u_long host_addr;  struct entry *next;};struct entry *permitted_hosts[TABLE_SIZE];/*  permitted -- return whether a given host is allowed to connect to the server.*/int permitted(host_addr)     u_long host_addr;{  int key;  struct entry *entry;    /* First find the hash key */  key = HASH(host_addr) % TABLE_SIZE;    /* Now check the chain for that hash key */  for(entry=permitted_hosts[key]; entry != NULL; entry=entry->next)    if (host_addr == entry->host_addr)       return(TRUE);  return(FALSE);} /* permitted *//*   add_host -- add the given host to the list of permitted hosts, provided it isn't              already there.*/	void add_host(host_addr)     u_long host_addr;{  int key;  struct entry *new_entry;    if (!permitted(host_addr)) {    if ((new_entry = (struct entry *) malloc(sizeof(struct entry))) == NULL) {      fprintf(stderr,"%s: unable to malloc space for permitted host entry\n",	      progname);      exit(1);    }; /* if */    new_entry->host_addr = host_addr;    key = HASH(host_addr) % TABLE_SIZE;    new_entry->next = permitted_hosts[key];    permitted_hosts[key] = new_entry;  }; /* if */} /* add_host *//*  setup_table -- initialise the table of hosts allowed to contact the server,                 by reading from the file specified by the GNU_SECURE		 environment variable                 Put in the local machine, and, if a security file is specifed,                 add each host that is named in the file.		 Return the number of hosts added.*/int setup_table(){  FILE *host_file;  char *file_name;  char hostname[HOSTNAMSZ];  u_long host_addr;  int i, hosts=0;    /* Make sure every entry is null */  for (i=0; i<TABLE_SIZE; i++)    permitted_hosts[i] = NULL;#if 0 /* Don't even want to allow access from the local host by default */  gethostname(hostname,HOSTNAMSZ);  if ((host_addr = internet_addr(hostname)) == -1) {    fprintf(stderr,"%s: unable to find %s in /etc/hosts or from YP", 	    progname,hostname);    exit(1);  }; /* if */  add_host(host_addr);					/* add local host */#endif   if (((file_name = getenv("GNU_SECURE")) != NULL &&    /* security file  */       (host_file = fopen(file_name,"r")) != NULL)) {	/* opened ok */    while ((fscanf(host_file,"%s",hostname) != EOF))	/* find a host */      if ((host_addr = internet_addr(hostname)) != -1) {/* get its addr */	add_host(host_addr);				/* add the addr */        hosts++;      }    fclose(host_file);  }; /* if */  return hosts;} /* setup_table *//*  internet_init -- initialize server, returning an internet socket that can                    be listened on.*/int internet_init(){  int ls;			/* socket descriptor */  struct servent *sp;		/* pointer to service information */  struct sockaddr_in server;	/* for local socket address */  char *ptr;			/* ptr to return from getenv */  if (setup_table() == 0)     return -1;  /* clear out address structure */  bzero((char *)&server,sizeof(struct sockaddr_in));    /* Set up address structure for the listen socket. */  server.sin_family = AF_INET;  server.sin_addr.s_addr = INADDR_ANY;  /* Find the information for the gnu server   * in order to get the needed port number.   */  if ((ptr=getenv("GNU_PORT")) != NULL)    server.sin_port = htons(atoi(ptr));  else if ((sp = getservbyname ("gnuserv", "tcp")) == NULL)    server.sin_port = htons(DEFAULT_PORT+getuid());  else    server.sin_port = sp->s_port;    /* Create the listen socket. */  if ((ls = socket (AF_INET,SOCK_STREAM, 0)) == -1) {    perror(progname);    fprintf(stderr,"%s: unable to create socket\n",progname);    exit(1);  }; /* if */    /* Bind the listen address to the socket. */  if (bind(ls,(struct sockaddr *) &server,sizeof(struct sockaddr_in)) == -1) {    perror(progname);    fprintf(stderr,"%s: unable to bind socket\n",progname);    exit(1);  }; /* if */  /* Initiate the listen on the socket so remote users   * can connect.    */  if (listen(ls,20) == -1) {    perror(progname);    fprintf(stderr,"%s: unable to listen\n",progname);    exit(1);  }; /* if */  return(ls);} /* internet_init *//*  handle_internet_request -- accept a request from a client and send the information                             to stdout (the gnu process).