Fix router module external IPs when only subnet specified

The router module used to support adding external fixed IPs
by specifying the subnet only, and the documentation still
allows for this. Unfortunately the logic currently results
in an error message stating that the ip_address cannot be
null.

This patch reinstates this functionality and adds tests to
avoid a future regression.

Change-Id: Ie29c7b2b763a58ea107cc50507e99f650ee9e53f

ci/roles/router/tasks/main.yml

@@ -558,6 +558,46 @@
   assert:
     that: router is not changed
 
+- name: Create router without explicit IP address
+  openstack.cloud.router:
+     cloud: "{{ cloud }}"
+     state: present
+     name: "{{ router_name }}"
+     enable_snat: false
+     interfaces:
+         - shade_subnet1
+     network: "{{ external_network_name }}"
+     external_fixed_ips:
+        - subnet_id: shade_subnet5
+  register: router
+
+- name: Assert idempotent module
+  assert:
+    that: router is changed
+
+- name: Update router without explicit IP address
+  openstack.cloud.router:
+     cloud: "{{ cloud }}"
+     state: present
+     name: "{{ router_name }}"
+     enable_snat: false
+     interfaces:
+         - shade_subnet1
+     network: "{{ external_network_name }}"
+     external_fixed_ips:
+        - subnet_id: shade_subnet5
+  register: router
+
+- name: Assert idempotent module
+  assert:
+    that: router is not changed
+
+- name: Delete router
+  openstack.cloud.router:
+     cloud: "{{ cloud }}"
+     state: absent
+     name: "{{ router_name }}"
+
 - name: Create router with simple interface
   openstack.cloud.router:
      cloud: "{{ cloud }}"

plugins/modules/router.py

@@ -372,6 +372,10 @@ class RouterModule(OpenStackModule):
             for p in external_fixed_ips:
                 if 'ip_address' in p:
                     req_fip_map[p['subnet_id']].add(p['ip_address'])
+                elif p['subnet_id'] in cur_fip_map:
+                    # handle idempotence of updating with no explicit ip
+                    req_fip_map[p['subnet_id']].update(
+                        cur_fip_map[p['subnet_id']])
 
             # Check if external ip addresses need to be added
             for fip in external_fixed_ips:
@@ -464,7 +468,7 @@ class RouterModule(OpenStackModule):
                 subnet = self.conn.network.find_subnet(
                     iface['subnet_id'], ignore_missing=False, **filters)
                 fip = dict(subnet_id=subnet.id)
-                if 'ip_address' in iface:
+                if iface.get('ip_address', None) is not None:
                     fip['ip_address'] = iface['ip_address']
                 external_fixed_ips.append(fip)