Flag when source device for public network does not exist (#1499)

Detect when the device provided for connecting the VM to a public
network via the host does not exist and attempt to provide a useful
error message to give end users a hint of how to correct.

Fixes: #1477

lib/vagrant-libvirt/config.rb

@@ -195,6 +195,9 @@ module VagrantPlugins
       # serial consoles
       attr_accessor :serials
 
+      # internal helper attributes
+      attr_accessor :host_device_exclude_prefixes
+
       def initialize
         @uri               = UNSET_VALUE
         @driver            = UNSET_VALUE
@@ -342,6 +345,9 @@ module VagrantPlugins
         @qemu_use_agent  = UNSET_VALUE
 
         @serials           = UNSET_VALUE
+
+        # internal options to help override behaviour
+        @host_device_exclude_prefixes = UNSET_VALUE
       end
 
       def boot(device)
@@ -972,6 +978,8 @@ module VagrantPlugins
         @qemu_use_agent = false if @qemu_use_agent == UNSET_VALUE
 
         @serials = [{:type => 'pty', :source => nil}] if @serials == UNSET_VALUE
+
+        @host_device_exclude_prefixes = ['docker', 'macvtap', 'virbr', 'vnet'] if @host_device_exclude_prefixes == UNSET_VALUE
       end
 
       def validate(machine)
@@ -1029,7 +1037,9 @@ module VagrantPlugins
           errors << "#{e}"
         end
 
-        machine.config.vm.networks.each do |_type, opts|
+        machine.config.vm.networks.each_with_index do |network, index|
+          type, opts = network
+
           if opts[:mac]
             if opts[:mac] =~ /\A([0-9a-fA-F]{12})\z/
               opts[:mac] = opts[:mac].scan(/../).join(':')
@@ -1038,6 +1048,13 @@ module VagrantPlugins
               errors << "Configured NIC MAC '#{opts[:mac]}' is not in 'xx:xx:xx:xx:xx:xx' or 'xxxxxxxxxxxx' format"
             end
           end
+
+          # only interested in public networks where portgroup is nil, as then source will be a host device
+          if type == :public_network && opts[:portgroup] == nil
+            if !host_devices.include?(opts[:dev])
+              errors << "network configuration #{index} for machine #{machine.name} is a public_network referencing host device '#{opts[:dev]}' which does not exist, consider adding ':dev => ....' referencing one of #{host_devices.join(", ")}"
+            end
+          end
         end
 
         if !machine.provider_config.volume_cache.nil? and machine.provider_config.volume_cache != UNSET_VALUE
@@ -1170,6 +1187,16 @@ module VagrantPlugins
           @proxy_command = nil
         end
       end
+
+      def host_devices
+        @host_devices ||= begin
+          require 'socket'
+
+          Socket.getifaddrs.map { |iface| iface.name }.uniq.select do |dev|
+            dev != "lo" && !@host_device_exclude_prefixes.any? { |exclude| dev.start_with?(exclude) }
+          end
+        end
+      end
     end
   end
 end

spec/unit/config_spec.rb

@@ -630,6 +630,53 @@ describe VagrantPlugins::ProviderLibvirt::Config do
       end
     end
 
+    context 'with public_network defined' do
+      let(:host_devices) { [
+        instance_double(Socket::Ifaddr),
+        instance_double(Socket::Ifaddr),
+      ] }
+      before do
+        machine.config.vm.network :public_network, dev: 'eth0', ip: "192.168.2.157"
+        expect(Socket).to receive(:getifaddrs).and_return(host_devices)
+        expect(host_devices[0]).to receive(:name).and_return('eth0')
+        expect(host_devices[1]).to receive(:name).and_return('virbr0')
+      end
+
+      it 'should validate use of existing device' do
+        assert_valid
+      end
+
+      context 'when default device not on host' do
+        before do
+          machine.config.vm.network :public_network, dev: 'eno1', ip: "192.168.2.157"
+        end
+
+        it 'should be invalid' do
+          assert_invalid
+        end
+      end
+
+      context 'when using excluded host device' do
+        before do
+          machine.config.vm.network :public_network, dev: 'virbr0', ip: "192.168.2.157"
+        end
+
+        it 'should be invalid' do
+          assert_invalid
+        end
+
+        context 'when user overrides to allow device' do
+          before do
+            subject.host_device_exclude_prefixes = []
+          end
+
+          it 'should validate' do
+            assert_valid
+          end
+        end
+      end
+    end
+
     context 'with nvram defined' do
       before do
         subject.nvram = '/path/to/some/nvram'