使用lua脚本为wireshake编写自定义协议解析器

以下内容转载自：转载地址

在网络通信应用中，我们往往需要自定义应用层通信协议，例如基于UDP的Real-Time Transport Protocol以及基于TCP的RTP over HTTP。鉴于RTP协议的广泛性，wireshark(ethereal)内置了对RTP协议的支持，调试解析非常方便。RTP over HTTP作为一种扩展的RTP协议，尚未得到wireshark的支持。在《RTP Payload Format for Transport of MPEG-4 Elementary Streams over http》中，使用wireshark只能抓获到原始的TCP数据包，需要我们自己解析蕴含其中的RTP报文，剥离RTP over HTTP 16字节的报文头，然后萃取出MP4V_ES码流数据。

怎么样使wireshark支持自定义通信协议的解析呢？基于GPL v2的wireshark强大的插件系统支持用户编写自定义协议解析器插件。wireshark使用C语言编写而成，它支持动态链接库形式的插件扩展。除此之外，wireshark内置了Lua脚本引擎，可以使用Lua脚本语言编写dissector插件。打开C:/Program Files/Wireshark/init.lua，确保disable_lua = false，以开启wireshark的Lua Console。

Lua是一种功能强大的、快速的、轻量的、嵌入式的脚本语言，使用Lua编写wireshark dissector插件是非常方便的。本文例解使用Lua编写ROH（RTP over HTTP）协议解析插件。

以下为GET http://219.117.194.183:60151/rtpOverHttp?Url=nphMpeg4/nil-640x480，获取MP4V_ES的一个片段，在没有ROH解析支持时，Packet 294显示为TCP报文。

关于RTP over HTTP报文的解析，参考《RTP Payload Format for Transport of MPEG-4 Elementary Streams over http》。关于Lua语法，参考Wireshark User’s Guide的《Lua Support in Wireshark》一节。

以下为自定义RTP over HTTP协议解析器插件代码roh.lua：

do

    --[[

    Proto.new(name, desc)

        name: displayed in the column of “Protocol” in the packet list

        desc: displayed as the dissection tree root in the packet details

    --]]

    local PROTO_ROH = Proto("ROH", "Rtp Over Http")

 

    --[[

    ProtoField:

        to be used when adding items to the dissection tree

    --]]

    --[[

    (1)Rtp Over Http Header

    --]]

    -- rtp over http header flag(1 byte)

    local f_roh_headerflag = ProtoField.uint8("ROH.HeaderFlag", "Header Flag", base.HEX)

    -- rtp over http interleaved channel(1 byte)

    local f_roh_interleave = ProtoField.uint8("ROH.InterleavedChannel", "Interleaved Channel", base.DEC)

    -- rtp over http packet length(2 bytes)

    local f_roh_packlen = ProtoField.uint16("ROH.PacketLen", "Packet Length", base.DEC)

    --[[

    (2)RTP Over Http

    --]]

    -- rtp header(1 byte = V:2+P:1+X:1+CC:4)

    local f_rtp_header = ProtoField.uint8("ROH.Header", "Rtp Header", base.HEX)

    -- rtp payloadtype(1 byte = M:1+PT:7)

    local f_rtp_payloadtype = ProtoField.uint8("ROH.PayloadType", "Rtp Payload Type", base.HEX)

    -- rtp sequence number(2 bytes)

    local f_rtp_sequence = ProtoField.uint16("ROH.Sequence", "Rtp Sequence Number", base.DEC)

    -- rtp timestamp(4 bytes)

    local f_rtp_timestamp = ProtoField.uint32("ROH.Timestamp", "Rtp Timestamp", base.DEC)

    -- rtp synchronization source identifier(4 bytes)

    local f_rtp_ssrc = ProtoField.uint32("ROH.SSRC", "Rtp SSRC", base.DEC)

 

    -- define the fields table of this dissector(as a protoField array)

    PROTO_ROH.fields = {f_roh_headerflag, f_roh_interleave, f_roh_packlen, f_rtp_header, f_rtp_payloadtype, f_rtp_sequence, f_rtp_timestamp, f_rtp_ssrc}

 

    --[[

    Data Section

    --]]

    local data_dis = Dissector.get("data")

 

    --[[

    ROH Dissector Function

    --]]

    local function roh_dissector(buf, pkt, root)

 

        -- check buffer length

        local buf_len = buf:len()

        if buf_len < 16

        then

            return false

        end

 

        -- check header flag

        if buf(0,2):uint() ~= 0x2400

        then

            return false

        end

 

        --[[

        packet list columns

        --]]

        pkt.cols.protocol = "ROH"

        pkt.cols.info = "Rtp Over Http"

 

        --[[

        dissection tree in packet details

        --]]

        -- tree root

        local t = root:add(PROTO_ROH, buf(0,16))

