Question

我写了一个解剖器，

我发现一个数据包里面包含几个不同的/无关紧要的消息，

有人可以指出这个问题吗？这甚至是个问题吗？

我重组TCP数据包......

这是解剖的功能： （FRAME_HEADER_LEN = 8）

static void
dissect_PROTOC(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
{
    //Reassembling TCP fragments
    tcp_dissect_pdus(tvb, pinfo, tree, TRUE, FRAME_HEADER_LEN,
                     get_PROTOC_message_len, dissect_PROTOC_message);

}

static guint get_PROTOC_message_len(packet_info *pinfo, tvbuff_t *tvb, int offset)
{
    /* the packet's size is "length" + 4bytes of TYPESIZE + 4bytes of LENGTHSIZE + 256bytes of CONTEXTIDSIZE */
    return (guint)(tvb_get_ntohl(tvb, offset + 4) + CONTEXT_ID_SIZE + TYPE_SIZE + LENGTH_SIZE); /* e.g. length is at offset 4 */
}

static void dissect_PROTOC_message(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
{
    /* my dissecting code */
    guint32 packet_type = tvb_get_ntohl(tvb, 0);

    col_set_str(pinfo->cinfo, COL_PROTOCOL, "PROTOC");
    /* Clear out stuff in the info column */
    col_clear(pinfo->cinfo,COL_INFO);
    col_add_fstr(pinfo->cinfo, COL_INFO, "%d > %d [%s]",pinfo->srcport, pinfo->destport,
             val_to_str(packet_type, packettypenames, "Unknown (0x%02x)"));

    if (tree) { /* we are being asked for details */
        proto_item *ti              = NULL;
        proto_tree *PROTOC_tree         = NULL;
        proto_item *PROTOC_data         = NULL;
        proto_tree *PROTOC_data_tree    = NULL;
        guint32 type    = 0;
        guint32 length  = 0;
        gint offset     = 0;

        ti = proto_tree_add_item(tree, proto_PROTOC, tvb, 0, -1, ENC_NA);
        proto_item_append_text(ti, ", Type: %s",
            val_to_str(packet_type, packettypenames, "Unknown (0x%02x)"));
        PROTOC_tree = proto_item_add_subtree(ti, ett_PROTOC);

        //getting type
        type = tvb_get_ntohl(tvb, offset);
        proto_tree_add_item(PROTOC_tree, hf_PROTOC_pdu_type, tvb, 0, TYPE_SIZE, ENC_BIG_ENDIAN);
        offset += TYPE_SIZE;

        //getting length for the data length
        length = tvb_get_ntohl(tvb, offset);
        proto_tree_add_item(PROTOC_tree, hf_PROTOC_len, tvb, offset, LENGTH_SIZE, ENC_BIG_ENDIAN);
        offset += LENGTH_SIZE;
        proto_tree_add_item(PROTOC_tree, hf_PROTOC_contextid, tvb, offset, CONTEXT_ID_SIZE, ENC_BIG_ENDIAN);
        offset += CONTEXT_ID_SIZE;
        PROTOC_data = proto_tree_add_item(PROTOC_tree, hf_PROTOC_data, tvb, offset, length, FALSE);
        PROTOC_data_tree = proto_item_add_subtree(PROTOC_data, ett_PROTOC_data);
        offset += length;

    }
}

Answer 1

我发现一个数据包里面包含几个不同的/无关紧要的消息，

...

我重组TCP数据包......

这对于通过TCP运行的协议来说非常常见;无法保证TCP段边界将对应于在TCP之上运行的协议中的数据包边界。 TCP段可以包含多个高级协议包的部分或全部，而更高级别的协议包可以由来自多个TCP段的数据组成。

一个数据包中的几个消息

1 个答案: