Sanitize bidi characters (#185)

* WIP

Signed-off-by: Milen Pivchev <milen.pivchev@gmail.com>

* Finalize

Signed-off-by: Milen Pivchev <milen.pivchev@gmail.com>

* Fix PR issues

Signed-off-by: Milen Pivchev <milen.pivchev@gmail.com>

---------

Signed-off-by: Milen Pivchev <milen.pivchev@gmail.com>

Author: mpivchev

Sources/NextcloudKit/Utils/FileNameSanitizer.swift

@@ -0,0 +1,36 @@
+// SPDX-FileCopyrightText: Nextcloud GmbH
+// SPDX-FileCopyrightText: 2025 Milen Pivchev
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+import Foundation
+
+extension String {
+    public func sanitizeForBidiCharacters(isFolder: Bool, isRTL: Bool = false) -> String {
+            let ns = self as NSString
+            let base = ns.deletingPathExtension
+            let ext = ns.pathExtension
+
+            guard !ext.isEmpty else { return base }
+
+            let dangerousBidiScalars: Set<UInt32> = [
+                0x202A, 0x202B, 0x202C, 0x202D, 0x202E,
+                0x200E, 0x200F, 0x2066, 0x2067, 0x2068,
+                0x2069, 0x061C
+            ]
+            let containsBidi = base.unicodeScalars.contains { dangerousBidiScalars.contains($0.value) }
+
+            if isRTL {
+                if containsBidi {
+                    return "\u{202C}\u{2066}.\(ext)\u{2069}" + base
+                } else {
+                    return ".\(ext)" + base
+                }
+            } else {
+                if containsBidi {
+                    return base + "\u{202C}\u{2066}.\(ext)\u{2069}"
+                } else {
+                    return base + "." + ext
+                }
+            }
+        }
+}

Tests/NextcloudKitUnitTests/FileSanitizingUnitTests.swift

@@ -0,0 +1,73 @@
+// SPDX-FileCopyrightText: Nextcloud GmbH
+// SPDX-FileCopyrightText: 2025 Milen Pivchev
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+import Testing
+import Foundation
+@testable import NextcloudKit
+
+@Suite(.serialized) struct FileSanitizingUnitTests {
+    // MARK: - Helper for test expectation
+    func expectedSanitized(for filename: String, isFolder: Bool, isRTL: Bool) -> String {
+        let ns = filename as NSString
+        let base = ns.deletingPathExtension
+        let ext = ns.pathExtension
+
+        if isFolder || ext.isEmpty { return base }
+
+        let dangerousBidiScalars: Set<UInt32> = [
+            0x202A, 0x202B, 0x202C, 0x202D, 0x202E,
+            0x200E, 0x200F, 0x2066, 0x2067, 0x2068,
+            0x2069, 0x061C
+        ]
+        let containsBidi = base.unicodeScalars.contains { dangerousBidiScalars.contains($0.value) }
+
+        if isRTL {
+            return containsBidi
+                ? "\u{202C}\u{2066}.\(ext)\u{2069}" + base
+                : ".\(ext)" + base
+        } else {
+            return containsBidi
+                ? base + "\u{202C}\u{2066}.\(ext)\u{2069}"
+                : base + "." + ext
+        }
+    }
+
+    // MARK: - Test Cases
+    @Test
+    func testSanitizeForBidiCharacters_UIRendering() {
+        let cases: [(String, Bool, Bool)] = [
+            // LTR, normal and malicious
+            ("invoice\u{202E}cod.exe", false, false),   // malicious RLO
+            ("archive.tar.gz", false, false),           // multiple dots
+            ("myFolder", true, false),                  // folder
+            ("document.txt", false, false),             // normal file
+            ("Foo\u{202E}dm.exe", false, false),        // another malicious
+
+            // RTL Hebrew / Arabic safe
+            ("תמונה.jpg", false, true),                 // Hebrew base
+            ("מכתב.pdf", false, true),                 // Hebrew base
+            ("שלום", true, true),                       // Hebrew folder
+            ("مرحبا", true, true),                      // Arabic folder
+            ("ملف.pdf", false, true),                   // Arabic file
+
+            // Mixed-language
+            ("report.ملف", false, true),                // English base, Arabic extension
+            ("وثيقة.docx", false, true),                // Arabic base, English extension
+            ("summary.תמונה", false, true),            // English base, Hebrew extension
+            ("מסמך.txt", false, true),                  // Hebrew base, English extension
+
+            // Mixed-language with malicious bidi
+            ("report\u{202E}cod.exe", false, true),     // English base + RLO trick
+            ("ملف\u{202E}cod.exe", false, true),       // Arabic base + RLO trick
+            ("תמונה\u{202E}cod.exe", false, true)      // Hebrew base + RLO trick
+        ]
+
+        for (filename, isFolder, isRTL) in cases {
+            let result = filename.sanitizeForBidiCharacters(isFolder: isFolder, isRTL: isRTL)
+            let expected = expectedSanitized(for: filename, isFolder: isFolder, isRTL: isRTL)
+            #expect(result == expected, "Failed for filename: \(filename), isFolder: \(isFolder), isRTL: \(isRTL)")
+        }
+    }
+}
+