use the SafePath.coffee file in the client too

services/web/public/coffee/ide/directives/SafePath.coffee

@@ -0,0 +1,47 @@
+# This file is shared between the frontend and server code of web, so that
+# filename validation is the same in both implementations.  
+# Both copies must be kept in sync:
+#   app/coffee/Features/Project/SafePath.coffee
+#   public/coffee/ide/directives/SafePath.coffee
+
+load = () ->
+	BADCHAR_RX = ///
+		[
+			\/ # no slashes
+			\* # no asterisk
+			\u0000-\u001F # no control characters (0-31)
+			\u007F        # no delete
+			\u0080-\u009F # no unicode control characters (C1)
+			\uD800-\uDFFF # no unicode surrogate characters
+		]
+		///g
+
+	BADFILE_RX = ///
+		(^\.$)      # reject . as a filename
+		|	(^\.\.$)  # reject .. as a filename
+		| (^\s+)    # reject leading space
+		| (\s+$)    # reject trailing space
+		///g
+
+	MAX_PATH = 1024 # Maximum path length, in characters. This is fairly arbitrary.
+
+	SafePath =
+		clean: (filename) ->
+			filename = filename.replace BADCHAR_RX, '_'
+			# for BADFILE_RX replace any matches with an equal number of underscores
+			filename = filename.replace BADFILE_RX, (match) -> 
+				return new Array(match.length + 1).join("_")
+			return filename
+
+		isCleanFilename: (filename) ->
+			return SafePath.isAllowedLength(filename) &&
+				not filename.match(BADCHAR_RX) &&
+				not filename.match(BADFILE_RX)
+
+		isAllowedLength: (pathname) ->
+			return pathname.length > 0 && pathname.length <= MAX_PATH
+
+if define?
+	define [], load
+else
+	module.exports = load()

services/web/public/coffee/ide/directives/validFile.coffee

@@ -1,26 +1,7 @@
 define [
 	"base"
-], (App) ->
-
-	# copied from app/coffee/Features/Project/SafePath.coffee
-
-	BADCHAR_RX = ///
-	[
-		\/ # no slashes
-		\* # no asterisk
-		\u0000-\u001F # no control characters (0-31)
-		\u007F        # no delete
-		\u0080-\u009F # no unicode control characters (C1)
-		\uD800-\uDFFF # no unicode surrogate characters
-	]
-	///g
-
-	BADFILE_RX = ///
-		(^\.$)      # reject . as a filename
-		| (^\.\.$)  # reject .. as a filename
-		| (^\s+)    # reject leading space
-		| (\s+$)    # reject trailing space
-	///g
+	"ide/directives/SafePath"
+], (App, SafePath) ->
 
 	MAX_PATH = 1024 # Maximum path length, in characters. This is fairly arbitrary.
 
@@ -29,8 +10,5 @@ define [
 			require: 'ngModel'
 			link: (scope, element, attrs, ngModelCtrl) ->
 				ngModelCtrl.$validators.validFile = (filename) ->
-					isValid = filename.length > 0 && filename.length < MAX_PATH &&
-						not filename.match(BADCHAR_RX) &&
-						not filename.match(BADFILE_RX)
-					return isValid
+					return SafePath.isCleanFilename filename
 		}