Path: utzoo!attcan!utgpu!news-server.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!aplcen!haven!umbc3!umbc5.umbc.edu!petey
From: petey@umbc5.umbc.ed
Newsgroups: comp.unix.questions
Subject: Sockets and buffering
Message-ID: <3791@umbc3.UMBC.EDU>
Date: 19 Aug 90 17:00:18 GMT
Sender: newspost@umbc3.UMBC.EDU
Reply-To: petey@umbc5.umbc.edu
Distribution: usa
Organization: University of Maryland, Baltimore County
Lines: 113


Hello everyone.  I have a problem and have included some code with
questions in it.  Our system is running Ultrix on a Decstation 5400.

What im trying to do is set up a small server that allows multiple
users to telnet into and echo back to them anything they type.

Only problem is, when I do reads and writes, there are extremely bad
delays on the echo.  Ive been attempting to use FD_SET, FD_ISSET
to determine if a socket is ready to be read from or written to.
I dont know if im on the right track.  Basically my problem is
I dont have the documentation explaining how to use
select, FD_ISSET, FD_SET together to accomplish this.

Also, when you set up a socket, everytime you wish to check for new
connections, it seems you have to select on the first available
unused file descriptor.  ex: select(sock+1, etc etc )
When you set up a port number, and someone attempts to connect,
does unix automatically route them to the next available file descriptor?

What if you have 10 fd's used in a row and #5 disconnects,
will unix route the next call to #5, or to #11???

Thanx in advance for the help!!!
Send email to me please...

						Petey

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#include <fcntl.h>
#include <signal.h>

#define TRUE 1
#define FALSE 0
#define MAXHOSTNAME 50
#define BUFSIZE 128

main(argc,argv)  /* argv[1] = port number */
char *argv[];
int argc;
{
        int lastsock; /* accept connect with lastsock */
        int x,y;      /* all purpose counter */
	int sock, length;
	struct sockaddr_in server;
	char buf[BUFSIZE];
	int rval;             /* read return values */
	/****************************************************/
	fd_set in, out;    /* fuzzy on how to CORRECTLY use */
	/****************************************************/
	struct timeval to;
	char myhostname[MAXHOSTNAME+1];
        int temp;

	for(x=0;x<64;x++) close(x);        /* close everything */
	signal(SIGPIPE, SIG_IGN); 
	sock = socket(AF_INET, SOCK_STREAM, 0); /* Create socket */
	if (sock < 0) {
		printf("opening stream socket\n");
		exit(1);
	}
        setsockopt(sock,SOL_SOCKET,SO_REUSEADDR, (char *)&temp,sizeof(temp));
	server.sin_family = AF_INET;
	server.sin_addr.s_addr = INADDR_ANY; 
	server.sin_port = htons(atoi(argv[1]));
        fcntl(sock,F_SETFL, FNDELAY) == -1;
	if (bind(sock, &server, sizeof(server))) {
		perror("binding stream socket");
		exit(1);
	}
	printf("Socket has port #%d\n", ntohs(server.sin_port));
/*********************** Socket Intialization compelete *******************/
	listen(sock, 5);

	do {    /* main DO loop */
	/*** so when do i use this FD stuff??? */
		FD_ZERO(&in);
		FD_ZERO(&out);
		FD_SET(sock, &in);
		to.tv_sec = 0;
                to.tv_usec =1;
		if (select(sock + 1 , &in, &out,0, &to) < 0) {
			perror("select");
			continue;
		}
		if (FD_ISSET(sock, &in)) {  /* if phone ringing */
                   lastsock = accept(sock, (struct sockaddr *)0, (int *)0);
			if (lastsock == -1)
			     printf("error on accept\n");
                        else {
			     /* non=blocking i/o */
			     fcntl(lastsock,F_SETFL, FNDELAY);
			     fcntl(lastsock,F_SETFD,1);
			     }
		} 
/******************* READ Data from the sockets *****************************/

/**** THE BIG QUESTION !!!! */
     bzero(buf, sizeof(buf));
/* How do I tell when the socket is ready for reading? */
     rval = read(lastsock,buf,sizeof(buf)); 
     if (rval == 0 )   /* If 0, SHUTDOWN THE SOCKET! */ 
       close(lastsock);   /* error reading, close the socket */  
     else 
/* How do i tell when it ready for writing?!!!! */
       rval =  write(lastsock, buf, sizeof(buf));
} while (TRUE);  /* end do loop */
} /* end main */