golang/xenlight: use struct pointers in keyed union fields

Currently, when marshalig Go types with keyed union fields, we assign the
value of the struct (e.g. DomainBuildInfoTypeUnionHvm) which implements the
interface of the keyed union field (e.g. DomainBuildInfoTypeUnion).
As-is, this means that if a populated DomainBuildInfo is marshaled to
e.g. JSON, unmarshaling back to DomainBuildInfo will fail.

When the encoding/json is unmarshaling data into a Go type, and
encounters a JSON object, it basically can either marshal the data into
an empty interface, a map, or a struct. It cannot, however, marshal data
into an interface with at least one method defined on it (e.g.
DomainBuildInfoTypeUnion). Before this check is done, however, the
decoder will check if the Go type is a pointer, and dereference it if
so. It will then use the type of this value as the "target" type.

This means that if the TypeUnion field is populated with a
DomainBuildInfoTypeUnion, the decoder will see a non-empty interface and
fail. If the TypeUnion field is populated with a
*DomainBuildInfoTypeUnionHvm, it dereferences the pointer and sees a
struct instead, allowing decoding to continue normally.

Since there does not appear to be a strict need for NOT using pointers
in these fields, update code generation to set keyed union fields to
pointers of their implementing structs.

Signed-off-by: Nick Rosbrook <rosbrookn@ainfosec.com>
Reviewed-by: George Dunlap <george.dunlap@citrix.com>

diff --git a/tools/golang/xenlight/gengotypes.py b/tools/golang/xenlight/gengotypes.py
index ef3279a910ec2602f4e6554c312e802e404f7e82..ac1cf060dd8577585f7bf4fb63302d3deeb6cff2 100644 (file)
--- a/tools/golang/xenlight/gengotypes.py
+++ b/tools/golang/xenlight/gengotypes.py
@@ -404,7 +404,7 @@ def xenlight_golang_union_from_C(ty = None, union_name = '', struct_name = ''):
         s += 'if err := {0}.fromC(xc);'.format(goname)
         s += 'err != nil {{\n return fmt.Errorf("converting field {0}: %v", err)\n}}\n'.format(goname)
 
-        s += 'x.{0} = {1}\n'.format(field_name, goname)
+        s += 'x.{0} = &{1}\n'.format(field_name, goname)
 
     # End switch statement
     s += 'default:\n'
@@ -570,7 +570,7 @@ def xenlight_golang_union_to_C(ty = None, union_name = '',
         gotype  = xenlight_golang_fmt_name(cgotype)
 
         field_name = xenlight_golang_fmt_name('{0}_union'.format(keyname))
-        s += 'tmp, ok := x.{0}.({1})\n'.format(field_name,gotype)
+        s += 'tmp, ok := x.{0}.(*{1})\n'.format(field_name,gotype)
         s += 'if !ok {\n'
         s += 'return errors.New("wrong type for union key {0}")\n'.format(keyname)
         s += '}\n'

