feat: add reverse transformation support

experimental/plugins/plugintypes/transformation.go

@@ -8,4 +8,6 @@ package plugintypes
 // If a transformation fails to run it will return the same string
 // and an error, errors are only used for logging, it won't stop
 // the execution of the rule
-type Transformation = func(input string) (string, bool, error)
+// "updated" is used for transformation cache, if true, the cache
+// will be updated
+type Transformation = func(input string) (result string, updated bool, err error)

internal/transformations/reverse.go

@@ -0,0 +1,18 @@
+// Copyright 2023 Juan Pablo Tosso and the OWASP Coraza contributors
+// SPDX-License-Identifier: Apache-2.0
+
+package transformations
+
+func reverse(data string) (string, bool, error) {
+	if len(data) <= 1 {
+		return data, false, nil
+	}
+	rns := []rune(data) // convert to rune, not bytes
+	for i, j := 0, len(rns)-1; i < j; i, j = i+1, j-1 {
+		// swap the letters of the string,
+		// like first with last and so on.
+		rns[i], rns[j] = rns[j], rns[i]
+	}
+	res := string(rns)
+	return res, res != data, nil
+}

internal/transformations/testdata/reverse.json

@@ -0,0 +1,38 @@
+[
+    {
+        "output": "desrever si siht",
+        "name": "reverse",
+        "input": "this is reversed",
+        "type": "tfn",
+        "ret": 0
+    },
+    {
+        "output": "síht sì dèsrèvèr",
+        "name": "reverse",
+        "input": "rèvèrsèd ìs thís",
+        "type": "tfn",
+        "ret": 0
+    },
+    {
+        "output": "esaC\u0000tseT",
+        "name": "reverse",
+        "input": "Test\u0000Case",
+        "type": "tfn",
+        "ret": 0        
+    },
+    {
+        "output": "",
+        "name": "reverse",
+        "input": "",
+        "type": "tfn",
+        "ret": 0
+    },
+    {
+        "output": "a",
+        "name": "reverse",
+        "input": "a",
+        "type": "tfn",
+        "ret": 0
+    }
+
+]

internal/transformations/transformations.go

@@ -50,6 +50,7 @@ func init() {
 	Register("removeWhitespace", removeWhitespace)
 	Register("replaceComments", replaceComments)
 	Register("replaceNulls", replaceNulls)
+	Register("reverse", reverse)
 	Register("sha1", sha1T)
 	Register("uppercase", upperCase)
 	Register("urlDecode", urlDecode)