Defender SDK Relay Signer Client

Defender Relay Signer Client lets you send transactions to any supported network using private relayers. Each relayer has its own secure private key, and a set of API keys. You can send transactions via your relayers by POSTing to the Defender HTTP API, or using this library.

Install

npm install @openzeppelin/defender-sdk-relay-signer-client
# or
yarn add @openzeppelin/defender-sdk-relay-signer-client

This library also includes an ethers.js signer and a web3.js provider, that uses the Relay to sign and broadcast its transactions.

Usage

Start by creating a new relayer using either the Defender console or API for a network of your choice. Write down the API key and secret. Then use them to create a new Relayer instance in your code:

import { Relayer } from '@openzeppelin/defender-sdk-relay-signer-client';
const relayer = new Relayer({ apiKey: API_KEY, apiSecret: API_SECRET });

And use the relayer instance to send a transaction:

const tx = await relayer.sendTransaction({
  to: '0x6b175474e89094c44da98b954eedeac495271d0f',
  value: '0x16345785d8a0000',
  data: '0x5af3107a',
  speed: 'fast',
  gasLimit: 100000,
});

The sendTransaction call returns once the transaction has been signed by the relayer. To monitor the transaction status, see Querying below.

Speed

Instead of the usual gasPrice or maxFeePerGas/maxPriorityFeePerGas, the Relayer may also accept a speed parameter that can be one of safeLow, average, fast, or fastest. These values are mapped to actual gas prices when the transaction is sent or resubmitted and vary depending on the state of the network.

If speed is provided, the transaction would be priced according to the EIP1559Pricing relayer policy.

NOTE: Mainnet gas prices and priority fees are calculated based on the values reported by EthGasStation, EtherChain, GasNow, BlockNative, and Etherscan. In Polygon and its testnet, the gas station is used. In other networks, gas prices are obtained from a call to eth_gasPrice or eth_feeHistory to the network.

Return data

The returned transaction object tx will have the following shape:

interface RelayerTransactionBase {
  transactionId: string; // Defender transaction identifier
  hash: string; // Ethereum transaction hash
  to: string;
  from: string;
  value?: string;
  data?: string;
  speed: 'safeLow' | 'average' | 'fast' | 'fastest';
  gasLimit: number;
  nonce: number;
  status: 'pending' | 'sent' | 'submitted' | 'inmempool' | 'mined' | 'confirmed' | 'failed';
  chainId: number;
  validUntil: string;
}

Querying transactions

The relayer object also has a getTransaction function that returns a transaction object as described above. This method receives the transactionId, not the transaction hash:

const latestTx = await relayer.getTransaction(tx.transactionId);

Transaction can be queried by nonce as well:

const latestTx = await relayer.getTransactionByNonce(tx.nonce);

Alternatively, the relayer can also be used to list the latest transactions sent, optionally filtering by status and creation time.

const since = await relayer.list({
  since: new Date(Date.now() - 60 * 1000),
  status: 'pending', // can be 'pending', 'mined', or 'failed'
  limit: 5,
  usePagination: true,
  sort: 'desc', // available only in combination with pagination
  next: '', // optional: include when the response has this value to fetch the next set of results
});

The list function now accepts several parameters to facilitate pagination, such as limit, usePagination, sort, and next. The sort parameter is available only when pagination is enabled, and the next parameter is optional, used to fetch the next set of results when included in the response.

When using pagination by setting usePagination to true, the format of the response will be different from the default. The response will be an object containing two properties: items and next. The items property is an array of RelayerTransaction objects, representing the fetched list of transactions. The next property is an optional string. If present, it can be used as the value for the next parameter in a subsequent request to retrieve the next set of transactions.

{ items: RelayerTransaction[]; next?: string }

Defender will update the transaction status every minute, marking it as confirmed after 12 confirmations. The transaction information will be stored for 30 days.

Why querying?

The getTransaction and getTransactionByNonce functions are important to monitor the transaction status, since Defender may choose to resubmit the transaction with a different gas price, effectively changing its hash. This means that, if you monitor your transaction only via getTransactionReceipt(tx.hash) calls to a node, you may not get the latest info if it was replaced.

Defender may replace a transaction by increasing its gas price if it has not been mined for a period of time, and the gas price costs have increased since the transaction was originally submitted. Also, in a case where a transaction consistently fails to be mined, Defender may replace it by a no-op (a transaction with no value or data) in order to advance the sender account nonce.

Relayer Status

To gain better insight into the current status of a relayer, you can use the getRelayerStatus method. This method provides real-time information about a relayer, such as its nonce, transaction quota, and the number of pending transactions.

To get the current status of a relayer:

const status = await relayer.getRelayerStatus('58b3d255-e357-4b0d-aa16-e86f745e63b9');

The response will be of the shape:

export interface RelayerStatus {
  relayerId: string; // Unique identifier for the relayer
  name: string; // Name of the relayer
  nonce: number; // Current relayer nonce
  address: string; // Address of the relayer
  numberOfPendingTransactions: number; // Number of transactions: pending|sent|submitted|inmempool
  paused: boolean; // If the relayer is paused or not
  pendingTxCost?: string; // The total cost of all pending transactions, if available
  txsQuotaUsage: number; // Used transaction quota for the relayer
  rpcQuotaUsage: number; // Used RPC quota for the relayer
  lastConfirmedTransaction?: {
    // Details of the last confirmed transaction
    hash: string,
    status: string,
    minedAt: string,
    sentAt: string,
    nonce: number,
  };
}

This method can be particularly helpful in monitoring and managing your relayer resources more effectively.

