SYNOPSIS

or #ethereumjs on freenode

Implements Ethereum's VM in Javascript.

Fork Support

This library always only supports the currently active Ethereum mainnet fork rules with its latest release, old fork rules are dropped with new releases once a HF occured.

The current major 2.3.x release series supports the Byzantium fork changes. For a Spurious Dragon compatible version of this library install the latest of the 2.2.x series (see Changelog).

INSTALL

npm install ethereumjs-vm

USAGE

var VM = require('ethereumjs-vm')

//create a new VM instance
var vm = new VM()
var code = '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'

vm.runCode({
  code: Buffer.from(code, 'hex'), // code needs to be a Buffer
  gasLimit: Buffer.from('ffffffff', 'hex')
}, function(err, results){
  console.log('returned: ' + results.return.toString('hex'));
})

Also more examples can be found here

• examples
• old blog post

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

• new VM([opts])
• VM methods
  • vm.runBlockchain([blockchain], [cb])
  • vm.runBlock(opts, cb)
  • vm.runTx(opts, cb)
  • vm.runCode(opts, cb)
  • vm.generateCanonicalGenesis(cb)
  • vm.generateGenesis(cb)
• VM debugging hooks
  • vm.onStep

new VM([StateTrie], [blockchain])

Creates a new VM object

• StateTrie - The Patricia Merkle Tree that contains the state. If no trie is given the VM will create an in memory trie.
• blockchain - an instance of the Blockchain. If no blockchain is given a fake blockchain will be used.
• opts
  • state - the state trie
  • blockchain - an instance of ethereumjs-blockchain
  • activatePrecompiles - create entries in the state tree for the precompiled contracts

VM methods

vm.runBlockchain(blockchain, cb)

Process blocks and adds them to the blockchain.

• blockchain - A blockchain that to process
• cb - The callback. It is given an err parameter if it fails

---

vm.runBlock(opts, cb)

Processes the block running all of the transactions it contains and updating the miner's account.

• opts.block - The Block to process
• opts.generate - a Boolean; whether to generate the stateRoot. If false runBlock will check the stateRoot of the block against the Trie
• cb - The callback. It is given two arguments, an error string containing an error that may have happened or null, and a results object with the following properties:
  • receipts - the receipts from the transactions in the block
  • results - an Array for results from the transactions in the block

---

vm.runTx(opts, cb)

Process a transaction.

• opts.tx - A Transaction to run.
• opts.block - The block to which the tx belongs. If omitted a blank block will be used.
• cb - The callback. It is given two arguments, an error string containing an error that may have happened or null, and a results object with the following properties:
  • amountSpent - the amount of ether used by this transaction as a bignum
  • gasUsed - the amount of gas used by the transaction
  • vm - contains the results from running the code, if any, as described in vm.runCode(params, cb)

---

vm.runCode(opts, cb)

Runs EVM code

• opts.code - The EVM code to run given as a Buffer
• opts.data - The input data given as a Buffer
• opts.value - The value in ether that is being sent to opt.address. Defaults to 0
• opts.block - The Block the tx belongs to. If omitted a blank block will be used.
• opts.gasLimit - The gas limit for the code given as a Buffer
• opts.account - The Account that the executing code belongs to. If omitted an empty account will be used
• opts.address - The address of the account that is executing this code. The address should be a Buffer of bytes. Defaults to 0
• opts.origin - The address where the call originated from. The address should be a Buffer of 20bits. Defaults to 0
• opts.caller - The address that ran this code. The address should be a Buffer of 20bits. Defaults to 0
• cb - The callback. It is given two arguments, an error string containing an error that may have happened or null and a results object with the following properties
  • gas - the amount of gas left as a bignum
  • gasUsed - the amount of gas as a bignum the code used to run.
  • gasRefund - a Bignum containing the amount of gas to refund from deleting storage values
  • selfdestruct - an Object with keys for accounts that have selfdestructed and values for balance transfer recipient accounts.
  • logs - an Array of logs that the contract emitted.
  • exception - 0 if the contract encountered an exception, 1 otherwise.
  • exceptionError - a String describing the exception if there was one.
  • return - a Buffer containing the value that was returned by the contract

---

vm.stateManager.generateCanonicalGenesis(cb)

Generates the Canonical genesis state.

---

vm.stateManager.generateGenesis(genesisData, cb)

Generate the genesis state.

