internal/legacy: extract legacy support out from the impl package
The impl package currently supports wrapping legacy v1 enums and messages
so that they implement the v2 reflective APIs. This functionality is necessary
for v1 and v2 to interoperate. However, the existence of this functionality
presents several problems:
* A significant portion of the complexity in impl is for legacy wrapping.
* This complexity is linked into a Go binary even if all the other messages
in the binary natively support v2 reflection.
* It presents a cyclic dependency when trying to generate descriptor proto.
Suppose you are generating descriptor.proto. The generated code would want to
depend on the impl package because impl is the runtime implementation for
protobuf messages. However, impl currently depends depends on descriptor in
order to wrap legacy enum and messages since it needs the ability to dynamically
create new protobuf descriptor types. In the case of descriptor.proto, it would
presumably be generated with native reflection support, so the legacy wrapping
logic is unneccessary.
To break the dependency of impl on descriptor, we move the legacy support logic
to a different package and instead add hooks in impl so that legacy support could
be dynamically registered at runtime. This is dependency injection.
Change-Id: I01a582908ed5629993f6699e9bf2f4bee93857a4
Reviewed-on: https://go-review.googlesource.com/c/151877
Reviewed-by: Herbie Ong <herbie@google.com>
diff --git a/internal/legacy/extension.go b/internal/legacy/extension.go
new file mode 100644
index 0000000..700bc43
--- /dev/null
+++ b/internal/legacy/extension.go
@@ -0,0 +1,206 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package legacy
+
+import (
+ "fmt"
+ "reflect"
+
+ papi "github.com/golang/protobuf/protoapi"
+ ptag "github.com/golang/protobuf/v2/internal/encoding/tag"
+ pimpl "github.com/golang/protobuf/v2/internal/impl"
+ pvalue "github.com/golang/protobuf/v2/internal/value"
+ pref "github.com/golang/protobuf/v2/reflect/protoreflect"
+ ptype "github.com/golang/protobuf/v2/reflect/prototype"
+)
+
+func legacyExtensionDescFromType(t pref.ExtensionType) *papi.ExtensionDesc {
+ if t, ok := t.(dualExtensionType); ok {
+ return t.desc
+ }
+
+ // Determine the parent type if possible.
+ var parent papi.Message
+ if mt, ok := t.ExtendedType().(pref.MessageType); ok {
+ // Create a new parent message and unwrap it if possible.
+ mv := mt.New()
+ t := reflect.TypeOf(mv)
+ if mv, ok := mv.(pvalue.Unwrapper); ok {
+ t = reflect.TypeOf(mv.ProtoUnwrap())
+ }
+
+ // Check whether the message implements the legacy v1 Message interface.
+ mz := reflect.Zero(t).Interface()
+ if mz, ok := mz.(papi.Message); ok {
+ parent = mz
+ }
+ }
+
+ // Determine the v1 extension type, which is unfortunately not the same as
+ // the v2 ExtensionType.GoType.
+ extType := t.GoType()
+ switch extType.Kind() {
+ case reflect.Bool, reflect.Int32, reflect.Int64, reflect.Uint32, reflect.Uint64, reflect.Float32, reflect.Float64, reflect.String:
+ extType = reflect.PtrTo(extType) // T -> *T for singular scalar fields
+ case reflect.Ptr:
+ if extType.Elem().Kind() == reflect.Slice {
+ extType = extType.Elem() // *[]T -> []T for repeated fields
+ }
+ }
+
+ // Reconstruct the legacy enum full name, which is an odd mixture of the
+ // proto package name with the Go type name.
+ var enumName string
+ if t.Kind() == pref.EnumKind {
+ // Derive Go type name.
+ // For legacy enums, unwrap the wrapper to get the underlying Go type.
+ et := t.EnumType().(pref.EnumType)
+ var ev interface{} = et.New(0)
+ if u, ok := ev.(pvalue.Unwrapper); ok {
+ ev = u.ProtoUnwrap()
+ }
+ enumName = reflect.TypeOf(ev).Name()
+
+ // Derive the proto package name.
+ // For legacy enums, obtain the proto package from the raw descriptor.
+ var protoPkg string
+ if fd := parentFileDescriptor(et); fd != nil {
+ protoPkg = string(fd.Package())
+ }
+ if ed, ok := ev.(legacyEnum); ok && protoPkg == "" {
+ b, _ := ed.EnumDescriptor()
+ protoPkg = legacyLoadFileDesc(b).GetPackage()
+ }
+
+ if protoPkg != "" {
+ enumName = protoPkg + "." + enumName
+ }
+ }
+
+ // Derive the proto file that the extension was declared within.
+ var filename string
+ if fd := parentFileDescriptor(t); fd != nil {
+ filename = fd.Path()
+ }
+
+ // Construct and return a v1 ExtensionDesc.
