feat: specify subscriptions as a series of OpenRPC fragments

[aatifsyed]

I've got low confidence on what this actually looks like for Lotus - our code is certainly inconsistent.

@elmattic could you review, and also provide a trace of all JSON messages (with origins) for the full lifecycle when speaking to Lotus?

[elmattic]

Here's a breakdown of messages between a WebSocket client (User) and Lotus (Node):

Subscription

User to Node:

{"jsonrpc":"2.0","id":23,"method":"Filecoin.ChainNotify","params":[]}

I've chosen to init subscription with id set to 23 so it differs from the channelID.
Here id can be of type:

• Number
• String

---

Subscription response

Node to User:

{"jsonrpc":"2.0","result":1,"id":23}

Here result contains the channelID. channelID must be of type Number.

---

Notification*

Node to User:

{"jsonrpc":"2.0","method":"xrpc.ch.val","params":[1,<payload>]}

Here params is of type List and the first element corresponds to the channelID of the subscription.

The second element is the notification value.

(*) User can get zero, one or many notifications.

---

Channel cancelation

User to Node:

{"jsonrpc":"2.0","method":"xrpc.cancel","params":[23]}

Here params is of type List and the first element is the subscription id.

---

Channel cancelation response

Node to User:

{"jsonrpc":"2.0","method":"xrpc.ch.close","params":[1]}

Here params is of type List and the first element is the channelID.

[aatifsyed]

Excellent, thanks @elmattic that answers all the questions :)