Remote Staking via XCM¶

December 14, 2022 | by Kevin Neilson

Introduction¶

In this tutorial, we’ll stake DEV tokens remotely by sending XCM instructions from an account on the Moonbase relay chain (equivalent to the Polkadot relay chain). This tutorial assumes a basic familiarity with XCM and Remote Execution via XCM. You don’t have to be an expert on these topics but you may find it helpful to have some XCM knowledge as background.

There are actually two possible approaches for staking on Moonbeam remotely via XCM. We could send a remote EVM call that calls the staking precompile, or we could use XCM to call the parachain staking pallet directly without interacting with the EVM. For this tutorial, we’ll be taking the latter approach and interacting with the parachain staking pallet directly.

Note that there are still limitations in what you can remotely execute through XCM messages. In addition, developers must understand that sending incorrect XCM messages can result in the loss of funds. Consequently, it is essential to test XCM features on a TestNet before moving to a production environment.

Checking Prerequisites¶

For development purposes this tutorial is written for Moonbase Alpha and Moonbase relay using TestNet funds. For prerequisites:

A Moonbase Alpha relay chain account funded with some UNIT, the native token of the Moonbase relay chain. If you have a Moonbase Alpha account funded with DEV tokens, you can swap some DEV for xcUNIT here on Moonbeam Swap. Then withdraw the xcUNIT from Moonbase Alpha to your account on the Moonbase relay chain using apps.moonbeam.network
You'll need to calculate the multilocation derivative account of your Moonbase Alpha relay chain account and fund it with DEV tokens. You can get DEV tokens for testing on Moonbase Alpha once every 24 hours from the Moonbase Alpha Faucet

Calculating your Multilocation Derivative Account¶

Copy the account of your existing or newly created account on the Moonbase relay chain. You're going to need it to calculate the corresponding multilocation-derivative account, which is a special type of account that’s keyless (the private key is unknown). Transactions from a multilocation-derivative account can be initiated only via valid XCM instructions from the corresponding account on the relay chain. In other words, you are the only one who can initiate transactions on your multilocation-derivative account - and if you lose access to your Moonbase relay account, you’ll also lose access to your multilocation-derivative account.

To generate the multilocation-derivative account, first clone the xcm-tools repo. Run yarn to install the necessary packages, and then run:

yarn calculate-multilocation-derivative-account \
--w wss://wss.api.moonbase.moonbeam.network \
--a INSERT_MOONBASE_RELAY_ACCOUNT \
--p PARACHAIN_ID_IF_APPLIES \
--n westend

Let's review the parameters passed along with this command:

The -w flag corresponds to the endpoint we’re using to fetch this information
The -a flag corresponds to your Moonbase relay chain address
The -p flag corresponds to the parachain ID of the origin chain (if applies), if you are sending the XCM from the relay chain, you don't need to provide this parameter
The -n flag corresponds to the name of the relay chain that Moonbase relay is based on

The script will return 32-byte and 20-byte addresses. We’re interested in the Ethereum-style account - the 20-byte one. Feel free to look up your multilocation derivative account on Moonscan. You’ll note that this account is empty. You’ll now need to fund this account with at least 1.1 DEV. As this is the amount that the faucet dispenses, you'll need to make a minimum of two faucet requests or you can always reach out to us on Discord for additional DEV tokens.

Preparing to Stake on Moonbase Alpha¶

First and foremost, you’ll need the address of the collator you want to delegate to. To locate it, head to the Moonbase Alpha Staking dApp in a second window. Ensure you’re on the correct network, then press Select a Collator. Press the icon next to your desired collator to copy its address. You’ll also need to make a note of the number of delegations your collator has. The PS-31 collator shown below has 64 delegations at the time of writing.

Moonbeam Network Apps Dashboard

Remote Staking via XCM with the Polkadot.js API¶

This tutorial will cover the two-step process to perform remote staking operations. The first step we'll take is to generate the encoded call data for delegating a collator. Secondly, we'll send the encoded call data via XCM from the relay chain to Moonbase Alpha, which will result in the execution of the delegation.

Generate the Encoded Call Data¶

We'll be using the delegate function of the Parachain Staking Pallet, which accepts four parameters: candidate, amount, candidateDelegationCount, and delegationCount.

