Add conversion filters for serial numbers (#713)

* Refactoring.

* Add parse_filter and to_filter plugins.

* Mention filters when serial numbers are accepted or returned.

plugins/module_utils/serial.py

@@ -0,0 +1,56 @@
+# -*- coding: utf-8 -*-
+#
+# Copyright (c) 2024, Felix Fontein <felix@fontein.de>
+# GNU General Public License v3.0+ (see LICENSES/GPL-3.0-or-later.txt or https://www.gnu.org/licenses/gpl-3.0.txt)
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+from __future__ import absolute_import, division, print_function
+__metaclass__ = type
+
+from ansible.module_utils.common.text.converters import to_native
+
+from ansible_collections.community.crypto.plugins.module_utils.crypto.math import (
+    convert_int_to_hex,
+)
+
+
+def th(number):
+    abs_number = abs(number)
+    mod_10 = abs_number % 10
+    mod_100 = abs_number % 100
+    if mod_100 not in (11, 12, 13):
+        if mod_10 == 1:
+            return 'st'
+        if mod_10 == 2:
+            return 'nd'
+        if mod_10 == 3:
+            return 'rd'
+    return 'th'
+
+
+def parse_serial(value):
+    """
+    Given a colon-separated string of hexadecimal byte values, converts it to an integer.
+    """
+    value = to_native(value)
+    result = 0
+    for i, part in enumerate(value.split(':')):
+        try:
+            part_value = int(part, 16)
+            if part_value < 0 or part_value > 255:
+                raise ValueError('the value is not in range [0, 255]')
+        except ValueError as exc:
+            raise ValueError("The {idx}{th} part {part!r} is not a hexadecimal number in range [0, 255]: {exc}".format(
+                idx=i + 1, th=th(i + 1), part=part, exc=exc))
+        result = (result << 8) | part_value
+    return result
+
+
+def to_serial(value):
+    """
+    Given an integer, converts its absolute value to a colon-separated string of hexadecimal byte values.
+    """
+    value = convert_int_to_hex(value).upper()
+    if len(value) % 2 != 0:
+        value = '0' + value
+    return ':'.join(value[i:i + 2] for i in range(0, len(value), 2))