Replacing transactions

You can use the relayer methods replaceTransactionById or replaceTransactionByNonce to replace a transaction given its nonce or transactionId (not hash) if it has not been mined yet. You can use this to increase the speed of a transaction, or replace your tx by an empty value transfer (with a gas limit of 21000) to cancel a transaction that is no longer valid.

// Cancel a transaction with nonce 42 by sending a zero-value transfer to replace it
const tx = await relayer.replaceTransactionByNonce(42, {
  to: '0x6b175474e89094c44da98b954eedeac495271d0f',
  value: '0x00',
  data: '0x',
  speed: 'fastest',
  gasLimit: 21000,
});

You can also replace by nonce using the ethers.js and web3.js adapters listed below.

Signing

You can sign any hex string (0x123213) according to the EIP-191 Signed Data Standard (prefixed by \x19Ethereum Signed Message:\n) using a sign method of the relayer. Pay attention, that the message has to be a hex string.

const signResponse = await relayer.sign({ message: msg });

Also, you can sign typed data according to the EIP-712 Specification using a signTypedData method of the relayer by providing both the domainSeparator and the hashStruct(message) as parameters. Heads up that both are hashes so they should be 32-bytes long.

const signTypedDataResponse = await relayer.signTypedData({
  domainSeparator,
  hashStructMessage,
});

Return data

Once your data is signed, the following response will be returned:

export interface SignedMessagePayload {
  sig: Hex;
  r: Hex;
  s: Hex;
  v: number;
}

Network calls

You can also use Defender for making arbitrary JSON RPC calls to the network via the call method. All JSON RPC methods are supported, except for event filters and websocket subscriptions.

const balance = await relayer.call('eth_getBalance', ['0x6b175474e89094c44da98b954eedeac495271d0f', 'latest']);

Ethers.js

You can use the defender-relay-client with ethers.js v5 directly. The package exports a DefenderRelaySigner signer that is used to send transactions, and a DefenderRelayProvider provider that is used to make calls to the network through Defender.

Make sure to have ethers installed in your project, and initialize a new defender signer instance like:

const { DefenderRelayProvider, DefenderRelaySigner } = require('@openzeppelin/defender-sdk-relay-signer-client/ethers');
const { ethers } = require('ethers');

const credentials = { apiKey: API_KEY, apiSecret: API_SECRET };
const provider = new DefenderRelayProvider(credentials);
const signer = new DefenderRelaySigner(credentials, provider, { speed: 'fast' });

You can then use it to send any transactions, such as executing a contract function. The tx object returned will be a regular ethers.js TransactionResponse object, with the addition of Defender's transactionId field.

const erc20 = new ethers.Contract(ERC20_ADDRESS, ERC20_ABI, signer);
const tx = await erc20.functions.transfer(beneficiary, (1e18).toString());
const mined = await tx.wait();

The signMessage method is supported as well, allowing to sign an arbitrary data with a relayer key.

const signed = await signer.signMessage('Funds are safu!');

The _signTypedData method is also supported to sign EIP712 messages

const signedEIP712Message = await signer._signTypedData(domain, types, value);

Limitations

The current implementation of the DefenderRelaySigner for ethers.js has the following limitations:

• Due to validations set up in ethers.js, it is not possible to specify the transaction speed for an individual transaction when sending it. It must be set during the signer construction, and will be used for all transactions sent through it.
• A wait on the transaction to be mined will only wait for the current transaction hash (see Querying). If Defender Relayer replaces the transaction with a different one, this operation will time out. This is ok for fast transactions, since Defender only reprices after a few minutes. But if you expect the transaction to take a long time to be mined, then ethers' wait may not work. Future versions will also include an ethers provider aware of this.

Web3.js

You can also use the @openzeppelin/defender-sdk-relay-signer-client with web3.js via a DefenderRelayProvider which routes all JSON RPC calls through Defender, and uses a Relayer for signing and broadcasting transactions.

const { DefenderRelayProvider } = require('@openzeppelin/defender-sdk-relay-signer-client/web3');
const Web3 = require('web3');

const credentials = { apiKey: API_KEY, apiSecret: API_SECRET };
const provider = new DefenderRelayProvider(credentials, { speed: 'fast' });
const web3 = new Web3(provider);

You can then use the web3 instance to query and send transactions as you would normally do:

const [from] = await web3.eth.getAccounts();
const erc20 = new web3.eth.Contract(ERC20_ABI, ERC20_ADDRESS, { from });
const tx = await erc20.methods.transfer(beneficiary, (1e18).toString()).send();

You can also sign messages using the Relayer key via the sign method:

const signature = await web3.eth.sign('0xdead', from);

The package also includes two composable lower-level providers, the DefenderRelaySenderProvider and DefenderRelayQueryProvider. The former intercepts all sendTransaction methods and serves them via the Relayer, while the latter uses Defender's JSON RPC interface for all method calls. The DefenderRelayProvider shown above combines the two.

Note that these web3.js providers currently have the same limitations as the ethers.js one described above.

Using in Actions

Defender Actions natively support integration with Defender Relay, allowing to send transactions without providing API keys. In your actions's code, just require('defender-sdk') and construct a new relayer instance using the credentials object injected by the action. This will give you a relayer object already configured.

const { Defender } = require('@openzeppelin/defender-sdk');

exports.handler = async function (credentials) {
  const client = new Defender(credentials);

  const txRes = await client.relaySigner.sendTransaction({
    to: '0xc7464dbcA260A8faF033460622B23467Df5AEA42',
    value: 100,
    speed: 'fast',
    gasLimit: '21000',
  });

  console.log(txRes);
  return txRes.hash;
};

FAQ

Can I use this package in a browser?

This package is not designed to be used in a browser environment. Using this package requires sensitive API KEYS that should not be exposed publicly.