Web3 ProviderEngine is a tool for composing your own web3 providers.
Originally created for MetaMask, but has been superceded by json-rpc-engine in combination with our eth-json-rpc-middleware. This module is not very actively maintained, so we recommend using that one instead.
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';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)