第十二章 W55MH32 NetBIOS示例标题

|报文解析|

NetBIOS Name Service

    Transaction ID: 0xa753    (唯一标识此查询，用于匹配请求与响应)

    Flags: 0x0110, Opcode: Name query, Recursion desired, Broadcast            (表示这是一个 广播 查询请求)

    Questions: 1              (字段说明仅查询一个设备名称)

    Answer RRs: 0             (在响应报文中，该字段会显示解析到的记录数)

    Authority RRs: 0          (在响应报文中，用于指示哪些服务器可以授权回答该查询)

    Additional RRs: 0         (在某些NetBIOS响应中可能用于携带更多解析信息)

|报文原文|

a7 54 01 10 00 01 00 00 00 00 00 00

while (1)
{
    do_netbios(SOCKET_ID);
}

do_netbios()函数需要传入一个参数，该参数是socket号，do_netbios()函数如下：

void do_netbios(uint8_t sn)
{
    unsigned char state;
    unsigned int  len;
    state = getSn_SR(sn);
    switch (state)
    {
    case SOCK_UDP:
        if ((len = getSn_RX_RSR(sn)) > 0)
        {
            unsigned char     rem_ip_addr[4];
            uint16_t          rem_udp_port;
            char              netbios_name[NETBIOS_NAME_LEN + 1];
            NETBIOS_HDR      *netbios_hdr;
            NETBIOS_NAME_HDR *netbios_name_hdr;
            len = recvfrom(sn, (unsigned char *)&netbios_rx_buf, len, rem_ip_addr, &rem_udp_port);
            printf("rem_ip_addr=%d.%d.%d.%d:%d\r\n", rem_ip_addr[0], rem_ip_addr[1], rem_ip_addr[2], rem_ip_addr[3], rem_udp_port);
            netbios_hdr      = (NETBIOS_HDR *)netbios_rx_buf;
            netbios_name_hdr = (NETBIOS_NAME_HDR *)(netbios_hdr + 1);
            // If the packet is a NetBIOS query packet
            if (((netbios_hdr->flags & ntohs(NETB_HFLAG_OPCODE)) == ntohs(NETB_HFLAG_OPCODE_NAME_QUERY)) && ((netbios_hdr->flags & ntohs(NETB_HFLAG_RESPONSE)) == 0) && (netbios_hdr->questions == ntohs(1)))
            {
                printf("netbios name query question\r\n");
                // Decode the NetBIOS package
                netbios_name_decoding((char *)(netbios_name_hdr->encname), netbios_name, sizeof(netbios_name));
                printf("name is %s\r\n", netbios_name);
                // If the query is made against the native Netbios
                if (strcmp(netbios_name, NETBIOS_W5500_NAME) == 0)
                {
                    uint8_t       ip_addr[4];
                    NETBIOS_RESP *resp = (NETBIOS_RESP *)netbios_tx_buf;
                    // Handle the header of the NetBIOS response packet
                    resp->resp_hdr.trans_id      = netbios_hdr->trans_id;
                    resp->resp_hdr.flags         = htons(NETB_HFLAG_RESPONSE | NETB_HFLAG_OPCODE_NAME_QUERY | NETB_HFLAG_AUTHORATIVE | NETB_HFLAG_RECURS_DESIRED);
                    resp->resp_hdr.questions     = 0;
                    resp->resp_hdr.answerRRs     = htons(1);
                    resp->resp_hdr.authorityRRs  = 0;
                    resp->resp_hdr.additionalRRs = 0;
                    // Process the header data of the NetBIOS response packet
                    memcpy(resp->resp_name.encname, netbios_name_hdr->encname, sizeof(netbios_name_hdr->encname));
                    resp->resp_name.nametype = netbios_name_hdr->nametype;
                    resp->resp_name.type     = netbios_name_hdr->type;
                    resp->resp_name.cls      = netbios_name_hdr->cls;
                    resp->resp_name.ttl      = htonl(NETBIOS_NAME_TTL);
                    resp->resp_name.datalen  = htons(sizeof(resp->resp_name.flags) + sizeof(resp->resp_name.addr));
                    resp->resp_name.flags    = htons(NETB_NFLAG_NODETYPE_BNODE);
                    getSIPR(ip_addr);
                    memcpy(resp->resp_name.addr, ip_addr, 4);
                    // Send a response packet
                    sendto(sn, (unsigned char *)resp, sizeof(NETBIOS_RESP), rem_ip_addr, rem_udp_port);
                    printf("send response\r\n");
                }
            }
        }
        break;

    case SOCK_CLOSED:
        close(sn);
        socket(sn, Sn_MR_UDP, NETBIOS_PORT, 0);
        break;

    default:
        break;
    }
}

进入do_netbios()函数会执行一个UDP协议的状态机，当收到消息后，首先会判断是否为NetBIOS报文，如果为NetBIOS报文则会进入netbios_name_decoding()函数解析NetBIOS名称，当名称与W55MH32的NetBIOS名称一致时，则返回响应报文。

static int netbios_name_decoding(char *name_enc, char *name_dec, int name_dec_len)
{
    char *pname;
    char  cname;
    char  cnbname;
    int   index = 0;
    // Decode the name of the former NetBIOS
    pname = name_enc;
    for (;;)
    {
        /* Every two characters of the first level-encoded name
         * turn into one character in the decoded name. */
        cname = *pname;
        if (cname == '\0')
            break; // no more characters
        if (cname == '.')
            break; // scope ID follows
        if (cname < 'A' || cname > 'Z')
        {
            // Not legal.
            return -1;
        }
        cname   -= 'A';
        cnbname  = cname << 4;
        pname++;

        cname = *pname;
        if (cname == '\0' || cname == '.')
        {
            /* No more characters in the name - but we're in
             * the middle of a pair.  Not legal. */
            return -1;
        }
        if (cname < 'A' || cname > 'Z')
        {
            // Not legal.
            return -1;
        }
        cname   -= 'A';
        cnbname |= cname;
        pname++;

        // Do we have room to store the character?
        if (index < NETBIOS_NAME_LEN)
        {
            // Yes - store the character.
            name_dec[index++] = (cnbname != ' ' ? cnbname : '\0');
        }
    }
    return 0;
}

7 运行结果