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POUsing select() system call for listening on stdin and the server
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copied!<p>I want to use select system call to multiplex STDIN and SOCKFD (connected to a server) such that I must be listening to both STDIN and SOCKFD and depending upon where the data is available for read I must proceed further.</p> <p>Note: #define STDIN 0</p> <p>This is what happens when I do the following. </p> <ul> <li>I connect to the server the usual way [ socket() then connect() ] </li> <li>I add STDIN and connection socket descriptor 'SOCKFD' to the fd_set (named 'readset') meant for reading. </li> <li>Then I call select(). </li> <li>Use FD_ISSET to determine which fd is ready for read. </li> </ul> <p>The problem with this set up is that FD_ISSET is always true for both the fd. Once I get connected to the server I see FD_ISSET(sockfd, &readset) is always true and so is FD_ISSET(STDIN, &readset) whether, the server is sending data or not or if I am entering data from keyboard or not. </p> <p>What could I be doing wrong? </p> <p>/* connection successful */</p> <pre><code>FD_ZERO(&connset); while(1) { FD_SET(sockfd,&connset); /* add sockfd to connset */ FD_SET(STDIN,&connset); /* add STDIN to connset */ fdmax=sockfd; if(select(fdmax+1,&readset,NULL,NULL,NULL)<0){ fprintf(stdout, "select() error\n"); exit(0); } /* select returned * check which socket is set */ if(FD_ISSET(sockfd,&connset)) { /* * Server sends msglen * client reads msg of length msglen * client prints it to stdout * client waits for next activity of its listen sockets */ size=4; ptr=(char *)&msglen; while(1) { if((nread=recv(sockfd,ptr,size,0)),MSG_DONTWAIT) { close(sockfd); exit(0); } size-=nread; ptr+=nread; } bytesToRead = ntohl(msglen); readbuf = (char *)malloc(sizeof(char)*(bytesToRead+1)); ptr=readbuf; while(1) { nread=recv(sockfd,ptr,bytesToRead,MSG_DONTWAIT); if(nread<=0) { close(sockfd); exit(0); } bytesToRead-=nread; ptr+=nread; } /* msg read successfully */ *ptr='\0'; fprintf(stdout, "in: %s\n",readbuf); free(readbuf); } if(FD_ISSET(STDIN,&connset)) { /* data at STDIN */ fgets(buf,2,stdin); /* read the first newline char (< enter >) */ fprintf(stdout,"Enter msg: "); fgets(buf,MAXLEN,stdin); /* read the msg */ buf[strlen(buf)-1]='\0'; msglen = htonl((uint32_t)(strlen(buf)-1)); ptr = (char *)&msglen; bytesToSend = sizeof(uint32_t); cnt = bytesToSend; while(cnt>0) { if((nsent=send(sockfd,ptr,cnt,0))>0) { cnt-=nsent; ptr+=nsent; } else { fprintf(stdout,"send error\n"); exit(0); } } ptr=buf; bytesToSend=(uint32_t)(strlen(buf)-1); cnt=bytesToSend; while(cnt>0) { if((nsent=send(sockfd,ptr,cnt,0))>0) { cnt-=nsent; ptr+=nsent; } else { fprintf(stdout,"send error\n"); exit(0); } } } } return 0; </code></pre> <p>}</p>

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