Added '' as a valid value for gateway_ip

If the gateway_ip attribute on neutron_subnet is set to an empty string
('') then it will trigger removing the DHCP gateway setting from the
subnet.  This is equivalent to the --no-gateway flag in the CLI.

Change-Id: Id4b74062d5b5b2fb335167af4e7cfcc32c4db703

lib/puppet/provider/neutron_subnet/neutron.rb

@@ -28,7 +28,7 @@ def self.instances
         :id                        => attrs['id'],
         :cidr                      => attrs['cidr'],
         :ip_version                => attrs['ip_version'],
-        :gateway_ip                => attrs['gateway_ip'],
+        :gateway_ip                => parse_gateway_ip(attrs['gateway_ip']),
         :allocation_pools          => parse_allocation_pool(attrs['allocation_pools']),
         :host_routes               => parse_host_routes(attrs['host_routes']),
         :dns_nameservers           => parse_dns_nameservers(attrs['dns_nameservers']),
@@ -48,6 +48,11 @@ def self.prefetch(resources)
     end
   end
 
+  def self.parse_gateway_ip(value)
+    return '' if value.nil?
+    return value
+  end
+
   def self.parse_allocation_pool(values)
     allocation_pools = []
     return [] if values.empty?
@@ -89,7 +94,11 @@ def create
     end
 
     if @resource[:gateway_ip]
-      opts << "--gateway-ip=#{@resource[:gateway_ip]}"
+      if @resource[:gateway_ip] == ''
+        opts << '--no-gateway'
+      else
+        opts << "--gateway-ip=#{@resource[:gateway_ip]}"
+      end
     end
 
     if @resource[:enable_dhcp]
@@ -139,7 +148,7 @@ def create
         :id                        => attrs['id'],
         :cidr                      => attrs['cidr'],
         :ip_version                => attrs['ip_version'],
-        :gateway_ip                => attrs['gateway_ip'],
+        :gateway_ip                => self.class.parse_gateway_ip(attrs['gateway_ip']),
         :allocation_pools          => self.class.parse_allocation_pool(attrs['allocation_pools']),
         :host_routes               => self.class.parse_host_routes(attrs['host_routes']),
         :dns_nameservers           => self.class.parse_dns_nameservers(attrs['dns_nameservers']),
@@ -158,7 +167,11 @@ def destroy
   end
 
   def gateway_ip=(value)
-    auth_neutron('subnet-update', "--gateway-ip=#{value}", name)
+    if value == ''
+      auth_neutron('subnet-update', '--no-gateway', name)
+    else
+      auth_neutron('subnet-update', "--gateway-ip=#{value}", name)
+    end
   end
 
   def enable_dhcp=(value)

lib/puppet/type/neutron_subnet.rb

@@ -31,7 +31,10 @@
   end
 
   newproperty(:gateway_ip) do
-    desc 'The default gateway used by devices in this subnet'
+    desc <<-EOT
+    The default gateway provided by DHCP to devices in this subnet.  If set to
+    '' then no gateway IP address will be provided via DHCP.
+    EOT
   end
 
   newproperty(:enable_dhcp) do

spec/unit/provider/neutron_subnet/neutron_spec.rb

@@ -42,6 +42,13 @@
       provider.gateway_ip=('10.0.0.2')
     end
 
+    it 'should call subnet-update to remove gateway_ip with empty string' do
+      provider.expects(:auth_neutron).with('subnet-update',
+                                           '--no-gateway',
+                                           subnet_name)
+      provider.gateway_ip=('')
+    end
+
     it 'should call subnet-update to change enable_dhcp' do
       provider.expects(:auth_neutron).with('subnet-update',
                                            '--enable-dhcp=True',