Add seed parameter to random_mac filter (#51841)

docs/docsite/rst/user_guide/playbooks_filters.rst

@@ -378,6 +378,10 @@ To get a random MAC address from a string prefix starting with '52:54:00'::
 
 Note that if anything is wrong with the prefix string, the filter will issue an error.
 
+As of Ansible version 2.9, it's also possible to initialize the random number generator from a seed. This way, you can create random-but-idempotent MAC addresses::
+
+    "{{ '52:54:00' | random_mac(seed=inventory_hostname) }}"
+
 .. _random_filter:
 
 Random Number Filter

lib/ansible/plugins/filter/core.py

@@ -36,7 +36,7 @@ import yaml
 
 import datetime
 from functools import partial
-from random import Random, SystemRandom, shuffle, randint
+from random import Random, SystemRandom, shuffle
 
 from jinja2.filters import environmentfilter, do_groupby as _do_groupby
 
@@ -533,7 +533,7 @@ def list_of_dict_key_value_elements_to_dict(mylist, key_name='key', value_name='
     return dict((item[key_name], item[value_name]) for item in mylist)
 
 
-def random_mac(value):
+def random_mac(value, seed=None):
     ''' takes string prefix, and return it completed with random bytes
         to get a complete 6 bytes MAC address '''
 
@@ -558,8 +558,12 @@ def random_mac(value):
     if len(err):
         raise AnsibleFilterError('Invalid value (%s) for random_mac: %s' % (value, err))
 
+    if seed is None:
+        r = SystemRandom()
+    else:
+        r = Random(seed)
     # Generate random int between x1000000000 and xFFFFFFFFFF
-    v = randint(68719476736, 1099511627775)
+    v = r.randint(68719476736, 1099511627775)
     # Select first n chars to complement input prefix
     remain = 2 * (6 - len(mac_items))
     rnd = ('%x' % v)[:remain]

test/integration/targets/filters/tasks/main.yml

@@ -242,6 +242,12 @@
             - "'00:00:00:00:00' | random_mac is match('^00:00:00:00:00:[a-f0-9][a-f0-9]$')"  
             - "'00:00:00' | random_mac != '00:00:00' | random_mac"
 
+- name: Verify random_mac filter with seed
+  assert:
+    that:
+      - "'00:00:00' | random_mac(seed='test') == '00:00:00' | random_mac(seed='test')"
+      - "'00:00:00' | random_mac(seed='test') != '00:00:00' | random_mac(seed='another_test')"
+
 - name: Verify that union can be chained
   vars:
     unions: '{{ [1,2,3]|union([4,5])|union([6,7]) }}'