Custom JanusGraph specific type handler for TinkerPop Gremlin Go driver.

@janusgraph_adapter.go

package gremlin

import (
	"encoding/binary"
	"errors"
	"fmt"

	gremlingo "github.com/apache/tinkerpop/gremlin-go/v3/driver"
)

const (
	valueFlagNone byte = 0
)

func readTemp(data *[]byte, i *int, len int) *[]byte {
	tmp := make([]byte, len)
	for j := 0; j < len; j++ {
		tmp[j] = (*data)[j+*i]
	}
	*i += len
	return &tmp
}

func readUint32Safe(data *[]byte, i *int) uint32 {
	return binary.BigEndian.Uint32(*readTemp(data, i, 4))
}

func readByteSafe(data *[]byte, i *int) byte {
	*i++
	return (*data)[*i-1]
}

func readLongSafe(data *[]byte, i *int) int64 {
	return int64(binary.BigEndian.Uint64(*readTemp(data, i, 8)))
}

func readString(data *[]byte, i *int) (interface{}, error) {
	sz := int(readUint32Safe(data, i))
	if sz == 0 {
		return "", nil
	}
	*i += sz
	return string((*data)[*i-sz : *i]), nil
}

// janusgraphRelationIdentifierReader reads a JanusGraph relation identifier from the given byte slice.
// It expects the data to be in a specific format and returns a map containing the relation identifier details.
//
// The format is as follows:
// - 4 bytes: custom data type (0x1001)
// - 1 byte: value flag (0x00)
// - 1 byte: outVertexId type (0x00 for long, 0x01 for string)
//   - if 0x00: 8 bytes: outVertexId (long)
//   - if 0x01: 4 bytes: outVertexId length, followed by outVertexId string
// - 8 bytes: typeId (long)
// - 8 bytes: relationId (long)
// - 1 byte: inVertexId type (0x00 for long, 0x01 for string)
//   - if 0x00: 8 bytes: inVertexId (long)
//   - if 0x01: 4 bytes: inVertexId length, followed by inVertexId string
//
// https://github.com/JanusGraph/janusgraph-python/blob/cd812fc0614047d25a2cabd143902806a74a8465/janusgraph_python/structure/io/graphbinaryV1.py#L133
func janusgraphRelationIdentifierReader(data *[]byte, i *int) (interface{}, error) {
	const relationIdentifierType = 0x1001
	const (
		longMarker   = 0
		stringMarker = 1
	)

	// expect type code
	customDataTyp := readUint32Safe(data, i)
	if customDataTyp != relationIdentifierType {
		return nil, fmt.Errorf("unknown type code. got 0x%x, expected 0x%x", customDataTyp, relationIdentifierType)
	}

	// value flag, expect this to be non-nullable
	if readByteSafe(data, i) != valueFlagNone {
		return nil, errors.New("expected non-null value")
	}

	// outVertexId
	var (
		outVertexID any
		err         error
	)
	if readByteSafe(data, i) == stringMarker {
		outVertexID, err = readString(data, i)
		if err != nil {
			return nil, fmt.Errorf("unable to read outVertexId: %w", err)
		}
	} else {
		outVertexID = readLongSafe(data, i)
	}

	typeID := readLongSafe(data, i)
	// relationID
	relationID := readLongSafe(data, i)

	// inVertexId
	var inVertexID any
	if readByteSafe(data, i) == stringMarker {
		inVertexID, err = readString(data, i)
		if err != nil {
			return nil, fmt.Errorf("unable to read inVertexId: %w", err)
		}
	} else {
		inVertexID = readLongSafe(data, i)
	}

	return map[string]any{
		"outVertexId": outVertexID,
		"typeId":      typeID,
		"relationId":  relationID,
		"inVertexId":  inVertexID,
	}, nil
}

func init() {
	// https://issues.apache.org/jira/browse/TINKERPOP-2802
	gremlingo.RegisterCustomTypeReader("janusgraph.RelationIdentifier", janusgraphRelationIdentifierReader)
}

README.md

Custom JanusGraph type handler

It registers janusgraph.RelationIdentifier generated by JanusGraph when trying to do path().by(elementMap()) which is raising a Serialization error.

E0409: unknown custom data type to deserialize janusgraph.RelationIdentifier

Linked to issues:

• https://issues.apache.org/jira/browse/TINKERPOP-2802
• https://issues.apache.org/jira/browse/TINKERPOP-2828