使用UDP作为服务端，上位机发送数据，延时好几秒才收到是怎么回事？

发布于 2023-05-16 11:47:51 浏览：541 订阅该版

基于net_sample例程做了UDP的服务器，测试发现上位机发送的数据会延时收到，调用的是SAL中的recvfrom,这个是什么原因呢？

```c
static void udpserv(void *param)
{
    int sock;
    int bytes_read;
    socklen_t addr_len;
    struct sockaddr_in server_addr, client_addr;

/* 创建一个socket，类型是SOCK_DGRAM，UDP类型 */
    if ((sock = socket(AF_INET, SOCK_DGRAM, 0)) == -1)
    {
        rt_kprintf("Socket error\n");
        return;
    }

int set = 1;
    setsockopt(sock, SOL_SOCKET, SO_BROADCAST, &set, sizeof(int));//接收广播消息
    /* 初始化服务端地址 */
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(UDP_SERVER);
    server_addr.sin_addr.s_addr = INADDR_ANY;
    rt_memset(&(server_addr.sin_zero), 0, sizeof(server_addr.sin_zero));

/* 绑定socket到服务端地址 */
    if (bind(sock, (struct sockaddr *)&server_addr,
             sizeof(struct sockaddr)) == -1)
    {
        /* 绑定地址失败 */
        rt_kprintf("Bind error\n");
        return;
    }

addr_len = sizeof(struct sockaddr);
    rt_kprintf("UDPServer Waiting for client ...\n");
    int ret;
    while (1)
    {
        /* 从sock中收取最大BUFSZ - 1字节数据 */
        bytes_read = recvfrom(sock, &RecSndBuf, BUFSZ - 1, 0,
                              (struct sockaddr *)&client_addr, &addr_len);

RecSndBuf[bytes_read] = '\0'; /* 把末端清零 */

// /* 输出接收的数据 */
       if((RecSndBuf[0] == 0xAA) && (RecSndBuf[1] == 0x55)) 
       {
            LOG_HEX("udp raw",16,RecSndBuf,bytes_read);
            ret = ParseRawCmd(RecSndBuf,bytes_read,RecSndBuf,BUFSZ);
            if(ret > 0)
            {
                ret = sendto(sock, RecSndBuf, ret, 0,
                (struct sockaddr *)&client_addr, sizeof(struct sockaddr));
                if(ret <= 0)
                {
                    LOG_W("udp send failed\n");
                }
            }
       }
       else  //json命令交互
       {
            if(ParseJsonCmd(RecSndBuf,RecSndBuf,BUFSZ) >=0)
            {
                LOG_W("response:%s,len[%d]\n",RecSndBuf,strlen(RecSndBuf));
                ret = sendto(sock, RecSndBuf, strlen(RecSndBuf), 0,
                (struct sockaddr *)&client_addr, sizeof(struct sockaddr));
                if(ret <= 0)
                {
                    LOG_W("udp send failed\n");
                }
                else
                {
                    LOG_I("udp response success\n");
                }
                    
            }
            else
            {
                    LOG_W("cmd has no response!\n");
            }        
       }

}

closesocket(sock);
}
```