Re: [PATCH] [Ncat] Fix EOF handling

[bensonk () acm wwu edu]

The standard netcat behavior as defined by the canonical implementation
by hobbit explicitly does not halt on EOF.  I would recommend reversing
the option, and instead providing an option like "-q N" in gentoo's netcat.
The "-q N" option means "after EOF, exit after N seconds". 

Benson

On Sat, Apr 18, 2009 at 08:10:23PM +0200, Daniel Roethlisberger wrote:
> Ncat currently doesn't handle EOF events in a very intuitive way.
> Usability for scripting mainly depends on the ability to pipe
> into and out of Ncat:
>
> me@server $ ncat -l 1234 | tar xvf -
> me@client $ tar cvf - somedir | ncat server 1234
>
> Currently, this does not work as expected, neither in the client
> nor in the server.
>
> In connect mode, EOF on standard input does not cause Ncat to
> exit.  `cat file | ncat somewhere 1234' will keep running forever
> until Ncat receives a SIGINT.  To be suitable for scripting, Ncat
> must exit after EOF on stdin.
>
> In listen mode, closing the TCP connection on the client side
> does not cause Ncat to flush stdout and exit, because Ncat is
> waiting for other connections.  SIGINT does not help here,
> because Ncat will not write the remaining buffered bytes to
> stdout in that case, so a received file will have some missing
> bytes at the end.
>
> Cince this behaviour can be considered a feature, the attached
> patch adds a `-k' option, modelled after the *BSD nc(1) option of
> the same name.  `-l -k' gives current behaviour, while just `-l'
> gives the expected, scriptable single-shot behaviour which is
> default for all netcat variants I am aware of (which is why I'd
> propose to make it the default).
>
> The attached patches fix EOF handling in both connect and listen
> mode as I'd expect Ncat to handle EOF.  Comments?
>
> -- 
> Daniel Roethlisberger
> http://daniel.roe.ch/

> Index: ncat/ncat_connect.c
> ===================================================================
> --- ncat/ncat_connect.c       (revision 12996)
> +++ ncat/ncat_connect.c       (working copy)
> @@ -250,11 +250,9 @@
>          }   /* end switch */
>  
>      } else if (status == NSE_STATUS_EOF) {
> -        /* Close up, got EOF from network side */
> -        if (nsi == cs->sock_nsi) {
> -            nsi_delete(cs->stdin_nsi, NSOCK_PENDING_NOTIFY);
> -            nsi_delete(cs->sock_nsi, NSOCK_PENDING_NOTIFY);
> -        }
> +        /* Close up, got EOF either on network side or on standard input. */
> +        nsi_delete(cs->stdin_nsi, NSOCK_PENDING_NOTIFY);
> +        nsi_delete(cs->sock_nsi, NSOCK_PENDING_NOTIFY);
>      } else if (status == NSE_STATUS_ERROR) {
>          if (socket_errno() == EINPROGRESS)
>              /* XXX: this is weird. errno always seems to be incorrect on ret from nsock. */

