Providers

The Ethereum eco-system provides many methods of interacting with the blockchain. In ethers.js we expose a Provider API that covers the breadth of operations, however often it is useful to inter-operate with other existing APIs and libraries.

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MetaMask

The MetaMask plug-in enables Ethereum for the Chrome browser, making it easy for people new ecosystem to get started, exposing the Ethereum network as a standard Web3 Provider.

Connecting to MetaMask

// MetaMask injects a Web3 Provider as "web3.currentProvider", so
// we can wrap it up in the ethers.js Web3Provider, which wraps a
// Web3 Provider and exposes the ethers.js Provider API.

const provider = new ethers.providers.Web3Provider(web3.currentProvider);

// There is only ever up to one account in MetaMask exposed
const signer = provider.getSigner();

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TestRPC / Ganache

The Ganache (formerly TestRPC) is a mock-blockchain which helps create temporary instances of an Ethereum node for testing.

NOTE:

Ganache is not entirely standards-compliant and may not always behave properly. If you are getting deeper into Ethereum development, we recommend installing Geth or Parity and using a development chain

Connecting to a Ganache Node

// Once a Ganache node is running, it behaves very similar to a
// JSON-RPC API node.

const url = "http://localhost:8545";

// Or if you are running the UI version, use this instead:
// const url = "http://localhost:7545"

const provider = new ethers.providers.JsonRpcProvider(url);

// Getting the accounts
const signer0 = provider.getSigner(0);
const signer1 = provider.getSigner(1);

Using an In-Process Ganache Instance

// If you would like to run an in-process instance of Ganache, you can
// use a method similar to the MetaMask solution; we wrap the Web3 Provider
// API with an ethers.js Web3Provider, which exposes the ethers.js API
// from a Web3 Provider

const ganache = Ganache.provider(ganacheOptions);
const provider = new ethers.providers.Web3Provider(ganache);

// Getting the accounts
const signer0 = provider.getSigner(0);
const signer1 = provider.getSigner(1);

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Custom Provider

This is a much more advanced topic, and most people should not need to work this low level. But it is provided for those rare instances where you need some custom connection logic.

A provider must only implement the method perform(method, params). All data passed into a provider is sanitized by the BaseProvider subclass, and all results are normalized before returning them to the user.

For this example, we will build a DebugProvider, which will simple proxy all commands through another Provider, but dump all data going back and forth.

Sub-Class Provider for Debugging

const ethers = require('ethers');

class DebugProvider extends ethers.providers.BaseProvider {
    readonly provider: ethers.providers.Provider;

    constructor(provider) {
        super(provider.getNetork());
        this.provider = provider;
    }

    // This should return a Promise (and may throw erros)
    // method is the method name (e.g. getBalance) and params is an
    // object with normalized values passed in, depending on the method
    perform(method, params): Promise<any> {
        this.provider.perform(method, params).then((result) => {
            console.log('DEBUG', method, params, '=>', result);
        }, (error) => {
            console.log('DEBUG:ERROR', method, params, '=>', error);
            throw error;
        });
    }
}

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