json: Add backward compatibility with VfkitMagic

The previous commits added a VfkitMagic property which for now defaults
to true for backwards compatibility with older gvproxy versions.
However, this default was not used when unmarshalling a json vm
configuration made with an older vfkit version. This could cause
unexpected issues with networking.

This commit sets VfkitMagic to true by default when unmarshalling json.

Signed-off-by: Christophe Fergeau <[email protected]>

Author: cfergeau

pkg/config/json.go

@@ -110,6 +110,9 @@ func unmarshalIgnition(rawMsg json.RawMessage) (Ignition, error) {
 func unmarshalVirtioNet(rawMsg json.RawMessage) (*VirtioNet, error) {
 	var dev virtioNetForMarshalling
 
+	// defaults to true for backwards compatibility with vfkit versions which did not have this field
+	dev.VfkitMagic = true
+
 	err := json.Unmarshal(rawMsg, &dev)
 	if err != nil {
 		return nil, err
@@ -121,6 +124,10 @@ func unmarshalVirtioNet(rawMsg json.RawMessage) (*VirtioNet, error) {
 		}
 		dev.VirtioNet.MacAddress = macAddr
 	}
+	// vfkitMagic is only useful in combination with unixSocketPath
+	if dev.UnixSocketPath == "" {
+		dev.VfkitMagic = false
+	}
 	return &dev.VirtioNet, nil
 }
 

pkg/config/json_test.go

@@ -339,6 +339,42 @@ type jsonStabilityTest struct {
 	expectedJSON  string
 }
 
+func TestVirtioNetBackwardsCompat(t *testing.T) {
+	jsonStr := `{"vcpus":3,"memoryBytes":4194304000,"bootloader":{"kind":"linuxBootloader","vmlinuzPath":"/vmlinuz","initrdPath":"/initrd","kernelCmdLine":"console=hvc0"},"devices":[{"kind":"virtionet","nat":false,"unixSocketPath":"/some/path/to/socket","macAddress":"00:11:22:33:44:55"}]}`
+
+	var unmarshalledVM VirtualMachine
+	err := json.Unmarshal([]byte(jsonStr), &unmarshalledVM)
+	require.NoError(t, err)
+
+	vm := newLinuxVM(t)
+	require.NoError(t, err)
+	dev, err := VirtioNetNew("00:11:22:33:44:55")
+	require.NoError(t, err)
+	dev.SetUnixSocketPath("/some/path/to/socket")
+	err = vm.AddDevice(dev)
+	require.NoError(t, err)
+	require.True(t, dev.VfkitMagic)
+
+	require.Equal(t, *vm, unmarshalledVM)
+
+	/* Check that the vfkitMagic default can be overridden */
+	jsonStr = `{"vcpus":3,"memoryBytes":4194304000,"bootloader":{"kind":"linuxBootloader","vmlinuzPath":"/vmlinuz","initrdPath":"/initrd","kernelCmdLine":"console=hvc0"},"devices":[{"kind":"virtionet","nat":false,"unixSocketPath":"/some/path/to/socket","macAddress":"00:11:22:33:44:55","vfkitMagic":false}]}`
+
+	err = json.Unmarshal([]byte(jsonStr), &unmarshalledVM)
+	require.NoError(t, err)
+
+	vm = newLinuxVM(t)
+	require.NoError(t, err)
+	dev, err = VirtioNetNew("00:11:22:33:44:55")
+	require.NoError(t, err)
+	dev.SetUnixSocketPath("/some/path/to/socket")
+	dev.VfkitMagic = false
+	err = vm.AddDevice(dev)
+	require.NoError(t, err)
+
+	require.Equal(t, *vm, unmarshalledVM)
+}
+
 func TestJSON(t *testing.T) {
 	t.Run("json", func(t *testing.T) {
 		for name := range jsonTests {