lwip_tcp client保活机制的应用

向右看齐 2022-05-09 14:04 556阅读 0赞

## lwip\_tcp Unbeatable client ##

项目测试记录：2018/10/16  
保活机制的设置参考：  
[http://blog.sina.com.cn/s/blog\_62a85b950102vrr4.html][http_blog.sina.com.cn_s_blog_62a85b950102vrr4.html]  
（先自行了解保活机制）  
LWIP中包括两个定时器函数：一个函数每 250 ms调用一次(快速定时器)；另一个函数每500ms调用一次(慢速定时器)。

tcp\_slowtmr函数的部分代码：

static unsigned char Close_Wait_keep_cnt_sent = 0;
        /* Check if KEEPALIVE should be sent */
        if(ip_get_option(pcb, SOF_KEEPALIVE) &&      //如果使用了保活机制
           ((pcb->state == ESTABLISHED) ||
            (pcb->state == CLOSE_WAIT))) {
          if((u32_t)(tcp_ticks - pcb->tmr) >
             (pcb->keep_idle + TCP_KEEP_DUR(pcb)) / TCP_SLOW_INTERVAL)      //2小时+9*75秒后断开连接
          {
            LWIP_DEBUGF(TCP_DEBUG, ("tcp_slowtmr: KEEPALIVE timeout. Aborting connection to %"U16_F".%"U16_F".%"U16_F".%"U16_F".\n",
                                    ip4_addr1_16(&pcb->remote_ip), ip4_addr2_16(&pcb->remote_ip),
                                    ip4_addr3_16(&pcb->remote_ip), ip4_addr4_16(&pcb->remote_ip)));
    
            ++pcb_remove;          //设置两个局部变量，后需删除控制块
            ++pcb_reset;           //复位连接
          }
          else if((u32_t)(tcp_ticks - pcb->tmr) >
                  (pcb->keep_idle + pcb->keep_cnt_sent * TCP_KEEP_INTVL(pcb))
                  / TCP_SLOW_INTERVAL)
          {
            tcp_keepalive(pcb);    //发送保活探查报文
            pcb->keep_cnt_sent++;  //保活报文数加1
            if(pcb->state == CLOSE_WAIT)   Close_Wait_keep_cnt_sent++;
            else  Close_Wait_keep_cnt_sent = 0;
          }
          if(pcb->state == CLOSE_WAIT){
              if(Close_Wait_keep_cnt_sent > pcb->keep_cnt) //close wait timeout for (pcb->keep_idle + TCP_KEEP_DUR(pcb))
              {
                  ++pcb_remove;          //设置两个局部变量，后需删除控制块
                  ++pcb_reset;           //复位连接
              }
          }
        }

保活机制（ip\_get\_option(pcb, SOF\_KEEPALIVE)）打开后，保证在ESTABLISHED和CLOSE\_WAIT两状态下发生异常（ESTABLISHED状态的异常如网线断开，CLOSE\_WAIT状态的异常如sever主动断开。），并发送完保活探查报文后（发送次数由pcb->keep\_cnt决定），程序能够执行pcb\_remove和pcb\_reset的置位。

/* If the PCB should be removed, do it. */
        if (pcb_remove) {
          struct tcp_pcb *pcb2;
          tcp_err_fn err_fn;
          void *err_arg;
          tcp_pcb_purge(pcb);
          /* Remove PCB from tcp_active_pcbs list. */
          if (prev != NULL) {
            LWIP_ASSERT("tcp_slowtmr: middle tcp != tcp_active_pcbs", pcb != tcp_active_pcbs);
            prev->next = pcb->next;
          } else {
            /* This PCB was the first. */
            LWIP_ASSERT("tcp_slowtmr: first pcb == tcp_active_pcbs", tcp_active_pcbs == pcb);
            tcp_active_pcbs = pcb->next;
          }
    
          if (pcb_reset) {
            tcp_rst(pcb->snd_nxt, pcb->rcv_nxt, &pcb->local_ip, &pcb->remote_ip,
              pcb->local_port, pcb->remote_port);
          }
    
          err_fn = pcb->errf;    //错误回调函数
          err_arg = pcb->callback_arg;  //错误回调函数参数
          pcb2 = pcb;
          pcb = pcb->next;
          memp_free(MEMP_TCP_PCB, pcb2);
    
          tcp_active_pcbs_changed = 0;
          TCP_EVENT_ERR(err_fn, err_arg, ERR_ABRT);   
          if (tcp_active_pcbs_changed) {
            goto tcp_slowtmr_start;
          }
        }

pcb\_remove置位后，上面的代码会生效，重点是在这里可以加载一个错误回调函数，我们可以在错误回调函数中处理异常。然而这个错误回调函数我们需要在客户端初始化的时候给它注册。

u_sTcp_pcb[i] = tcp_new();
               tcp_bind(u_sTcp_pcb[i], &IPAddr, pConnectMesg->wSrcPort);
               if(byCliServ == LWIP_CLIENT)
                {
                    if(u_sTcp_pcb[i] != NULL)
                        ip_set_option(u_sTcp_pcb[i], SOF_KEEPALIVE);
    
                    tcp_connect(u_sTcp_pcb[i], &RemoteIP, pConnectMesg->wDstPort, pConnectMesg->pTcpConnected); 
                    tcp_arg(u_sTcp_pcb[i], (void *)pConnectMesg);   //指定网络错误回调函数的参数
                    tcp_err(u_sTcp_pcb[i], echo_client_conn_err);   //注册网络错误回调函数
                    tcp_recv(u_sTcp_pcb[i], pConnectMesg->pTcpRecv);  
                    return u_sTcp_pcb[i];
                }

下面就该是错误回调函数的函数体了：

static void echo_client_conn_err(void *arg, err_t err)
    {
        int i = 0;
        err_t ERR;
        struct ip_addr  SeverIP;
        NETCONNECTMESG * pReconnectMesg = (NETCONNECTMESG *)arg;
    
        if(err != ERR_ABRT)  return;
        IP4_ADDR(&SeverIP, pReconnectMesg->aDstIP[0], pReconnectMesg->aDstIP[1],
                pReconnectMesg->aDstIP[2], pReconnectMesg->aDstIP[3]);
    
    
        for(i = 0; i < LWIP_MAX_CONNECT; i++)
        {
            if(u_sTcp_pcb[i] != NULL)
            {
                ERR = tcp_close(u_sTcp_pcb[i]);
                if(ERR == ERR_OK)
                    u_sTcp_pcb[i] = NULL;
            }
            if(u_sTcp_pcb[i] == NULL)
            {
                u_sTcp_pcb[i] = tcp_new();
                if(u_sTcp_pcb[i] != NULL)
                    ip_set_option(u_sTcp_pcb[i], SOF_KEEPALIVE);
                tcp_bind(u_sTcp_pcb[i], IP_ADDR_ANY, pReconnectMesg->wSrcPort);
    
                tcp_connect(u_sTcp_pcb[i], &SeverIP, pReconnectMesg->wDstPort, pReconnectMesg->pTcpConnected);
                tcp_arg(u_sTcp_pcb[i], pReconnectMesg);
                tcp_err(u_sTcp_pcb[i], echo_client_conn_err);
                tcp_recv(u_sTcp_pcb[i], pReconnectMesg->pTcpRecv);
                return;
            }
        }
    }

目前测试，client是打不死的小强。

[http_blog.sina.com.cn_s_blog_62a85b950102vrr4.html]: http://blog.sina.com.cn/s/blog_62a85b950102vrr4.html