Add ability to clear DNS entries on static DNS

Execution Module:
- Passing no DNS servers will clear the list.
- Update documentation
- Added a note about clearing DNS entries

State Module
- An empty list in dns_servers will clear the entires
- None in dns_servers will do nothing (default behavior)
- Update Documentation

salt/modules/win_ip.py

@@ -319,6 +319,19 @@ def set_static_dns(iface, *addrs):
     '''
     Set static DNS configuration on a Windows NIC
 
+    Args:
+
+        iface (str): The name of the interface to set
+
+        addrs (*):
+            One or more DNS servers to be added
+
+            .. note::
+                If no DNS servers are passed the list will be cleared.
+
+    Returns:
+        dict: A dictionary containing the new DNS settings
+
     CLI Example:
 
     .. code-block:: bash
@@ -326,6 +339,15 @@ def set_static_dns(iface, *addrs):
         salt -G 'os_family:Windows' ip.set_static_dns 'Local Area Connection' '192.168.1.1'
         salt -G 'os_family:Windows' ip.set_static_dns 'Local Area Connection' '192.168.1.252' '192.168.1.253'
     '''
+    # Clear the list of DNS servers if not passed
+    if not addrs:
+        log.debug('Clearing list of DNS servers')
+        cmd = ['netsh', 'int', 'ip', 'set', 'dns',
+               'name={0}'.format(iface),
+               'source=static',
+               'address=none']
+        __salt__['cmd.run'](cmd, python_shell=False)
+        return {'Interface': iface, 'DNS Server': []}
     addr_index = 1
     for addr in addrs:
         if addr_index == 1:

salt/states/win_network.py

@@ -103,10 +103,8 @@ def _validate(dns_proto, dns_servers, ip_proto, ip_addrs, gateway):
                 'set to \'static\'.'
             )
     else:
-        if not dns_servers:
-            errors.append(
-                'The dns_servers param is required to set static DNS servers.'
-            )
+        if dns_servers is None:
+            pass
         elif not isinstance(dns_servers, list):
             errors.append(
                 'The dns_servers param must be formatted as a list.'
@@ -214,31 +212,60 @@ def managed(name,
     '''
     Ensure that the named interface is configured properly.
 
-    name
+    Args:
+
+        name (str):
             The name of the interface to manage
 
-    dns_proto : None
+        dns_proto (str): None
             Set to ``static`` and use the ``dns_servers`` parameter to provide a
             list of DNS nameservers. set to ``dhcp`` to use DHCP to get the DNS
             servers.
 
-    dns_servers : None
-        A list of static DNS servers.
+        dns_servers (list): None
+            A list of static DNS servers. To clear the list of DNS servers pass
+            an empty list. ``[]``
 
-    ip_proto : None
+        ip_proto (str): None
             Set to ``static`` and use the ``ip_addrs`` and (optionally) ``gateway``
             parameters to provide a list of static IP addresses and the default
             gateway. Set to ``dhcp`` to use DHCP.
 
-    ip_addrs : None
-        A list of static IP addresses.
+        ip_addrs (list): None
+            A list of static IP addresses with netmask flag, ie: 192.168.0.11/24
 
-    gateway : None
-        A list of static IP addresses.
+        gateway (str): None
+            The gateway to set for the interface
 
-    enabled : True
+        enabled (bool): True
             Set to ``False`` to ensure that this interface is disabled.
 
+    Returns:
+        dict: A dictionary of old and new settings
+
+    Example:
+
+    .. code-block:: yaml
+
+        Ethernet1:
+          network.managed:
+            - dns_proto: static
+            - dns_servers:
+              - 8.8.8.8
+              - 8.8.8.4
+            - ip_proto: static
+            - ip_addrs:
+              - 192.168.0.100/24
+
+    Clear DNS entries example:
+
+    .. code-block:: yaml
+
+        Ethernet1:
+          network.managed:
+            - dns_proto: static
+            - dns_servers: []
+            - ip_proto: dhcp
     '''
     ret = {
         'name': name,
@@ -317,6 +344,12 @@ def managed(name,
                            ip_proto,
                            ip_addrs,
                            gateway)
+
+        # If dns_servers is the default `None` make no changes
+        # To clear the list, pass an empty dict
+        if dns_servers is None:
+            changes.pop('dns_servers')
+
         if not changes:
             return ret
 
@@ -357,8 +390,7 @@ def managed(name,
         if changes.get('dns_proto') == 'dhcp':
             __salt__['ip.set_dhcp_dns'](name)
 
-        elif changes.get('dns_servers'):
-            if changes.get('dns_servers'):
+        elif 'dns_servers' in changes:
             __salt__['ip.set_static_dns'](name, *changes['dns_servers'])
 
         if changes.get('ip_proto') == 'dhcp':