Source: size.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/reflect/protoreflect"
	"google.golang.org/protobuf/runtime/protoiface"
)

Size returns the size in bytes of the wire-format encoding of m.

func Size(m Message) int {
	return MarshalOptions{}.Size(m)
}

Size returns the size in bytes of the wire-format encoding of m.

Treat a nil message interface as an empty message; nothing to output.

	if m == nil {
		return 0
	}

	return o.size(m.ProtoReflect())
}

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

func (o MarshalOptions) size(m protoreflect.Message) (size int) {
	methods := protoMethods(m)
	if methods != nil && methods.Size != nil {
		out := methods.Size(protoiface.SizeInput{
			Message: m,
		})
		return out.Size
	}

This is not efficient, but we don't have any choice. This case is mainly used for legacy types with a Marshal method.

		out, _ := methods.Marshal(protoiface.MarshalInput{
			Message: m,
		})
		return len(out.Buf)
	}
	return o.sizeMessageSlow(m)
}

func (o MarshalOptions) sizeMessageSlow(m protoreflect.Message) (size int) {
	if messageset.IsMessageSet(m.Descriptor()) {
		return o.sizeMessageSet(m)
	}
	m.Range(func(fd protoreflect.FieldDescriptor, v protoreflect.Value) bool {
		size += o.sizeField(fd, v)
		return true
	})
	size += len(m.GetUnknown())
	return size
}

func (o MarshalOptions) sizeField(fd protoreflect.FieldDescriptor, value protoreflect.Value) (size int) {
	num := fd.Number()
	switch {
	case fd.IsList():
		return o.sizeList(num, fd, value.List())
	case fd.IsMap():
		return o.sizeMap(num, fd, value.Map())
	default:
		return protowire.SizeTag(num) + o.sizeSingular(num, fd.Kind(), value)
	}
}

func (o MarshalOptions) sizeList(num protowire.Number, fd protoreflect.FieldDescriptor, list protoreflect.List) (size int) {
	if fd.IsPacked() && list.Len() > 0 {
		content := 0
		for i, llen := 0, list.Len(); i < llen; i++ {
			content += o.sizeSingular(num, fd.Kind(), list.Get(i))
		}
		return protowire.SizeTag(num) + protowire.SizeBytes(content)
	}

	for i, llen := 0, list.Len(); i < llen; i++ {
		size += protowire.SizeTag(num) + o.sizeSingular(num, fd.Kind(), list.Get(i))
	}
	return size
}

func (o MarshalOptions) sizeMap(num protowire.Number, fd protoreflect.FieldDescriptor, mapv protoreflect.Map) (size int) {
	mapv.Range(func(key protoreflect.MapKey, value protoreflect.Value) bool {
		size += protowire.SizeTag(num)
		size += protowire.SizeBytes(o.sizeField(fd.MapKey(), key.Value()) + o.sizeField(fd.MapValue(), value))
		return true
	})
	return size