/* server4.c server skeleton for ex4 20 */
/* gcc -o server4_fork server4_fork.c -lnsl -lsocket -lresolv */

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

/* how many pending connections */
#define BACKLOG 3

/* size of the send/receive buffer */
#define MAXMSG 1000

/* official network end-of-line is CR LF */
#define EOL "\015\012"

/* this macro can be used to check errors, see client.c to do without */
#define ERRORCHEK(var, value, command)  if (var == value) {     \
                                            perror(command);    \
                                            exit(1);            \
                                        }

/* signal handled to clean the child processes by wait() */
void sigchld_handler(int s)
{
    while(wait(NULL) > 0);
}


int main(int argc, char *argv[])
{
  int ssock, csock;  			/* listen on ss, new connection on csock */
  struct sockaddr_in own_addr;	/* my address information */
  struct sockaddr_in c_addr;	/* client address information */
  unsigned int sin_size = sizeof(struct sockaddr_in);
  int status, numbytes, childpid;
  char rbuf[MAXMSG]; /* receive buffer */
  char sbuf[MAXMSG*2]; /* send buffer */
  char yes='1';
  struct sigaction sa;
  int port = 9876;      /* default port */


  /* port as optional parameter */
  if (argc > 1)
	  port = atoi(argv[1]);

  /* get socket */
  ssock = socket(AF_INET, SOCK_STREAM, 0);
  ERRORCHEK(ssock, -1, "socket");

  /* reuse port immediately */
  status = setsockopt(ssock, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int));
  ERRORCHEK(status, -1, "setsockopt");

  /* fill in the own address */
  own_addr.sin_family = AF_INET;         
  own_addr.sin_port = htons(port);
  own_addr.sin_addr.s_addr = INADDR_ANY; /* automatically fill with own IP */
  memset(&(own_addr.sin_zero), '\0', 8);

  /* bind to port */
  status = bind(ssock, (struct sockaddr *)&own_addr, sin_size);
  ERRORCHEK(status, -1, "bind");

  /* listen the port */
  status = listen(ssock, BACKLOG);
  ERRORCHEK(status, -1, "listen");

  /* setup signal handler */
  sa.sa_handler = sigchld_handler;
  sigemptyset(&sa.sa_mask);
  sa.sa_flags = SA_RESTART;
  status = sigaction(SIGCHLD, &sa, NULL);
  ERRORCHEK(status, -1, "sigaction");

  while(1) {  /* main accept() loop */
	  sin_size = sizeof(struct sockaddr_in);
	  csock = accept(ssock, (struct sockaddr *)&c_addr, &sin_size);
	  if (csock == -1) {
		  perror("accept");
		  continue; /* do not exit even if a connection failed */
	  }

	  printf("server: new client: %s\n", inet_ntoa(c_addr.sin_addr));

	  /* start new process */

	  /* remember to check the return value of fork() for errors (-1) */
	  /* this saves the system is case of exhausted resources */
	  childpid = fork();
	  ERRORCHEK(childpid, -1, "fork");

	  if (childpid == 0) {
		  /* child process */

		  /* child does not use original server socket */
		  close(ssock);

		  /* serve until quit was received */
		  do {
			  numbytes=recv(csock, rbuf, MAXMSG-1, 0);
			  if (numbytes == -1) {
				  perror("recv");
				  continue;
			  } else if (numbytes == 0) {
				  /* connection closed */
				  continue;
			  }
			  /* terminate message to make a string */
			  rbuf[numbytes] = '\0';

			  printf("Message was \"%s\"\n", rbuf);

			  /* construct reply */
			  sprintf(sbuf, "You %s:%d sent me \"%s\"%s", inet_ntoa(c_addr.sin_addr),
					  ntohs(c_addr.sin_port), rbuf, EOL);

			  /* send reply */
			  numbytes = send(csock, sbuf, strlen(sbuf), 0);
			  ERRORCHEK(numbytes, -1, "send");

			  if (numbytes != strlen(sbuf))
				  printf("Only %d bytes sent! Should have used repeated send...\n", numbytes);
		  } while (!strstr(rbuf, "quit"));

		  /* after service, close connection and exit */
		  close(csock);
		  exit(0);
		  /* REMEMBER TO exit() THE CHILD PROCESS IN ALL CASES !!!! */

	  } else { /* if (childpid) */
		  /* parent process */
		  printf("Child process %d was created\n", childpid);
		  /* parent does not need new socket */
		  close(csock);

	  } /* else */

  } /* while(1) */

  close(ssock);

  exit(0);

} /* main() */