Zenithar · March 5, 2025 07:01 · Mar 5, 2025 · Mar 4, 2025 · Mar 4, 2025 · Mar 4, 2025
diff --git a/@janusgraph_adapter.go b/@janusgraph_adapter.go
@@ -43,6 +43,21 @@ func readString(data *[]byte, i *int) (interface{}, error) {
 	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

diff --git a/README.md b/README.md
@@ -3,6 +3,8 @@
 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
diff --git a/janusgraph_adapter.go → @janusgraph_adapter.go b/janusgraph_adapter.go → @janusgraph_adapter.go
diff --git a/@README.md → README.md b/@README.md → README.md
diff --git a/README.md → @README.md b/README.md → @README.md
diff --git a/_README.md → README.md b/_README.md → README.md
diff --git a/README.md → _README.md b/README.md → _README.md
diff --git a/README.md b/README.md
@@ -0,0 +1,8 @@
+# Custom JanusGraph type handler
+
+It registers `janusgraph.RelationIdentifier` generated by JanusGraph when trying to 
+do `path().by(elementMap())` which is raising a Serialization error.
+
+Linked to issues:
+* https://issues.apache.org/jira/browse/TINKERPOP-2802
+* https://issues.apache.org/jira/browse/TINKERPOP-2828
diff --git a/janusgraph_adapter.go b/janusgraph_adapter.go
@@ -0,0 +1,105 @@
+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
+}
+
+// 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)
+}