Add some code from Patrick for debugging lpeg grammars

nselib/lpeg-utility.lua

@@ -9,6 +9,7 @@ local assert = assert
 
 local lpeg = require "lpeg"
 local stdnse = require "stdnse"
+local pairs = pairs
 
 _ENV = {}
 
@@ -88,4 +89,32 @@ function escaped_quote (quot, esc)
   }
 end
 
+---
+-- Adds hooks to a grammar to print debugging information
+--
+-- Debugging LPeg grammars can be difficult. Calling this function on your
+-- grammmar will cause it to print ENTER and LEAVE statements for each rule, as
+-- well as position and subject after each successful rule match.
+--
+-- For convenience, the modified grammar is returned; a copy is not made
+-- though, and the original grammar is modified as well.
+--
+-- @param grammar The LPeg grammar to modify
+-- @param printer A printf-style formatting printer function to use.
+--                Default: stdnse.debug1
+-- @return The modified grammar.
+function debug (grammar, printer)
+  printer = printer or stdnse.debug1
+  -- Original code credit: http://lua-users.org/lists/lua-l/2009-10/msg00774.html
+  for k, p in pairs(grammar) do
+    local enter = lpeg.Cmt(lpeg.P(true), function(s, p, ...)
+      printer("ENTER %s", k) return p end)
+    local leave = lpeg.Cmt(lpeg.P(true), function(s, p, ...)
+      printer("LEAVE %s", k) return p end) * (lpeg.P("k") - lpeg.P "k");
+    grammar[k] = lpeg.Cmt(enter * p + leave, function(s, p, ...)
+      printer("---%s---", k) printer("pos: %d, [%s]", p, s:sub(1, p-1)) return p end)
+  end
+  return grammar
+end
+
 return _ENV