        -- child items

        -- ROH Header

        t:add(f_roh_headerflag, buf(0,1))

        t:add(f_roh_interleave, buf(1,1))

        t:add(f_roh_packlen, buf(2,2))

        -- ROH

        -- (1)header

        t:add(f_rtp_header, buf(4,1))

        -- (2)payloadtype

        t:add(f_rtp_payloadtype, buf(5,1))

        -- (3)sequence number

        t:add(f_rtp_sequence, buf(6,2))

        -- (4)timestamp

        t:add(f_rtp_timestamp, buf(8,4))

        -- (5)ssrc

        t:add(f_rtp_ssrc, buf(12,4))

 

        if buf_len > 16

        then

            local data_len = buf:len()-16;

 

            local d = root:add(buf(16, data_len), "Data")

            d:append_text("("..data_len.." bytes)")

            d:add(buf(16, data_len), "Data: ")

            d:add(buf(16,0), "[Length: "..data_len.."]")

 

            local start_code = buf(16,4):uint()

            if start_code == 0x000001b0

            then

                d:add(buf(16,0), "[Stream Info: VOS]")

            elseif start_code == 0x000001b6

            then

                local frame_flag = buf(20,1):uint()

                if frame_flag<2^6

                then

                    d:add(buf(16,0), "[Stream Info: I-Frame]")

                elseif frame_flag<2^7

                then

                    d:add(buf(16,0), "[Stream Info: P-Frame]")

                else

                    d:add(buf(16,0), "[Stream Info: B-Frame]")

                end

            end

        end

 

        return true

    end

 

    --[[

    Dissect Process

    --]]

    function PROTO_ROH.dissector(buf, pkt, root)

        if roh_dissector(buf, pkt, root)

        then

        -- valid ROH diagram

        else

            data_dis:call(buf, pkt, root)

        end

    end

 

    --[[

    Specify Protocol Port

    --]]

    local tcp_encap_table = DissectorTable.get("tcp.port")

    tcp_encap_table:add(60151, PROTO_ROH)

end

通过菜单“ToolsàLuaàEvaluate”打开Lua调试窗口，将以上代码输入Evaluate窗口，然后点击“Evaluate”按钮，若无错误提示，且末尾提示“--[[  Evaluated --]]”，则说明代码无语法错误。这时，通过菜单“HelpàSupported Protocols”可以发现，wireshark已经添加了ROH协议调试支持，在Display Filter中输入“roh”，则可以看到具体解析结果。

将以上代码保存为C:/Program Files/Wireshark/roh.lua。在C:/Program Files/Wireshark/init.lua末尾添加代码行：dofile("roh.lua")。这样在以后启动wireshark时，自动加载roh.lua。

增加roh.Lua插件扩展后，Packet 294将解析为RTP over HTTP报文。最后的Data部分为剥离16字节报文头后的码流。

由于尚未掌握Lua的位域（bitfield）操作，因此上面对于RTP的解析不完整，第一个字节（V:2+P:1+X:1+CC:4）和第二字节（M:1+PT:7）的相关位域没有解析出来。

既然wireshark内置了对RTP协议的支持，我们在解析完RTP over HTTP的头4个字节后，可以将余下的报文交由RTP协议解析器解析。以下为调用内置RTP协议解析器代码roh_rtp.lua：

do

    --[[

    Proto.new(name, desc)

        name: displayed in the column of “Protocol” in the packet list

        desc: displayed as the dissection tree root in the packet details

    --]]

    local PROTO_ROH = Proto("ROH", "Rtp Over Http")

    local PROTO_PANASONIC_PTZ = Proto("PANASONIC_PTZ", "Panasonic PTZ Protocol")

 

    --[[

    ProtoField:

        to be used when adding items to the dissection tree

    --]]

    --[[

    1.ROH ProtoField

    --]]

    --rtp over http header flag(1 byte)

    local f_roh_headerflag = ProtoField.uint8("ROH.HeaderFlag", "Header Flag", base.HEX)

    --rtp over http interleaved channel(1 byte)

    local f_roh_interleave = ProtoField.uint8("ROH.InterleavedChannel", "Interleaved Channel", base.DEC)

    --rtp over http packet length(2 bytes)

    local f_roh_packlen = ProtoField.uint16("ROH.PacketLen", "Packet Length", base.DEC)

    --define the fields table of this dissector(as a protoField array)

    PROTO_ROH.fields = {f_roh_headerflag, f_roh_interleave, f_roh_packlen}

 

    --[[

    2.PANASONIC_PTZ ProtoField

    --]]

    -- panasonic ptz header flag(32 ascii)

    local f_panasonic_ptz_flag = ProtoField.bytes("PANASONIC_PTZ", "Header Flag")

    -- panasonic ptz command(6~17 ascii)

    local f_panasonic_ptz_cmd = ProtoField.bytes("PANASONIC_PTZ", "Command")