In order to generate the encoded call data, we'll need to assemble the arugments for each of the delegate parameters and use them to build a transaction which will call the delegate function. We are not submitting a transaction, but simplying preparing one to get the encoded call data. We'll take the following steps to build our script:

Create a Polkadot.js API provider
Assemble the arguments for each of the parameters of the delegate function:
- candidate- for this example we'll use the PS-31 collator: 0x3A7D3048F3CB0391bb44B518e5729f07bCc7A45D. To retrieve the entire list of candidates, you can refer back to the Preparing to Stake section
- amount - we'll stake the minimum amount, which is 1 DEV or 1000000000000000000 Wei. You can find a unit converter on Moonscan
- candidateDelegationCount - we'll retrieve using the candidateInfo function of the Parachain Staking Pallet to get the exact count. Alternatively, you can enter the upper bound of 300 because this estimation is only used to determine the weight of the call
- delegationCount - we'll retrieve using the delegatorState function of the Parachain Staking Pallet to get the exact count. Alternatively, you can specify an upper bound here of 100
Craft the parachainStaking.delegate extrinsic with each of the required arguments
Use the transaction to get the encoded call data for the delegation

import { ApiPromise, WsProvider } from '@polkadot/api';
const provider = new WsProvider('wss://wss.api.moonbase.moonbeam.network');

const candidate = '0x3A7D3048F3CB0391bb44B518e5729f07bCc7A45D';
const amount = '1000000000000000000';

const main = async () => {
  const api = await ApiPromise.create({ provider: provider });

  // Fetch the your existing number of delegations and the collators existing delegations
  let delegatorDelegationCount;
  const delegatorInfo = await api.query.parachainStaking.delegatorState(
    'INSERT_ACCOUNT' // Use the account you're delegating with
  );

  if (delegatorInfo.toHuman()) {
    delegatorDelegationCount = delegatorInfo.toHuman()['delegations'].length;
  } else {
    delegatorDelegationCount = 0;
  }

  const collatorInfo = await api.query.parachainStaking.candidateInfo(
    candidate
  );
  const candidateDelegationCount = collatorInfo.toHuman()['delegationCount'];
  const tx = api.tx.parachainStaking.delegate(
    candidate,
    amount,
    candidateDelegationCount,
    delegatorDelegationCount
  );

  // Get SCALE encoded call data
  const encodedCall = tx.method.toHex();
  console.log(`Encoded Call Data: ${encodedCall}`);

  api.disconnect();
};
main();

Note

If running this as a TypeScript project, be sure to set the strict flag under compilerOptions to false in your tsconfig.json.

If you'd prefer not to set up a local environment, you can run a code snippet in the JavaScript console of Polkadot.js Apps.

Code to run in the Polkadot.js Apps JavaScript console

const candidate = '0x3A7D3048F3CB0391bb44B518e5729f07bCc7A45D';
const amount = '1000000000000000000';

// Fetch the your existing number of delegations and the collators existing delegations
let delegatorDelegationCount;
// Use the account you're delegating with
const delegatorInfo = await api.query.parachainStaking.delegatorState('INSERT_ACCOUNT');

if (delegatorInfo.toHuman()) {
  delegatorDelegationCount = delegatorInfo.toHuman()['delegations'].length;
} else {
  delegatorDelegationCount = 0;
}

const collatorInfo = await api.query.parachainStaking.candidateInfo(candidate);
const candidateDelegationCount = collatorInfo.toHuman()['delegationCount'];
const tx = api.tx.parachainStaking.delegate(candidate, amount, candidateDelegationCount, delegatorDelegationCount);

// Get SCALE Encoded Call Data
const encodedCall = tx.method.toHex();
console.log(`Encoded Call Data: ${encodedCall}`);

Assemble and Send XCM Instructions via the Polkadot.js API¶

In this section, we'll be using the Polkadot.js API to construct and send XCM instructions via the send extrinsic of the XCM Pallet on the Alphanet relay chain. The XCM message will transport our remote execution instructions to the Moonbase Alpha parachain to ultimately stake our desired amount of DEV tokens to a chosen collator.

The send function of the XCM Pallet accepts two parameters: dest and message. You can start assembling these parameters by taking the following steps:

Build the multilocation of the DEV token on Moonbase Alpha for the dest:

const dest = { V3: { parents: 0, interior: { X1: { Parachain: 1000 } } } };

Build the WithdrawAsset instruction, which will require you to define:

The multilocation of the DEV token on Moonbase Alpha
The amount of DEV tokens to withdraw

const instr1 = {
  WithdrawAsset: [
    {
      id: {
        Concrete: { parents: 0, interior: { X1: { PalletInstance: 3 } } },
      },
      fun: { Fungible: 100000000000000000n },
    },
  ],
},

Build the BuyExecution instruction, which will require you to define:

