Source: decode.go in package google.golang.org/protobuf/proto


package proto

import (
	"google.golang.org/protobuf/encoding/protowire"
	"google.golang.org/protobuf/internal/encoding/messageset"
	"google.golang.org/protobuf/internal/errors"
	"google.golang.org/protobuf/internal/flags"
	"google.golang.org/protobuf/internal/genid"
	"google.golang.org/protobuf/internal/pragma"
	"google.golang.org/protobuf/reflect/protoreflect"
	"google.golang.org/protobuf/reflect/protoregistry"
	"google.golang.org/protobuf/runtime/protoiface"
)

UnmarshalOptions configures the unmarshaler. Example usage: err := UnmarshalOptions{DiscardUnknown: true}.Unmarshal(b, m)

type UnmarshalOptions struct {
	pragma.NoUnkeyedLiterals

Merge merges the input into the destination message. The default behavior is to always reset the message before unmarshaling, unless Merge is specified.

	Merge bool

AllowPartial accepts input for messages that will result in missing required fields. If AllowPartial is false (the default), Unmarshal will return an error if there are any missing required fields.

	AllowPartial bool

If DiscardUnknown is set, unknown fields are ignored.

	DiscardUnknown bool

Resolver is used for looking up types when unmarshaling extension fields. If nil, this defaults to using protoregistry.GlobalTypes.

	Resolver interface {
		FindExtensionByName(field protoreflect.FullName) (protoreflect.ExtensionType, error)
		FindExtensionByNumber(message protoreflect.FullName, field protoreflect.FieldNumber) (protoreflect.ExtensionType, error)
	}
}

Unmarshal parses the wire-format message in b and places the result in m.

func Unmarshal(b []byte, m Message) error {
	_, err := UnmarshalOptions{}.unmarshal(b, m.ProtoReflect())
	return err
}

Unmarshal parses the wire-format message in b and places the result in m.

func (o UnmarshalOptions) Unmarshal(b []byte, m Message) error {
	_, err := o.unmarshal(b, m.ProtoReflect())
	return err
}

UnmarshalState parses a wire-format message and places the result in m. This method permits fine-grained control over the unmarshaler. Most users should use Unmarshal instead.

func (o UnmarshalOptions) UnmarshalState(in protoiface.UnmarshalInput) (protoiface.UnmarshalOutput, error) {
	return o.unmarshal(in.Buf, in.Message)
}

unmarshal is a centralized function that all unmarshal operations go through. For profiling purposes, avoid changing the name of this function or introducing other code paths for unmarshal that do not go through this.

func (o UnmarshalOptions) unmarshal(b []byte, m protoreflect.Message) (out protoiface.UnmarshalOutput, err error) {
	if o.Resolver == nil {
		o.Resolver = protoregistry.GlobalTypes
	}
	if !o.Merge {
		Reset(m.Interface())
	}
	allowPartial := o.AllowPartial
	o.Merge = true
	o.AllowPartial = true
	methods := protoMethods(m)
	if methods != nil && methods.Unmarshal != nil &&
		!(o.DiscardUnknown && methods.Flags&protoiface.SupportUnmarshalDiscardUnknown == 0) {
		in := protoiface.UnmarshalInput{
			Message:  m,
			Buf:      b,
			Resolver: o.Resolver,
		}
		if o.DiscardUnknown {
			in.Flags |= protoiface.UnmarshalDiscardUnknown
		}
		out, err = methods.Unmarshal(in)
	} else {
		err = o.unmarshalMessageSlow(b, m)
	}
	if err != nil {
		return out, err
	}
	if allowPartial || (out.Flags&protoiface.UnmarshalInitialized != 0) {
		return out, nil
	}
	return out, checkInitialized(m)
}

func (o UnmarshalOptions) unmarshalMessage(b []byte, m protoreflect.Message) error {
	_, err := o.unmarshal(b, m)
	return err
}

func (o UnmarshalOptions) unmarshalMessageSlow(b []byte, m protoreflect.Message) error {
	md := m.Descriptor()
	if messageset.IsMessageSet(md) {
		return o.unmarshalMessageSet(b, m)
	}
	fields := md.Fields()

Parse the tag (field number and wire type).

		num, wtyp, tagLen := protowire.ConsumeTag(b)
		if tagLen < 0 {
			return protowire.ParseError(tagLen)
		}
		if num > protowire.MaxValidNumber {
			return errors.New("invalid field number")
		}

Find the field descriptor for this field number.

