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    16.0.3 • Public • Published

    Web3 ProviderEngine

    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    Originally created for MetaMask, but has been superceded by json-rpc-engine in combination with our eth-json-rpc-middleware.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('BLOCK CHANGED:', '#'+block.number.toString('hex'), '0x'+block.hash.toString('hex'))
    // network connectivity error
    engine.on('error', function(err){
      // report connectivity errors
    // start polling for blocks

    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




    npm i web3-provider-engine

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    • sethkfman
    • brad.decker
    • danfinlay
    • kumavis
    • rekmarks
    • metamaskbot
    • gudahtt