Web3 ProviderEngine

Web3 ProviderEngine is a tool for composing your own web3 providers.

Status: WIP - expect breaking changes and strange behaviour

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()

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)

Current RPC method support:

static

• web3_clientVersion
• net_version
• net_listening
• net_peerCount
• eth_protocolVersion
• eth_hashrate
• eth_mining
• eth_syncing

filters

• eth_newBlockFilter
• eth_newPendingTransactionFilter
• eth_newFilter
• eth_uninstallFilter
• eth_getFilterLogs
• eth_getFilterChanges

accounts manager

• eth_coinbase
• eth_accounts
• eth_sendTransaction
• eth_sign

vm

• eth_call
• eth_estimateGas

db source

• db_putString
• db_getString
• db_putHex
• db_getHex

compiler

• eth_getCompilers
• eth_compileLLL
• eth_compileSerpent
• eth_compileSolidity

shh gateway

• shh_version
• shh_post
• shh_newIdentity
• shh_hasIdentity
• shh_newGroup
• shh_addToGroup

data source ( fallback to rpc )

• eth_gasPrice
• eth_blockNumber
• eth_getBalance
• eth_getBlockByHash
• eth_getBlockByNumber
• eth_getBlockTransactionCountByHash
• eth_getBlockTransactionCountByNumber
• eth_getCode
• eth_getStorageAt
• eth_getTransactionByBlockHashAndIndex
• eth_getTransactionByBlockNumberAndIndex
• eth_getTransactionByHash
• eth_getTransactionCount
• eth_getTransactionReceipt
• eth_getUncleByBlockHashAndIndex
• eth_getUncleByBlockNumberAndIndex
• eth_getUncleCountByBlockHash
• eth_getUncleCountByBlockNumber
• eth_sendRawTransaction
• eth_getLogs ( not used in web3.js )

( not supported )

• eth_getWork
• eth_submitWork
• eth_submitHashrate ( not used in web3.js )