module_params_get*: Fail on empty string in string list parameters

So far it is possible to pass list parameters with empty strings to the
modules. The use of empty strings in list does not make a lot of sense,
though. The simple solution is to add a check to module_params_get for
empty strings in returned lists.

The option allow_empty_string can be set to True to allow an empty string
in the list with a list len of 1. The option defaults to False. It is
needed for some parameters the modules, like for example userauthtype in
the user module. It is using "" to reset to the default value.

module_params_get_lowercase has been changed to use module_params_get to
have one place to add the check.

Due to an issue in Ansible it is possible to use the empty string "" for
lists with choices, even if the empty list is not part of the choices.
Ansible issue https://github.com/ansible/ansible/issues/77108

plugins/module_utils/ansible_freeipa_module.py

@@ -398,11 +398,32 @@ else:
 
         return value
 
-    def module_params_get(module, name):
-        return _afm_convert(module.params.get(name))
-
-    def module_params_get_lowercase(module, name):
+    def module_params_get(module, name, allow_empty_string=False):
         value = _afm_convert(module.params.get(name))
+
+        # Fail on empty strings in the list or if allow_empty_string is True
+        # if there is another entry in the list together with the empty
+        # string.
+        # Due to an issue in Ansible it is possible to use the empty string
+        # "" for lists with choices, even if the empty list is not part of
+        # the choices.
+        # Ansible issue https://github.com/ansible/ansible/issues/77108
+        if isinstance(value, list):
+            for val in value:
+                if isinstance(val, (str, unicode)) and not val:
+                    if not allow_empty_string:
+                        module.fail_json(
+                            msg="Parameter '%s' contains an empty string" %
+                            name)
+                    elif len(value) > 1:
+                        module.fail_json(
+                            msg="Parameter '%s' may not contain another "
+                            "entry together with an empty string" % name)
+
+        return value
+
+    def module_params_get_lowercase(module, name, allow_empty_string=False):
+        value = module_params_get(module, name, allow_empty_string)
         if isinstance(value, list):
             value = [v.lower() for v in value]
         if isinstance(value, (str, unicode)):
@@ -897,7 +918,7 @@ else:
                 finally:
                     temp_kdestroy(ccache_dir, ccache_name)
 
-        def params_get(self, name):
+        def params_get(self, name, allow_empty_string=False):
             """
             Retrieve value set for module parameter.
 
@@ -905,11 +926,13 @@ else:
             ----------
             name: string
                 The name of the parameter to retrieve.
+            allow_empty_string: bool
+                The parameter allowes to have empty strings in a list
 
             """
-            return module_params_get(self, name)
+            return module_params_get(self, name, allow_empty_string)
 
-        def params_get_lowercase(self, name):
+        def params_get_lowercase(self, name, allow_empty_string=False):
             """
             Retrieve value set for module parameter as lowercase, if not None.
 
@@ -917,9 +940,11 @@ else:
             ----------
             name: string
                 The name of the parameter to retrieve.
+            allow_empty_string: bool
+                The parameter allowes to have empty strings in a list
 
             """
-            return module_params_get_lowercase(self, name)
+            return module_params_get_lowercase(self, name, allow_empty_string)
 
         def params_fail_used_invalid(self, invalid_params, state, action=None):
             """