    --define the fields table of this dissector(as a protoField array)

    PROTO_PANASONIC_PTZ.fields = {f_panasonic_ptz_flag, f_panasonic_ptz_cmd}

 

    --[[

    Data Section

    --]]

    local data_dis = Dissector.get("data")

 

    --[[

    ROH Dissector Function

    --]]

    local function roh_dissector(buf, pkt, root)

        -- check buffer length

        local buf_len = buf:len()

        if buf_len < 16

        then

            return false

        end

       

        -- check header flag

        if buf(0,2):uint() ~= 0x2400

        then

            return false

        end

 

        --[[

        packet list columns

        --]]

        pkt.cols.protocol = "ROH"

        pkt.cols.info = "Rtp Over Http"

 

        --[[

        dissection tree in packet details

        --]]

        -- tree root

        local t = root:add(PROTO_ROH, buf(0,4))

        -- child items

        t:add(f_roh_headerflag, buf(0,1))

        t:add(f_roh_interleave, buf(1,1))

        t:add(f_roh_packlen, buf(2,2))

 

        return true

    end

 

    --[[

    PANASONIC_PTZ Dissector Function Helper

    --]]

    local function get_cmd_len(buf)

        local found=0

        for i=0,17 do

            if buf(i,1):uint() == 0x26

            then

                found = i

                break

            end

        end

        return found

    end

 

    --[[

    PANASONIC_PTZ Dissector Function

    --]]

    local function panasonic_ptz_dissector(buf, pkt, root)

 

        -- check buffer length

        local buf_len = buf:len()

        if buf_len < 32

        then

            return false

        end

 

        -- check header flag

        if buf(0,32):string() ~= "GET /nphControlCamera?Direction="

        then

            return false

        end

 

        -- check direction

        local sub_buf = buf(32, 18):tvb()

        local cmd_len = get_cmd_len(sub_buf)

 

        if cmd_len > 0

        then

            --[[

            packet list columns

            --]]

            pkt.cols.protocol = "PANASONIC_PTZ"

            pkt.cols.info = "Panasonic PTZ Protocol"

 

            --[[

            dissection tree in packet details

            --]]

            -- tree root

            local t = root:add(PROTO_PANASONIC_PTZ, buf(0,buf_len))

            -- child items

            local flag = t:add(f_panasonic_ptz_flag, buf(0,32))

            flag:add(buf(0,31), "["..buf(0,31):string().."]")

            local cmd = t:add(f_panasonic_ptz_cmd, buf(32,cmd_len))

            cmd:add(buf(32,cmd_len), "["..buf(32,cmd_len):string().."]")

        else

            return false

        end

 

        return true

    end

 

    --[[

    Dissect Process

    --]]

    function PROTO_ROH.dissector(buf, pkt, root)

        if roh_dissector(buf, pkt, root)

        then

            -- skip over rtp over http header

            local rtp_buf = buf(4,buf:len()-4):tvb()

            -- call internal rtp dissector

            local rtp_dissector = Dissector.get("rtp")

            rtp_dissector:call(rtp_buf, pkt, root)

        elseif panasonic_ptz_dissector(buf, pkt, root)

        then

            -- valid ptz datagram

        else

            data_dis:call(buf, pkt, root)

        end

    end

 

    --[[

    Specify Protocol Port

    --]]

    local tcp_encap_table = DissectorTable.get("tcp.port")

    tcp_encap_table:add(60151, PROTO_ROH)

end

此外，wireshark内置了对MP4V_ES码流解析器，选择菜单“EditàPreferencesàProtocolsàMP4V_ES”，在“MP4V_ES dynamic payload type：”中填写“96”。

将以上代码保存为C:/Program Files/Wireshark/roh_rtp.lua。在C:/Program Files/Wireshark/init.lua末尾添加代码行：dofile("roh_rtp.lua")，在dofile("roh.lua")前添加“--”注释，以免端口冲突（在roh.lua中tcp.port=60151）。保存init.lua后，重启wireshark。

自定义应用层协议基于传输层（UDP/TCP），自定义的协议端口号不能与wireshark内置应用层协议冲突。若将ROH协议指定为TCP 80，则需要选择菜单“AnalyzeàEnabled Protocols”勾掉HTTP，这样TCP 80的报文将按照ROH协议解析。

在Display Filter中输入“roh”可查看RTP+MP4V_ES解析结果，如下图所示：

此外，在Display Filter中输入“panasonic_ptz”可查看PTZ控制报文。

 

参考：

《Programming in Lua》

《Lua 5.0 Reference Manual》

《Small is Beautiful: the design of Lua》

《Lua Scripting in Wireshark》

 

《为Wireshark 开发插件》

《使用lua脚本编写wireshark协议插件》

《使用lua编写Wireshark的dissector插件》

《用Lua语言编写Wireshark dissector插件》

《Lua和Wireshark配合，调试通信程序》