The multilocation of the DEV token on Moonbase Alpha
The amount of DEV tokens to buy for execution
The weight limit

const instr2 = {
  BuyExecution: [
    {
      id: {
        Concrete: { parents: 0, interior: { X1: { PalletInstance: 3 } } },
      },
      fun: { Fungible: 100000000000000000n },
    },
    { Unlimited: null },
  ],
},

Build the Transact instruction, which will require you to define:
- The origin type, which will be SovereignAccount
- The required weight for the transaction. You'll need to define a value for refTime, which is the amount of computational time that can be used for execution, and the proofSize, which is the amount of storage in bytes that can be used. It is recommended that the weight given to this instruction needs to be around 10% more of 25000 times the gas limit for the call you want to execute via XCM
- The encoded call data for delegating a collator, which we generated in the previous section
```
const instr3 = {
  Transact: {
    originType: 'SovereignAccount',
    requireWeightAtMost: { refTime: 40000000000n, proofSize: 0n },
    call: {
      encoded:
        '0x0c113a7d3048f3cb0391bb44b518e5729f07bcc7a45d000064a7b3b6e00d00000000000000002c01000025000000',
    },
  },
},    
```

Combine the XCM instructions into a versioned XCM message:

const message = { V3: [instr1, instr2, instr3] };

Now that you have the values for each of the parameters, you can write the script to send the XCM message. You'll take the following steps:

Provide the values for each of the parameters of the send function
Create the Polkadot.js API provider using the WSS endpoint of the Alphanet relay chain
Create a Keyring instance using the mnemonic of your relay chain account, which will be used to send the transaction
Craft the xcmPallet.send extrinsic with the dest and message
Send the transaction using the signAndSend extrinsic and the Keyring instance you created in the third step

Remember

This is for demo purposes only. Never store your private key in a JavaScript file.

import { ApiPromise, WsProvider, Keyring } from '@polkadot/api';

const privateKey = 'INSERT_PRIVATE_KEY';

// 1. Define the dest and message arguments
const dest = { V3: { parents: 0, interior: { X1: { Parachain: 1000 } } } };
const message = {
  V3: [
    {
      WithdrawAsset: [
        {
          id: {
            Concrete: { parents: 0, interior: { X1: { PalletInstance: 3 } } },
          },
          fun: { Fungible: 100000000000000000n },
        },
      ],
    },
    {
      BuyExecution: [
        {
          id: {
            Concrete: { parents: 0, interior: { X1: { PalletInstance: 3 } } },
          },
          fun: { Fungible: 100000000000000000n },
        },
        { Unlimited: null },
      ],
    },
    {
      Transact: {
        originKind: 'SovereignAccount',
        requireWeightAtMost: { refTime: 40000000000n, proofSize: 0n },
        call: {
          encoded:
            '0x0c113a7d3048f3cb0391bb44b518e5729f07bcc7a45d000064a7b3b6e00d00000000000000002c01000025000000',
        },
      },
    },
  ],
};

const performRemoteDelegation = async () => {
  // 2. Construct API provider
  const wsProvider = new WsProvider(
    'wss://frag-moonbase-relay-rpc-ws.g.moonbase.moonbeam.network'
  );
  const api = await ApiPromise.create({ provider: wsProvider });

  // 3. Initialize wallet key pairs
  const keyring = new Keyring({ type: 'sr25519' });
  // For demo purposes only. Never store your private key or mnemonic in a JavaScript file
  const otherPair = keyring.addFromUri(privateKey);
  console.log(`Derived Address from Private Key: ${otherPair.address}`);

  // 4. Define the transaction using the send method of the xcm pallet
  const tx = api.tx.xcmPallet.send(dest, message);

  // 5. Sign and send the transaction
  const txHash = await tx.signAndSend(otherPair);
  console.log(`Submitted with hash ${txHash}`);

  api.disconnect();
};

performRemoteDelegation();

Note

Remember that your multilocation derivative account must be funded with at least 1.1 DEV or more to ensure you have enough to cover the stake amount and transaction fees.

In the above snippet, besides submitting the remote staking via XCM transaction, we also print out the transaction hash to assist with any debugging.

And that’s it! To verify that your delegation was successful, you can visit Subscan to check your staking balance. Be advised that it may take a few minutes before your staking balance is visible on Subscan. Additionally, be aware that you will not be able to see this staking operation on Moonscan, because we initiated the delegation action directly via the Parachain Staking Pallet (on the Substrate side) rather than through the Staking Precompile (on the EVM).

This tutorial is for educational purposes only. As such, any contracts or code created in this tutorial should not be used in production.

Last update: May 13, 2023
| Created: December 10, 2022