在特定情况下AT组件可能无法读完数据

发布于 2018-12-29 21:34:26 浏览：1711 订阅该版

在AT组件的 at_recvfrom 函数中有如下代码段
/* socket passively closed, receive function return 0 */

if (sock->state == AT_SOCKET_CLOSED)
    {
        result = 0;
        goto __exit;
    }
    else if (sock->state != AT_SOCKET_CONNECT)
    {
        LOG_E("received data error, current socket (%d) state (%d) is error.", socket, sock->state);
        result = -1;
        goto __exit;
    }

/* receive packet list last transmission of remaining data */
    rt_mutex_take(sock->recv_lock, RT_WAITING_FOREVER);
    if((recv_len = at_recvpkt_get(&(sock->recvpkt_list), (char *)mem, len)) > 0)
    {
        rt_mutex_release(sock->recv_lock);
        goto __exit;
    }
    rt_mutex_release(sock->recv_lock);

中间省略.........

while (1)
    {
        /* wait the receive semaphore */
        if (rt_sem_take(sock->recv_notice, timeout) < 0)
        {
            LOG_E("AT socket (%d) receive timeout (%d)!", socket, timeout);
            result = -1;
            goto __exit;
        }
        else
        {
            if (sock->state == AT_SOCKET_CONNECT)
            {
                /* get receive buffer to receiver ring buffer */
                rt_mutex_take(sock->recv_lock, RT_WAITING_FOREVER);
                recv_len = at_recvpkt_get(&(sock->recvpkt_list), (char *) mem, len);
                rt_mutex_release(sock->recv_lock);
                if (recv_len > 0)
                {
                    break;
                }
            }
            else
            {
                LOG_D("received data exit, current socket (%d) is closed by remote.", socket);
                result = 0;
                goto __exit;
            }
        }

}

在实际一个项目应用中通讯过程是这样的：客户端与服务器端采样TCP短连接方式，客户端有数据发送时发起TCP连接，
成功后发送数据到服务器端，服务器端对收到的数据进行校验然并给客户端一个应答数据包然后主动关闭TCP连接。
其中客户端发送数据后立即调用select函数等待服务器端的应答包，当服务器端返回应答包后被唤醒，可能是因为客户端
采用单片机处理速度比较慢，所以客户端在select函数返回准备去读取数据时，服务器端已经断开连接了，这时候sock->state
的状态已经变为AT_SOCKET_CLOSED，这样一来客户端就收不到最后服务器端返回的应答包，客户端认为发送失败了导致
不断的重复发送上一包数据，可能有时候客户端又偶尔能收到一次服务器端的应答数据包，发现这个问题后我讲上面的代码稍微调整了一下顺序
变为如下：

/* receive packet list last transmission of remaining data */
    rt_mutex_take(sock->recv_lock, RT_WAITING_FOREVER);
    if((recv_len = at_recvpkt_get(&(sock->recvpkt_list), (char *)mem, len)) > 0)
    {
        rt_mutex_release(sock->recv_lock);
        goto __exit;
    }
    rt_mutex_release(sock->recv_lock);

/* socket passively closed, receive function return 0 */
    if (sock->state == AT_SOCKET_CLOSED)
    {
        result = 0;
        goto __exit;
    }
    else if (sock->state != AT_SOCKET_CONNECT)
    {
        LOG_E("received data error, current socket (%d) state (%d) is error.", socket, sock->state);
        result = -1;
        goto __exit;
    }
即先看看缓存中有没有数据包如果有就直接读取返回，如果没有再去判断sock的状态，后面的也做了相应的修改，如下

while (1)
    {
        /* wait the receive semaphore */
        if (rt_sem_take(sock->recv_notice, timeout) < 0)
        {
            LOG_E("AT socket (%d) receive timeout (%d)!", socket, timeout);
            result = -1;
            goto __exit;
        }
        else
        {
                /* get receive buffer to receiver ring buffer */
                rt_mutex_take(sock->recv_lock, RT_WAITING_FOREVER);
                recv_len = at_recvpkt_get(&(sock->recvpkt_list), (char *) mem, len);
                rt_mutex_release(sock->recv_lock);
                if (recv_len > 0)
                {
                    break;
                }
             if (sock->state ！= AT_SOCKET_CONNECT)
            {
                LOG_D("received data exit, current socket (%d) is closed by remote.", socket);
                result = 0;
                goto __exit;
            }
        }

}

之后长时间测试再没遇到收不到最后应答包的问题，不知道有没有更好的解决方案

4 个回答

Cheney_Chen 2019-01-02

这家伙很懒，什么也没写！

s2010202069 2019-01-04

这家伙很懒，什么也没写！

>楼主提出的问题已经在最新的更新中修复，解决方式类似于楼主的解决方式，详细可以查看这个 PR https://gith ...

