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int establish(void) {
  /*  This will store the listening socket's address  */
  struct sockaddr_in sa; 

  /*  This will hold the listening socket  */
  int s;                              

  /*  Fill up the structure with address and port number  */

  sa.sin_port = htons(portnum);

  /*  Other system calls like socket()  */

  if (bind(
        s, 
        (struct sockaddr *) &sa, 
        sizeof(struct sockaddr_in)) < 0) 
  {
    /* Perform cleanup */  
  }  

  /* Return */
}

int main(void) {
   int s = establish();

  /*  Block with accept() until a client connects  */
   
   switch (fork()) {
      case -1 :  /* Error, clean up and quit */
      case  0 :  /* This is the child, handle the client */
      default :  /* This is the parent, continue blocking */
   }
} 

/*  Code with elevated privileges  */

int establish(void) {
  /*  This will store the listening socket's address  */
  struct sockaddr_in sa;
 
  /*  This will hold the listening socket  */
  int s;                              

  /* Fill up the structure with address and port number */

  sa.sin_port = htons(portnum);

  /* Other system calls like socket() */

  if (bind(
        s, 
        (struct sockaddr *) &sa, 
        sizeof(struct sockaddr_in)) < 0)  
  { 
    /* Perform cleanup */  
  }

  /* Return */  
}

int main(void) {
  int s = establish();

  /* Drop privileges permanently */
  if (setuid(getuid()) == -1) {   
     /*  Handle the error  */
  }

  if (setuid(0) != -1) {
    /* Privileges can be restored, handle error */
  }

  /* Block with accept() until a client connects */
      
  switch (fork()) {
     case -1: /* Error, clean up and quit */
     case  0: /* Close all open file descriptors
               * This is the child, handle the client 
               */
     default: /* This is the parent, continue blocking */
  }
}