Hide error traceback for nmap.new_try() handled exceptions. Fixes #2463

CHANGELOG

@@ -1,5 +1,10 @@
 #Nmap Changelog ($Id$); -*-text-*-
 
+o [NSE][GH#2463] NSE "exception handling" with nmap.new_try() will no longer
+  result in a stack traceback in debug output nor a "ERROR: script execution
+  failed" message in script output, since the intended behavior has always been
+  to end the script immediately without output. [Daniel Miller]
+
 o Upgrade libssh2 to 1.10.0.
 
 o [NSE][GH#2496] Fix newtargets support: since Nmap 7.92, scripts could not add

nse_main.lua

@@ -523,7 +523,15 @@ do
       self.action_started = true
       return self:resume(timeouts);
     elseif not ok then
-      if debugging() > 0 then
+      -- Extend this to create new types of errors with custom handling.
+      -- nmap.new_try does equivalent of: error({errtype="nmap.new_try", message="TIMEOUT"})
+      if type(r1) == "table" and r1.errtype == "nmap.new_try" then
+        -- nmap.new_try "exception" is closing the script
+        if debugging() > 0 then
+          self:d("Finished %THREAD_AGAINST. Reason: %s\n", r1.message);
+        end
+        r1 = r1.message
+      elseif debugging() > 0 then
         self:d("%THREAD_AGAINST threw an error!\n%s\n", traceback(self.co, tostring(r1)));
       else
         self:set_output("ERROR: Script execution failed (use -d to debug)");

nse_nmaplib.cc

@@ -624,7 +624,14 @@ static int l_log_write (lua_State *L)
 
 static int finalize_cleanup (lua_State *L, int status, lua_KContext ctx)
 {
-  lua_settop(L, 2);
+  lua_settop(L, 2); // top of stack: error message
+  lua_createtable(L, 0, 2); // error object table
+  lua_pushliteral(L, "errtype");
+  lua_pushliteral(L, "nmap.new_try");
+  lua_rawset(L, -3);
+  lua_pushliteral(L, "message"); // stack: err(string), err(table), "message"
+  lua_rotate(L, -3, -1); // stack: err(table), "message", err(string)
+  lua_rawset(L, -3);
   return lua_error(L);
 }