Read from telnet socket in C

Question

I would like to retrieve modem list from the CMTS, and I wrote a telnet client in C, that is executing this. The problem is that sometimes I do not get all the data from the CMTS. (If I reduce the 'delay' waiting time, the more I do not get all the data.)

char buf[50000];
int nbytes, sock;
struct sockaddr_in cmts;

cmts.sin_family      = AF_INET;
cmts.sin_port        = htons( 23 );
cmts.sin_addr.s_addr = inet_addr("192.168.1.1");

sock = socket( PF_INET, SOCK_STREAM, 0 );

if ( sock < 0 ) {
    perror("Socket creation error!");
    exit (EXIT_FAILURE);
}

if ( connect( sock, (struct sockaddr *) &cmts, sizeof( cmts ) ) < 0 ) {
    perror("Connect process error!");
    exit (EXIT_FAILURE);
}

write( sock, "testuser\n", 9 );
write( sock, "testenapwd\n", 11 );
write( sock, "terminal length 0\n", 18 );
usleep( 100000 );
read( sock, buf, sizeof( buf ) );
usleep( 100000 );
write( sock, "show cable modem\n", 17 );
usleep( 100000 );

while ( 1 ) {
    nbytes = 0;
    ioctl( sock, FIONREAD, &nbytes );

    if ( !nbytes ) { break; }
    else {
        memset( buf, 0, sizeof( buf ) );
        nbytes = read( sock, buf, sizeof( buf ) -1 );
        printf("%s", buf);
        printf(">>>%d<<<\n", nbytes);  // for debug
    }

    usleep( 300000 );   // delay
}

close( sock );
exit (EXIT_SUCCESS);

Answer 1

Take a look at this Beej's Guide to Network Programming

It's recommended to use the recv and send functions when it comes to networking.

recv returns the number of bytes received, or -1 if an error occurred. The return value will be 0 when the peer has performed an orderly shutdown.