cmd/protoc-gen-go: unexport implementation-specific XXX fields
We modify protoc-gen-go to stop generating exported XXX fields.
The unsafe implementation is unaffected by this change since unsafe
can access fields regardless of visibility. However, for the purego
implementation, we need to respect Go visibility rules as enforced
by the reflect package.
We work around this by generating a exporter function that given
a reference to the message and the field to export, returns a reference
to the unexported field value. This exporter function is protected by
a constant such that it is not linked into the final binary in non-purego
build environment.
Updates golang/protobuf#276
Change-Id: Idf5c1f158973fa1c61187ff41440acb21c5dac94
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/185141
Reviewed-by: Damien Neil <dneil@google.com>
diff --git a/internal/impl/message.go b/internal/impl/message.go
index 82107df..ec9be4e 100644
--- a/internal/impl/message.go
+++ b/internal/impl/message.go
@@ -29,6 +29,10 @@
// Once set, this field must never be mutated.
PBType pref.MessageType
+ // Exporter must be provided in a purego environment in order to provide
+ // access to unexported fields.
+ Exporter exporter
+
// OneofWrappers is list of pointers to oneof wrapper struct types.
OneofWrappers []interface{}
@@ -51,6 +55,11 @@
extensionFieldInfos map[pref.ExtensionType]*extensionFieldInfo
}
+// exporter is a function that returns a reference to the ith field of v,
+// where v is a pointer to a struct. It returns nil if it does not support
+// exporting the requested field (e.g., already exported).
+type exporter func(v interface{}, i int) interface{}
+
var prefMessageType = reflect.TypeOf((*pref.Message)(nil)).Elem()
// getMessageInfo returns the MessageInfo (if any) for a type.
@@ -120,8 +129,8 @@
type structInfo struct {
sizecacheOffset offset
- extensionOffset offset
unknownOffset offset
+ extensionOffset offset
fieldsByNumber map[pref.FieldNumber]reflect.StructField
oneofsByName map[pref.Name]reflect.StructField
@@ -132,8 +141,8 @@
func (mi *MessageInfo) makeStructInfo(t reflect.Type) structInfo {
si := structInfo{
sizecacheOffset: invalidOffset,
- extensionOffset: invalidOffset,
unknownOffset: invalidOffset,
+ extensionOffset: invalidOffset,
fieldsByNumber: map[pref.FieldNumber]reflect.StructField{},
oneofsByName: map[pref.Name]reflect.StructField{},
@@ -141,17 +150,26 @@
oneofWrappersByNumber: map[pref.FieldNumber]reflect.Type{},
}
+ if f, _ := t.FieldByName("sizeCache"); f.Type == sizecacheType {
+ si.sizecacheOffset = offsetOf(f, mi.Exporter)
+ }
if f, _ := t.FieldByName("XXX_sizecache"); f.Type == sizecacheType {
- si.sizecacheOffset = offsetOf(f)
+ si.sizecacheOffset = offsetOf(f, mi.Exporter)
}
- if f, _ := t.FieldByName("XXX_InternalExtensions"); f.Type == extensionFieldsType {
- si.extensionOffset = offsetOf(f)
- }
- if f, _ := t.FieldByName("XXX_extensions"); f.Type == extensionFieldsType {
- si.extensionOffset = offsetOf(f)
+ if f, _ := t.FieldByName("unknownFields"); f.Type == unknownFieldsType {
+ si.unknownOffset = offsetOf(f, mi.Exporter)
}
if f, _ := t.FieldByName("XXX_unrecognized"); f.Type == unknownFieldsType {
- si.unknownOffset = offsetOf(f)
+ si.unknownOffset = offsetOf(f, mi.Exporter)
+ }
+ if f, _ := t.FieldByName("extensionFields"); f.Type == extensionFieldsType {
+ si.extensionOffset = offsetOf(f, mi.Exporter)
+ }
+ if f, _ := t.FieldByName("XXX_InternalExtensions"); f.Type == extensionFieldsType {
+ si.extensionOffset = offsetOf(f, mi.Exporter)
+ }
+ if f, _ := t.FieldByName("XXX_extensions"); f.Type == extensionFieldsType {
+ si.extensionOffset = offsetOf(f, mi.Exporter)
}
// Generate a mapping of field numbers and names to Go struct field or type.
@@ -209,15 +227,15 @@
var fi fieldInfo
switch {
case fd.ContainingOneof() != nil:
- fi = fieldInfoForOneof(fd, si.oneofsByName[fd.ContainingOneof().Name()], si.oneofWrappersByNumber[fd.Number()])
+ fi = fieldInfoForOneof(fd, si.oneofsByName[fd.ContainingOneof().Name()], mi.Exporter, si.oneofWrappersByNumber[fd.Number()])
case fd.IsMap():
- fi = fieldInfoForMap(fd, fs)
+ fi = fieldInfoForMap(fd, fs, mi.Exporter)
case fd.IsList():
- fi = fieldInfoForList(fd, fs)
+ fi = fieldInfoForList(fd, fs, mi.Exporter)
case fd.Kind() == pref.MessageKind || fd.Kind() == pref.GroupKind:
- fi = fieldInfoForMessage(fd, fs)
+ fi = fieldInfoForMessage(fd, fs, mi.Exporter)
default:
- fi = fieldInfoForScalar(fd, fs)
+ fi = fieldInfoForScalar(fd, fs, mi.Exporter)
}
mi.fields[fd.Number()] = &fi
}
@@ -225,7 +243,7 @@
mi.oneofs = map[pref.Name]*oneofInfo{}
for i := 0; i < mi.PBType.Descriptor().Oneofs().Len(); i++ {
od := mi.PBType.Descriptor().Oneofs().Get(i)
- mi.oneofs[od.Name()] = makeOneofInfo(od, si.oneofsByName[od.Name()], si.oneofWrappersByType)
+ mi.oneofs[od.Name()] = makeOneofInfo(od, si.oneofsByName[od.Name()], mi.Exporter, si.oneofWrappersByType)
}
}