How to generate GraphSON data for export with Remote Traversal?

Example Code(JAVA):

Cluster cluster = Cluster.open(yml.getFile());
DriverRemoteConnection driver = DriverRemoteConnection.using(cluster, "graph_traversal");
GraphTraversalSource allGraph = AnonymousTraversalSource.traversal().withRemote(driver);

// Using Io --> generate a file in server-side
allGraph.Io("File.json").write().iterate()

// Using GraphSONWriter 
GraphSONMapper mapper = GraphSONMapper.build().addRegistry(JanusGraphIoRegistry.instance()).version(GraphSONVersion.V3_0).create();
GraphSONWriter writer = GraphSONWriter.build().mapper(mapper).create();
ByteArrayOutputStream output = new ByteArrayOutputStream();

// output --> "" (Empty)
writer.writeGraph(output, allGraph.getGraph());

// output --> "~" (Only Vertex Ids)
writer.writeVertices(output, allGraph.V());

I'm trying to export a Graph as GraphSON with remote server. But IO step doesn't provide a functionality for remote-export. With GraphSonWriter, It doesn't write the contents properly. How can I export a graph in GraphSON format with remote-server environment?

Thank you.

Until TinkerPop provides better support around the g.io() step for remote environments, it still only works well for reading and writing local to where the Gremlin execution occurs. If you want to export a graph to GraphSON at a remote source then there are a few options depending on the graph you are using. You tagged this question with JanusGraph so I'll focus on that. You could:

1. Send a script than instantiates a GraphSONWriter on the server and then provide writeGraph() an OutputStream that will write to a byte[] or String and then return that to your client.
2. I assume this is a "small" graph that will likely fit in memory so just do g.E().subgraph('sg').cap('sg') and copy the whole graph to a subgraph. That will yield you a TinkerGraph on the client and from there you can use io() as you like to write the graph locally to GraphSON. This only works if you are using Java as other languages don't yet support subgraph() well.
3. Forgo use of Gremlin Server and create a local JanusGraph instance and then io() will work as normal.