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@cogitojs/cogito-ethereum

@cogitojs/cogito-ethereum is a high level convenience package that provides a more declarative way of working with cogito-web3-provider, telepath, and Ethereum contracts.

Usage

Add @cogitojs/cogito-ethereum as a dependency

$ yarn add `@cogitojs/cogito-ethereum`

@cogitojs/cogito-ethereum aims at making working with cogito-web3-provider, telepath, and Ethereum contracts easier. Using @cogitojs/cogito-ethereum you do not have know all the details about web3 providers, cogito-web3-provider, and telepath, in order to setup a working cogito ecosystem.

@cogitojs/cogito-ethereum's main abstraction is CogitoEthereum.

Before we learn how to use CogitoEthereum, we need first make sure we have a good understanding how CogitoEthereum handles the Ethereum contracts.

Working with Contracts

Developers working with Ethereum contract often use a convenience package truffle-contract. To get an instance of a contract you first import truffle-contract. What you will get from importing truffle-contract is a function that takes a contract definition as an argument and returns a proxy object that you can use to interact with your contract. Before you can do that, however, you still need to set the provider on the returned proxy object:

import Web3 from 'web3'
import initContract from 'truffle-contract'
import { SimpleStorage } from '@cogitojs/demo-app-contracts'

const providerUrl = 'http://localhost:9545' // example for the local development
const provider = new Web3.providers.HttpProvider(providerUrl)
const web3 = new Web3(provider)
const contractProxy = initContract(SimpleStorage())
contractProxy.setProvider(provider)
// or if you got web3 already initialized
contractProxy.setProvider(web3.currentProvider)

Please, note that @cogitojs/demo-app-contracts exports a function that returns the actual contract JSON blob. We could also directly return a function, but that would make mocking with jest.mock('@cogitojs/demo-app-contracts') not possible. jest.mock can only mock exported functions. This is why in the snipped above we are calling SipleStorage() instead of just using SimpleStorage. In the following examples we will directly import JSON blobs from JSON files.

To get the actual instance of the contract, you can use one of the proxy methods: deployed(), at(), or new(). Please refer to the documentation of truffle-contract for more information.

Creating an instance of CogitoEthereum

CogitoEtheruem expects an array of contracts JSON blobs as the first constructor argument:

import DataStoreJSON from 'contracts/DataStore.json'
import DataRequestJSON from 'contracts/DataRequest.json'
import DataResponseJSON from 'contracts/DataResponse.json'
import { CogitoEthereum } from '@cogitojs/cogito-ethereum'

const cogitoEthereum = new CogitoEthereum([ DataStoreJSON, DataRequestJSON, DataResponseJSON ])

CogitoEtheruem takes care for setting up a new Web3 instance that uses the CogitoProvider from @cogitojs/cogito-web3-provider as the currentProvider (cogitoWeb3), the associated telepath channel (telepathChannel), and an object with contract proxies corresponding to each contract JSON blob passed in the first constructor argument (contractsProxies). cogitoWeb3, telepathChannel, and contractsProxies together are called a context and can be retrieved using CogitoEthereum instance method: getContext:

const {
  cogitoWeb3,
  telepathChannel,
  contractsProxies
} = await cogitoEthereum.getContext({ appName: 'Demo App' })

getContext expect an object as an argument: { channelId, channelKey, appName }. If channelId and/or channelKey are not provided, a new random value will be created, and the resulting channelId and channelKey will be used to create a telepath channel instance. Notice, that the appName attribute is required.

The returned telepathChannel attribute refers to an instance of a JsonRpcChannel that is returned by the createChannel method of the instance of Telepath. It provides the channel id as telepathChannel.id, the channel key as telepathChannel.key, allows to send a JSON-RPC request using send(request), and provides a convenience method to get the telepath connection url via telepathChannel.createConnectUrl(). This connection url can be use to generate the QR-Code to be scanned by the Cogito app in order to establish a secure connection with the JavaScript client. To learn more about Telepath, connection URLs, and QR-Codes, please refer to the documentation of the telepath-js package.

cogitoWeb3 holds a reference to a valid Web3 object that uses CogitoProvider as the provider. It means that requests for requesting Ethereum accounts (cogitoWeb3.eth.getAccounts(), see also eth_accounts) or sending Ethereum transactions (cogitoWeb3.eth.sendTransaction, see also eth_sendTransaction) will be redirect to the client via associated telepath channel.

Finally, contractsProxies is an object with attributes referring to the contract proxies corresponding to the provided contract JSON blobs. For example:

const cogitoEthereum = new CogitoEthereum([ DataStore, DataRequest, DataResponse ])
const { contractsProxies } = await cogitoEthereum.getContext({ appName: 'Demo App' })
const { DataStore, DataRequest, DataResponse } = contractsProxies
const dataStoreContractInstance = await DataStore.deployed()
const dataRequestContractInstance = await DataRequest.at(await dataStoreContractInstance.getDataRequest())
const dataResponseContractInstance = await DataResponse.at(await dataStoreContractInstance.getDataResponse())

The names of the attributes in the contractsProxies object correspond to the name of the contracts as given by the contractName attribute of the corresponding contract JSON blob.

Finally, CogitoEthereum accepts an optional second argument holding the queuing service url to be used with telepath. The default is https://telepath.cogito.mobi.