mongo-go-driver UUID decoder & encoder for Golang

mongo_registry.go

// This is a value (de|en)coder for the github.com/google/uuid UUID type. For best experience, register
// mongoRegistry to mongo client instance via options, e.g.
//  clientOptions := options.Client().SetRegistry(mongoRegistry)
//
// Only BSON binary subtype 0x04 is supported.
//
// Use as you please
package repository

import (
	"fmt"
	"github.com/google/uuid"
	"go.mongodb.org/mongo-driver/bson"
	"go.mongodb.org/mongo-driver/bson/bsoncodec"
	"go.mongodb.org/mongo-driver/bson/bsonrw"
	"go.mongodb.org/mongo-driver/bson/bsontype"
	"reflect"
)

var (
	tUUID   = reflect.TypeOf(uuid.UUID{})
	uuidSubtype = byte(0x04)

	mongoRegistry = bson.NewRegistryBuilder().
		RegisterTypeEncoder(tUUID, bsoncodec.ValueEncoderFunc(uuidEncodeValue)).
		RegisterTypeDecoder(tUUID, bsoncodec.ValueDecoderFunc(uuidDecodeValue)).
		Build()
)

func uuidEncodeValue(ec bsoncodec.EncodeContext, vw bsonrw.ValueWriter, val reflect.Value) error {
	if !val.IsValid() || val.Type() != tUUID {
		return bsoncodec.ValueEncoderError{Name: "uuidEncodeValue", Types: []reflect.Type{tUUID}, Received: val}
	}
	b := val.Interface().(uuid.UUID)
	return vw.WriteBinaryWithSubtype(b[:], uuidSubtype)
}

func uuidDecodeValue(dc bsoncodec.DecodeContext, vr bsonrw.ValueReader, val reflect.Value) error {
	if !val.CanSet() || val.Type() != tUUID {
		return bsoncodec.ValueDecoderError{Name: "uuidDecodeValue", Types: []reflect.Type{tUUID}, Received: val}
	}

	var data []byte
	var subtype byte
	var err error
	switch vrType := vr.Type(); vrType {
	case bsontype.Binary:
		data, subtype, err = vr.ReadBinary()
		if subtype != uuidSubtype {
			return fmt.Errorf("unsupported binary subtype %v for UUID", subtype)
		}
	case bsontype.Null:
		err = vr.ReadNull()
	case bsontype.Undefined:
		err = vr.ReadUndefined()
	default:
		return fmt.Errorf("cannot decode %v into a UUID", vrType)
	}

	if err != nil {
		return err
	}
	uuid2, err := uuid.FromBytes(data)
	if err != nil {
		return err
	}
	val.Set(reflect.ValueOf(uuid2))
	return nil
}

I'm pretty new to go lang and I am trying to create a microservice with a mongo database. I found this code linked from StackOverflow. I can see the code is then used to decode the "BSON Binary of subtype 0x00".

My question, dumb as it may be as a newbie to golang, is what data type do I put in my type definition in my model struct? Do I continue with the uuid.UUID from github.com/google/uuid?

Hi Tyrone, when using your mongo client, please make sure you are using the mongo client after you call SetRegistry() on it. You can see the comment I left at the top of the file clarifying this.

EDIT: Usually when you see subtype 0x00, it means you've supplied a byte slice (or maybe a UUID type that is represented by a byte slice) that is not recognised by mongo as any particular subtype so it defaults to 0.

Thank you very much for the code!
Any ideas on how to make the typing of the type skip when uuid is equal to uuid.Nil ?

I have tried with this code but then the document is not written to the database

func uuidEncodeValue(ec bsoncodec.EncodeContext, vw bsonrw.ValueWriter, val reflect.Value) error {
	if !val.IsValid() || val.Type() != tUUID {
		return bsoncodec.ValueEncoderError{Name: "uuidEncodeValue", Types: []reflect.Type{tUUID}, Received: val}
	}
	b := val.Interface().(uuid.UUID)

        if b == uuid.Nil {
		return nil
	}

	return vw.WriteBinaryWithSubtype(b[:], uuidSubtype)
}

Copied and replaced deprecated functions, it works like charm!! Hats off

@SupaHam Would you kindly add an explicit license to this code snippet? It's great and really useful, and I see the // Use as you please comment, thanks for that :D

But I'm just concerned that for commercial development I'm doing that comment may not be enough to say that this is clean and permitted to include. A reference to BSD or MIT license would be enough. Something like:

// Available under MIT license, see details at https://opensource.org/license/MIT