• genesisData - an Object whose keys are addresses and values are strings representing initial allocation of ether.
• cb - The callback

var genesisData = {
  "51ba59315b3a95761d0863b05ccc7a7f54703d99": "1606938044258990275541962092341162602522202993782792835301376",
  "e4157b34ea9615cfbde6b4fda419828124b70c78": "1606938044258990275541962092341162602522202993782792835301376"
}

vm.generateGenesis(genesisData, function(){
  console.log('generation done');
})

events

All events are instances of async-eventemmiter. If an event handler has an arity of 2 the VM will pause until the callback is called

step

The step event is given an Object and callback. The Object has the following properties.

• pc - a Number representing the program counter
• opcode - the next opcode to be ran
• gasLeft - a bignum standing for the amount of gasLeft
• stack - an Array of Buffers containing the stack.
• storageTrie - the storage trie for the account
• account - the Account which owns the code running.
• address - the address of the account
• depth - the current number of calls deep the contract is
• memory - the memory of the VM as a buffer
• cache - The account cache. Contains all the accounts loaded from the trie. It is an instance of functional red black tree

beforeBlock

Emits the block that is about to be processed.

afterBlock

Emits the results of the processing a block.

beforeTx

Emits the Transaction that is about to be processed.

afterTx

Emits the result of the transaction.

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.

TESTING

Running Tests

Tests can be found in the tests directory, with FORK_CONFIG set in tests/tester.js. There are test runners for State tests and Blockchain tests. VM tests are disabled since Frontier gas costs are not supported any more. Tests are then executed by the ethereumjs-testing utility library using the official client-independent Ethereum tests.

For a wider picture about how to use tests to implement EIPs you can have a look at this reddit post or the associated YouTube video introduction to core development with Ethereumjs-vm.

Running different Test Types

Running all the tests:

npm test

Running the State tests:

node ./tests/tester -s

Running the Blockchain tests:

node ./tests/tester -b

State tests run significantly faster than Blockchain tests, so it is often a good choice to start fixing State tests.

Running Specific Tests

Running all the blockchain tests in a file:

node ./tests/tester -b --file='randomStatetest303'

Running tests from a specific directory:

node ./tests/tester -b --dir='bcBlockGasLimitTest'

Running a specific state test case:

node ./tests/tester -s --test='stackOverflow'

Only run test cases with selected data, gas and/or value values (see attribute description in test docs), provided by the index of the array element in the test transaction section:

node tests/tester -s --test='CreateCollisionToEmpty' --data=0 --gas=1 --value=0

Run a state test from a specified source file not under the tests directory: node ./tests/tester -s --customStateTest='{path_to_file}'

Skipping Tests

There are three types of skip lists (BROKEN, PERMANENT and SLOW) which can be found in tests/tester.js. By default tests from all skip lists are omitted.

You can change this behaviour with:

node tests/tester -s --skip=BROKEN,PERMANENT

to skip only the BROKEN and PERMANENT tests and include the SLOW tests. There are also the keywords NONE or ALL for convenience.

It is also possible to only run the tests from the skip lists:

node tests/tester -s --runSkipped=SLOW

Debugging

Local Debugging

For state tests you can use the --jsontrace flag to output opcode trace information.

Blockchain tests support --debug to verify the postState:

node ./tests/tester -b --debug --test='ZeroValue_SELFDESTRUCT_ToOneStorageKey_OOGRevert_d0g0v0_EIP158'

All/most State tests are replicated as Blockchain tests in a GeneralStateTests sub directory in the Ethereum tests repo, so for debugging single test cases the Blockchain test version of the State test can be used.

Debugging Tools

For comparing EVM traces here are some instructions for setting up pyethereum to generate corresponding traces for state tests.

Compare TAP output from blockchain/state tests and produces concise diff of the differences between them (example):

curl https://gist.githubusercontent.com/jwasinger/6cef66711b5e0787667ceb3db6bea0dc/raw/0740f03b4ce90d0955d5aba1e0c30ce698c7145a/gistfile1.txt > output-wip-byzantium.txt
curl https://gist.githubusercontent.com/jwasinger/e7004e82426ff0a7137a88d273f11819/raw/66fbd58722747ebe4f7006cee59bbe22461df8eb/gistfile1.txt > output-master.txt
python utils/diffTestOutput.py output-wip-byzantium.txt output-master.txt

An extremely rich and powerful toolbox is the evmlab from holiman, both for debugging and creating new test cases or example data.

LICENSE

MPL-2.0