Add support for grabbing the container ip from lxc dns server

lib/vagrant-lxc/container.rb

@@ -73,6 +73,34 @@ module Vagrant
         end
       end
 
+      def dhcp_ip
+        ip = ''
+        # Right after creation lxc reports the container as running
+        # before DNS is returning the right IP, so have to wait for a while
+        retryable(:on => LXC::Errors::ExecuteError, :tries => 10, :sleep => 1) do
+          # By default LXC supplies a dns server on 10.0.3.1 so we request the IP
+          # of our target from there.
+          # Tks to: https://github.com/neerolyte/vagueant/blob/master/bin/vagueant#L340
+          r = (raw 'dig', @name, '@10.0.3.1', '+short')
+
+          # If the command was a failure then raise an exception that is nicely
+          # handled by Vagrant.
+          if r.exit_code != 0
+            if @interrupted
+              @logger.info("Exit code != 0, but interrupted. Ignoring.")
+            else
+              raise LXC::Errors::ExecuteError, :command => command.inspect
+            end
+          end
+
+          ip = r.stdout.gsub("\r\n", "\n").strip
+          if ip.empty?
+            raise LXC::Errors::ExecuteError, 'Unable to identify container ip'
+          end
+        end
+        ip
+      end
+
       # TODO: Review code below this line, it was pretty much a copy and paste from VirtualBox base driver
       def execute(*command, &block)
         # Get the options hash if it exists

spec/unit/container_spec.rb

@@ -175,4 +175,20 @@ describe Vagrant::LXC::Container do
       subject.state.should == :stopped
     end
   end
+
+  describe 'dhcp ip' do
+    let(:name) { 'random-container-name' }
+    let(:ip)   { "10.0.3.123" }
+
+    before do
+      subject.stub(:raw) {
+        mock(stdout: "#{ip}\n", exit_code: 0)
+      }
+    end
+
+    it 'digs the container ip from lxc dns server' do
+      subject.dhcp_ip.should == ip
+      subject.should have_received(:raw).with('dig', name, '@10.0.3.1', '+short')
+    end
+  end
 end