SYNOPSIS

Implements Ethereum's VM in Javascript.

Fork Support

The VM currently supports the following hardfork rules:

• Byzantium
• Constantinople
• Petersburg (default)
• Istanbul (beta)

If you are still looking for a Spurious Dragon compatible version of this library install the latest of the 2.2.x series (see Changelog).

Istanbul Harfork Support

A feature-complete Istanbul HF implementation is available since the v4.1.0 VM release. You can activate an Istanbul VM by using the istanbul hardfork option flag.

Supported Istanbul EIPs:

• EIP-152: Blake 2b F precompile, PR #584
• EIP-1108: Reduce alt_bn128 precompile gas costs,
  PR #540 (already released in v4.0.0)
• EIP-1344: Add ChainID Opcode, PR #572
• EIP-1884: Trie-size-dependent Opcode Repricing, PR #581
• EIP-2200: Rebalance net-metered SSTORE gas costs, PR #590

Note that Istanbul support is still labeled as beta. All implementations have only basic test coverage since the official Ethereum consensus tests are not yet merged. There might be also last minute changes to EIPs during the testing period.

INSTALL

npm install ethereumjs-vm

USAGE

const BN = require('bn.js')
var VM = require('ethereumjs-vm').default

// Create a new VM instance
// For explicity setting the HF use e.g. `new VM({ hardfork: 'petersburg' })`
const vm = new VM()

const STOP = '00'
const ADD = '01'
const PUSH1 = '60'

// Note that numbers added are hex values, so '20' would be '32' as decimal e.g.
const code = [PUSH1, '03', PUSH1, '05', ADD, STOP]

vm.on('step', function(data) {
  console.log(`Opcode: ${data.opcode.name}\tStack: ${data.stack}`)
})

vm.runCode({
  code: Buffer.from(code.join(''), 'hex'),
  gasLimit: new BN(0xffff),
})
  .then(results => {
    console.log('Returned : ' + results.returnValue.toString('hex'))
    console.log('gasUsed  : ' + results.gasUsed.toString())
  })
  .catch(err => console.log('Error    : ' + err))

Example

This projects contain the following examples:

1. ./examples/run-blockchain: Loads tests data, including accounts and blocks, and runs all of them in the VM.
2. ./examples/run-code-browser: Show how to use this library in a browser.
3. ./examples/run-solidity-contract: Compiles a Solidity contract, and calls constant and non-constant functions.
4. ./examples/run-transactions-complete: Runs a contract-deployment transaction and then calls one of its functions.
5. ./examples/decode-opcodes: Decodes a binary EVM program into its opcodes.

All of the examples have their own README.md explaining how to run them.

BROWSER

To build for standalone use in the browser, install browserify and check run-transactions-simple example. This will give you a global variable EthVM to use. The generated file will be at ./examples/run-transactions-simple/build.js.

API

VM

For documentation on VM instantiation, exposed API and emitted events see generated API docs.

StateManger

The API for the StateManager is currently in Beta, separate documentation can be found here, see also release notes from the v2.5.0 VM release for details on the StateManager rewrite.

Internal Structure

The VM processes state changes at many levels.

• runBlockchain
  • for every block, runBlock
• runBlock
  • for every tx, runTx
  • pay miner and uncles
• runTx
  • check sender balance
  • check sender nonce
  • runCall
  • transfer gas charges
• runCall
  • checkpoint state
  • transfer value
  • load code
  • runCode
  • materialize created contracts
  • revert or commit checkpoint
• runCode
  • iterate over code
  • run op codes
  • track gas usage
• OpFns
  • run individual op code
  • modify stack
  • modify memory
  • calculate fee

The opFns for CREATE, CALL, and CALLCODE call back up to runCall.

VM's tracing events

You can subscribe to the following events of the VM:

• beforeBlock: Emits a Block right before running it.
• afterBlock: Emits RunBlockResult right after running a block.
• beforeTx: Emits a Transaction right before running it.
• afterTx: Emits a RunTxResult right after running a transaction.
• beforeMessage: Emits a Message right after running it.
• afterMessage: Emits an EVMResult right after running a message.
• step: Emits an InterpreterStep right before running an EVM step.
• newContract: Emits a NewContractEvent right before creating a contract. This event contains the deployment code, not the deployed code, as the creation message may not return such a code.

Asynchronous event handlers

You can perform asynchronous operations from within an event handler and prevent the VM to keep running until they finish.

In order to do that, your event handler has to accept two arguments. The first one will be the event object, and the second one a function. The VM won't continue until you call this function.

If an exception is passed to that function, or thrown from within the handler or a function called by it, the exception will bubble into the VM and interrupt it, possibly corrupting its state. It's strongly recommended not to do that.

Synchronous event handlers

If you want to perform synchronous operations, you don't need to receive a function as the handler's second argument, nor call it.

Note that if your event handler receives multiple arguments, the second one will be the continuation function, and it must be called.

If an exception is thrown from withing the handler or a function called by it, the exception will bubble into the VM and interrupt it, possibly corrupting its state. It's strongly recommended not to throw from withing event handlers.

DEVELOPMENT

Developer documentation - currently mainly with information on testing and debugging - can be found here.

EthereumJS

See our organizational documentation for an introduction to EthereumJS as well as information on current standards and best practices.

If you want to join for work or do improvements on the libraries have a look at our contribution guidelines.

LICENSE

MPL-2.0