Example/doc for how to talk to a PubSub server about jsonrpc

[tomusdrw]

If you have a running server from this example:
https://github.com/paritytech/jsonrpc/blob/a95e135017c3a29fbda5dad88dc62f8797792443/pubsub/examples/pubsub.rs

You need to issue a standard RPC with {"id":1,"jsonrpc":"2.0","method":"subscribe_hello"} and then you should start seeing subscriptions coming to your client.
The transport used in the example is TCP, so you can for instance use netcat to connect to the server:

$ netcat localhost 3030 -
{"id":1,"jsonrpc":"2.0","method":"subscribe_hello"}
{"jsonrpc":"2.0","result":5,"id":1}
{"jsonrpc":"2.0","method":"hello","params":[10]}
{"jsonrpc":"2.0","method":"hello","params":[10]}
{"jsonrpc":"2.0","method":"hello","params":[10]}

[faern]

I'm running the example using macros at https://github.com/paritytech/jsonrpc/blob/a95e135017c3a29fbda5dad88dc62f8797792443/macros/examples/pubsub-macros.rs

But I get this:

$ netcat localhost 3030 -
{"id":1,"jsonrpc":"2.0","method":"hello_subscribe"}
{"jsonrpc":"2.0","error":{"code":-32601,"message":"Method not found"},"id":1}

[faern]

I did get your example to work with the example not using macros. But using the macros would be sweet.

[tomusdrw]

Hmm, you're right. It turned out that the alias invocation in macros was invalid (it was overriding the implementation with alias to non-existent method).

Please try with #121 or remove alias in the example.

[faern]

That worked better! Thanks. Now I get:

$ netcat localhost 3030 -
{"id":1,"jsonrpc":"2.0","method":"hello_subscribe","params":[10]}
{"jsonrpc":"2.0","result":0,"id":1}
{"jsonrpc":"2.0","method":"hello","params":{"result":"Hello World!","subscription":0}}
{"jsonrpc":"2.0","method":"hello","params":{"result":"Hello World!","subscription":0}}
{"jsonrpc":"2.0","method":"hello","params":{"result":"Hello World!","subscription":0}}
....

Now I will just move on to try to get this running on the WebSocket server.

[tomusdrw]

You can have a look how we wrapped the ws::Sender into mpsc::Sender:
https://github.com/paritytech/parity/pull/5456/files#diff-047350db0c9925ab2d582dfcd955f0a4R173

I'm considering moving this into this crate though.
If you manage to get the example running feel free to contribue it to ws/examples :)

[faern]

I got the server running. But when I try to communicate with in using a python websocket client I get this response:

{"jsonrpc":"2.0","error":{"code":-32090,"message":"Subscriptions are not available on this transport."},"id":1}

Is there anything I can do about that? Would the ws crate need some modifications or which part is it that stops subscriptions to work over ws?

[tomusdrw]

Could you post the example somewhere? For PubSub to work you need to ensure that MetadataExtractor will create a Session object (that definitely needs more detailed documentation).

[faern]

Ah. My bad. I removed the call to session_meta_extractor. Now I'm trying to figure out how to make that work. Looking at the code you sent, but it uses rpc::PubSubSession which is not part of this repository.

[faern]

It kind of escalates with the WsRpcExtractor and the Sender struct implementing Future etc. There is hopefully a simpler way that I have not found yet.

[tomusdrw]

It's actually just a re-export of jsonrpc_pubsub::Session. I'll prepare an example today for you :)

[faern]

Thank you. That would be awesome.

[tomusdrw]

Please have a look at #126. I've moved the implementation of mpsc::Sender to this crate.

[faern]

@tomusdrw Thanks for the help! Got it working and also got an example based on macros working. Merging that PR would solve/close this issue.

[tomusdrw]

Awesome! Glad to hear that.