MetaMask
Web3 ProviderEngine
Web3 ProviderEngine is a tool for composing your own web3 providers.
[!CAUTION] This package has been deprecated.
This package was originally created for MetaMask, but has been replaced by
@metamask/json-rpc-engine,@metamask/eth-json-rpc-middleware,@metamask/eth-json-rpc-provider, and various other packages.Here is an example of how to create a provider using those packages:
import { providerFromMiddleware } from '@metamask/eth-json-rpc-provider'; import { createFetchMiddleware } from '@metamask/eth-json-rpc-middleware'; import { valueToBytes, bytesToBase64 } from '@metamask/utils'; import fetch from 'cross-fetch'; const rpcUrl = '[insert RPC URL here]'; const fetchMiddleware = createFetchMiddleware({ btoa: (stringToEncode) => bytesToBase64(valueToBytes(stringToEncode)), fetch, rpcUrl, }); const provider = providerFromMiddleware(fetchMiddleware); provider.sendAsync( { id: 1, jsonrpc: '2.0', method: 'eth_chainId' }, (error, response) => { if (error) { console.error(error); } else { console.log(response.result); } } );This example was written with v12.1.0 of
@metamask/eth-json-rpc-middleware, v3.0.1 of@metamask/eth-json-rpc-provider, and v8.4.0 of@metamask/utils.
Composable
Built to be modular - works via a stack of 'sub-providers' which are like normal web3 providers but only handle a subset of rpc methods.
The subproviders can emit new rpc requests in order to handle their own; e.g. eth_call may trigger eth_getAccountBalance, eth_getCode, and others.
The provider engine also handles caching of rpc request results.
const ProviderEngine = require('web3-provider-engine')
const CacheSubprovider = require('web3-provider-engine/subproviders/cache.js')
const FixtureSubprovider = require('web3-provider-engine/subproviders/fixture.js')
const FilterSubprovider = require('web3-provider-engine/subproviders/filters.js')
const VmSubprovider = require('web3-provider-engine/subproviders/vm.js')
const HookedWalletSubprovider = require('web3-provider-engine/subproviders/hooked-wallet.js')
const NonceSubprovider = require('web3-provider-engine/subproviders/nonce-tracker.js')
const RpcSubprovider = require('web3-provider-engine/subproviders/rpc.js')
var engine = new ProviderEngine()
var web3 = new Web3(engine)
// static results
engine.addProvider(new FixtureSubprovider({
web3_clientVersion: 'ProviderEngine/v0.0.0/javascript',
net_listening: true,
eth_hashrate: '0x00',
eth_mining: false,
eth_syncing: true,
}))
// cache layer
engine.addProvider(new CacheSubprovider())
// filters
engine.addProvider(new FilterSubprovider())
// pending nonce
engine.addProvider(new NonceSubprovider())
// vm
engine.addProvider(new VmSubprovider())
// id mgmt
engine.addProvider(new HookedWalletSubprovider({
getAccounts: function(cb){ ... },
approveTransaction: function(cb){ ... },
signTransaction: function(cb){ ... },
}))
// data source
engine.addProvider(new RpcSubprovider({
rpcUrl: 'https://testrpc.metamask.io/',
}))
// log new blocks
engine.on('block', function(block){
console.log('================================')
console.log('BLOCK CHANGED:', '#'+block.number.toString('hex'), '0x'+block.hash.toString('hex'))
console.log('================================')
})
// network connectivity error
engine.on('error', function(err){
// report connectivity errors
console.error(err.stack)
})
// start polling for blocks
engine.start()When importing in webpack:
import * as Web3ProviderEngine from 'web3-provider-engine';
import * as RpcSource from 'web3-provider-engine/subproviders/rpc';
import * as HookedWalletSubprovider from 'web3-provider-engine/subproviders/hooked-wallet';Built For Zero-Clients
The Ethereum JSON RPC was not designed to have one node service many clients. However a smaller, lighter subset of the JSON RPC can be used to provide the blockchain data that an Ethereum 'zero-client' node would need to function. We handle as many types of requests locally as possible, and just let data lookups fallback to some data source ( hosted rpc, blockchain api, etc ). Categorically, we don’t want / can’t have the following types of RPC calls go to the network:
- id mgmt + tx signing (requires private data)
- filters (requires a stateful data api)
- vm (expensive, hard to scale)
Running tests
yarn test