/* par.ex8.39.c SJ */
/* Compile at cs:
 *  gcc -Wall -o par.ex8.39 par.ex8.39.c -lnsl -lsocket -lresolv -lm
 * Compile at linux:
 *  gcc -Wall -o par.ex8.39 par.ex8.39.c -lm
*/

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

#define MAXPART 100
#define RATIO 5
#define PRIMELEN 12
#define INBUF 100
#define DEL " "
#define EOL "\n"

void sendall(int sock, char *buf);

/* signal handler to wait all child processes */
void sigchld_handler(int s)
{
  while(wait(NULL) > 0);
}

int isprime(int x);
int findprimes(int min, int max, char *primes);

int main(int argc, char **argv)
{
  int numbytes, newbytes, first, last, pid, count;

  char inbuf[INBUF+1];
  char outbuf[MAXPART*PRIMELEN/RATIO + 1];

  struct sockaddr_in remote_addr, my_addr;
  int sock, newsock;
  int sin_size;
  char yes='1';

  struct sigaction sa;

  /* check parameters */
  if ((argc != 2) || (atoi(argv[1]) < 1024)) {
	  fprintf(stderr, "Usage: %s port\n", argv[0]);
	  exit(1);
  }

  /* create socket */
  if ((sock = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
	  perror("socket");
	  exit(1);
  }

  if (setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) == -1) {
	  perror("setsockopt");
	  exit(1);
  }

  my_addr.sin_family = AF_INET;    // host byte order
  my_addr.sin_port = htons(atoi(argv[1]));  // short, network byte order
  my_addr.sin_addr.s_addr = INADDR_ANY;	// automatically fill with my IP
  memset(&(my_addr.sin_zero), '\0', 8);  // zero the rest of the struct

  /* bind to the port */
  if (bind(sock, (struct sockaddr *)&my_addr, sizeof(struct sockaddr)) == -1) {
	  perror("bind");
	  exit(1);
  }

  /* open port for connections */
  if (listen(sock, 5) == -1) {
	  perror("listen");
	  exit(1);
  }

  /* register signal handler which waits (acknowledges) all childs */
  sa.sa_handler = sigchld_handler;
  sigemptyset(&sa.sa_mask);
  sa.sa_flags = SA_RESTART;
  if (sigaction(SIGCHLD, &sa, NULL) == -1) {
	  perror("sigaction");
	  exit(1);
  }
  
  /* serve forever */
  while(1) {
	  sin_size = sizeof(struct sockaddr_in);

	  /* accept new connection */
	  if ((newsock = accept(sock, (struct sockaddr *)&remote_addr, &sin_size)) == -1) {
		  perror("accept");
		  continue;
	  }

	  printf("got connection from %s\n",inet_ntoa(remote_addr.sin_addr));

	  /* create a child process to handle the new connection */
	  pid = fork();

	  if (!pid) {
		  /* child process, handle one request */

		  numbytes = 0;
		  /* receive until 2 integers have been received */
		  do {
			  newbytes = recv(newsock, inbuf+numbytes, INBUF, 0);
			  if (newbytes == -1) {
				  perror("recv");
				  close(newsock);
				  exit(1);
			  }
			  numbytes += newbytes;
			  inbuf[numbytes] = '\0';   /* terminate string */
		  } while (newbytes && (sscanf(inbuf, "%d %d", &first, &last) < 2));

		  /* check request */
		  count = sscanf(inbuf, "%d %d", &first, &last);
		  if ((count != 2) || (first < 1))
			  sprintf(outbuf, "Need two positive integers!\n");
		  if (first > last)
			  sprintf(outbuf, "First may not be larger than second!\n");
		  else if (last - first + 1 > MAXPART)
			  sprintf(outbuf, "I check at most %d numbers at a time!\n", MAXPART);
		  else {

			  /* request ok */

			  /* print */
			  puts(inbuf);

			  /* find the primes to string */
			  count = findprimes(first, last, outbuf);
			  printf("found %d primes\n", count);
		  }

		  /* send reply */
		  sendall(newsock, outbuf);

		  /* close and exit */
		  close(newsock);
		  exit(0);
	  }

	  /* parent just closes newsock */
	  close(newsock);
  }

  close(sock);

  exit(0);

}


void sendall(int sock, char *buf)
{
  int len, bs;
  len = strlen(buf);
  while (len > 0) {
	  bs = send(sock, buf, len, 0);
	  if (bs == -1) {
		  perror("send");
		  return;
	  } else if (bs == 0) {
		  printf("Connection closed prematurely\n");
		  return;
	  }

	  len -= bs;
  }
} /* sendall() */

int findprimes(int min, int max, char *primes)
{
  int i, n = 0, plen = 0;
  for (i = min; i <= max; i++)
      if (isprime(i)) {
		  plen = sprintf(primes, "%d ", i);
          primes += plen;
		  n++;
      }
  sprintf(primes, "\n");
  return n;
}

/* check whether a number is prime or not */
int isprime(int x)
{
  int i, s = sqrt(x);
  if (x == 1)
	  return 0;
  if (x < 4)
      return 1;
  if (! (x%2) )
      return 0;
  for (i = 3; i <= s; i += 2)
      if (! (x%i))
          return 0;
  return 1;
}