C - 使用 select() 制作 UTP 服务器/客户端聊天室

Question

我应该让服务器将它从客户端获得的消息广播到所有其他连接的客户端。

实际广播有效，但我不知道如何阻止客户端无限打印“[client]Received from friends:”当我 CTRL+C 服务器时，

或

当我 CTRL+C 任何连接的客户端时，如何阻止服务器无限打印“[server]Message received...”。或者如何在某处添加验证，以便客户端在尝试发送字符串“quit”时断开连接

也许我要求的太多了，但有人可以向我解释一下 select(..) 到底是做什么的吗？我知道它正在监视 FD，但我无法完全理解 1 秒后发生的事情（逐步）。它是否经过所有 FD，每个 1 秒然后重复？我有点明白这个想法，但不完全明白。 不管怎样都谢谢你

服务器

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <netinet/in.h>
#include <unistd.h>
#include <errno.h>
#include <stdio.h>
#include <arpa/inet.h>
#include <string.h>
#include <stdlib.h>


#define PORT 3050     //The port used by Clients

extern int errno;

char * conv_addr (struct sockaddr_in address)
{
  static char str[25];
  char port[7];


  strcpy (str, inet_ntoa (address.sin_addr));   /* client IP */

  bzero (port, 7);   /* PORT */
  sprintf (port, ":%d", ntohs (address.sin_port));
  strcat (str, port);
  return (str);
}

void Msgs(int fd,int sd,fd_set fds,int nr);

int main ()
{
  struct sockaddr_in server_addr;        /* struct for Server */
  struct sockaddr_in client_addr;        /* struct for Clients */
  fd_set readfds;                        /* ready-to-read File Descriptors */
  fd_set actfds;                         /* active/existant File Descriptors */
  struct timeval tv;                     /* time thing, for select() */
  int ServerSocketFD, ClientSocketFD;       /* Socket descriptors */
  int optval=1;             /* ????*/
  int fd;           /* FD used to pass through all FDs */
  int nfds;         /* max number of FDs */


  (ServerSocketFD = socket (AF_INET, SOCK_STREAM, 0));


  setsockopt(ServerSocketFD, SOL_SOCKET, SO_REUSEADDR, &optval, sizeof(optval) );


  bzero (&server_addr, sizeof (server_addr));

  server_addr.sin_family = AF_INET;
  server_addr.sin_addr.s_addr = htonl (INADDR_ANY);
  server_addr.sin_port = htons (PORT);


  bind (ServerSocketFD, (struct sockaddr *) &server_addr, sizeof(struct sockaddr) );


  listen (ServerSocketFD, 5);     //listen to maximum 5 clients,no more

  FD_ZERO (&actfds);                    
  FD_SET (ServerSocketFD, &actfds);     /* Add the only existant one for now */

  tv.tv_sec = 1;        /* wait 1s */
  tv.tv_usec = 0;

  nfds = ServerSocketFD;    /* max value of currently used FDs */

  printf ("[server] Waiting at port :%d...\n", PORT);
  fflush (stdout);


  while (1)      /* serve clients CONCURRENTLY */
    {
        bcopy ((char *) &actfds, (char *) &readfds, sizeof (readfds));          /* copy all existing FDs in actfds vector to the read-to-read-FDs vector */

        select(nfds+1, &readfds, NULL, NULL, &tv);

        if (FD_ISSET (ServerSocketFD, &readfds))     /* if ServerSocket is ready to read stuff */
        {
            bzero (&client_addr, sizeof (client_addr));

            int len = sizeof (client_addr);
            ClientSocketFD = accept (ServerSocketFD, (struct sockaddr *) &client_addr, &len);

            if (nfds < ClientSocketFD) /* adjust max FD, for select */
                nfds = ClientSocketFD;

