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select.go
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select.go
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package pbutil
import (
"encoding/json"
"errors"
"strings"
"google.golang.org/protobuf/encoding/protojson"
"google.golang.org/protobuf/proto"
"google.golang.org/protobuf/reflect/protoreflect"
"google.golang.org/protobuf/types/known/fieldmaskpb"
"google.golang.org/protobuf/types/known/structpb"
)
var ErrBadMask = errors.New("invalid mask")
func Select(msg proto.Message, paths ...string) (*structpb.Struct, error) {
mask, err := newFieldMask(msg, paths...)
if err != nil {
return nil, err
}
msgStruct := emptyStruct()
for _, path := range mask.GetPaths() {
if err := addMessagePathToStruct(msg, path, msgStruct); err != nil {
return nil, err
}
}
return msgStruct, nil
}
func emptyStruct() *structpb.Struct {
s, _ := structpb.NewStruct(map[string]interface{}{})
return s
}
func messageStruct(msg proto.Message) (*structpb.Struct, error) {
jsonMsg, err := protojson.Marshal(msg)
if err != nil {
return nil, err
}
var mapMsg map[string]interface{}
if err := json.Unmarshal(jsonMsg, &mapMsg); err != nil {
return nil, err
}
return structpb.NewStruct(mapMsg)
}
func fieldValueToStructValue(msg protoreflect.Message, fieldName string) (*structpb.Value, error) {
field := msg.Descriptor().Fields().ByTextName(fieldName)
value := msg.Get(field)
if field.Kind() != protoreflect.MessageKind {
msgVal := value.Interface()
return structpb.NewValue(msgVal)
}
structValue, err := messageStruct(value.Message().Interface())
if err != nil {
return nil, err
}
return structpb.NewStructValue(structValue), nil
}
func newFieldMask(msg proto.Message, paths ...string) (*fieldmaskpb.FieldMask, error) {
mask, err := fieldmaskpb.New(msg, paths...)
if err != nil {
return nil, err
}
mask.Normalize()
if !mask.IsValid(msg) {
return nil, ErrBadMask
}
return mask, nil
}
func addMessagePathToStruct(msg proto.Message, path string, strct *structpb.Struct) error {
parts := strings.Split(path, ".")
leafStruct := strct
leafMessage := msg.ProtoReflect()
for _, part := range parts[:len(parts)-1] {
if _, ok := leafStruct.Fields[part]; !ok {
leafStruct.Fields[part] = structpb.NewStructValue(emptyStruct())
}
leafStruct = leafStruct.Fields[part].GetStructValue()
leafMessage = leafMessage.Get(leafMessage.Descriptor().Fields().ByTextName(part)).Message()
}
lastPart := parts[len(parts)-1]
structValue, err := fieldValueToStructValue(leafMessage, lastPart)
if err != nil {
return err
}
leafStruct.Fields[lastPart] = structValue
return nil
}