使用NetBIOS名称ping W55MH32

本篇总结

本例程在 W55MH32 上实现 NetBIOS 名称解析功能，使 PC 端可直接通过 NetBIOS 名称 ping 设备。

硬件平台：本例程基于 W55MH32L-EVB 开发板运行。

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|报文解析|
NetBIOS Name Service
  Transaction ID: 0xa754        (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

NetBIOS 的优势

在实际应用中，设备通常使用 DHCP 方式配置网络地址，IP 地址会动态变化。NetBIOS 协议将固定的名称映射到动态 IP，用户只需记住设备名称即可访问，无需每次查看 IP 地址。W55MH32 SDK 内置了完整的 NetBIOS 名称服务库（netbios.c/h），名称解码、报文组包、UDP 状态机全部由库函数处理。

while (1)
{
    do_netbios(SOCKET_ID);
}

/**
*@brief  Execute the NetBIOS name resolver
*@param  socket number
*@return no
*/
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_W55MH32_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;
    }
}

状态机说明

SOCK_CLOSED 状态下初始化 UDP socket 并绑定 NETBIOS_PORT（137）端口；SOCK_UDP 状态下接收数据，判断是否为 NetBIOS 查询报文。若查询名称与设备名称 NETBIOS_W55MH32_NAME 匹配，则通过 getSIPR() 获取自身 IP，构造响应报文并通过 sendto() 发送给请求端。

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;
}

请注意

测试实例需要 PC 端和 W55MH32 处于同一网段。在 PC 端打开 CMD，使用 ping W55MH32 即可通过名称访问设备，无需关心设备的 IP 地址。