metatx-server

This package is for serverside processing of ethereum meta transactions. It is the server side component of metatx-client, but it can also be used on it's own.

Exposes a class MetaTxHandler that should be instantiated like this:

const metaTxHandler = new MetaTxHandler(
  relayerPrivKey,     // required arg. The private key that will relay transactions
  provider,           // required arg. Your web3 provider
  txRelayAddress,     // required arg. The address of your relayer contract
  txRelayABI,         // required arg. The abi of your relayer contract
  logger              // optional arg. Your logger, if you use one. Should have levels info and error
)

Methods:

getRelayerAddress => returns the given relayer address

getRelayNonce (address) => returns the nonce held in the relayer contract of the given address. A relayer nonce is required to prevent replay attacks.

initSimpleSigner => generates an eth-signer signer from the relayer private key given in the contructor

getSenderKeyPair (senderPrivKey) => generates a keypair from any given private key

initTxRelaySigner (senderPrivKey, _whitelist) => generates an eth-signer signer for the given sender private key. senderPrivKey is required, whitelist is optional.

estimateGas (tx, txSender) => estimates gas cost of a transaction, formatted in rlp.

isMetaSignatureValid (metaSignedTx, metaNonce) => verified that a meta signature is valid. metaSignedTx is a signed meta transaction and metaNonce is the nonce of the sender as of the relayer contract.

signMetaTx (txParams, senderPrivKey, relayNonce, whitelist) => prepares a signed meta transaction. txParams is an object that can be constructed like this:

const tx = {
  from: address,
  to: contractAddress,
  value: 0,
  data: Contract.methods.methodName(methodArgs).encodeABI()
};

senderPrivKey is the private key of the from address is txParams. relayNonce is optional, and will default to the relayer address set in the constructor. whitelist is also optional.

signRelayerTx (txHex) => Signs a meta transaction for forwarding to the relayer contract. txHex should be the signed meta tx in rlp encoding. Also estimates the gas price needed to execute the transaction.

sendRawTransaction (signedRawTx) => signes and sends a raw transaction to provider

handle (req) => Fully handles a request to the server to process a meta transaction. Can be used like this:

const relay = async (req, res) => {
  try {
    const result = await MetaTxHandler.handle(req)
    return res.status(200).json({ result })
  } catch (err) {
    return res.status(error.code).json({ error: error.message })
  }