Unable to specify value for JANUSGRAPH_RELATION_DELIMITER when creating JanusGraphGraphSONMessageSerializer

[matthall88]

JanusGraph server allows users to specify an environment variable (JANUSGRAPH_RELATION_DELIMITER) to override the default relation delimiter char.
If this is used then the JanusGraphGraphSONMessageSerializer throws an exception when (de)serializing a response that contains relationships.

  System.ArgumentException: Not a valid relation identifier: odxce:Sfoo-entity-1:mxh:Sfoo-entity-2                                                                                                         
    at JanusGraph.Net.RelationIdentifier..ctor(String stringRepresentation)                                                                                                                                                     
    at JanusGraph.Net.IO.GraphSON.RelationIdentifierDeserializer.Objectify(JsonElement graphsonObject, GraphSONReader reader)                                                                                                   
    at Gremlin.Net.Structure.IO.GraphSON.GraphSONReader.ReadValueOfType(JsonElement typedValue, String graphSONType)                                                                                                            
    at Gremlin.Net.Structure.IO.GraphSON.GraphSONReader.ToObject(JsonElement graphSon)                                                                                                                                          
    at Gremlin.Net.Structure.IO.GraphSON.MapSerializer.Objectify(JsonElement graphsonObject, GraphSONReader reader)                                                                                                             
    at Gremlin.Net.Structure.IO.GraphSON.GraphSONReader.ReadValueOfType(JsonElement typedValue, String graphSONType)                                                                                                            
    at Gremlin.Net.Structure.IO.GraphSON.GraphSONReader.ToObject(JsonElement graphSon)                                                                                                                                          
    at Gremlin.Net.Structure.IO.GraphSON.ListSerializer.Objectify(JsonElement graphsonObject, GraphSONReader reader)                                                                                                            
    at Gremlin.Net.Structure.IO.GraphSON.GraphSONReader.ReadValueOfType(JsonElement typedValue, String graphSONType)                                                                                                            
    at Gremlin.Net.Structure.IO.GraphSON.GraphSONReader.ToObject(JsonElement graphSon)                                                                                                                                          
    at Gremlin.Net.Structure.IO.GraphSON.GraphSONMessageSerializer.DeserializeMessageAsync(Byte[] message, CancellationToken cancellationToken)                                                                                 │
    at JanusGraph.Net.IO.GraphSON.JanusGraphGraphSONMessageSerializer.DeserializeMessageAsync(Byte[] message, CancellationToken cancellationToken)                                                                              │
    at Gremlin.Net.Driver.Connection.HandleReceivedAsync(Byte[] received)                                                                                                                                                       
    at Gremlin.Net.Driver.Connection.ReceiveMessagesAsync()                                                                                                                                                                     
    at Gremlin.Net.Driver.ProxyConnection.SubmitAsync[T](RequestMessage requestMessage, CancellationToken cancellationToken)                                                                                                    
    at Gremlin.Net.Driver.GremlinClient.SubmitAsync[T](RequestMessage requestMessage, CancellationToken cancellationToken)

This can be seen to be caused by the RelationIdentifier class code:

        private const char ToStringDelimiter = '-';

        /// <summary>
        ///     Initializes a new instance of the <see cref="RelationIdentifier" /> class.
        /// </summary>
        /// <param name="stringRepresentation">The underlying relation id.</param>
        public RelationIdentifier(string stringRepresentation)
        {
            StringRepresentation = stringRepresentation;

            var elements = stringRepresentation.Split(ToStringDelimiter);
            if (elements.Length != 3 && elements.Length != 4)
                throw new ArgumentException($"Not a valid relation identifier: {stringRepresentation}");

            if (elements[1][0] == LongEncoding.StringEncodingMarker)
            {
                OutVertexId = elements[1].Substring(1);
            }
            else
            {
                OutVertexId = LongEncoding.Decode(elements[1]);
            }
            TypeId = LongEncoding.Decode(elements[2]);
            RelationId = LongEncoding.Decode(elements[0]);
            if (elements.Length == 4)
            {
                if (elements[3][0] == LongEncoding.StringEncodingMarker)
                {
                    InVertexId = elements[3].Substring(1);
                }
                else
                {
                    InVertexId = LongEncoding.Decode(elements[3]);
                }
            }
        }

where the relation delimiter is hard coded to "-"

[FlorianHockmann]

Right, looks like this isn't supported by JanusGraph.Net. Do you want to submit a PR for this?