Wireshark 插件：通过每个 UDP 帧多个数据包剖析有效负载

Question

我正在编写一个 Wireshark 插件来剖析将多个应用程序级数据包放入单个 UDP 帧中的协议。没有封闭协议来指示帧中有多少个数据包。因此，本质上，来自网络的有效负载将如下所示：

uint64  sequence1
uint64  data1
uint8  flags1
uint64  sequence2
uint64  data2
uint8  flags2
: : :
uint64  sequence_n
uint64  data_n
uint8  flags_n

在实际处理此信息的服务器代码中，我只是循环遍历帧，直到到达末尾。在查看wireshark源代码中包含的插件时，我没有看到任何协议执行这样的循环。

我知道其他协议每帧打包多个有效负载。在 Wireshark 解析器中处理此类协议的规范或标准方法是什么？

Answer 1

我找到了一个对我有用的答案。我只是在解析器中循环，对我处理的每个字段增加一个 offset 值，直到 offset > 。 tvb_reported_length(tvb)。在每个循环中，我向父树项目添加一个新的子树，以便框架内的每个单独的消息都位于其自己的树中。

编辑：为了您的娱乐，这里是完整的CQS的解剖代码，包括处理每个 UDP 帧多个数据包的代码：

static int dissect_cqs(tvbuff_t* tvb, 
                       packet_info* pinfo, 
                       proto_tree* tree)
{
    guint offset = 0;
    proto_item* ti = 0;
    char msgcat = '\0';
    gint field_sz;
    static const char soh = 0x01, us = 0x1F, etx = 0x03;
    proto_tree* cqs_tree, *frame_tree, *packet_tree;
    guint8 ts_hour, ts_minute,ts_second;
    char ts_msec_str[3];
    char cattype [2];
    int found = 0;
    guint i;
    char seq_str[9+1];
    guint32 seq;
    guint32 firstseq = 0, msgcount = 0;
    guint framegaps = 0;

    col_set_str(pinfo->cinfo, COL_PROTOCOL, "CQS");
    col_clear(pinfo->cinfo, COL_INFO);

    ti = proto_tree_add_item(tree, proto_cqs, tvb, offset, -1, FALSE); 
    cqs_tree = proto_item_add_subtree(ti, ett_cqs);
    ti = proto_tree_add_item(cqs_tree, hf_cqs_frame_subtree, tvb, offset, -1, FALSE);
    frame_tree = proto_item_add_subtree(ti, ett_frame);

    /** APPEND THE LEADING CONTROL CHARACTER **/
    field_sz = 1;    ti = proto_tree_add_item(frame_tree, hf_cqs_ctrl, tvb, offset, field_sz, FALSE) ; offset += field_sz;


    while( offset < tvb_reported_length(tvb) )
    {
        /** get the message type, category & sequence number **/
        tvb_memcpy(tvb, cattype, offset, 2);
        tvb_memcpy(tvb, seq_str, offset+8, 9);
        seq_str[9] = 0;
        seq = atol(seq_str);

        ++msgcount;
        if( !firstseq )
            firstseq = seq;
        else
            framegaps += (seq - firstseq) - (msgcount - 1);

        ti = proto_tree_add_none_format(frame_tree, hf_cqs_packet_subtree, tvb, offset, 24, "CQS Packet [%ld]", seq);
        if( ti )    packet_tree = proto_item_add_subtree(ti, ett_packet);
        else        packet_tree = 0;

        /** dissect the packet header **/
        cattype[0] = tvb_get_guint8(tvb, offset);
        field_sz = 1;    ti = proto_tree_add_item(packet_tree, hf_cqs_hdr_msgcat, tvb, offset, field_sz, FALSE) ; offset += field_sz;
        cattype[1] = tvb_get_guint8(tvb, offset);
        field_sz = 1;    ti = proto_tree_add_item(packet_tree, hf_cqs_hdr_msgtype, tvb, offset, field_sz, FALSE) ; offset += field_sz;
        field_sz = 1;    ti = proto_tree_add_item(packet_tree, hf_cqs_hdr_msgnet, tvb, offset, field_sz, FALSE) ; offset += field_sz;
        field_sz = 2;    ti = proto_tree_add_item(packet_tree, hf_cqs_hdr_retran, tvb, offset, field_sz, FALSE) ; offset += field_sz;
        field_sz = 1;    ti = proto_tree_add_item(packet_tree, hf_cqs_hdr_hdrid, tvb, offset, field_sz, FALSE) ; offset += field_sz;
        field_sz = 2;    ti = proto_tree_add_item(packet_tree, hf_cqs_hdr_rsv, tvb, offset, field_sz, FALSE) ; offset += field_sz;
        field_sz = 9;    ti = proto_tree_add_item(packet_tree, hf_cqs_hdr_seq, tvb, offset, field_sz, FALSE) ; offset += field_sz;
        field_sz = 1;    ti = proto_tree_add_item(packet_tree, hf_cqs_hdr_partid, tvb, offset, field_sz, FALSE) ; offset += field_sz;
        ts_hour = tvb_get_guint8(tvb, offset) - '0';
        ts_minute = tvb_get_guint8(tvb, offset+1) - '0';
        ts_second = tvb_get_guint8(tvb, offset+2) - '0';
        ts_msec_str[0] = tvb_get_guint8(tvb, offset+3);
        ts_msec_str[1] = tvb_get_guint8(tvb, offset+4);
        ts_msec_str[2] = tvb_get_guint8(tvb, offset+5);
        field_sz = 6;    ti = proto_tree_add_item(packet_tree, hf_cqs_hdr_time, tvb, offset, field_sz, FALSE) ; offset += field_sz;
        if( tree )
        {
            proto_item_set_text(ti, "CQS Timestamp: %02d:%02d:%02d.%c%c%c %cM", (ts_hour > 11) ? (ts_hour-12) : ts_hour, ts_minute, ts_second, ts_msec_str[0], ts_msec_str[1], ts_msec_str[2], (ts_hour > 11) ? 'P' : 'A');
        }

        /** COUNT UP BYTES UNTIL WE FIND A CONTROL CHARACTER **/
        field_sz = 0;
        found = 0;
        for( i = 0; !found && offset+i < tvb_reported_length(tvb); ++i )
        {
            char c = tvb_get_guint8(tvb, offset+i);
            switch( c )
            {
            case 0x01 : /** SOH **/
            case 0x1F : /** US **/
            case 0x03 : /* ETX **/
                found = 1;
                break;
            default :
                ++field_sz;
                break;
            }
        }
        /** APPEND THE DATA PAYLOAD **/
        ti = proto_tree_add_item(packet_tree, hf_cqs_payload, tvb, offset, field_sz, FALSE) ; offset += field_sz;

        /** APPEND THE TRAILING CONTROL CHARACTER **/
        field_sz = 1;    ti = proto_tree_add_item(frame_tree, hf_cqs_ctrl, tvb, offset, field_sz, FALSE) ; offset += field_sz;
    }

    ti = proto_tree_add_uint(cqs_tree, hf_cqs_frame_first_seq, tvb, 0, 0, firstseq);
    ti = proto_tree_add_uint(cqs_tree, hf_cqs_frame_expected_seq, tvb, 0, 0, firstseq+msgcount);
    ti = proto_tree_add_uint(cqs_tree, hf_cqs_frame_msgcount, tvb, 0, 0, msgcount);
    ti = proto_tree_add_uint(cqs_tree, hf_cqs_frame_gaps, tvb, 0, 0, framegaps);


    return tvb_length(tvb);
}