mcshd.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/utsname.h>
#include <string.h>
#include <syslog.h>

#include "wrappedsockets.h"

#define MAXLEN 1024
#define DELAY 2
#define TTL 5

int main(int argc, char *argv[])
{
  int receivingSocket, sendingSocket;
  u_char ttl;
  struct sockaddr_in mcast_group;
  struct utsname name;

  if ((argc < 3) || (argc > 4)) {
    fprintf(stderr, "Usage: %s mcast_group port [ttl]\n", argv[0]);
    exit(1);
  }

  memset(&mcast_group, 0, sizeof(mcast_group));
  mcast_group.sin_family = AF_INET;
  mcast_group.sin_port = htons((unsigned short int)strtol(argv[2], NULL, 0));
  mcast_group.sin_addr.s_addr = inet_addr(argv[1]);

  allocateSocket(&sendingSocket);
  ttl = (argc == 4) ? strtol(argv[3], NULL, 0) : TTL;
  allocateSocket(&receivingSocket);
  enableSocketReuse(&receivingSocket);
  enableMulticastLoop(&receivingSocket);
  bindSocket(&receivingSocket, mcast_group);
  joinMulticastGroup(mcast_group.sin_addr, &receivingSocket);
  getSystemNodeName(&name);

  char buffer[MAXLEN + 1];
  FILE *fp;

  if (fork() == 0) {
    setsid();
    chdir("/");
    uname(0);
    openlog("mcshd", LOG_CONS, LOG_USER);

    for (;;) {
      memset(buffer, 0, sizeof(buffer));
      recvfrom(receivingSocket, buffer, MAXLEN, 0, NULL, NULL);
      
      if (strstr(buffer, "STARTOFCOMMAND: ") != NULL) {
        syslog(LOG_INFO, "Received command: %s", buffer);

        fp = popen(buffer+16, "r");
        
        if (fp != NULL) {
          while (fgets(buffer, MAXLEN, fp) != NULL) {
            sendto(sendingSocket, buffer, strlen(buffer)+1, 0, (const struct sockaddr *)&mcast_group, sizeof(mcast_group));
          }
          
          snprintf(buffer, MAXLEN, "ENDOFCOMMAND");
          sendto(sendingSocket, buffer, strlen(buffer)+1, 0, (const struct sockaddr *)&mcast_group, sizeof(mcast_group));
          pclose(fp);
        }
      }
    }
  }
  exit(0);
}