DataType error encountered for various commands with 3.6.1+ #87

[Teague Bick]

I am using JanusGraph and see a break after 3.6.1 (seen in 3.7.0 as well).

3.6.0 works fine, but 3.6.1 and later run into the below issues.  Is there a better place to open

Stack trace:

```
(venv) ➜  entities git:(teague.bick/accupath) ✗ ./demo.py                      
Traceback (most recent call last):
  File "/Users/teague.bick/Workspace/experimental/entities/./demo.py", line 12, in <module>
    g.V().has_label("person").to_list()
  File "/Users/teague.bick/Workspace/experimental/entities/venv/lib/python3.9/site-packages/gremlin_python/process/traversal.py", line 65, in to_list
    return list(iter(self))
  File "/Users/teague.bick/Workspace/experimental/entities/venv/lib/python3.9/site-packages/gremlin_python/process/traversal.py", line 48, in __next__
    self.traversal_strategies.apply_strategies(self)
  File "/Users/teague.bick/Workspace/experimental/entities/venv/lib/python3.9/site-packages/gremlin_python/process/traversal.py", line 684, in apply_strategies
    traversal_strategy.apply(traversal)
  File "/Users/teague.bick/Workspace/experimental/entities/venv/lib/python3.9/site-packages/gremlin_python/driver/remote_connection.py", line 78, in apply
    remote_traversal = self.remote_connection.submit(traversal.bytecode)
  File "/Users/teague.bick/Workspace/experimental/entities/venv/lib/python3.9/site-packages/gremlin_python/driver/driver_remote_connection.py", line 105, in submit
    results = result_set.all().result()
  File "/Users/teague.bick/.pyenv/versions/3.9.17/lib/python3.9/concurrent/futures/_base.py", line 446, in result
    return self.__get_result()
  File "/Users/teague.bick/.pyenv/versions/3.9.17/lib/python3.9/concurrent/futures/_base.py", line 391, in __get_result
    raise self._exception
  File "/Users/teague.bick/Workspace/experimental/entities/venv/lib/python3.9/site-packages/gremlin_python/driver/resultset.py", line 90, in cb
    f.result()
  File "/Users/teague.bick/.pyenv/versions/3.9.17/lib/python3.9/concurrent/futures/_base.py", line 439, in result
    return self.__get_result()
  File "/Users/teague.bick/.pyenv/versions/3.9.17/lib/python3.9/concurrent/futures/_base.py", line 391, in __get_result
    raise self._exception
  File "/Users/teague.bick/.pyenv/versions/3.9.17/lib/python3.9/concurrent/futures/thread.py", line 58, in run
    result = self.fn(*self.args, **self.kwargs)
  File "/Users/teague.bick/Workspace/experimental/entities/venv/lib/python3.9/site-packages/gremlin_python/driver/connection.py", line 90, in _receive
    status_code = self._protocol.data_received(data, self._results)
  File "/Users/teague.bick/Workspace/experimental/entities/venv/lib/python3.9/site-packages/gremlin_python/driver/protocol.py", line 96, in data_received
    message = self._message_serializer.deserialize_message(message)
  File "/Users/teague.bick/Workspace/experimental/entities/venv/lib/python3.9/site-packages/gremlin_python/driver/serializer.py", line 280, in deserialize_message
    result = self._graphbinary_reader.to_object(b)
  File "/Users/teague.bick/Workspace/experimental/entities/venv/lib/python3.9/site-packages/gremlin_python/structure/io/graphbinaryV1.py", line 203, in to_object
    return self.deserializers[DataType(bt)].objectify(buff, self, nullable)
  File "/Users/teague.bick/Workspace/experimental/entities/venv/lib/python3.9/site-packages/gremlin_python/structure/io/graphbinaryV1.py", line 502, in objectify
    return cls.is_null(buff, reader, cls._read_list, nullable)
  File "/Users/teague.bick/Workspace/experimental/entities/venv/lib/python3.9/site-packages/gremlin_python/structure/io/graphbinaryV1.py", line 231, in is_null
    return None if nullable and buff.read(1)[0] == 0x01 else else_opt(buff, reader)
  File "/Users/teague.bick/Workspace/experimental/entities/venv/lib/python3.9/site-packages/gremlin_python/structure/io/graphbinaryV1.py", line 509, in _read_list
    the_list.append(r.read_object(b))
  File "/Users/teague.bick/Workspace/experimental/entities/venv/lib/python3.9/site-packages/gremlin_python/structure/io/graphbinaryV1.py", line 194, in read_object
    return self.to_object(b)
  File "/Users/teague.bick/Workspace/experimental/entities/venv/lib/python3.9/site-packages/gremlin_python/structure/io/graphbinaryV1.py", line 203, in to_object
    return self.deserializers[DataType(bt)].objectify(buff, self, nullable)
KeyError: <DataType.custom: 0>
```

Example Code:
```
#!/usr/bin/env python

from gremlin_python.process.anonymous_traversal import traversal
from gremlin_python.driver.driver_remote_connection import DriverRemoteConnection
from gremlin_python.process.graph_traversal import __

g = traversal().with_remote(DriverRemoteConnection('ws://localhost:8182/gremlin', 'g'))

g.add_v('person').property('name', 'marko').iterate()
g.add_v('person').property('name', 'vadas').iterate()

g.V().has_label("person").to_list()   # This is the error line
```

[Yang Xia]

Hi Teague,

I'm not entirely sure of the error that would have caused this on the Janus server side, but in terms of driver serialization related changes, 3.6.1 and above had a switch in default serializer from GraphSON to GraphBinary in gremlin python (see https://tinkerpop.apache.org/docs/current/upgrade/#_tinkerpop_3_6_1). 

I'd suggest try switching to GraphSon in your example code and see if it works, which I believe can be done via DRC (might need some tweaks when trying):

remote_conn = DriverRemoteConnection(gremlin_server_url, 'g',
                                     message_serializer=serializer.GraphSONSerializersV3d0())
g = traversal().with_remote(remote_conn)

Also please feel free to join the TinkerPop Discord channel (https://discord.gg/tinkerpop) if you haven't yet, folks are usually on to monitor questions and discussions.  

Cheers,

Yang

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[Teague Bick]

That worked like a charm!

Using the serializer as a pointer, I was able to find a few issues in JanusGraph, where this appears to be a known (and maybe expected) issue - https://github.com/JanusGraph/janusgraph/issues/4127

Also, thank you for the discord, I'll join up!