此程序来捕获无线流量。

我得到了一个错误：

tshark: Lua: on packet 3 Error During execution of Listener Packet Callback:
/root/statistics.lua:21: attempt to call field 'tostring' (a nil value)
tshark: Lua: on packet 12 Error During execution of Listener Packet Callback happened  2 times:
 /root/statistics.lua:21: attempt to call field 'tostring' (a nil value)

请帮我解决这个问题。先谢谢了！