> Index: ncat/ncat_core.h
> ===================================================================
> --- ncat/ncat_core.h  (revision 12996)
> +++ ncat/ncat_core.h  (working copy)
> @@ -21,6 +21,7 @@
>      int af;
>      int broker;
>      int listen;
> +    int keepopen;
>      int sendonly;
>      int recvonly;
>      int telnet;
> Index: ncat/ncat_listen.c
> ===================================================================
> --- ncat/ncat_listen.c        (revision 12996)
> +++ ncat/ncat_listen.c        (working copy)
> @@ -33,7 +33,7 @@
>  
>  static void handle_connection(void);
>  static void read_stdin(void);
> -static void read_socket(int recv_fd);
> +static int read_socket(int recv_fd);
>  
>  /* reap child processes */
>  static void sig_chld(int signo)
> @@ -114,7 +114,8 @@
>                  read_stdin();
>              } else {
>                  /* Read from a client and write to stdout. */
> -                read_socket(i);
> +                if (!read_socket(i) && !o.keepopen)
> +                    return 0;
>              }
>  
>              fds_ready--;
> @@ -242,8 +243,9 @@
>      broadcast(&fds, &fdlist, buf, nbytes);
>  }
>  
> -/* Read from a client socket and write to stdout. */
> -void read_socket(int recv_fd)
> +/* Read from a client socket and write to stdout.
> + * Returns zero if connection has been closed, non-zero otherwise. */
> +int read_socket(int recv_fd)
>  {
>      char buf[DEFAULT_TCP_BUF_LEN];
>      struct fdinfo *fdn = get_fdinfo(&fdlist, recv_fd);
> @@ -279,7 +281,7 @@
>          if (conn_count == 0)
>              FD_CLR(STDIN_FILENO, &master);
>  
> -        return;
> +        return 0;
>      }
>  
>      if(o.linedelay)
> @@ -301,6 +303,7 @@
>      if (o.ssl && fdn->ssl && SSL_pending(fdn->ssl))
>          goto readagain;
>  #endif
> +    return 1;
>  }
>  
>  /* This is sufficiently different from the TCP code (wrt SSL, etc) that it
> Index: ncat/ncat_main.c
> ===================================================================
> --- ncat/ncat_main.c  (revision 12996)
> +++ ncat/ncat_main.c  (working copy)
> @@ -153,6 +153,7 @@
>          {"help",            no_argument,        NULL,         'h'},
>          {"delay",           required_argument,  NULL,         'd'},
>          {"listen",          no_argument,        NULL,         'l'},
> +        {"keep-open",       no_argument,        NULL,         'k'},
>          {"output",          required_argument,  NULL,         'o'},
>          {"hex-dump",        required_argument,  NULL,         'x'},
>          {"idle-timeout",    required_argument,  NULL,         'i'},
> @@ -191,7 +192,7 @@
>      while (1) {
>          /* handle command line arguments */
>          int option_index;
> -        int c = getopt_long(argc, argv, "46Cc:e:g:G:i:m:hp:d:lo:x:ts:uvw:n",
> +        int c = getopt_long(argc, argv, "46Cc:e:g:G:i:m:hp:d:klo:x:ts:uvw:n",
>                              long_options, &option_index);
>  
>          /* That's the end of the options. */
> @@ -263,6 +264,9 @@
>          case 's':
>              source = optarg;
>              break;
> +        case 'k':
> +            o.keepopen = 1;
> +            break;
>          case 'l':
>              o.listen = 1;
>              break;
> @@ -371,6 +375,7 @@
>              printf("  -p, --source-port port     Specify source port to use (doesn't affect -l)\n");
>              printf("  -s, --source addr          Specify source address to use (doesn't affect -l)\n");
>              printf("  -l, --listen               Bind and listen for incoming connections\n");
> +            printf("  -k, --keep-open            Keep listening after first connection is closed\n");
>              printf("  -n, --nodns                Do not resolve hostnames via DNS\n");
>              printf("  -t, --telnet               Answer Telnet negotiations\n");
>              printf("  -u, --udp                  Use UDP instead of default TCP\n");
> @@ -553,6 +558,10 @@
>      if (o.cmdexec && o.hexlogfd != -1)
>          bye("Invalid option combination: `-e' and `-x'.");
>  
> +    /* keep-open requires listen mode. */
> +    if (o.keepopen && !o.listen)
> +        bye("Invalid option combination: `-k' without `-l'.");
> +
>      if (o.listen)
>          return ncat_listen_mode();
>      else
> Index: ncat/ncat_core.c
> ===================================================================
> --- ncat/ncat_core.c  (revision 12996)
> +++ ncat/ncat_core.c  (working copy)
> @@ -38,6 +38,7 @@
>      o.af = AF_INET;
>      o.broker = 0;
>      o.listen = 0;
> +    o.keepopen = 0;
>      o.sendonly = 0;
>      o.recvonly = 0;
>      o.telnet = 0;

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