Description Sönke Schwardt-Krummrich 2013-01-23 14:02:51 CET

If one or more UCR variables get changed, the handler() function of UCR modules will be called. This function gets two arguments:
- a ConfigRegistry() object
- a dictionary containing the changes 
  → each key of that represents a UCR variable name
  → for each key a tuple consisting of old and new UCR value is stored

handler(ucr, changes)
→ ucr: { 'cron/autostart': 'yes', 'update/secure_apt': 'yes', … }
→ changes: { 'changedUCRVariable1': ( 'oldValue', 'newValue' ),
             'changedUCRVariable2': ( 'oldValue', 'newValue' ),
             'newVariable': ( None, 'newValue' ),
             'removedVariable': ( 'oldValue', '' ),
             'VariableToEmptyString': ( 'oldValue', '' ),
            }

During UCR module registration ("ucr register packagename") the second positional argument ("changes") contains no tuple but a simple string or None. Each variable that is specified in the .info-File ("Variables: ldap/hostdn") will be looked up for its current value that is stored in the dictionary. If regular expressions are used or the variable is unset, the value None is stored instead of a string.

---[foo.info]---
Type: module
Module: foo.py
Variables: foo/.*
Variables: unknown/variable
Variables: ldap/hostdn
Variables: hostname
---

Values passed as "changes" to handler() during "ucr register":

{'hostname': 'master', 
 'unknown/variable': None,
 'foo/.*': None, 
 'ldap/hostdn': 'cn=master,cn=dc,cn=computers,dc=nstx,dc=ucsschool'
}


There are some inconsistencies that should be fixed in future:
- during registration:
  - all variables matching a given regexp should be expanded
  - a tuple of two values should be passed for each variable to the freshly 
    registered module to be consistend with later API:
    { 'hostname': (None, 'master'), 
      'unknown/variable': (None, None),
      'foo/bar': (None, 'test'),
      'foo/baz': (None, 'test2'),
      'ldap/hostdn': (None, 'cn=master,cn=dc,cn=computers,dc=example,dc=com')
    }
- after registration when variables change:
  - when variables get removed, the old value and None should be stored in the 
    "changes" dictionary, to be able to distinct variables that have been 
    removed and variables that have been set to empty string.