Session support

[maldrake]

This PR provides an initial implementation of session support. If merged, it should close #113.

• The change adds two functions, openSession and closeSession to the GremlinClient, both synchronous and asynchronous.
• Internally, the openSession function creates a new pool with just a single connection for the session, along with tracking the session name, which the client of the library will most often set to the String representation of a UUID. An alternative would've been to just create a single Connection rather than a pool of 1, but using the pool allowed for greater re-use of existing functions without changes, because many of the functions involved in sending messages take a managed connection from the pool.
• Queries that are sent using execute are sent to the session processor wi the session name, until the session is closed.

Notably, I did learn a few things that might be viewed as limitations on the implementation.

• Sessions are supported only for text queries, not binary traversals. This seems to be a design choice on the server end, so I don't think there's anything that can be done about it in the client.
• The server sends WebSocket ping requests to the client as keep-alive test. The Gremlin client currently doesn't recognize or know how to handle those pings (by sending a pong response). Implementing robust handling for those would likely require either a monitoring thread to read and respond to them, or an asynchronous equivalent. For now, I resolved the problem by setting idleConnectionTimeout and keepAliveInterval to disable the ping/pong keep-alive messages altogether, to avoid that complexity. That should work fine for my use case but could be a limitation for others.

As always, I welcome any review comments or requests for changes that I need to make in order for the PR to be suitable to merge.

[wolf4ood]

Hi @maldrake

Thanks for the PR looks great!.

I was just thinking if it make sense to create another instance GremlinClient on open_session without modifying the current client or create a new type which wraps the GremlinClient with the session logic?
WDYT?

[maldrake]

@wolf4ood,

Yes, that makes a lot of sense. I hadn't done that initially because I thought it would make it easier to interoperate with other parts of the code (e.g. traversals), if I could avoid changing the GremlinClient type. That was before I realized sessions don't support binary traversals, and I never went back to re-think that design later. I'll work up a change to the PR submit it soon.

[maldrake]

Ok, in this new commit, I changed create_session to create a new client under a newtype of SessionedClient. How does this look?

[maldrake]

Hi @wolf4ood, I wanted to check in on this PR, in case it fell to the wayside in favor of other priorities. Any other changes I can make, to make it more suitable for merging? Thanks!

[wolf4ood]

Hi @maldrake

sorry i did completely miss the notification on this.
Thansk for this PR :)