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/message.go b/internal/legacy/message.go
new file mode 100644
index 0000000..a81bb2e
--- /dev/null
+++ b/internal/legacy/message.go
@@ -0,0 +1,308 @@
+// 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"
+ "strings"
+ "sync"
+ "unicode"
+
+ descriptorV1 "github.com/golang/protobuf/protoc-gen-go/descriptor"
+ ptag "github.com/golang/protobuf/v2/internal/encoding/tag"
+ pimpl "github.com/golang/protobuf/v2/internal/impl"
+ scalar "github.com/golang/protobuf/v2/internal/scalar"
+ pref "github.com/golang/protobuf/v2/reflect/protoreflect"
+ ptype "github.com/golang/protobuf/v2/reflect/prototype"
+)
+
+// legacyWrapMessage wraps v as a protoreflect.ProtoMessage,
+// where v must be a *struct kind and not implement the v2 API already.
+func legacyWrapMessage(v reflect.Value) pref.ProtoMessage {
+ mt := legacyLoadMessageType(v.Type())
+ return mt.MessageOf(v.Interface()).Interface()
+}
+
+var messageTypeCache sync.Map // map[reflect.Type]*MessageType
+
+// legacyLoadMessageType dynamically loads a *MessageType for t,
+// where t must be a *struct kind and not implement the v2 API already.
+func legacyLoadMessageType(t reflect.Type) *pimpl.MessageType {
+ // Fast-path: check if a MessageType is cached for this concrete type.
+ if mt, ok := messageTypeCache.Load(t); ok {
+ return mt.(*pimpl.MessageType)
+ }
+
+ // Slow-path: derive message descriptor and initialize MessageType.
+ md := legacyLoadMessageDesc(t)
+ mt := new(pimpl.MessageType)
+ mt.Type = ptype.GoMessage(md, func(pref.MessageType) pref.ProtoMessage {
+ p := reflect.New(t.Elem()).Interface()
+ return mt.MessageOf(p).Interface()
+ })
+ messageTypeCache.Store(t, mt)
+ return mt
+}
+
+var messageDescCache sync.Map // map[reflect.Type]protoreflect.MessageDescriptor
+
+// legacyLoadMessageDesc returns an MessageDescriptor derived from the Go type,
+// which must be a *struct kind and not implement the v2 API already.
+func legacyLoadMessageDesc(t reflect.Type) pref.MessageDescriptor {
+ return messageDescSet{}.Load(t)
+}
+
+type messageDescSet struct {
+ visited map[reflect.Type]*ptype.StandaloneMessage
+ descs []*ptype.StandaloneMessage
+ types []reflect.Type
+}
+
+func (ms messageDescSet) Load(t reflect.Type) pref.MessageDescriptor {
+ // Fast-path: check if a MessageDescriptor is cached for this concrete type.
+ if mi, ok := messageDescCache.Load(t); ok {
+ return mi.(pref.MessageDescriptor)
+ }
+
+ // Slow-path: initialize MessageDescriptor from the Go type.
+
+ // Processing t recursively populates descs and types with all sub-messages.
+ // The descriptor for the first type is guaranteed to be at the front.
+ ms.processMessage(t)
+
+ // Within a proto file it is possible for cyclic dependencies to exist
+ // between multiple message types. When these cases arise, the set of
+ // message descriptors must be created together.
+ mds, err := ptype.NewMessages(ms.descs)
+ if err != nil {
+ panic(err)
+ }
+ for i, md := range mds {
+ // Protobuf semantics represents map entries under-the-hood as
+ // pseudo-messages (has a descriptor, but no generated Go type).
+ // Avoid caching these fake messages.
+ if t := ms.types[i]; t.Kind() != reflect.Map {
+ messageDescCache.Store(t, md)
+ }
+ }
+ return mds[0]
+}
+
+func (ms *messageDescSet) processMessage(t reflect.Type) pref.MessageDescriptor {
+ // Fast-path: Obtain a placeholder if the message is already processed.
+ if m, ok := ms.visited[t]; ok {
+ return ptype.PlaceholderMessage(m.FullName)
+ }
+
+ // Slow-path: Walk over the struct fields to derive the message descriptor.
