WIP: WebSockets subscriptions

[TonioMacaronio]

Work for #145

[barrasso]

Looks great @BaldyAsh!

Can you please show some example usage for this?

For a particular Ethereum address, how can I get:

• pending transactions
• incoming/outgoing/internal transactions

Might be best to include it in Usage.md

Thanks

[TonioMacaronio]

@barrasso hi, the work in progress. When I finish all usage info will be added to Usage.md

[TonioMacaronio]

@barrasso hi, everything is almost done. Currently I'm building frameworks to test them on real project. You can see how to get latest pending transactions using Infura websockets API here https://github.com/matter-labs/web3swift/blob/subscriptions/Documentation/Usage.md#infura-websockets
Also this PR contains some fixes of recent bugs with sending transactions.
When the build is complete, I will push it and you can also try it.

[barrasso]

@BaldyAsh Great work! 👍🏼

In addition to the Infura subscriptions, is there a method to subscribe to my own custom node via websockets?

For example:

let delegate: Web3SocketDelegate = DelegateClass() // Some delegate class which will receive messages from endpoint
let socketProvider = SocketProvider.connectToSocket("ws://my.ropsten.dnp.dappnode.eth:8546", delegate: delegate)
try! socketProvider.subscribeOnNewPendingTransactions()

[TonioMacaronio]

@barrasso you will be able to use custom node in that way:

let socketProvider = WebsocketProvider.connectToSocket(endpoint: <URL>, delegate: <Web3SocketDelegate>)!

But currently I'm thinking is it a good idea to provide subscribe methods like newPendingTransactions for custom websocket provider by default. Maybe it's better to force user to build his own subscriptions and give him just possibility to send message to websocket via writeMessage, because endpoint API may differ from Infuras' and default methods should not mislead newcomers

[TonioMacaronio]

@barrasso think its done, already tested with frameworks. I'll merge it and create pod. This closes #145 #149 #143 #140 #133