C套接字关闭检测

Question

我正在阅读这篇关于 How to detect when the client closes the connection 的文章

但是当我运行这篇文章中的代码时(将其粘贴在下面):

fd = accept(listenSocket);
pid_t childProcess = fork();
if (childProcess == (pid_t)-1) {
    perror("Unable to create new process for client connection");
    exit(1);
}
else if (childProcess == 0) {
    // read from socket, process queries, etc.
}
else {
    // use the poll system call to be notified about socket status changes
    struct pollfd pfd;
    pfd.fd = fd;
    pfd.events = POLLIN | POLLHUP | POLLRDNORM;
    pfd.revents = 0;
    while (pfd.revents == 0) {
        // call poll with a timeout of 100 ms
        if (poll(&pfd, 1, 100) > 0) {
            // if result > 0, this means that there is either data available on the
            // socket, or the socket has been closed
            char buffer[32];
            if (recv(fd, buffer, sizeof(buffer), MSG_PEEK | MSG_DONTWAIT) == 0) {
                // if recv returns zero, that means the connection has been closed:
                // kill the child process
                kill(childProcess, SIGKILL);
                waitpid(childProcess, &status, WNOHANG);
                close(fd);
                // do something else, e.g. go on vacation
            }
        }
    }
}

当客户端断开连接时，上述逻辑(在服务器端)根本不会遇到最后一个 else 语句。因此逻辑实际上不可能检测到断开连接。

现在这个帖子对于套接字断开连接检测来说正确吗？

Answer 1

我在linux下使用

#include <sys/socket.h>

我的检测已经工作了很多年。套接字是一个服务器。通过recv的返回码进行检测。

...
cl = accept (sock, (struct sockaddr *) &sock_clnt, (socklen_t *) &len);
unsigned char c;
for (;;)
{
    int ret = recv (cl, &c, 1, MSG_DONTWAIT);

    if (ret == 1)
    {
        // 1 byte received
        ..
    }
    else if (ret == -1) // socket open but no data
    {
        // socket open but no data
        ...
    }
    else 
    {
        // ret = 0, socket opened but now client left
        ...
    }
    // sleep
    ...
}
...