Thread: [Help] Best way of using sockets

I need a little bit of help undestanding this part of the code.. from the page.. http://www.tenouk.com/Module41.html, i know it's commented but i need an easier explanation about the for loop, how does it really works and about the sets for the select. Also how does it recognise if it is a new connection?
Thanks

Code:

/* add the listener to the master set */
FD_SET(listener, &master);
/* keep track of the biggest file descriptor */
fdmax = listener; /* so far, it's this one*/
/* loop */
for(;;)
{
/* copy it */
read_fds = master;
if(select(fdmax+1, &read_fds, NULL, NULL, NULL) == -1)
{
    perror("Server-select() error lol!");
    exit(1);
}
printf("Server-select() is OK...\n");
/*run through the existing connections looking for data to be read*/
for(i = 0; i <= fdmax; i++)
{
    if(FD_ISSET(i, &read_fds))
    { /* we got one... */
    if(i == listener)
     {
         /* handle new connections */
        addrlen = sizeof(clientaddr);
if((newfd = accept(listener, (struct sockaddr *)&clientaddr, &addrlen)) == -1)
{
    perror("Server-accept() error lol!");
}
else
{
    printf("Server-accept() is OK...\n");
FD_SET(newfd, &master); /* add to master set */
if(newfd > fdmax)
{ /* keep track of the maximum */
    fdmax = newfd;
}
printf("&#37;s: New connection from %s on socket %d\n", argv[0], inet_ntoa(clientaddr.sin_addr), newfd);
}
}
else
{
/* handle data from a client */
if((nbytes = recv(i, buf, sizeof(buf), 0)) <= 0)
{
/* got error or connection closed by client */
if(nbytes == 0)
 /* connection closed */
 printf("%s: socket %d hung up\n", argv[0], i);
else
perror("recv() error lol!");
/* close it... */
close(i);
/* remove from master set */
FD_CLR(i, &master);
}
else
{
/* we got some data from a client*/
for(j = 0; j <= fdmax; j++)
{
/* send to everyone! */
if(FD_ISSET(j, &master))
{
       /* except the listener and ourselves */
       if(j != listener && j != i)
       {
              if(send(j, buf, nbytes, 0) == -1)
                     perror("send() error lol!");
       }
}

Urf. I hate reading code that isn't indented, especially when I don't know what it does.

Code:

/* add the listener to the master set */
FD_SET (listener, &master);
/* keep track of the biggest file descriptor */
fdmax = listener;                /* so far, it's this one */
/* loop */
for (;;)
{
    /* copy it */
    read_fds = master;
    if (select (fdmax + 1, &read_fds, NULL, NULL, NULL) == -1)
    {
        perror ("Server-select() error lol!");
        exit (1);
    }
    printf ("Server-select() is OK...\n");
    /*run through the existing connections looking for data to be read*/
    for (i = 0; i <= fdmax; i++)
    {
        if (FD_ISSET (i, &read_fds))
        {                        /* we got one... */
            if (i == listener)
            {
                /* handle new connections */
                addrlen = sizeof (clientaddr);
                if ((newfd =
                    accept (listener, (struct sockaddr *) &clientaddr,
                    &addrlen)) == -1)
                {
                    perror ("Server-accept() error lol!");
                }
                else
                {
                    printf ("Server-accept() is OK...\n");
                                 /* add to master set */
                    FD_SET (newfd, &master);
                    if (newfd > fdmax)
                    {            /* keep track of the maximum */
                        fdmax = newfd;
                    }
                    printf ("&#37;s: New connection from %s on socket %d\n",
                        argv[0], inet_ntoa (clientaddr.sin_addr), newfd);
                }
            }
            else
            {
                /* handle data from a client */
                if ((nbytes = recv (i, buf, sizeof (buf), 0)) <= 0)
                {
                    /* got error or connection closed by client */
                    if (nbytes == 0)
                        /* connection closed */
                        printf ("%s: socket %d hung up\n", argv[0], i);
                    else
                        perror ("recv() error lol!");
                    /* close it... */
                    close (i);
                    /* remove from master set */
                    FD_CLR (i, &master);
                }
                else
                {
                    /* we got some data from a client*/
                    for (j = 0; j <= fdmax; j++)
                    {
                        /* send to everyone! */
                        if (FD_ISSET (j, &master))
                        {
                            /* except the listener and ourselves */
                            if (j != listener && j != i)
                            {
                                if (send (j, buf, nbytes, 0) == -1)
                                    perror ("send() error lol!");
                            }
                        }

Much better . . .

I don't know much about socket programming, but I think a set of sockets is like an array of them. Just thought I'd clear that up at the beginning.

How does it handle new connections? Well . . .

Code:

            if (i == listener)
            {
                /* handle new connections */
                addrlen = sizeof (clientaddr);
                if ((newfd =
                    accept (listener, (struct sockaddr *) &clientaddr,
                    &addrlen)) == -1)
                {
                    perror ("Server-accept() error lol!");
                }
                else
                {
                    printf ("Server-accept() is OK...\n");
                                 /* add to master set */
                    FD_SET (newfd, &master);
                    if (newfd > fdmax)
                    {            /* keep track of the maximum */
                        fdmax = newfd;
                    }
                    printf ("%s: New connection from %s on socket %d\n",
                        argv[0], inet_ntoa (clientaddr.sin_addr), newfd);
                }
            }

The program has opened a listener socket, and when it receives a connection on that one, it must be a new one. It adds it to the list, and there you go.

I make it sound so simple.

[edit] I much prefer this tutorial: http://beej.us/guide/bgnet/output/ht...et.html#listen [/edit]