config: allow for setting URI from environment

Users are allowed to set a LIBVIRT_DEFAULT_URI environment variable that
controls tools (i.e. virsh, virt-install, etc) that communicate with
libvirt. Let's allow for that mechanism to be used here.

lib/vagrant-libvirt/config.rb

@@ -622,14 +622,21 @@ module VagrantPlugins
         @qemu_env.merge!(options)
       end
 
-      # code to generate URI from a config moved out of the connect action
-      def _generate_uri
+      # code to generate URI from from either the LIBVIRT_URI environment
+      # variable or a config moved out of the connect action
+      def _generate_uri(qemu_use_session)
+
+        # If the LIBVIRT_DEFAULT_URI var is set, we'll use that
+        if ENV.fetch('LIBVIRT_DEFAULT_URI', '') != ""
+          return ENV['LIBVIRT_DEFAULT_URI']
+        end
+
         # builds the Libvirt connection URI from the given driver config
         # Setup connection uri.
         uri = @driver.dup
         virt_path = case uri
                     when 'qemu', 'kvm'
-                      @qemu_use_session ? '/session' : '/system'
+                      qemu_use_session ? '/session' : '/system'
                     when 'openvz', 'uml', 'phyp', 'parallels'
                       '/system'
                     when '@en', 'esx'
@@ -670,6 +677,14 @@ module VagrantPlugins
         uri
       end
 
+      def _parse_uri(uri)
+        begin
+          URI.parse(uri)
+        rescue
+          raise "@uri set to invalid uri '#{uri}'"
+        end
+      end
+
       def finalize!
         @driver = 'kvm' if @driver == UNSET_VALUE
         @host = nil if @host == UNSET_VALUE
@@ -693,10 +708,21 @@ module VagrantPlugins
         @management_network_domain = nil if @management_network_domain == UNSET_VALUE
         @system_uri      = 'qemu:///system' if @system_uri == UNSET_VALUE
 
-        @qemu_use_session = false if @qemu_use_session == UNSET_VALUE
+        # If uri isn't set then let's build one from various sources.
+        # Default to passing false for qemu_use_session if it's not set.
+        if @uri == UNSET_VALUE
+          @uri = _generate_uri(@qemu_use_session == UNSET_VALUE ? false : @qemu_use_session)
+        end
 
-        # generate a URI if none is supplied
-        @uri = _generate_uri if @uri == UNSET_VALUE
+        # Set qemu_use_session based on the URI if it wasn't set by the user
+        if @qemu_use_session == UNSET_VALUE
+          uri = _parse_uri(@uri)
+          if (uri.scheme.start_with? "qemu") && (uri.path.include? "session")
+            @qemu_use_session = true
+          else
+            @qemu_use_session = false
+          end
+        end
 
         # Domain specific settings.
         @title = '' if @title == UNSET_VALUE
@@ -818,6 +844,14 @@ module VagrantPlugins
       def validate(machine)
         errors = _detected_errors
 
+        # The @uri and @qemu_use_session should not conflict
+        uri = _parse_uri(@uri)
+        if (uri.scheme.start_with? "qemu") && (uri.path.include? "session")
+          if @qemu_use_session != true
+            errors << "the URI and qemu_use_session configuration conflict: uri:'#{@uri}' qemu_use_session:'#{@qemu_use_session}'"
+          end
+        end
+
         machine.provider_config.disks.each do |disk|
           if disk[:path] && (disk[:path][0] == '/')
             errors << "absolute volume paths like '#{disk[:path]}' not yet supported"

spec/unit/config_spec.rb

@@ -18,6 +18,54 @@ describe VagrantPlugins::ProviderLibvirt::Config do
         stub_const("ENV", fake_env)
       end
 
+      context 'when LIBVIRT_DEFAULT_URI is defined' do
+        it 'should always use this value' do
+          fake_env['LIBVIRT_DEFAULT_URI'] = "custom:///custom_path"
+
+          subject.finalize!
+          expect(subject.uri).to eq("custom:///custom_path")
+          expect(subject.qemu_use_session).to eq(false)
+        end
+
+        context 'when LIBVIRT_DEFAULT_URI contains "qemu"' do
+          [
+            [
+              'set qemu_use_session if "session" present',
+              'qemu:///session',
+              true,
+            ],
+            [
+              'handle different protocol additions',
+              'qemu+ssh:///session',
+              true,
+            ],
+            [
+              'handle options before and after path',
+              'qemu://remote/session?keyfile=my_id_rsa',
+              true,
+            ],
+            [
+              'identify when session not set',
+              'qemu://remote/system',
+              false,
+            ],
+            [
+              'handle session appearing elsewhere',
+              'qemu://remote/system?keyfile=my_session_id',
+              false,
+            ],
+          ].each do |title, uri, session|
+            it "should #{title}" do
+              fake_env['LIBVIRT_DEFAULT_URI'] = uri
+
+              subject.finalize!
+              expect(subject.uri).to eq(uri)
+              expect(subject.qemu_use_session).to eq(session)
+            end
+          end
+        end
+      end
+
       context 'when @driver is defined' do
         defaults = {'id_ssh_key_file' => nil}
         [
@@ -130,11 +178,13 @@ describe VagrantPlugins::ProviderLibvirt::Config do
   end
 
   def assert_invalid
+    subject.finalize!
     errors = subject.validate(machine)
     raise "No errors: #{errors.inspect}" if errors.values.all?(&:empty?)
   end
 
   def assert_valid
+    subject.finalize!
     errors = subject.validate(machine)
     raise "Errors: #{errors.inspect}" unless errors.values.all?(&:empty?)
   end