+ return &papi.ExtensionDesc{
+ Type: t,
+ ExtendedType: parent,
+ ExtensionType: reflect.Zero(extType).Interface(),
+ Field: int32(t.Number()),
+ Name: string(t.FullName()),
+ Tag: ptag.Marshal(t, enumName),
+ Filename: filename,
+ }
+}
+
+func legacyExtensionTypeFromDesc(d *papi.ExtensionDesc) pref.ExtensionType {
+ if d.Type != nil {
+ return dualExtensionType{d.Type, d}
+ }
+
+ // Derive basic field information from the struct tag.
+ t := reflect.TypeOf(d.ExtensionType)
+ isOptional := t.Kind() == reflect.Ptr && t.Elem().Kind() != reflect.Struct
+ isRepeated := t.Kind() == reflect.Slice && t.Elem().Kind() != reflect.Uint8
+ if isOptional || isRepeated {
+ t = t.Elem()
+ }
+ f := ptag.Unmarshal(d.Tag, t)
+
+ // Construct a v2 ExtensionType.
+ conv := pvalue.NewLegacyConverter(t, f.Kind, Export{})
+ xd, err := ptype.NewExtension(&ptype.StandaloneExtension{
+ FullName: pref.FullName(d.Name),
+ Number: pref.FieldNumber(d.Field),
+ Cardinality: f.Cardinality,
+ Kind: f.Kind,
+ Default: f.Default,
+ Options: f.Options,
+ EnumType: conv.EnumType,
+ MessageType: conv.MessageType,
+ ExtendedType: Export{}.MessageTypeOf(d.ExtendedType),
+ })
+ if err != nil {
+ panic(err)
+ }
+ xt := pimpl.Export{}.ExtensionTypeOf(xd, reflect.Zero(t).Interface())
+ return dualExtensionType{xt, d}
+}
+
+type dualExtensionType struct {
+ pref.ExtensionType
+ desc *papi.ExtensionDesc
+}
+
+// TODO: Provide custom stringer for dualExtensionType.
+
+// legacyExtensionTypeOf returns a protoreflect.ExtensionType where the GoType
+// is the underlying v1 Go type instead of the wrapper types used to present
+// v1 Go types as if they satisfied the v2 API.
+//
+// This function is only valid if xd.Kind is an enum or message.
+func legacyExtensionTypeOf(xd pref.ExtensionDescriptor, t reflect.Type) pref.ExtensionType {
+ // Step 1: Create an ExtensionType where GoType is the wrapper type.
+ conv := pvalue.NewLegacyConverter(t, xd.Kind(), Export{})
+ xt := ptype.GoExtension(xd, conv.EnumType, conv.MessageType)
+
+ // Step 2: Wrap ExtensionType such that GoType presents the legacy Go type.
+ xt2 := &legacyExtensionType{ExtensionType: xt}
+ if xd.Cardinality() != pref.Repeated {
+ xt2.typ = t
+ xt2.new = func() interface{} {
+ return xt.New().(pvalue.Unwrapper).ProtoUnwrap()
+ }
+ xt2.valueOf = func(v interface{}) pref.Value {
+ if reflect.TypeOf(v) != xt2.typ {
+ panic(fmt.Sprintf("invalid type: got %T, want %v", v, xt2.typ))
+ }
+ if xd.Kind() == pref.EnumKind {
+ return xt.ValueOf(Export{}.EnumOf(v))
+ } else {
+ return xt.ValueOf(Export{}.MessageOf(v))
+ }
+ }
+ xt2.interfaceOf = func(v pref.Value) interface{} {
+ return xt.InterfaceOf(v).(pvalue.Unwrapper).ProtoUnwrap()
+ }
+ } else {
+ xt2.typ = reflect.PtrTo(reflect.SliceOf(t))
+ xt2.new = func() interface{} {
+ return reflect.New(xt2.typ.Elem()).Interface()
+ }
+ xt2.valueOf = func(v interface{}) pref.Value {
+ if reflect.TypeOf(v) != xt2.typ {
+ panic(fmt.Sprintf("invalid type: got %T, want %v", v, xt2.typ))
+ }
+ return pref.ValueOf(pvalue.ListOf(v, conv))
+ }
+ xt2.interfaceOf = func(pv pref.Value) interface{} {
+ v := pv.List().(pvalue.Unwrapper).ProtoUnwrap()
+ if reflect.TypeOf(v) != xt2.typ {
+ panic(fmt.Sprintf("invalid type: got %T, want %v", v, xt2.typ))
+ }
+ return v
+ }
+ }
+ return xt2
+}
+
+type legacyExtensionType struct {
+ pref.ExtensionType
+ typ reflect.Type
+ new func() interface{}
+ valueOf func(interface{}) pref.Value
+ interfaceOf func(pref.Value) interface{}
+}
+
+func (x *legacyExtensionType) GoType() reflect.Type { return x.typ }
+func (x *legacyExtensionType) New() interface{} { return x.new() }
+func (x *legacyExtensionType) ValueOf(v interface{}) pref.Value { return x.valueOf(v) }
+func (x *legacyExtensionType) InterfaceOf(v pref.Value) interface{} { return x.interfaceOf(v) }
+
+// TODO: Provide custom stringer with the new GoType.