*/void handle_internet_request(ls)int ls;				/* listen socket */{  int s;  int addrlen = sizeof(struct sockaddr_in);  struct sockaddr_in peer;	/* for peer socket address */  bzero((char *)&peer,sizeof(struct sockaddr_in));  if ((s = accept(ls,(struct sockaddr *)&peer,&addrlen)) == -1) {    perror(progname);    fprintf(stderr,"%s: unable to accept\n",progname);    exit(1);  }; /* if */      /* Check that access is allowed - if not return crud to the client */  if (!permitted(peer.sin_addr.s_addr)) {    send_string(s,"gnudoit: Connection refused\ngnudoit: unable to connect to remote");    close(s);    return;  }; /* if */  echo_request(s);  } /* handle_internet_request */#endif /* INTERNET_DOMAIN_SOCKETS */#ifdef UNIX_DOMAIN_SOCKETS/*  unix_init -- initialize server, returning an unix-domain socket that can               be listened on.*/int unix_init(){  int ls;			/* socket descriptor */  struct sockaddr_un server; 	/* unix socket address */  if ((ls = socket(AF_UNIX,SOCK_STREAM, 0)) < 0) {    perror(progname);    fprintf(stderr,"%s: unable to create socket\n",progname);    exit(1);  }; /* if */  /* Set up address structure for the listen socket. */#ifdef HIDE_UNIX_SOCKET  sprintf(server.sun_path,"/tmp/gsrvdir%d",geteuid());  if (mkdir(server.sun_path, 0700) < 0) {    /* assume it already exists, and try to set perms */    if (chmod(server.sun_path, 0700) < 0) {      perror(progname);      fprintf(stderr,"%s: can't set permissions on %s\n",	      progname, server.sun_path);      exit(1);    }  }  strcat(server.sun_path,"/gsrv");  unlink(server.sun_path);	/* remove old file if it exists */#else /* HIDE_UNIX_SOCKET */  sprintf(server.sun_path,"/tmp/gsrv%d",geteuid());  unlink(server.sun_path);	/* remove old file if it exists */#endif /* HIDE_UNIX_SOCKET */  server.sun_family = AF_UNIX;   if (bind(ls,(struct sockaddr *)&server,strlen(server.sun_path)+2) < 0) {    perror(progname);    fprintf(stderr,"%s: unable to bind socket\n",progname);    exit(1);  }; /* if */  chmod(server.sun_path,0700);	/* only this user can send commands */  if (listen(ls,20) < 0) {    perror(progname);    fprintf(stderr,"%s: unable to listen\n",progname);    exit(1);  }; /* if */  signal(SIGPIPE,SIG_IGN);	/* in case user kills client */  return(ls);} /* unix_init *//*  handle_unix_request -- accept a request from a client and send the information                         to stdout (the gnu process).*/void handle_unix_request(ls)int ls;				/* listen socket */{  int s;  int len = sizeof(struct sockaddr_un);  struct sockaddr_un server; 	/* for unix socket address */  server.sun_family = AF_UNIX;  if ((s = accept(ls,(struct sockaddr *)&server,&len)) < 0) {    perror(progname);    fprintf(stderr,"%s: unable to accept\n",progname);  }; /* if */  echo_request(s);  } /* handle_unix_request */#endif /* UNIX_DOMAIN_SOCKETS */main(argc,argv)     int argc;     char *argv[];{  int ils = -1;			/* internet domain listen socket */  int uls = -1;			/* unix domain listen socket */  int chan;			/* temporary channel number */#ifdef SYSV_IPC  struct msgbuf *msgp;		/* message buffer */#endif /* SYSV_IPC */  progname = argv[0];  for(chan=3; chan < _NFILE; close(chan++)) /* close unwanted channels */    ;#ifdef USE_LITOUT  {    /* this is to allow ^D to pass to emacs */    int d = LLITOUT;    (void) ioctl(fileno(stdout), TIOCLBIS, &d);  }#endif#ifdef SYSV_IPC  ipc_init(&msgp);		/* get a msqid to listen on, and a message buffer */#endif /* SYSV_IPC */#ifdef INTERNET_DOMAIN_SOCKETS  ils = internet_init();	/* get a internet domain socket to listen on */#endif /* INTERNET_DOMAIN_SOCKETS */#ifdef UNIX_DOMAIN_SOCKETS  uls = unix_init();		/* get a unix domain socket to listen on */#endif /* UNIX_DOMAIN_SOCKETS */  while (1) {#ifdef SYSV_IPC    handle_ipc_request(msgp);#else /* NOT SYSV_IPC */    fd_set rmask;    FD_ZERO(&rmask);    FD_SET(fileno(stdin), &rmask);    if (uls >= 0)      FD_SET(uls, &rmask);    if (ils >= 0)      FD_SET(ils, &rmask);        if (select(max2(fileno(stdin),max2(uls,ils)) + 1, &rmask, 	       (fd_set *)NULL, (fd_set *)NULL, (struct timeval *)NULL) < 0) {      perror(progname);      fprintf(stderr,"%s: unable to select\n",progname);      exit(1);    }; /* if */#ifdef UNIX_DOMAIN_SOCKETS    if (uls > 0 && FD_ISSET(uls, &rmask))      handle_unix_request(uls);#endif#ifdef INTERNET_DOMAIN_SOCKETS    if (ils > 0 && FD_ISSET(ils, &rmask))      handle_internet_request(ils);#endif /* INTERNET_DOMAIN_SOCKETS */    if (FD_ISSET(fileno(stdin), &rmask))      /* from stdin (gnu process) */      handle_response();#endif /* NOT SYSV_IPC */  }; /* while */} /* main */#endif /* SYSV_IPC || UNIX_DOMAIN_SOCKETS || INTERNET_DOMAIN_SOCKETS */