#include <sys/socket.h>
#include <sys/un.h>
#include <sys/types.h>
#include <sys/socket.h>

#include <unistd.h>

#include <assert.h>
#include <stdio.h>
#include <stdlib.h>

#define NAME "./sock"

#define check(x) if ((x) == -1) { \
    perror(#x); \
    exit(EXIT_FAILURE); \
  }

void parent() {
  unlink(NAME);
  int sock;
  check(sock = socket(AF_UNIX, SOCK_DGRAM, 0));
  struct sockaddr_un addr = {
    .sun_family = AF_UNIX,
    .sun_path = NAME
  };
  check(bind(sock, (struct sockaddr*)&addr, sizeof(addr)));
  struct sockaddr_un client_addr;
  socklen_t client_addr_len;
  printf("[parent] waiting for a message...\n");
  char buf[10];
  ssize_t r;
  check(r = recvfrom(sock, buf, sizeof(buf) - 1, 0, (struct sockaddr*)&client_addr, &client_addr_len));
  buf[r] = '\0';
  printf("[parent] received %ld bytes: %s\n", r, buf);
  check(r = sendto(sock, buf, r - 1, 0, (struct sockaddr*)&client_addr, client_addr_len));
  printf("[parent] exiting\n");
}

void child() {
  int sock;
  check(sock = socket(AF_UNIX, SOCK_DGRAM, 0));
  struct sockaddr_un addr = {
    .sun_family = AF_UNIX,
    .sun_path = "\0"
  };
  struct sockaddr_un dest = {
    .sun_family = AF_UNIX,
    .sun_path = NAME
  };
  check(bind(sock, (struct sockaddr*)&addr, sizeof(addr)));
  printf("[child] waiting 1 sec...\n");
  sleep(1);
  check(sendto(sock, "hello", 5, 0, (struct sockaddr*)&dest, sizeof(dest)));
  printf("[child] msg sent, avaiting response\n");
  struct sockaddr_un client_addr;
  socklen_t client_addr_len;
  char buf[10];
  ssize_t r;
  check(r = recvfrom(sock, buf, sizeof(buf) - 1, 0, (struct sockaddr*)&client_addr, &client_addr_len));
  buf[r] = '\0';
  printf("[child] received %ld bytes: %s\n", r, buf);
  printf("[child] exiting\n");
}

int main() {
  int pid;
  check(pid = fork());
  if (pid != 0) {
    parent();
  } else {
    child();
  }
  return 0;
}