Adds zero-byte option(-z) for Ncat. Fixes #22 and #225

ncat/ncat_connect.c

@@ -1078,6 +1078,13 @@ int ncat_connect(void)
     return rc == NSOCK_LOOP_ERROR ? 1 : 0;
 }
 
+static void send_udp_null(nsock_pool nsp)
+{
+  char *NULL_PROBE = "\0";
+  int length = 1;
+  nsock_write(nsp, cs.sock_nsi, write_socket_handler, -1, NULL, NULL_PROBE, length);
+}
+
 static void connect_handler(nsock_pool nsp, nsock_event evt, void *data)
 {
     enum nse_status status = nse_status(evt);
@@ -1086,10 +1093,12 @@ static void connect_handler(nsock_pool nsp, nsock_event evt, void *data)
     ncat_assert(type == NSE_TYPE_CONNECT || type == NSE_TYPE_CONNECT_SSL);
 
     if (status == NSE_STATUS_ERROR) {
-        loguser("%s.\n", socket_strerror(nse_errorcode(evt)));
+        if (!o.zerobyte||o.verbose)
+          loguser("%s.\n", socket_strerror(nse_errorcode(evt)));
         exit(1);
     } else if (status == NSE_STATUS_TIMEOUT) {
-        loguser("%s.\n", socket_strerror(ETIMEDOUT));
+        if (!o.zerobyte||o.verbose)
+          loguser("%s.\n", socket_strerror(ETIMEDOUT));
         exit(1);
     } else {
         ncat_assert(status == NSE_STATUS_SUCCESS);
@@ -1104,7 +1113,10 @@ static void connect_handler(nsock_pool nsp, nsock_event evt, void *data)
     }
 #endif
 
-    connect_report(cs.sock_nsi);
+    if (o.proto != IPPROTO_UDP && o.zerobyte) {
+      connect_report(cs.sock_nsi);
+      nsock_loop_quit(nsp);
+    }
 
     /* Create IOD for nsp->stdin */
     if ((cs.stdin_nsi = nsock_iod_new2(nsp, 0, NULL)) == NULL)
@@ -1134,12 +1146,15 @@ static void post_connect(nsock_pool nsp, nsock_iod iod)
 
     /* Start the initial reads. */
 
-    if (!o.sendonly)
+    if (!o.sendonly && !o.zerobyte)
         nsock_read(nsp, cs.sock_nsi, read_socket_handler, -1, NULL);
 
-    if (!o.recvonly)
+    if (!o.recvonly && !o.zerobyte)
         nsock_readbytes(nsp, cs.stdin_nsi, read_stdin_handler, -1, NULL, 0);
 
+    if (o.zerobyte && o.proto==IPPROTO_UDP)
+      send_udp_null(nsp);
+
     /* The --idle-timeout option says to exit after a certain period of
        inactivity. We start a timer here and reset it on every read event; see
        refresh_idle_timer. */
@@ -1158,6 +1173,7 @@ static void read_stdin_handler(nsock_pool nsp, nsock_event evt, void *data)
 
     ncat_assert(type == NSE_TYPE_READ);
 
+
     if (status == NSE_STATUS_EOF) {
         shutdown(nsock_iod_get_sd(cs.sock_nsi), SHUT_WR);
         /* In --send-only mode or non-TCP mode, exit after EOF on stdin. */
@@ -1212,7 +1228,8 @@ static void read_socket_handler(nsock_pool nsp, nsock_event evt, void *data)
             nsock_loop_quit(nsp);
         return;
     } else if (status == NSE_STATUS_ERROR) {
-        loguser("%s.\n", socket_strerror(nse_errorcode(evt)));
+        if (!o.zerobyte||o.verbose)
+          loguser("%s.\n", socket_strerror(nse_errorcode(evt)));
         exit(1);
     } else if (status == NSE_STATUS_TIMEOUT) {
         loguser("%s.\n", socket_strerror(ETIMEDOUT));
@@ -1259,6 +1276,11 @@ static void write_socket_handler(nsock_pool nsp, nsock_event evt, void *data)
         ncat_assert(status == NSE_STATUS_SUCCESS);
     }
 
+    if (o.zerobyte){
+      ncat_assert(o.proto == IPPROTO_UDP);
+      nsock_read(nsp, cs.sock_nsi, read_socket_handler, -1, NULL);
+      return;
+    }
     /* The write to the socket was successful. Allow reading more from stdin
        now. */
     nsock_readbytes(nsp, cs.stdin_nsi, read_stdin_handler, -1, NULL, 0);
@@ -1276,6 +1298,13 @@ static void idle_timer_handler(nsock_pool nsp, nsock_event evt, void *data)
 
     ncat_assert(status == NSE_STATUS_SUCCESS);
 
+    if (o.zerobyte&&o.proto==IPPROTO_UDP){
+      if (o.verbose)
+        loguser("UDP packet sent successfully\n");
+      nsock_loop_quit(nsp);
+      return;
+    }
+
     loguser("Idle timeout expired (%d ms).\n", o.idletimeout);
 
     exit(1);

ncat/ncat_core.c

@@ -200,6 +200,7 @@ void options_init(void)
     o.execmode = EXEC_PLAIN;
     o.proxy_auth = NULL;
     o.proxytype = NULL;
+    o.zerobyte = 0;
 
 #ifdef HAVE_OPENSSL
     o.ssl = 0;

ncat/ncat_core.h

@@ -205,6 +205,7 @@ struct options {
     int sslverify;
     char *ssltrustfile;
     char *sslciphers;
+    int zerobyte;
 };
 
 extern struct options o;

ncat/ncat_main.c

@@ -334,7 +334,7 @@ int main(int argc, char *argv[])
     while (1) {
         /* handle command line arguments */
         int option_index;
-        int c = getopt_long(argc, argv, "46UCc:e:g:G:i:km:hp:d:lo:x:ts:uvw:n",
+        int c = getopt_long(argc, argv, "46UCc:e:g:G:i:km:hp:d:lo:x:ts:uvw:n:z",
                             long_options, &option_index);
 
         /* That's the end of the options. */
@@ -458,6 +458,9 @@ int main(int argc, char *argv[])
         case 't':
             o.telnet = 1;
             break;
+        case 'z':
+            o.zerobyte = 1;
+            break;
         case 0:
             if (strcmp(long_options[option_index].name, "version") == 0) {
                 print_banner();
@@ -606,6 +609,7 @@ int main(int argc, char *argv[])
 "      --sctp                 Use SCTP instead of default TCP\n"
 "  -v, --verbose              Set verbosity level (can be used several times)\n"
 "  -w, --wait <time>          Connect timeout\n"
+"  -z                         Zero-I/O mode, report connection status only\n"
 "      --append-output        Append rather than clobber specified output files\n"
 "      --send-only            Only send data, ignoring received; quit on EOF\n"
 "      --recv-only            Only receive data, never send anything\n"
@@ -723,6 +727,16 @@ int main(int argc, char *argv[])
         }
     }
 
+    if (o.zerobyte) {
+      if (o.listen)
+        bye("Services designed for LISTENING can't be used with -z");
+      if (o.telnet)
+        bye("Invalid option combination: -z and -t.");
+      if (o.execmode||o.cmdexec)
+        bye("Command execution can't be done along with option -z.");
+      if (!o.idletimeout && o.proto == IPPROTO_UDP)
+        o.idletimeout = 2 * 1000;
+    }
     /* Default port */
     if (o.listen && o.proxytype && !o.portno && srcport == -1)
         o.portno = DEFAULT_PROXY_PORT;