How to implement select asynchronous communication under Linux

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1. Server

/*select_server.c 2011.9.2 by yyg*/ #include #include #include #include #include #include #include #include #include #include #include #include #include #define MAXBUF 1024 int main(int argc, char **argv){ int sockfd,new_fd; socklen_t len; struct sockaddr_in my_addr, their_addr; unsigned int myport,lisnum; char buf[MAXBUF+1]; fd_set rfds; struct timeval(argv[1]){ myport = atoi(argv[1]); } else myport = 7838; if(argv[2]){ lisnum = atoi(argv[2]); } else lisnum =2; if((sockfd = socket(PF_INET,SOCK_STREAM,0))== -1){ perror("socket"); exit(1); } bzero(&my_addr,sizeof(my_addr)); my_addr.sin_family = PF_INET; my_addr.sin_port = htons(myport); if(argv[3]) my_addr.sin_addr.s_addr = INADDR_ANY; the if(bind(sockfd,(struct sockaddr *)&my_addr,sizeof(struct sockaddr)) == -1){ perror("bind"); exit(1); } the if(listen(sockfd, lisnum) == -1){ perror("listen"); exit(1); } the while(1){ printf("\n----waiting for new connecting to start new char----\n"); len = sizeof(struct sockaddr); if((new_fd = accept(sockfd,(struct sockaddr *)&their_addr,&len)) == -1){ perror("accept"); exit(errno); } else printf("server: got connection from %s,port %d,socked %d\n",\   inet_ntoa(their_addr.sin_addr),\ ntohs(their_addr. sin_port), new_fd);   /*Start processing data sending and receiving on each new connection*/ //printf("\n---ready to go.now you can chatting...input enter,then you can chat---\n"); while(1){ /*Empty the collection*/ FD_ZERO(&rfds); /*Add standard input handle 0 to the collection*/ FD_SET(0,&rfds); maxfd = 0; /*Add the current connection handle new_fd to the collection*/ FD_SET(new_fd,&rfds); if(new_fd > maxfd) maxfd = new_fd; /*Set the maximum waiting time*/ tv.tv_sec = 1; tv.tv_usec = 0; retval = select(maxfd+1,&rfds,NULL,NULL,&tv); if(retval == -1){ printf("select error!%s\n", strerror(errno)); break; } `` else if(retval == 0){ //printf("no message come, user no press the button, please wait...\n"); continue; } else{ If(FD_ISSET(new_fd,&rfds)){ /* If there is a message on the connected socket, it will be received and displayed */       bzero(buf,MAXBUF+1); /*Receive the message sent by the other party, up to MAXBUF bytes*/ len = recv(new_fd, buf, MAXBUF, 0); if(len > 0)       printf("recv msg success:%s! %d bytes rcv.\n ",buf,len); else{         if(len < 0){       printf("recv msg fail.the errno is:%d,error info is %s.\n",errno,strerror(errno)); } else printf("quit.\n"); break; } }// FD_ISSET = sockfd case If(FD_ISSET(0,&rfds)){/*If the user has input, then read the content and send it*/ bzero(buf, MAXBUF+1); fgets(buf, MAXBUF, stdin); If(!strncasecmp(buf, "quit", 4)){ printf("self request to quit the chating\n"); break; } /*Send a message to the server*/ len = send(new_fd, buf, strlen(buf)-1 , 0); `` if(len < 0){ printf("mgs:%s send fail!errno is:%d,error info is:%s\n", buf, errno, strerror(errno)); break; }else{      printf("msg: %s\t send success, send %d bytes!\n", buf, len); } }//FD_ISSET = 0 `` }//select processing ends `` }/*inside while*/ close(new_fd); /* Handle the end of data sending and receiving on each new connection */ printf("would you want to chatting with another one?(no->quit)"); fflush(stdout); bzero(buf,MAXBUF+1); fgets(buf,MAXBUF,stdin); if(!strncasecmp(buf,"no",2)){ printf("quit the chatting!\n"); break; } the }/*outer while*/ close(sockfd); return 0; }

2. Client

/*select_client.c 2011.9.2 by yyg*/ #include #include #include #include #include #include #include #include #include #include #include #include #include #define MAXBUF 1024 int main(int argc, char **argv){ int sockfd,len; struct sockaddr_in dest; char buffer[MAXBUF+1]; fd_set rfds; struct timeval(argc != 3){ printf("the param style wrong!\n"); exit(0); } /*Create a socket for tcp communication*/ if((sockfd = socket(AF_INET,SOCK_STREAM,0)) < 0){ perror("socket"); exit(errno); } /*Initialize the address and port information of the server (the other side)*/ bzero(&dest,sizeof(dest)); dest.sin_family = AF_INET; dest.sin_port = htons(atoi(argv[2])); if(inet_aton(argv[1],(struct in_addr *)&dest.sin_addr.s_addr) == 0){ perror(argv[1]); exit(errno); } /*connect to the server*/ if(connect(sockfd,(struct sockaddr*)&dest,sizeof(dest)) !=0){ perror("connect"); exit(errno); } printf("\n---ready to chatting...---\n"); while(1){ /* Clear the collection */ FD_ZERO(&rfds); /*Add standard input handle 0 to the collection*/ FD_SET(0,&rfds); maxfd = 0; /*Add the current connection handle socket to the collection*/ FD_SET(sockfd,&rfds); if(sockfd > maxfd) maxfd = sockfd; /*Set the maximum waiting time*/ tv.tv_sec = 1; tv.tv_usec = 0; /*Start waiting*/ retval = select(maxfd+1,&rfds,NULL,NULL,&tv); if(retval == -1){ printf("select error,quit!\n"); break; }else if(retval == 0){ continue; }else{ If(FD_ISSET(sockfd,&rfds)){ /* If there is a message on the connected socket, it will be received and displayed */      bzero(buffer,MAXBUF+1); /*Receive the message sent by the other party, up to MAXBUF bytes*/ len = recv(sockfd, buffer, MAXBUF, 0); if(len > 0)     printf("recv msg success:%s! %d bytes rcv.\n ", buffer, len); else { `` if(len < 0){ printf("recv msg fail.the errno is:%d,error info is %s.\n",errno,strerror(errno)); } else   printf("quit.\n"); break; } }// FD_ISSET = sockfd case   if(FD_ISSET(0,&rfds)){ /* If the user has input, read the content and send it*/ bzero(buffer, MAXBUF+1); fgets(buffer, MAXBUF, stdin); If(!strncasecmp(buffer, "quit", 4)){ printf("self request to quit the chating\n"); break; } /*Send a message to the server*/ len = send(sockfd, buffer, strlen(buffer)-1 , 0); `` if(len < 0){ printf("mgs:%s send fail!errno is:%d,error info is:%s\n", buffer, errno, strerror(errno)); break; }else{     printf("msg: %s\t send success, send %d bytes!\n", buffer, len); } }//FD_ISSET = 0 `` }//select processing ends }//Process chat while loop /* close the connection */ close(sockfd); return 0; }

Operation result:

Terminal 1: Server

[root@localhost net]# ./select_server 7838 ----waiting for new connecting to start new char---- server: got connection from 172.31.100.236,port 59462,socked 4 recv msg success:kfldsjfk! 8 bytes rcv. 456354 msg: 456354 send success, send 6 bytes! recv msg success:453455! 6 bytes rcv.

Terminal 2: Client

[root@localhost net]# ./select_client 172.31.100.236 7838 ---ready to chatting...--- kfldsjfk msg: kfldsjfk send success, send 8 bytes! recv msg success:456354! 6 bytes rcv. 453455 msg: 453455 send success, send 6 bytes!

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