From 31420f12c1741cc8461d841e86010f1e676262c3 Mon Sep 17 00:00:00 2001
From: Juan Pablo Tosso <jptosso@gmail.com>
Date: Thu, 24 Aug 2023 17:23:27 +0200
Subject: [PATCH] add reverse transformation support

---
 .../plugins/plugintypes/transformation.go     |  4 +-
 internal/transformations/reverse.go           | 18 +++++++++
 .../transformations/testdata/reverse.json     | 38 +++++++++++++++++++
 internal/transformations/transformations.go   |  1 +
 4 files changed, 60 insertions(+), 1 deletion(-)
 create mode 100644 internal/transformations/reverse.go
 create mode 100644 internal/transformations/testdata/reverse.json

diff --git a/experimental/plugins/plugintypes/transformation.go b/experimental/plugins/plugintypes/transformation.go
index e9b699b16..0d1b87e8a 100644
--- a/experimental/plugins/plugintypes/transformation.go
+++ b/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)
diff --git a/internal/transformations/reverse.go b/internal/transformations/reverse.go
new file mode 100644
index 000000000..e80cad640
--- /dev/null
+++ b/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
+}
diff --git a/internal/transformations/testdata/reverse.json b/internal/transformations/testdata/reverse.json
new file mode 100644
index 000000000..abb642f70
--- /dev/null
+++ b/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
+    }
+
+]
\ No newline at end of file
diff --git a/internal/transformations/transformations.go b/internal/transformations/transformations.go
index bcfa533b6..f795fa70e 100644
--- a/internal/transformations/transformations.go
+++ b/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("urlDecode", urlDecode)
 	Register("urlDecodeUni", urlDecodeUni)