ElasticSearch Autodiscovery

elasticsearch_discover_example.c

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
 
int main(void)
{
  struct sockaddr_in socket_addr;

  int socketDescriptor = socket(AF_INET, SOCK_DGRAM, 0);
  if (socketDescriptor < 0) { perror("Error creating socket - "); exit(1); }

  socklen_t socketLen = sizeof(socket_addr);

  memset(&socket_addr, 0, sizeof(struct sockaddr_in));
  socket_addr.sin_family      = AF_INET;
  socket_addr.sin_port        = htons(54328);
  socket_addr.sin_addr.s_addr = inet_addr("224.2.2.4");

  struct ip_mreq imr;

  imr.imr_multiaddr.s_addr = inet_addr("224.2.2.4");
  imr.imr_interface.s_addr = htonl(INADDR_ANY);

  if (setsockopt(socketDescriptor, IPPROTO_IP, IP_ADD_MEMBERSHIP, &imr, sizeof(struct ip_mreq)) < 0) { perror("Error in setsockopt (IP_ADD_MEMBERSHIP) - "); exit(1); }

  unsigned char loop = 0;
  setsockopt(socketDescriptor, IPPROTO_IP, IP_MULTICAST_LOOP, &loop, sizeof(loop));

  if (bind(socketDescriptor, (struct sockaddr *) &socket_addr, sizeof(socket_addr)) < 0) { perror("Error binding - "); exit(1); }

  int cnt = sendto(socketDescriptor, "{\"request\": {\"cluster_name\": \"elasticsearch\"} }\n", 48, 0, (struct sockaddr *) &socket_addr, socketLen);
  if (cnt < 0) {  perror("Error in sendto - "); exit(1); }

  char buf[256];
  memset(&buf, 0, sizeof(buf));

  cnt = recvfrom(socketDescriptor, buf, sizeof(buf), 0, (struct sockaddr *) &socket_addr, &socketLen);
  if (cnt < 0) { perror("Error in recvfrom - "); exit(1); }
  printf("%s\n", buf);

}