#include <iostream>
#include <sys/socket.h>
#include <string.h>
#include <arpa/inet.h>

int main() {
  printf("START TEST SERVER\n");

  int sockfd = socket(AF_INET, SOCK_DGRAM, 0); // SOCK_DGRAM : UDP
  if (sockfd < 0)
    printf("ERROR opening socket\n");

  int optval = 1;
  if(setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, (const void *)&optval , sizeof(int)) == -1) {
    printf("ERROR setsockopt\n");
  }

  struct sockaddr_in serveraddr;
  unsigned short portno = 32500;
  memset((char *) &serveraddr, 0x00,  sizeof(serveraddr));
  serveraddr.sin_family = AF_INET;
  serveraddr.sin_addr.s_addr = htonl(INADDR_ANY);
  serveraddr.sin_port = htons(portno);

  if (bind(sockfd, (struct sockaddr *) &serveraddr, sizeof(serveraddr)) < 0)
    printf("ERROR on binding\n");

  struct sockaddr_in clientaddr;
  socklen_t clientlen = sizeof(clientaddr);

  char buf[100000];
  while (1) {
    printf("[%s] Wait data from Client(PORT : %d)\n", __FUNCTION__, portno);
    memset(buf, 0x00, sizeof(buf));

    int n = recvfrom(sockfd, buf, sizeof(buf), 0, (struct sockaddr *) &clientaddr, &clientlen);
    if (n < 0)
      printf("ERROR in recvfrom\n");
    printf("GET MESSAGE from fd:%d, port:%d ip:%lu : %.20s\n", sockfd, clientaddr.sin_port, clientaddr.sin_addr.s_addr, buf);
  }
}

#include <iostream>
#include <fstream>
#include <unistd.h>
#include <string.h>
#include <sys/socket.h>
#include <arpa/inet.h>

#define TESTMSG_LENGTH  1000

int main() {
    int sockfd;
    struct sockaddr_in serv;
    char buffer[TESTMSG_LENGTH] = {0,};
    pid_t pid = fork();

    sockfd = socket(AF_INET,SOCK_DGRAM,0);

    serv.sin_family = AF_INET;
    serv.sin_port = htons(32500);
    serv.sin_addr.s_addr = inet_addr("127.0.0.1");

    socklen_t m = sizeof(serv);
    if (pid == 0) { // child process
      printf("this is child process. FD:%d\n", sockfd);
      memset(buffer,'-',sizeof(buffer));
    } else if (pid > 0) {
      printf("this is parent process. FD:%d\n", sockfd);
      memset(buffer,'+',sizeof(buffer));
    } else {
      printf("fork FAIL\n");
      close(sockfd);
      return 0;
    }

    for(int i=0;i<10;i++) {
      sendto(sockfd, buffer, strlen(buffer), 0, (struct sockaddr *)&serv, m);
      if (pid > 0)
        usleep(1); // make race condition
    }

    close(sockfd);
    return 0;
}