C - 使用 select() 创建 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"[客户端]从朋友那里收到："当我 CTRL+C 服务器时，

或

如何阻止服务器无限打印"[服务器]收到消息..."当我 CTRL+C 任何连接的客户端时。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(逐步)发生了什么。它是否通过所有FD，每个FD1秒然后重复？我有点明白了，但不完全明白。 无论哪种方式都谢谢你

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...%sn", 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: %sn", reply);
}
}
close (ClientSocketFD);
}

Answer 1

我不知道

如何阻止客户端无限打印"[客户端]从朋友那里收到："当我 CTRL+C 服务器时

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: %.100sn", reply);
kill(pid, SIGTERM); // terminate also the child

(和#include <signal.h>)。

如何阻止服务器无限打印"[服务器]收到消息..."当我按 Ctrl+C 任何连接的客户端时

如果客户端终止，read()返回 0，因此调用

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

将Msgs()类型更改为

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

并在bytes = read (fd, msg, sizeof (buffer));添加后的Msgs()

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

有人可以向我解释一下选择(..)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(逐步)发生了什么。它是否通过所有FD，每个FD1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剩余时间，因此在没有FD活动的1秒之后，我们很可能最终得到零超时和无用的繁忙循环。只有当我们想在一定时间内没有被监控的 FD 准备就绪时执行某些操作时，我们才需要select()超时，因此在您的情况下，最好指定根本不超时：

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