/*
 * ISA 563, Spring 2011
 * Copyleft by Muhammad Abdulla
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <signal.h>

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <sys/wait.h>

extern int errno;

#define QLEN 20

/*
 * concurrent-echo-server.c -- demonstrates concurrent server-side processing using fork 
 */

#define PORTNUM 2345 

void child_handler(int sig)
{
  pid_t pid;

  pid = wait(NULL);

  printf("Child with PID %d exited.\n", pid);
}


int main ( int argc, char *argv[] )
{
   int n;
   int sock, conn;
   int val;
   struct sockaddr_in sin ;
   struct hostent *hen ;
   char buf[1024];

   struct sockaddr_in remote_addr ;
   socklen_t addr_len ;
   addr_len = sizeof ( remote_addr ) ;

   pid_t pid;

   signal(SIGCHLD, child_handler);

   // create socket
   sock = socket ( AF_INET, SOCK_STREAM, 0 ) ;
   if ( sock < 0 ) {
      fprintf ( stderr, "Can't create socket: %s\n", strerror(errno) ) ;
      exit(1) ;
   }

   memset ( &sin, 0, sizeof(sin) ) ;
   sin.sin_family = AF_INET ;
   sin.sin_addr.s_addr = INADDR_ANY ;
   sin.sin_port = htons ( (short) PORTNUM ) ;

   // try to bind to port_num
   val = bind ( sock, (struct sockaddr *)&sin, sizeof(sin) ) ;
   if ( val < 0 ) {
      fprintf ( stderr, "Can't bind socket: %s\n", strerror(errno) ) ;
      exit(1) ;
   }

   // we have to listen for TCP sockets 
   val = listen ( sock, QLEN ) ;
   if ( val < 0 ) {
      fprintf ( stderr, "Can't listen on socket: %s\n", strerror(errno) ) ;
      exit(1) ;
   }

   for ( ; ; ) {
      conn = accept ( sock, (struct sockaddr *)&remote_addr, &addr_len ) ;

      if (conn == -1) { // accept error
         if (errno == EINTR) { // caused by an interrupt
            continue; // try again
         } else {
            fprintf(stderr, "%s", strerror(errno));
         }
      }

      pid = fork();

      if ( pid == 0 ) {  // child processes the request
         // first close the listening socket
         close(sock);

         while ( (n = read(conn, buf, sizeof(buf))) > 0 ) {
            write(conn, buf, n);
         }

         // done processing request
         close(conn);
         exit(0);
      }

      // parent is here
      fprintf(stdout, "Child spawned with pid: %d\n", pid);
   }

   close(sock);
}