External contracts

[onbjerg]

This PR allows you to interact with external contracts (i.e. contracts that are assumed to not be an Aragon app), such as tokens.

It allows you to perform calls and filter for events, but provides no automatic caching or convenience functions.

Usage-ish

const token = app.external(address, jsonInterface)

// A call
// Returns an Observable that emits a single value (the return value, a Web3 `Result` object)
token.symbol()

// Events
// Returns an Observable that emits Web3-structured events over time
token.events()

Note that you need to supply (at least a partial) JSON interface to interact with the contract.

Example

As a minimum viable example for getting the symbol of a token (conforming to Human Standard Token) and setting the app identifier to be that symbol, this would suffice:

const Aragon = require('@aragon/client')

const app = new Aragon()
const token = app.external('0xdeadbeef', [
  {
    'constant': true,
    'inputs': [],
    'name': 'symbol',
    'outputs': [
      {
        'name': 'symbol',
        'type': 'string'
      }
    ],
    'payable': false,
    'type': 'function'
  }
])

token.symbol().subscribe(
  ({ symbol }) => app.identify(symbol)
)

Improvements

Some future improvements could include

• Transactions to external contracts, possibly with "universal transaction pathing"
• Convenience functions, such as an integration with store (see brief explanation in Allow calls to arbitrary contracts #75)

Closes #41 and partially adresses #43

[onbjerg]

Tested locally and working, need a go from either one of you @bpierre @sohkai

[sohkai]

❤️❤️❤️ so excited to have this ❤️❤️❤️

[sohkai]

Could be const?

[onbjerg]

yeah that's something I missed while iterating a bit

[sohkai]

Cool! I had no idea you could put in partial ABIs and everything would just work.

[sohkai]

I do find it slightly odd this isn't a forEach or reduce

[onbjerg]

could be a forEach, probably also a reduce but would feel a bit weird with reduce imo