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I'm running a gremlin server with bitsy using the conf and properties file given in the github repo (https://github.com/lambdazen/bitsy/tree/master/src/test/resources/gremlin-server). I have, of course, changed dbPath to an appropriate path.

My client is a kotlin application running gremlin console. I have no problem executing queries that result in string or map values, for example:

val encodedPasswd = getg().V().has("user", "login", login).values<String>("password").next()

However, when attempting to get vertices from queries:

val user = getg().V().has("user", "login", login).next()

I get a deserialization error:

[gremlin-driver-loop-1] WARN org.apache.tinkerpop.gremlin.driver.ser.AbstractGraphSONMessageSerializerV2d0 - Response [PooledUnsafeDirectByteBuf(ridx: 7446, widx: 7446, cap: 7446)] could not be deserialized by org.apache.tinkerpop.gremlin.driver.ser.AbstractGraphSONMessageSerializerV2d0.

org.apache.tinkerpop.shaded.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `org.apache.tinkerpop.gremlin.driver.message.ResponseMessage` (no Creators, like default construct, exist): cannot deserialize from Object value (no delegate- or property-based Creator)

 at [Source: (byte)"{"requestId":"5e78c0ba-64d2-4b31-8b04-262c3fa2b3b8","status":{"message":"Error during serialization: Direct self-reference leading to cycle (through reference chain: com.lambdazen.bitsy.store.VertexBean["id"])","code":599,"attributes":{"@type":"g:Map","@value":["stackTrace","org.apache.tinkerpop.gremlin.driver.ser.SerializationException: org.apache.tinkerpop.shaded.jackson.databind.exc.InvalidDefinitionException: Direct self-reference leading to cycle (through reference chain: com.lambdazen.bi"[truncated 6946 bytes]; line: 1, column: 2]

    at org.apache.tinkerpop.shaded.jackson.databind.exc.InvalidDefinitionException.from(InvalidDefinitionException.java:67)

    at org.apache.tinkerpop.shaded.jackson.databind.DeserializationContext.reportBadDefinition(DeserializationContext.java:1451)

    at org.apache.tinkerpop.shaded.jackson.databind.DeserializationContext.handleMissingInstantiator(DeserializationContext.java:1027)

    at org.apache.tinkerpop.shaded.jackson.databind.deser.BeanDeserializerBase.deserializeFromObjectUsingNonDefault(BeanDeserializerBase.java:1297)

    at org.apache.tinkerpop.shaded.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:326)

    at org.apache.tinkerpop.shaded.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:159)

    at org.apache.tinkerpop.gremlin.structure.io.graphson.GraphSONTypeDeserializer.deserialize(GraphSONTypeDeserializer.java:212)

    at org.apache.tinkerpop.gremlin.structure.io.graphson.GraphSONTypeDeserializer.deserializeTypedFromObject(GraphSONTypeDeserializer.java:86)

    at org.apache.tinkerpop.shaded.jackson.databind.deser.BeanDeserializerBase.deserializeWithType(BeanDeserializerBase.java:1178)

    at org.apache.tinkerpop.shaded.jackson.databind.deser.impl.TypeWrappedDeserializer.deserialize(TypeWrappedDeserializer.java:68)

    at org.apache.tinkerpop.shaded.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4013)

    at org.apache.tinkerpop.shaded.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3091)

    at org.apache.tinkerpop.gremlin.driver.ser.AbstractGraphSONMessageSerializerV2d0.deserializeResponse(AbstractGraphSONMessageSerializerV2d0.java:134)

    at org.apache.tinkerpop.gremlin.driver.handler.WebSocketGremlinResponseDecoder.decode(WebSocketGremlinResponseDecoder.java:50)

...

Cluster construction:

var cluster = Cluster.build()

    .serializer (

        GryoMessageSerializerV3d0 (

            GryoMapper.build()

                .addRegistry(BitsyIoRegistryV3d0.instance())

        )

    )

    .serializer (

        GraphSONMessageSerializerV3d0 (

            GraphSONMapper.build()

                .addRegistry(BitsyIoRegistryV3d0.instance())

            .create()

        )

    )

.create()

and traversal source construction:

fun getg() : GraphTraversalSource {

    return EmptyGraph.instance().traversal().withRemote(DriverRemoteConnection.using(cluster))

}

Relevant parts of my gradle:

dependencies {

    ...

    implementation('org.apache.tinkerpop:gremlin-driver:3.3.4')

    implementation("com.lambdazen.bitsy:bitsy:3.1.0")

    implementation("com.fasterxml.jackson.module:jackson-module-kotlin:2.9.+")

}

Why can't the driver deserialise messages from the server? What do I change to allow it to?

I'm not completely sure, but I'm guessing that Bitsy lacks full support for GraphSON 3.0. If you look at its IoRegistry implementation it registers no custom serializers for GraphSON (just for Gryo):

https://github.com/lambdazen/bitsy/blob/c0dd4b6c9d6dc9987d0168c91417eb04d80bf712/src/main/java/com/lambdazen/bitsy/BitsyIoRegistryV3d0.java

I assume that's the reason why you get a serialization error. If you switch to just using Gryo (which is probably recommended to some extent since you are on the JVM with Kotlin) I imagine you won't have this problem.

Note that your Cluster object definition is not configuring the way you expect either. By calling serializer() twice (i.e. once for Gryo and once for GraphSON) you actually overwrite the Gryo configuration and simply configure the object to work with GraphSON.

So, I think you would just do this:

var cluster = Cluster.build()

    .serializer (

        GryoMessageSerializerV3d0 (

            GryoMapper.build()

                .addRegistry(BitsyIoRegistryV3d0.instance())

        )

    )

.create()