Added auto decryption of invalid file names

Changed invalid file decoding and decryption. Function
DecryptName now shortens the filename until the filename is
decodable and decryptable. Will work with valid **and**
invalid Base64URL delimiter (valid delimiter [0-9a-zA-z_\\-].
If the filename is not decryptable at all, it returns the
original cipher name with flag suffix Changed cli tests to
generate decryptable and undecryptable file names with correct
encrypted content. Replacing #474, extends #393

internal/nametransform/names.go

@@ -61,7 +61,14 @@ func (n *NameTransform) DecryptName(cipherName string, iv []byte) (string, error
 		for _, pattern := range n.BadnamePatterns {
 			match, err := filepath.Match(pattern, cipherName)
 			if err == nil && match { // Pattern should have been validated already
-				return "GOCRYPTFS_BAD_NAME " + cipherName, nil
+				//find longest decryptable substring
+				for charpos := len(cipherName) - 1; charpos > 0; charpos-- {
+					res, err = n.decryptName(cipherName[:charpos], iv)
+					if err == nil {
+						return res + cipherName[charpos:] + " GOCRYPTFS_BAD_NAME", nil
+					}
+				}
+				return cipherName + " GOCRYPTFS_BAD_NAME", nil
 			}
 		}
 	}

tests/cli/cli_test.go

@@ -705,40 +705,86 @@ func TestSymlinkedCipherdir(t *testing.T) {
 func TestBadname(t *testing.T) {
 	dir := test_helpers.InitFS(t)
 	mnt := dir + ".mnt"
+	validFileName := "file"
+	invalidSuffix := ".invalid_file"
 
+	//use static suffix for testing
 	test_helpers.MountOrFatal(t, dir, mnt, "-badname=*", "-extpass=echo test")
 	defer test_helpers.UnmountPanic(mnt)
 
-	file := mnt + "/file"
+	//write one valid file
+	file := mnt + "/" + validFileName
 	err := ioutil.WriteFile(file, []byte("somecontent"), 0600)
 	if err != nil {
 		t.Fatal(err)
 	}
 
-	invalid_file_name := "invalid_file"
-	invalid_file := dir + "/" + invalid_file_name
-	err = ioutil.WriteFile(invalid_file, []byte("somecontent"), 0600)
+	//read encrypted file name
+	fread, err := os.Open(dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer fread.Close()
+
+	encryptedfilename := ""
+	ciphernames, err := fread.Readdirnames(0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, ciphername := range ciphernames {
+		if ciphername != "gocryptfs.conf" && ciphername != "gocryptfs.diriv" {
+			encryptedfilename = ciphername
+			//found cipher name of "file"
+		}
+	}
+
+	//Read encrypted file name to generated invalid filenames
+	fsource, err := os.Open(dir + "/" + encryptedfilename)
+	if err != nil {
+		t.Fatal(err)
+	}
+	content, err := ioutil.ReadAll(fsource)
+	if err != nil {
+		t.Fatal(err)
+	}
+	fsource.Close()
+	//write invalid file which should be decodable
+	err = ioutil.WriteFile(dir+"/"+encryptedfilename+invalidSuffix, content, 0600)
+	if err != nil {
+		t.Fatal(err)
+	}
+	//write invalid file which is not decodable (cropping the encrpyted file name)
+	err = ioutil.WriteFile(dir+"/"+encryptedfilename[:len(encryptedfilename)-2]+invalidSuffix, content, 0600)
 	if err != nil {
 		t.Fatal(err)
 	}
 
+	//check for filenames
 	f, err := os.Open(mnt)
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer f.Close()
-
 	names, err := f.Readdirnames(0)
-	found := false
+	if err != nil {
+		t.Fatal(err)
+	}
+	foundDecodable := false
+	foundUndecodable := false
 	for _, name := range names {
-		if strings.Contains(name, invalid_file_name) {
-			found = true
-			break
+		if strings.Contains(name, validFileName+invalidSuffix+" GOCRYPTFS_BAD_NAME") {
+			foundDecodable = true
+		} else if strings.Contains(name, encryptedfilename[:len(encryptedfilename)-2]+invalidSuffix+" GOCRYPTFS_BAD_NAME") {
+			foundUndecodable = true
 		}
 	}
 
-	if !found {
-		t.Errorf("did not find invalid name %s in %v", invalid_file_name, names)
+	if !foundDecodable {
+		t.Errorf("did not find invalid name %s in %v", validFileName+invalidSuffix+" GOCRYPTFS_BAD_NAME", names)
+	}
+
+	if !foundUndecodable {
+		t.Errorf("did not find invalid name %s in %v", encryptedfilename[:len(encryptedfilename)-2]+invalidSuffix+" GOCRYPTFS_BAD_NAME", names)
 	}
 }