#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <error.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <unistd.h>
#include <signal.h>
#include <sys/wait.h>
#include <sys/types.h>

#define errExit(msg)       \
   do                      \
   {                       \
      perror(msg);         \
      _exit(EXIT_FAILURE); \
   } while (0)

#define SOCK_PATH "/tmp/unix_sock.server"
#define DATA "Hello from server"
#define BUF 128
#define FINS "exit_s"
#define FINC "exit_c"

void child_handler(int sig)
{
   pid_t pid;
   while ((pid = waitpid(-1, NULL, WNOHANG)) > 0)
      ;
}

void session(int client_sock, struct sockaddr_un server_sockaddr, struct sockaddr_un client_sockaddr)
{
   int rc;
   char inbuf[BUF];
   char outbuf[BUF];
   int bytes_rec = 0;
   size_t bs = BUF;
   socklen_t len;
   pid_t ppid, pid;

   ppid = getppid();
   pid = getpid();

   len = sizeof(client_sockaddr);
   rc = getpeername(client_sock, (struct sockaddr *)&client_sockaddr, &len);
   if (rc == -1)
   {
      close(client_sock);
      errExit("getpeer");
   }
   else
   {
      printf("[%d] Client socket filepath: %s\n", pid, client_sockaddr.sun_path);
   }
   do
   {
      printf("waiting for %s...\n", client_sockaddr.sun_path);
      memset(inbuf, 0, bs);
      bytes_rec = recv(client_sock, inbuf, bs, 0);
      if (bytes_rec == -1)
      {
         close(client_sock);
         errExit("recv");
      }
      else
      {
         printf("[%s]:  %s\n", client_sockaddr.sun_path, inbuf);
      }

      memset(outbuf, 0, bs);
      strcpy(outbuf, DATA);
      printf("Sending data...\n");
      rc = send(client_sock, outbuf, strlen(outbuf) + 1, 0);
      if (rc == -1)
      {
         close(client_sock);
         errExit("send");
      }
      else
      {
         printf("Data sent!\n");
      }
      if (strcmp(inbuf, FINS) == 0)
      {
         kill(ppid, SIGKILL);
         break;
      }
   } while (strcmp(inbuf, FINC));
   memset(outbuf, 0, bs);
   sprintf(outbuf, "Exit %d\n", pid);
   rc = send(client_sock, outbuf, strlen(outbuf) + 1, 0);
   if (rc == -1)
   {
      close(client_sock);
      errExit("send");
   }
   close(client_sock);
   exit(0);
}

int main(void)
{

   int server_sock, client_sock, rc;
   socklen_t len;
   struct sockaddr_un server_sockaddr;
   struct sockaddr_un client_sockaddr;
   int backlog = 10;
   pid_t pid;

   struct sigaction new_act, old_act;
   sigemptyset(&new_act.sa_mask);
   new_act.sa_flags = SA_RESTART;
   new_act.sa_handler = child_handler;
   sigaction(SIGCHLD, &new_act, &old_act);

   len = sizeof(server_sockaddr);
   memset(&server_sockaddr, 0, sizeof(struct sockaddr_un));
   memset(&client_sockaddr, 0, sizeof(struct sockaddr_un));

   server_sock = socket(AF_UNIX, SOCK_STREAM, 0);
   if (server_sock == -1)
      errExit("socket");

   server_sockaddr.sun_family = AF_UNIX;
   strcpy(server_sockaddr.sun_path, SOCK_PATH);

   unlink(SOCK_PATH);
   rc = bind(server_sock, (struct sockaddr *)&server_sockaddr, len);
   if (rc == -1)
   {
      close(server_sock);
      errExit("bind");
   }

   rc = listen(server_sock, backlog);
   if (rc == -1)
   {
      close(server_sock);
      errExit("listen");
   }

   printf("socket listening...\n");

   do
   {
      client_sock = accept(server_sock, (struct sockaddr *)&client_sockaddr, &len);
      if (client_sock == -1)
      {
         close(server_sock);
         close(client_sock);
         errExit("accept");
      }
      if ((pid = fork()) == -1)
      {
         close(server_sock);
         close(client_sock);
         errExit("fork");
      }
      if (pid == 0)
         session(client_sock, server_sockaddr, client_sockaddr);
      close(client_sock);
   } while (1);

   close(server_sock);
   unlink(SOCK_PATH);

   return 0;
}