c - 为 socket recv TCP 设置超时

Question

我找到了一些关于如何操作的提示，但我不明白如何使用 setsockopt。我有一个无限循环调用 recv，如果客户端在 5 秒内没有发送任何内容，我想超时并 close(cli_socket)。

如果客户端只发送整个预期消息的一部分，我想重置计时器并再给他 5 秒。

目前我有这个:

while((cut = buffer.find("\r\n")) == -1)
        {
            struct timeval tv;
            tv.tv_sec = 5;
            setsockopt(cli_socket, SOL_SOCKET, SO_RCVTIMEO,(struct timeval *)&tv,sizeof(struct timeval));
            recv(cli_socket, tmpBuffer, 100, 0);
            buffer += tmpBuffer;
            memset(tmpBuffer, 0, 100);
        }

Answer 1

如果循环是EAGAIN 或EWOULDBLOCK，您应该测试recv 和break 的返回:

EAGAIN or EWOULDBLOCK
The socket is marked nonblocking and the receive operation would block, or a receive timeout had been set and the timeout expired before data was received

struct timeval tv = {5, 0};
setsockopt(cli_socket, SOL_SOCKET, SO_RCVTIMEO, (struct timeval *)&tv, sizeof(struct timeval));

while((cut = buffer.find("\r\n")) == -1)
{
    int numBytes = recv(cli_socket, tmpBuffer, 100, 0));

    /// Edit: recv does not return EAGAIN else, it return -1 on error.
    /// and in case of timeout, errno is set to EAGAIN or EWOULDBLOCK

    if (numBytes <= 0)
    {
        // nothing received from client in last 5 seconds
        break;
    }

    buffer.append(tmpBuffer, numBytes);
}

您还可以使用select 函数，使用起来并不复杂:

while((cut = buffer.find("\r\n")) == -1)
{
    timeval timeout = { 5, 0 };
    fd_set in_set;

    FD_ZERO(&in_set);
    FD_SET(cli_socket, &in_set);

    // select the set
    int cnt = select(cli_socket + 1, &in_set, NULL, NULL, &timeout);

    if (FD_ISSET(cli_socket, &in_set))
    {
        int numBytes = recv(cli_socket, tmpBuffer, 100, 0));
        if (numBytes <= 0)
        {
            // nothing received from client
            break;
        }

        buffer.append(tmpBuffer, numBytes);
    }
    else
    {
        // nothing received from client in last 5 seconds
        break;       
    }
}