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transform.go
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transform.go
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package protoutil
import (
"google.golang.org/protobuf/proto"
"google.golang.org/protobuf/reflect/protoreflect"
"google.golang.org/protobuf/types/known/anypb"
)
// TransformFunc is a function that transforms a protobuf value into a new protobuf value.
type TransformFunc func(protoreflect.FieldDescriptor, protoreflect.Value) (protoreflect.Value, error)
// Transform takes in a protobuf message and transforms any basic values with the given function.
func Transform(msg proto.Message, f TransformFunc) (proto.Message, error) {
t := transformer{callback: f}
src := msg.ProtoReflect()
dst := src.New()
err := t.transformMessage(dst, src)
if err != nil {
return nil, err
}
return dst.Interface(), nil
}
type transformer struct {
callback TransformFunc
}
func (t transformer) transformAny(dst, src *anypb.Any) error {
msg, err := src.UnmarshalNew()
if err != nil {
return err
}
srcMsg := msg.ProtoReflect()
dstMsg := srcMsg.New()
err = t.transformMessage(dstMsg, srcMsg)
if err != nil {
return err
}
a := NewAny(dstMsg.Interface())
dst.TypeUrl = a.TypeUrl
dst.Value = a.Value
return nil
}
func (t transformer) transformList(fd protoreflect.FieldDescriptor, dst, src protoreflect.List) error {
for i, n := 0, src.Len(); i < n; i++ {
v := src.Get(i)
switch vv := v.Interface().(type) {
case protoreflect.Message:
nv := dst.NewElement()
err := t.transformMessage(nv.Message(), vv)
if err != nil {
return err
}
dst.Append(nv)
default:
nv, err := t.callback(fd, v)
if err != nil {
return err
}
dst.Append(nv)
}
}
return nil
}
func (t transformer) transformMap(fd protoreflect.FieldDescriptor, dst, src protoreflect.Map) error {
var err error
src.Range(func(k protoreflect.MapKey, v protoreflect.Value) bool {
switch vv := v.Interface().(type) {
case protoreflect.Message:
nv := dst.NewValue()
err := t.transformMessage(nv.Message(), vv)
if err != nil {
return false
}
dst.Set(k, nv)
default:
nv, err := t.callback(fd, v)
if err != nil {
return false
}
dst.Set(k, nv)
}
return true
})
return err
}
func (t transformer) transformMessage(dst, src protoreflect.Message) error {
// most of this code is based on
// https://github.com/protocolbuffers/protobuf-go/blob/v1.25.0/proto/merge.go
if srcAny, ok := src.Interface().(*anypb.Any); ok {
if dstAny, ok := dst.Interface().(*anypb.Any); ok {
return t.transformAny(dstAny, srcAny)
}
}
var err error
src.Range(func(fd protoreflect.FieldDescriptor, v protoreflect.Value) bool {
switch {
case fd.IsList():
err = t.transformList(fd, dst.Mutable(fd).List(), v.List())
if err != nil {
return false
}
case fd.IsMap():
err = t.transformMap(fd, dst.Mutable(fd).Map(), v.Map())
if err != nil {
return false
}
case fd.Message() != nil:
err = t.transformMessage(dst.Mutable(fd).Message(), v.Message())
if err != nil {
return false
}
default:
var nv protoreflect.Value
nv, err = t.callback(fd, v)
if err != nil {
return false
}
dst.Set(fd, nv)
}
return true
})
if err != nil {
return err
}
if len(src.GetUnknown()) > 0 {
dst.SetUnknown(append(dst.GetUnknown(), src.GetUnknown()...))
}
return nil
}