---

看到了，不过新代码只改了第一部分，后面while（1）中还是没改也可能出现上面那种问题啊[table]
[tr][td]/* wait the receive semaphore */[/td][/tr]
[tr][td][/td][td]        if (rt_sem_take(sock->recv_notice, timeout) < 0)[/td][/tr]
[tr][td][/td][td]        {[/td][/tr]
[tr][td][/td][td]            LOG_E("AT socket (%d) receive timeout (%d)!", socket, timeout);[/td][/tr]
[tr][td][/td][td]            errno = EAGAIN;[/td][/tr]
[tr][td][/td][td]            result = -1;[/td][/tr]
[tr][td][/td][td]            goto __exit;[/td][/tr]
[tr][td][/td][td]        }[/td][/tr]
[tr][td][/td][td]        else[/td][/tr]
[tr][td][/td][td]        {[/td][/tr]
[tr][td][/td][td]            if (sock->state == AT_SOCKET_CONNECT)[/td][/tr]
[tr][td][/td][td]            {[/td][/tr]
[tr][td][/td][td]                /* get receive buffer to receiver ring buffer */[/td][/tr]
[tr][td][/td][td]                rt_mutex_take(sock->recv_lock, RT_WAITING_FOREVER);[/td][/tr]
[tr][td][/td][td]                recv_len = at_recvpkt_get(&(sock->recvpkt_list), (char *) mem, len);[/td][/tr]
[tr][td][/td][td]                rt_mutex_release(sock->recv_lock);[/td][/tr]
[tr][td][/td][td]                if (recv_len > 0)[/td][/tr]
[tr][td][/td][td]                {[/td][/tr]
[tr][td][/td][td]                    break;[/td][/tr]
[tr][td][/td][td]                }[/td][/tr]
[tr][td][/td][td]            }[/td][/tr]
[tr][td][/td][td]            else[/td][/tr]
[tr][td][/td][td]            {[/td][/tr]
[tr][td][/td][td]                LOG_D("received data exit, current socket (%d) is closed by remote.", socket);[/td][/tr]
[tr][td][/td][td]                result = 0;[/td][/tr]
[tr][td][/td][td]                goto __exit;[/td][/tr]
[tr][td][/td][td]            }[/td][/tr]
[tr][td][/td][td]        }[/td][/tr]
[/table]如果对方返回一个数据包后立刻断开TCP连接，这个线程从等待信号量返回，再去判断sock的状态也会是CLOSED，这样是不是还是可能丢数？

Cheney_Chen 2019-01-07

这家伙很懒，什么也没写！

[i=s] 本帖最后由 Cheney_Chen 于 2019-1-7 20:44 编辑 [/i]

返回一个数据包之后，AT 设备接收到数据 URC 会执行 recv 函数，之后才会接收到连接断开的 URC 再执行 closesocket 函数使得 socket 状态置为 AT_SOCKET_CLOSE，所以不管怎样，数据都会进缓冲区。再者 at_recv 函数在循环等待信号量之前，都会读一遍缓冲区中数据，所以应该可以避免这个问题。

```

/* receive packet list last transmission of remaining data */
    rt_mutex_take(sock->recv_lock, RT_WAITING_FOREVER);
    if((recv_len = at_recvpkt_get(&(sock->recvpkt_list), (char *)mem, len)) > 0)   // 先读取缓冲区的数据
    {
        rt_mutex_release(sock->recv_lock);
        goto __exit;
    }
    rt_mutex_release(sock->recv_lock);
        
    .........

while (1)
    {
        /* wait the receive semaphore */
        if (rt_sem_take(sock->recv_notice, timeout) < 0)
        {
            LOG_E("AT socket (%d) receive timeout (%d)!", socket, timeout);
            errno = EAGAIN;
            result = -1;
            goto __exit;
        }
        else
        {
            if (sock->state == AT_SOCKET_CONNECT)
            {
                /* get receive buffer to receiver ring buffer */
                rt_mutex_take(sock->recv_lock, RT_WAITING_FOREVER);
                recv_len = at_recvpkt_get(&(sock->recvpkt_list), (char *) mem, len);   //再等待信号量接收数据
                rt_mutex_release(sock->recv_lock);
                if (recv_len > 0)
                {
                    break;
                }
            }
            else
            {
                LOG_D("received data exit, current socket (%d) is closed by remote.", socket);
                result = 0;
                goto __exit;
            }
        }
}
```