selectserver.cpp

/*
 ** selectserver.c -- a cheezy multiperson chat server
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>

#define PORT "9034"   // port we're listening on

// get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa)
{
   if (sa->sa_family == AF_INET) {
      return &(((struct sockaddr_in*)sa)->sin_addr);
   }

   return &(((struct sockaddr_in6*)sa)->sin6_addr);
}

int main(void)
{
   fd_set master;    // master file descriptor list
   fd_set read_fds;  // temp file descriptor list for select()
   int fdmax;        // maximum file descriptor number

   int listener;     // listening socket descriptor
   int newfd;        // newly accept()ed socket descriptor
   struct sockaddr_storage remoteaddr; // client address
   socklen_t addrlen;

   char buf[256];    // buffer for client data
   int nbytes;

   char remoteIP[INET6_ADDRSTRLEN];

   int yes=1;        // for setsockopt() SO_REUSEADDR, below
   int i, j, rv;

   struct addrinfo hints, *ai, *p;

   FD_ZERO(&master);    // clear the master and temp sets
   FD_ZERO(&read_fds);

   // get us a socket and bind it
   memset(&hints, 0, sizeof hints);
   hints.ai_family = AF_UNSPEC;
   hints.ai_socktype = SOCK_STREAM;
   hints.ai_flags = AI_PASSIVE;
   if ((rv = getaddrinfo(NULL, PORT, &hints, &ai)) != 0)
   {
      fprintf(stderr, "selectserver: %s\n", gai_strerror(rv));
      exit(1);
   }

   for(p = ai; p != NULL; p = p->ai_next)
   {
      listener = socket(p->ai_family, p->ai_socktype, p->ai_protocol);
      if (listener < 0)
      {
         continue;
      }

      // lose the pesky "address already in use" error message
      setsockopt(listener, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int));

      if (bind(listener, p->ai_addr, p->ai_addrlen) < 0)
      {
         close(listener);
         continue;
      }

      break;
   }

   // if we got here, it means we didn't get bound
   if (p == NULL)
   {
      fprintf(stderr, "selectserver: failed to bind\n");
      exit(2);
   }

   freeaddrinfo(ai); // all done with this

   // listen
   if (listen(listener, 10) == -1)
   {
      perror("listen");
      exit(3);
   }

   // 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

   // main loop
   for(;;)
   {
      read_fds = master; // copy it
      if (select(fdmax+1, &read_fds, NULL, NULL, NULL) == -1)
      {
         perror("select");
         exit(4);
      }

      // run through the existing connections looking for data to read
      for(i = 0; i <= fdmax; i++)
      {
         if (FD_ISSET(i, &read_fds))
         { // we got one!!
            if (i == listener)
            {
               // handle new connections
               addrlen = sizeof remoteaddr;
               newfd = accept(listener,
                              (struct sockaddr *)&remoteaddr,
                              &addrlen);

               if (newfd == -1)
               {
                  perror("accept");
               }
               else
               {
                  FD_SET(newfd, &master); // add to master set
                  if (newfd > fdmax)
                  {    // keep track of the max
                     fdmax = newfd;
                  }
                  printf("selectserver: new connection from %s on "
                        "socket %d\n",
                        inet_ntop(remoteaddr.ss_family,
                                  get_in_addr((struct sockaddr*)&remoteaddr),
                                  remoteIP, INET6_ADDRSTRLEN),
                                  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("selectserver: socket %d hung up\n", i);
                  }
                  else
                  {
                     perror("recv");
                  }
                  close(i); // bye!
                  FD_CLR(i, &master); // remove from master set
               }
               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");
                           }
                        }
                     }
                  }
               }
            } // END handle data from client
         } // END got new incoming connection
      } // END looping through file descriptors
   } // END for(;;)--and you thought it would never end!

   return 0;
}