proto/message_set.go

// Copyright 2010 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 proto

/*
 * Support for message sets.
 */

import (
	"errors"

	"github.com/golang/protobuf/v2/reflect/protoreflect"
)

// errNoMessageTypeID occurs when a protocol buffer does not have a message type ID.
// A message type ID is required for storing a protocol buffer in a message set.
var errNoMessageTypeID = errors.New("proto does not have a message type ID")

// The first two types (_MessageSet_Item and messageSet)
// model what the protocol compiler produces for the following protocol message:
//   message MessageSet {
//     repeated group Item = 1 {
//       required int32 type_id = 2;
//       required string message = 3;
//     };
//   }
// That is the MessageSet wire format. We can't use a proto to generate these
// because that would introduce a circular dependency between it and this package.

type _MessageSet_Item struct {
	TypeId  *int32 `protobuf:"varint,2,req,name=type_id"`
	Message []byte `protobuf:"bytes,3,req,name=message"`
}

type messageSet struct {
	Item             []*_MessageSet_Item `protobuf:"group,1,rep"`
	XXX_unrecognized []byte
	// TODO: caching?
}

// Make sure messageSet is a Message.
var _ Message = (*messageSet)(nil)

// messageTypeIder is an interface satisfied by a protocol buffer type
// that may be stored in a MessageSet.
type messageTypeIder interface {
	MessageTypeId() int32
}

func (ms *messageSet) find(pb Message) *_MessageSet_Item {
	mti, ok := pb.(messageTypeIder)
	if !ok {
		return nil
	}
	id := mti.MessageTypeId()
	for _, item := range ms.Item {
		if *item.TypeId == id {
			return item
		}
	}
	return nil
}

func (ms *messageSet) Has(pb Message) bool {
	return ms.find(pb) != nil
}

func (ms *messageSet) Unmarshal(pb Message) error {
	if item := ms.find(pb); item != nil {
		return Unmarshal(item.Message, pb)
	}
	if _, ok := pb.(messageTypeIder); !ok {
		return errNoMessageTypeID
	}
	return nil // TODO: return error instead?
}

func (ms *messageSet) Marshal(pb Message) error {
	msg, err := Marshal(pb)
	if err != nil {
		return err
	}
	if item := ms.find(pb); item != nil {
		// reuse existing item
		item.Message = msg
		return nil
	}

	mti, ok := pb.(messageTypeIder)
	if !ok {
		return errNoMessageTypeID
	}

	mtid := mti.MessageTypeId()
	ms.Item = append(ms.Item, &_MessageSet_Item{
		TypeId:  &mtid,
		Message: msg,
	})
	return nil
}

func (ms *messageSet) Reset()         { *ms = messageSet{} }
func (ms *messageSet) String() string { return CompactTextString(ms) }
func (*messageSet) ProtoMessage()     {}

// Support for the message_set_wire_format message option.

func skipVarint(buf []byte) []byte {
	i := 0
	for ; buf[i]&0x80 != 0; i++ {
	}
	return buf[i+1:]
}

// unmarshalMessageSet decodes the extension map encoded in buf in the message set wire format.
// It is called by Unmarshal methods on protocol buffer messages with the message_set_wire_format option.
func unmarshalMessageSet(buf []byte, exts interface{}) error {
	m := extensionFieldsOf(exts)

	ms := new(messageSet)
	if err := Unmarshal(buf, ms); err != nil {
		return err
	}
	for _, item := range ms.Item {
		id := protoreflect.FieldNumber(*item.TypeId)
		msg := item.Message

		// Restore wire type and field number varint, plus length varint.
		// Be careful to preserve duplicate items.
		b := EncodeVarint(uint64(id)<<3 | WireBytes)
		if m.Has(id) {
			ext := m.Get(id)

			// Existing data; rip off the tag and length varint
			// so we join the new data correctly.
			// We can assume that ext.Raw is set because we are unmarshaling.
			o := ext.Raw[len(b):]   // skip wire type and field number
			_, n := DecodeVarint(o) // calculate length of length varint
			o = o[n:]               // skip length varint
			msg = append(o, msg...) // join old data and new data
		}
		b = append(b, EncodeVarint(uint64(len(msg)))...)
		b = append(b, msg...)

		m.Set(id, Extension{Raw: b})
	}
	return nil
}