如何在tty断开连接后正确关闭连接以强制客户端断开连接？

如何解决如何在tty断开连接后正确关闭连接以强制客户端断开连接？

很抱歉，但我怀疑该错误可能是在错误处理中，并且存在一些用于联网的必要样板。

我开始对单文件派生tcp服务器进行以下实现。

#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/select.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <netinet/in.h>
#include <netdb.h>
#include <string.h>
#include <arpa/inet.h>
#include <pthread.h>
#include <errno.h>
#include <pty.h>

#define PORT 9600
#define BUF_SIZE 128
#define SERVER_BACKLOG 10

void handle_conn(int conn_fd) {
  // Create a TTY / PTY pair and hook it up to the connection.
  int master_fd;
  char slave_name[100];
  pid_t pid = forkpty(&master_fd,slave_name,NULL,NULL);
  if (pid == -1) {
    fprintf(stderr,"Error on first fork: %d %s",errno,strerror(errno));
    return;
  } else if (pid == 0) { // Child process attached to slave pty
    execl("/bin/bash","bash",(char*) NULL);
  }

  // Set both fds to be non-blocking
  int flags = fcntl(master_fd,F_GETFL,0);
  fcntl(master_fd,F_SETFL,flags | O_NONBLOCK);
  flags = fcntl(conn_fd,0);
  fcntl(conn_fd,flags | O_NONBLOCK);

  // Parent continues here,shuffling data back and forth from the socket to
  // the master fd.
  int n;
  char c;
  while(1) {
    fd_set fds;
    FD_ZERO(&fds);
    FD_SET(conn_fd,&fds);
    FD_SET(master_fd,&fds);
    int numFds = select((conn_fd > master_fd ? conn_fd : master_fd) + 1,&fds,NULL);

    if (numFds == -1) {
      fprintf(stderr,"Error on select: %d %s",strerror(errno));
      return;
    }
    if (numFds == 0) {
      continue;
    }
    if (FD_ISSET(conn_fd,&fds)) {
      // Read from socket and write to tty.
      while ((n = read(conn_fd,&c,1)) > 0) {
        write(master_fd,1);
      }

      if (n == 0) {
        // Reached EOF
        break;
      }
      // Presumed n is -1
      if (errno != EAGAIN || errno != EWOULDBLOCK) {
        fprintf(stderr,"Error reading socket %d %s\n",strerror(errno));
        break;
      }
    }

    if (FD_ISSET(master_fd,&fds)) {
      // Read from tty and write to socket as long as things are still
      // readable.
      while ((n = read(master_fd,1)) > 0) {
        write(conn_fd,1);
      }

      if (n == 0) {
        // Reached EOF
        break;
      }

      // Presumed n is -1
      if (errno != EAGAIN && errno != EWOULDBLOCK) {
        fprintf(stderr,"Error reading master FD %d %s\n",strerror(errno));
        break;
      }
    }
  }
  printf("Closing connection [%d]\n",conn_fd);
  int err = close(conn_fd);
  if (err != 0) {
    fprintf(stderr,"Error while closing connection [%d]\n",conn_fd);
  }

  err = close(master_fd);
  if (err != 0) {
    fprintf(stderr,"Error while closing master fd [%d]\n",conn_fd);
  }
}

int main(int argc,char *argv[]) {
  int server_fd = socket(PF_INET,SOCK_STREAM,0);
  if (server_fd < 0) {
    fprintf(stderr,"Cannot create socket\n");
    return 1;
  }

  struct sockaddr_in server_addr;
  server_addr.sin_family = AF_INET;
  server_addr.sin_port = htons(PORT);
  int ok = inet_pton(AF_INET,"127.0.0.1",&server_addr.sin_addr);
  if (!ok) {
    fprintf(stderr,"Cannot parse IP address\n");
    return 1;
  }

  // Allow reuse of port.
  int optval = 1;
  setsockopt(server_fd,SOL_SOCKET,SO_REUSEPORT,&optval,sizeof(optval));

  int err = bind(server_fd,(struct sockaddr *) &server_addr,sizeof(server_addr));
  if (err != 0) {
    fprintf(stderr,"Cannot bind server: Error %d %s\n",strerror(errno));
    return 1;
  }

  err = listen(server_fd,SERVER_BACKLOG);
  if (err != 0) {
    fprintf(stderr,"Cannot listen\n");
    return 1;
  }

  printf("Server listening on port %d\n",PORT);

  int client_fd;
  struct sockaddr_in client_addr;
  socklen_t client_addr_len;
  while (1) {
    client_fd = accept(server_fd,(struct sockaddr *) &client_addr,&client_addr_len);
    if (client_fd < 0) {
      fprintf(stderr,"Cannot accept: Error %d %s\n",strerror(errno));
      return 1;
    }

    printf("New client [%d]\n",client_fd);

    // Using fork instead of threads here to avoid pitfalls involved with
    // mixing forking and threads,since this use case case of a tty host is
    // not expected to involve a great many requests.
    int pid = fork();
    if (pid == -1) {
      fprintf(stderr,"Error on forking to handle new connection: %d %s",strerror(errno));
      // Server does not need to die here.
      continue;
    } else if (pid == 0) { // Child will handle the connection and then return.
      handle_conn(client_fd);
      return 0;
    }
    // Parent continues to accept
  }
}

然后在另一个终端上，运行以下 netcat 客户端。

stty -icanon -echo; nc localhost 9600

现在，我可以在终端上使用ls键入cat或nc之类的命令。

但是，当我键入exit时，服务器将打印Error reading master FD 5 Input/output error\nClosing connection [4]，并且没有其他错误，因此我假定服务器已成功关闭连接，但是客户端继续挂起，直到我在客户端上按Control-C。

如何修改服务器代码以强制客户端断开连接？

解决方法

我发现了错误！原来，我忘记了在父进程中关闭套接字。一旦这样做，close（）就会在孩子中按预期工作。

对上述代码进行简单的修改如下，即可解决问题。

    ...
    // Parent continues to accept
    close(client_fd);