Source: discard.go in package github.com/golang/protobuf/proto


package proto

import (
	"google.golang.org/protobuf/reflect/protoreflect"
)

DiscardUnknown recursively discards all unknown fields from this message and all embedded messages. When unmarshaling a message with unrecognized fields, the tags and values of such fields are preserved in the Message. This allows a later call to marshal to be able to produce a message that continues to have those unrecognized fields. To avoid this, DiscardUnknown is used to explicitly clear the unknown fields after unmarshaling.

func DiscardUnknown(m Message) {
	if m != nil {
		discardUnknown(MessageReflect(m))
	}
}

func discardUnknown(m protoreflect.Message) {
	m.Range(func(fd protoreflect.FieldDescriptor, val protoreflect.Value) bool {

Handle singular message.

		case fd.Cardinality() != protoreflect.Repeated:
			if fd.Message() != nil {
				discardUnknown(m.Get(fd).Message())

Handle list of messages.

		case fd.IsList():
			if fd.Message() != nil {
				ls := m.Get(fd).List()
				for i := 0; i < ls.Len(); i++ {
					discardUnknown(ls.Get(i).Message())
				}

Handle map of messages.

		case fd.IsMap():
			if fd.MapValue().Message() != nil {
				ms := m.Get(fd).Map()
				ms.Range(func(_ protoreflect.MapKey, v protoreflect.Value) bool {
					discardUnknown(v.Message())
					return true
				})
			}
		}
		return true
	})

Discard unknown fields.

	if len(m.GetUnknown()) > 0 {
		m.SetUnknown(nil)
	}