		fd := fields.ByNumber(num)
		if fd == nil && md.ExtensionRanges().Has(num) {
			extType, err := o.Resolver.FindExtensionByNumber(md.FullName(), num)
			if err != nil && err != protoregistry.NotFound {
				return errors.New("%v: unable to resolve extension %v: %v", md.FullName(), num, err)
			}
			if extType != nil {
				fd = extType.TypeDescriptor()
			}
		}
		var err error
		if fd == nil {
			err = errUnknown
		} else if flags.ProtoLegacy {
			if fd.IsWeak() && fd.Message().IsPlaceholder() {
				err = errUnknown // weak referent is not linked in
			}
		}

Parse the field value.

		var valLen int
		switch {
		case err != nil:
		case fd.IsList():
			valLen, err = o.unmarshalList(b[tagLen:], wtyp, m.Mutable(fd).List(), fd)
		case fd.IsMap():
			valLen, err = o.unmarshalMap(b[tagLen:], wtyp, m.Mutable(fd).Map(), fd)
		default:
			valLen, err = o.unmarshalSingular(b[tagLen:], wtyp, m, fd)
		}
		if err != nil {
			if err != errUnknown {
				return err
			}
			valLen = protowire.ConsumeFieldValue(num, wtyp, b[tagLen:])
			if valLen < 0 {
				return protowire.ParseError(valLen)
			}
			if !o.DiscardUnknown {
				m.SetUnknown(append(m.GetUnknown(), b[:tagLen+valLen]...))
			}
		}
		b = b[tagLen+valLen:]
	}
	return nil
}

func (o UnmarshalOptions) unmarshalSingular(b []byte, wtyp protowire.Type, m protoreflect.Message, fd protoreflect.FieldDescriptor) (n int, err error) {
	v, n, err := o.unmarshalScalar(b, wtyp, fd)
	if err != nil {
		return 0, err
	}
	switch fd.Kind() {
	case protoreflect.GroupKind, protoreflect.MessageKind:
		m2 := m.Mutable(fd).Message()
		if err := o.unmarshalMessage(v.Bytes(), m2); err != nil {
			return n, err
		}

Non-message scalars replace the previous value.

		m.Set(fd, v)
	}
	return n, nil
}

func (o UnmarshalOptions) unmarshalMap(b []byte, wtyp protowire.Type, mapv protoreflect.Map, fd protoreflect.FieldDescriptor) (n int, err error) {
	if wtyp != protowire.BytesType {
		return 0, errUnknown
	}
	b, n = protowire.ConsumeBytes(b)
	if n < 0 {
		return 0, protowire.ParseError(n)
	}
	var (
		keyField = fd.MapKey()
		valField = fd.MapValue()
		key      protoreflect.Value
		val      protoreflect.Value
		haveKey  bool
		haveVal  bool
	)
	switch valField.Kind() {
	case protoreflect.GroupKind, protoreflect.MessageKind:
		val = mapv.NewValue()

Map entries are represented as a two-element message with fields containing the key and value.

	for len(b) > 0 {
		num, wtyp, n := protowire.ConsumeTag(b)
		if n < 0 {
			return 0, protowire.ParseError(n)
		}
		if num > protowire.MaxValidNumber {
			return 0, errors.New("invalid field number")
		}
		b = b[n:]
		err = errUnknown
		switch num {
		case genid.MapEntry_Key_field_number:
			key, n, err = o.unmarshalScalar(b, wtyp, keyField)
			if err != nil {
				break
			}
			haveKey = true
		case genid.MapEntry_Value_field_number:
			var v protoreflect.Value
			v, n, err = o.unmarshalScalar(b, wtyp, valField)
			if err != nil {
				break
			}
			switch valField.Kind() {
			case protoreflect.GroupKind, protoreflect.MessageKind:
				if err := o.unmarshalMessage(v.Bytes(), val.Message()); err != nil {
					return 0, err
				}
			default:
				val = v
			}
			haveVal = true
		}
		if err == errUnknown {
			n = protowire.ConsumeFieldValue(num, wtyp, b)
			if n < 0 {
				return 0, protowire.ParseError(n)
			}
		} else if err != nil {
			return 0, err
		}
		b = b[n:]

Every map entry should have entries for key and value, but this is not strictly required.

	if !haveKey {
		key = keyField.Default()
	}
	if !haveVal {
		switch valField.Kind() {
		case protoreflect.GroupKind, protoreflect.MessageKind:
		default:
			val = valField.Default()
		}
	}
	mapv.Set(key.MapKey(), val)
	return n, nil
}

errUnknown is used internally to indicate fields which should be added to the unknown field set of a message. It is never returned from an exported function.