+ if t.Kind() != reflect.Ptr || t.Elem().Kind() != reflect.Struct || t.Elem().PkgPath() == "" {
+ panic(fmt.Sprintf("got %v, want named *struct kind", t))
+ }
+
+ // Derive name and syntax from the raw descriptor.
+ m := new(ptype.StandaloneMessage)
+ mv := reflect.New(t.Elem()).Interface()
+ if _, ok := mv.(pref.ProtoMessage); ok {
+ panic(fmt.Sprintf("%v already implements proto.Message", t))
+ }
+ if md, ok := mv.(legacyMessage); ok {
+ b, idxs := md.Descriptor()
+ fd := legacyLoadFileDesc(b)
+
+ // Derive syntax.
+ switch fd.GetSyntax() {
+ case "proto2", "":
+ m.Syntax = pref.Proto2
+ case "proto3":
+ m.Syntax = pref.Proto3
+ }
+
+ // Derive full name.
+ md := fd.MessageType[idxs[0]]
+ m.FullName = pref.FullName(fd.GetPackage()).Append(pref.Name(md.GetName()))
+ for _, i := range idxs[1:] {
+ md = md.NestedType[i]
+ m.FullName = m.FullName.Append(pref.Name(md.GetName()))
+ }
+ } else {
+ // If the type does not implement legacyMessage, then the only way to
+ // obtain the full name is through the registry. However, this is
+ // unreliable as some generated messages register with a fork of
+ // golang/protobuf, so the registry may not have this information.
+ m.FullName = deriveFullName(t.Elem())
+ m.Syntax = pref.Proto2
+
+ // Try to determine if the message is using proto3 by checking scalars.
+ for i := 0; i < t.Elem().NumField(); i++ {
+ f := t.Elem().Field(i)
+ if tag := f.Tag.Get("protobuf"); tag != "" {
+ switch f.Type.Kind() {
+ case reflect.Bool, reflect.Int32, reflect.Int64, reflect.Uint32, reflect.Uint64, reflect.Float32, reflect.Float64, reflect.String:
+ m.Syntax = pref.Proto3
+ }
+ for _, s := range strings.Split(tag, ",") {
+ if s == "proto3" {
+ m.Syntax = pref.Proto3
+ }
+ }
+ }
+ }
+ }
+ ms.visit(m, t)
+
+ // Obtain a list of oneof wrapper types.
+ var oneofWrappers []reflect.Type
+ if fn, ok := t.MethodByName("XXX_OneofFuncs"); ok {
+ vs := fn.Func.Call([]reflect.Value{reflect.Zero(fn.Type.In(0))})[3]
+ for _, v := range vs.Interface().([]interface{}) {
+ oneofWrappers = append(oneofWrappers, reflect.TypeOf(v))
+ }
+ }
+ if fn, ok := t.MethodByName("XXX_OneofWrappers"); ok {
+ vs := fn.Func.Call([]reflect.Value{reflect.Zero(fn.Type.In(0))})[0]
+ for _, v := range vs.Interface().([]interface{}) {
+ oneofWrappers = append(oneofWrappers, reflect.TypeOf(v))
+ }
+ }
+
+ // Obtain a list of the extension ranges.
+ if fn, ok := t.MethodByName("ExtensionRangeArray"); ok {
+ vs := fn.Func.Call([]reflect.Value{reflect.Zero(fn.Type.In(0))})[0]
+ for i := 0; i < vs.Len(); i++ {
+ v := vs.Index(i)
+ m.ExtensionRanges = append(m.ExtensionRanges, [2]pref.FieldNumber{
+ pref.FieldNumber(v.FieldByName("Start").Int()),
+ pref.FieldNumber(v.FieldByName("End").Int() + 1),
+ })
+ }
+ }
+
+ // Derive the message fields by inspecting the struct fields.