            /* Add this accepted sockets' FD to the existing FDs */
            FD_SET (ClientSocketFD, &actfds);

            printf("[server] Client connected, with FD %d, from this address %s.\n",ClientSocketFD, conv_addr (client_addr));
            fflush (stdout);
        }

        for (fd = 0; fd <= nfds; fd++)  /* all FDs*/
        {
            if (fd != ServerSocketFD && FD_ISSET (fd, &readfds))        /* is a client ready to send/get messages? */
            {
                Msgs(fd,ServerSocketFD,actfds,nfds);
            }
        }
    }
}

void Msgs(int fd,int ServerSocketFD,fd_set fds,int nrFD)
{
  char buffer[100];     
  int bytes;        
  char msg[100];        

  bytes = read (fd, msg, sizeof (buffer));

  /*
  if(strstr(msg,"quit")!=0)
  {
    FD_CLR(fd, &fds);
    close(fd);
    exit(1);
  }
  */
  printf ("[server]Message received...%s\n", msg);

  for(int i=0;i<=nrFD;i++)
  {
    if(i!=fd && i!=ServerSocketFD)
    {
        write (i, msg, bytes);
    }
  }

}

客户

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <errno.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <netdb.h>
#include <string.h>
#include <arpa/inet.h>


extern int errno;

int port;

int main (int argc, char *argv[])
{

    int ClientSocketFD;         
    struct sockaddr_in server_addr; 
    char msg[100];      
    char reply[100];


    if (argc != 3)
    {
        printf ("[client] Sintax: %s <server_address> <port>\n", argv[0]);
        return -1;
    }


    port = atoi (argv[2]);
    ClientSocketFD = socket (AF_INET, SOCK_STREAM, 0);


    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = inet_addr(argv[1]);
    server_addr.sin_port = htons (port);


    connect(ClientSocketFD, (struct sockaddr *) &server_addr,sizeof (struct sockaddr));



    int pid;
    if((pid=fork())==-1)
    {
        perror("Error fork()");
        exit(10);
    }
    if(pid==0)  //CHILD
    {
        while(1)
        {
            bzero(msg,100);
            printf ("[client]Send something to other clients: ");
            fflush (stdout);

            read (0, msg, 100);     
            if(strstr(msg,"quit")!=0)
            {
                break;
            }

            write (ClientSocketFD, msg, 100);
        }

        exit(7);
    }
    else if(pid > 0) //PARENT
    {
        while(1)
        {
            bzero(reply,100);
            read (ClientSocketFD, reply, 100);

            printf ("[client]Received from friends: %s\n", reply);
        }
    }

    close (ClientSocketFD);

}

Answer 1

当我 CTRL+C 服务器时，我不知道如何阻止客户端无限打印“[client]Received from friends:”

如果服务器终止，read() 返回 0，因此将客户端 PARENT 中的 while(1) 循环替换为

        while (bzero(reply, 100), read(ClientSocketFD, reply, 100) > 0)
            printf("[client]Received from friends: %.100s\n", reply);
        kill(pid, SIGTERM); // terminate also the child

（和#include <signal.h>）。

当我 CTRL+C 任何连接的客户端时，如何阻止服务器无限打印“[server]Message received...”

read()如果客户端终止则返回0，所以调用

                Msgs(fd, ServerSocketFD, &actfds, nfds);

将Msgs() 类型更改为

void Msgs(int fd, int ServerSocketFD, fd_set *fds, int nrFD)

在Msgs()bytes = read (fd, msg, sizeof (buffer));之后添加

  if (bytes <= 0) { FD_CLR(fd, fds); close(fd); return; }

有人可以向我解释一下 select(..) 到底是做什么的吗？我知道它正在监视 FD，但我无法完全理解 1 秒后发生的事情（逐步）。它是否会遍历所有 FD，每个 1 秒然后重复？

正如 wildplasser 在他的评论中指出的那样，select() 可能会更改超时参数以指示还剩多少时间，因此在没有 FD 活动的 1 秒后，我们很可能会以零超时和无用的繁忙循环结束。我们需要select() 超时仅当我们想要在特定时间内没有任何受监控的FD准备好时做某事，所以在你的情况下最好完全不指定超时：

        select(nfds+1, &readfds, NULL, NULL, NULL);