diff --git a/tools/golang/xenlight/helpers.gen.go b/tools/golang/xenlight/helpers.gen.go
index b454b12d52fe21e499dfa2cd6591eed14dd72b12..db82537b42816bb7cc69e79eebd49552e0d8b92d 100644 (file)
--- a/tools/golang/xenlight/helpers.gen.go
+++ b/tools/golang/xenlight/helpers.gen.go
@@ -433,7 +433,7 @@ var connectionPty ChannelinfoConnectionUnionPty
 if err := connectionPty.fromC(xc);err != nil {
  return fmt.Errorf("converting field connectionPty: %v", err)
 }
-x.ConnectionUnion = connectionPty
+x.ConnectionUnion = &connectionPty
 case ChannelConnectionSocket:
 x.ConnectionUnion = nil
 case ChannelConnectionUnknown:
@@ -473,7 +473,7 @@ switch x.Connection{
 case ChannelConnectionUnknown:
 break
 case ChannelConnectionPty:
-tmp, ok := x.ConnectionUnion.(ChannelinfoConnectionUnionPty)
+tmp, ok := x.ConnectionUnion.(*ChannelinfoConnectionUnionPty)
 if !ok {
 return errors.New("wrong type for union key connection")
 }
@@ -1094,7 +1094,7 @@ var typeHvm DomainBuildInfoTypeUnionHvm
 if err := typeHvm.fromC(xc);err != nil {
  return fmt.Errorf("converting field typeHvm: %v", err)
 }
-x.TypeUnion = typeHvm
+x.TypeUnion = &typeHvm
 case DomainTypeInvalid:
 x.TypeUnion = nil
 case DomainTypePv:
@@ -1102,13 +1102,13 @@ var typePv DomainBuildInfoTypeUnionPv
 if err := typePv.fromC(xc);err != nil {
  return fmt.Errorf("converting field typePv: %v", err)
 }
-x.TypeUnion = typePv
+x.TypeUnion = &typePv
 case DomainTypePvh:
 var typePvh DomainBuildInfoTypeUnionPvh
 if err := typePvh.fromC(xc);err != nil {
  return fmt.Errorf("converting field typePvh: %v", err)
 }
-x.TypeUnion = typePvh
+x.TypeUnion = &typePvh
 default:
 return fmt.Errorf("invalid union key '%v'", x.Type)}
 x.ArchArm.GicVersion = GicVersion(xc.arch_arm.gic_version)
@@ -1427,7 +1427,7 @@ xc.tee = C.libxl_tee_type(x.Tee)
 xc._type = C.libxl_domain_type(x.Type)
 switch x.Type{
 case DomainTypeHvm:
-tmp, ok := x.TypeUnion.(DomainBuildInfoTypeUnionHvm)
+tmp, ok := x.TypeUnion.(*DomainBuildInfoTypeUnionHvm)
 if !ok {
 return errors.New("wrong type for union key type")
 }
@@ -1545,7 +1545,7 @@ hvm.mca_caps = C.uint64_t(tmp.McaCaps)
 hvmBytes := C.GoBytes(unsafe.Pointer(&hvm),C.sizeof_libxl_domain_build_info_type_union_hvm)
 copy(xc.u[:],hvmBytes)
 case DomainTypePv:
-tmp, ok := x.TypeUnion.(DomainBuildInfoTypeUnionPv)
+tmp, ok := x.TypeUnion.(*DomainBuildInfoTypeUnionPv)
 if !ok {
 return errors.New("wrong type for union key type")
 }
@@ -1570,7 +1570,7 @@ return fmt.Errorf("converting field E820Host: %v", err)
 pvBytes := C.GoBytes(unsafe.Pointer(&pv),C.sizeof_libxl_domain_build_info_type_union_pv)
 copy(xc.u[:],pvBytes)
 case DomainTypePvh:
-tmp, ok := x.TypeUnion.(DomainBuildInfoTypeUnionPvh)
+tmp, ok := x.TypeUnion.(*DomainBuildInfoTypeUnionPvh)
 if !ok {
 return errors.New("wrong type for union key type")
 }
@@ -2157,7 +2157,7 @@ var typeHostdev DeviceUsbdevTypeUnionHostdev
 if err := typeHostdev.fromC(xc);err != nil {
  return fmt.Errorf("converting field typeHostdev: %v", err)
 }
-x.TypeUnion = typeHostdev
+x.TypeUnion = &typeHostdev
 default:
 return fmt.Errorf("invalid union key '%v'", x.Type)}
 
@@ -2184,7 +2184,7 @@ xc.port = C.int(x.Port)
 xc._type = C.libxl_usbdev_type(x.Type)
 switch x.Type{
 case UsbdevTypeHostdev:
-tmp, ok := x.TypeUnion.(DeviceUsbdevTypeUnionHostdev)
+tmp, ok := x.TypeUnion.(*DeviceUsbdevTypeUnionHostdev)
 if !ok {
 return errors.New("wrong type for union key type")
 }
@@ -2375,7 +2375,7 @@ var connectionSocket DeviceChannelConnectionUnionSocket
 if err := connectionSocket.fromC(xc);err != nil {
  return fmt.Errorf("converting field connectionSocket: %v", err)
 }
-x.ConnectionUnion = connectionSocket
+x.ConnectionUnion = &connectionSocket
 case ChannelConnectionUnknown:
 x.ConnectionUnion = nil
 default:
@@ -2411,7 +2411,7 @@ break
 case ChannelConnectionPty:
 break
 case ChannelConnectionSocket:
-tmp, ok := x.ConnectionUnion.(DeviceChannelConnectionUnionSocket)
+tmp, ok := x.ConnectionUnion.(*DeviceChannelConnectionUnionSocket)
 if !ok {
 return errors.New("wrong type for union key connection")
 }
@@ -3948,7 +3948,7 @@ var typeDiskEject EventTypeUnionDiskEject
 if err := typeDiskEject.fromC(xc);err != nil {
  return fmt.Errorf("converting field typeDiskEject: %v", err)
 }
-x.TypeUnion = typeDiskEject
+x.TypeUnion = &typeDiskEject
 case EventTypeDomainCreateConsoleAvailable:
 x.TypeUnion = nil
 case EventTypeDomainDeath:
@@ -3958,13 +3958,13 @@ var typeDomainShutdown EventTypeUnionDomainShutdown
 if err := typeDomainShutdown.fromC(xc);err != nil {
  return fmt.Errorf("converting field typeDomainShutdown: %v", err)
 }
-x.TypeUnion = typeDomainShutdown
+x.TypeUnion = &typeDomainShutdown
 case EventTypeOperationComplete:
 var typeOperationComplete EventTypeUnionOperationComplete
 if err := typeOperationComplete.fromC(xc);err != nil {
  return fmt.Errorf("converting field typeOperationComplete: %v", err)
 }
-x.TypeUnion = typeOperationComplete
+x.TypeUnion = &typeOperationComplete
 default:
 return fmt.Errorf("invalid union key '%v'", x.Type)}
 