+ for i := 0; i < t.Elem().NumField(); i++ {
+ f := t.Elem().Field(i)
+ if tag := f.Tag.Get("protobuf"); tag != "" {
+ tagKey := f.Tag.Get("protobuf_key")
+ tagVal := f.Tag.Get("protobuf_val")
+ m.Fields = append(m.Fields, ms.parseField(tag, tagKey, tagVal, f.Type, m))
+ }
+ if tag := f.Tag.Get("protobuf_oneof"); tag != "" {
+ name := pref.Name(tag)
+ m.Oneofs = append(m.Oneofs, ptype.Oneof{Name: name})
+ for _, t := range oneofWrappers {
+ if t.Implements(f.Type) {
+ f := t.Elem().Field(0)
+ if tag := f.Tag.Get("protobuf"); tag != "" {
+ ft := ms.parseField(tag, "", "", f.Type, m)
+ ft.OneofName = name
+ m.Fields = append(m.Fields, ft)
+ }
+ }
+ }
+ }
+ }
+
+ return ptype.PlaceholderMessage(m.FullName)
+}
+
+func (ms *messageDescSet) parseField(tag, tagKey, tagVal string, goType reflect.Type, parent *ptype.StandaloneMessage) ptype.Field {
+ t := goType
+ 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(tag, t)
+
+ // Populate EnumType and MessageType.
+ if f.EnumType == nil && f.Kind == pref.EnumKind {
+ if ev, ok := reflect.Zero(t).Interface().(pref.ProtoEnum); ok {
+ f.EnumType = ev.ProtoReflect().Type()
+ } else {
+ f.EnumType = legacyLoadEnumDesc(t)
+ }
+ }
+ if f.MessageType == nil && (f.Kind == pref.MessageKind || f.Kind == pref.GroupKind) {
+ if mv, ok := reflect.Zero(t).Interface().(pref.ProtoMessage); ok {
+ f.MessageType = mv.ProtoReflect().Type()
+ } else if t.Kind() == reflect.Map {
+ m := &ptype.StandaloneMessage{
+ Syntax: parent.Syntax,
+ FullName: parent.FullName.Append(mapEntryName(f.Name)),
+ Options: &descriptorV1.MessageOptions{MapEntry: scalar.Bool(true)},
+ Fields: []ptype.Field{
+ ms.parseField(tagKey, "", "", t.Key(), nil),
+ ms.parseField(tagVal, "", "", t.Elem(), nil),
+ },
+ }
+ ms.visit(m, t)
+ f.MessageType = ptype.PlaceholderMessage(m.FullName)
+ } else if mv, ok := messageDescCache.Load(t); ok {
+ f.MessageType = mv.(pref.MessageDescriptor)
+ } else {
+ f.MessageType = ms.processMessage(t)
+ }
+ }
+ return f
+}
+
+func (ms *messageDescSet) visit(m *ptype.StandaloneMessage, t reflect.Type) {
+ if ms.visited == nil {
+ ms.visited = make(map[reflect.Type]*ptype.StandaloneMessage)
+ }
+ if t.Kind() != reflect.Map {
+ ms.visited[t] = m
+ }
+ ms.descs = append(ms.descs, m)
+ ms.types = append(ms.types, t)
+}
+
+// deriveFullName derives a fully qualified protobuf name for the given Go type
+// The provided name is not guaranteed to be stable nor universally unique.
+// It should be sufficiently unique within a program.
+func deriveFullName(t reflect.Type) pref.FullName {
+ sanitize := func(r rune) rune {
+ switch {
+ case r == '/':
+ return '.'
+ case 'a' <= r && r <= 'z', 'A' <= r && r <= 'Z', '0' <= r && r <= '9':
+ return r
+ default:
+ return '_'
+ }
+ }
+ prefix := strings.Map(sanitize, t.PkgPath())
+ suffix := strings.Map(sanitize, t.Name())
+ if suffix == "" {
+ suffix = fmt.Sprintf("UnknownX%X", reflect.ValueOf(t).Pointer())
+ }
+
+ ss := append(strings.Split(prefix, "."), suffix)
+ for i, s := range ss {
+ if s == "" || ('0' <= s[0] && s[0] <= '9') {
+ ss[i] = "x" + s
+ }
+ }
+ return pref.FullName(strings.Join(ss, "."))
+}
+
+// mapEntryName derives the message name for a map field of a given name.
+// This is identical to MapEntryName from parser.cc in the protoc source.
+func mapEntryName(s pref.Name) pref.Name {
+ var b []byte
+ nextUpper := true
+ for i := 0; i < len(s); i++ {
+ if c := s[i]; c == '_' {
+ nextUpper = true
+ } else {
+ if nextUpper {
+ c = byte(unicode.ToUpper(rune(c)))
+ nextUpper = false
+ }
+ b = append(b, c)
+ }
+ }
+ return pref.Name(append(b, "Entry"...))
+}