@@ -4019,7 +4019,7 @@ xc.for_user = C.uint64_t(x.ForUser)
 xc._type = C.libxl_event_type(x.Type)
 switch x.Type{
 case EventTypeDomainShutdown:
-tmp, ok := x.TypeUnion.(EventTypeUnionDomainShutdown)
+tmp, ok := x.TypeUnion.(*EventTypeUnionDomainShutdown)
 if !ok {
 return errors.New("wrong type for union key type")
 }
@@ -4030,7 +4030,7 @@ copy(xc.u[:],domain_shutdownBytes)
 case EventTypeDomainDeath:
 break
 case EventTypeDiskEject:
-tmp, ok := x.TypeUnion.(EventTypeUnionDiskEject)
+tmp, ok := x.TypeUnion.(*EventTypeUnionDiskEject)
 if !ok {
 return errors.New("wrong type for union key type")
 }
@@ -4043,7 +4043,7 @@ return fmt.Errorf("converting field Disk: %v", err)
 disk_ejectBytes := C.GoBytes(unsafe.Pointer(&disk_eject),C.sizeof_libxl_event_type_union_disk_eject)
 copy(xc.u[:],disk_ejectBytes)
 case EventTypeOperationComplete:
-tmp, ok := x.TypeUnion.(EventTypeUnionOperationComplete)
+tmp, ok := x.TypeUnion.(*EventTypeUnionOperationComplete)
 if !ok {
 return errors.New("wrong type for union key type")
 }
@@ -4118,13 +4118,13 @@ var typeCat PsrHwInfoTypeUnionCat
 if err := typeCat.fromC(xc);err != nil {
  return fmt.Errorf("converting field typeCat: %v", err)
 }
-x.TypeUnion = typeCat
+x.TypeUnion = &typeCat
 case PsrFeatTypeMba:
 var typeMba PsrHwInfoTypeUnionMba
 if err := typeMba.fromC(xc);err != nil {
  return fmt.Errorf("converting field typeMba: %v", err)
 }
-x.TypeUnion = typeMba
+x.TypeUnion = &typeMba
 default:
 return fmt.Errorf("invalid union key '%v'", x.Type)}
 
@@ -4163,7 +4163,7 @@ xc.id = C.uint32_t(x.Id)
 xc._type = C.libxl_psr_feat_type(x.Type)
 switch x.Type{
 case PsrFeatTypeCat:
-tmp, ok := x.TypeUnion.(PsrHwInfoTypeUnionCat)
+tmp, ok := x.TypeUnion.(*PsrHwInfoTypeUnionCat)
 if !ok {
 return errors.New("wrong type for union key type")
 }
@@ -4174,7 +4174,7 @@ cat.cdp_enabled = C.bool(tmp.CdpEnabled)
 catBytes := C.GoBytes(unsafe.Pointer(&cat),C.sizeof_libxl_psr_hw_info_type_union_cat)
 copy(xc.u[:],catBytes)
 case PsrFeatTypeMba:
-tmp, ok := x.TypeUnion.(PsrHwInfoTypeUnionMba)
+tmp, ok := x.TypeUnion.(*PsrHwInfoTypeUnionMba)
 if !ok {
 return errors.New("wrong type for union key type")
 }