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Implement state archival in dapps

When developing decentralized applications on Stellar, state archival is part of what we need to consider due to how data is stored on the network. This guide will help you understand how to work with state archival in your dapp.

Some state archival terminology we will be using in this guide are described in the state archival section.

Why managing state archival is important for applications​

Managing state archival is crucial for Stellar dapps for several reasons:

  • Data accessibility: Archived data becomes inaccessible, potentially breaking application functionality, so it's important to manage data lifecycle and know when to restore.
  • Cost efficiency: Different storage types have varying fees and archival behaviors, allowing developers to optimize costs. Due to this, some data may be more cost-effective to store in a way that causes it to be archived after a certain period.
  • Data lifecycle management: Proper management ensures that important data remains accessible while allowing temporary data to expire.
  • Application continuity: Ensuring contract instances and Wasm code remain live is essential for uninterrupted dapp operation. It is essential to check for contract availability before attempting to interact with the contract after a long period of inactivity.

Methods of implementing state archival on the client side​

1. Extending TTL from the smart contract​

This method involves invoking the extend_ttl() method from your smart contract to extend the TTL of the contract instance and its associated data. This method is useful when you want to keep the data accessible for a longer period. To use this method, your contract must not be archived at the time of calling.

extend_ttl() has two important parameters (T,N):

  • T is threshold, the current ledger height at which the extension should happen.
  • N is the new ledger height at which the data will expire.
  • Current TTL must be less than T for the extension to happen.
  • If N is less than the current ledger height, the TTL will not be extended and the call will be regarded as a no-op.
  • If N is greater than the current ledger height, the TTL will be extended to N.

Let's see a sample of how we can implement this in a smart contract:

#![no_std]
/// This is a simple contract that just extends TTL for its keys.
/// It's main purpose is to demonstrate how TTL extension can be tested,
use soroban_sdk::{contract, contractimpl, contracttype, Env};

#[contracttype]
pub enum DataKey {
    MyKey,
}

#[contract]
pub struct TtlContract;

#[contractimpl]
impl TtlContract {
    /// Creates a contract entry in every kind of storage.
    pub fn setup(env: Env) {
        env.storage().persistent().set(&DataKey::MyKey, &0);
        env.storage().instance().set(&DataKey::MyKey, &1);
        env.storage().temporary().set(&DataKey::MyKey, &2);
    }

    /// Extend the persistent entry TTL to 5000 ledgers, when its
    /// TTL is smaller than 1000 ledgers.
    pub fn extend_persistent(env: Env) {
        env.storage()
            .persistent()
            .extend_ttl(&DataKey::MyKey, 1000, 5000);
    }

    /// Extend the instance entry TTL to become at least 10000 ledgers,
    /// when its TTL is smaller than 2000 ledgers.
    pub fn extend_instance(env: Env) {
        env.storage().instance().extend_ttl(2000, 10000);
    }

    /// Extend the temporary entry TTL to become at least 7000 ledgers,
    /// when its TTL is smaller than 3000 ledgers.
    pub fn extend_temporary(env: Env) {
        env.storage()
            .temporary()
            .extend_ttl(&DataKey::MyKey, 3000, 7000);
    }
}

mod test;
info

The above contract shows how to extend the TTL of a Persistent, Instance, and Temporary data entry. The extend_ttl() method is used to extend the TTL of the data entry to a new ledger height.

Using the Extend TTL method in your Contract​

When we create DApps, we do not typically create buttons to extend the TTL of data entries. Instead, we can create a function that extends the TTL of the data entries when the DApp is used.

For example, we can increase the TTL of a temporary data entry called highestBid in a bidding DApp when a new bid is placed. This will ensure that the bid data remains accessible for as long as it is needed.

#![no_std]
use soroban_sdk::{contract, contractimpl, contracttype, Env};

#[contracttype]
pub enum DataKey {
    HighestBid,
}

#[contract]
pub struct BiddingContract;

#[contractimpl]
impl BiddingContract {
    /// Creates a contract entry in every kind of storage.
    pub fn setup(env: Env) {
        env.storage().temporary().set(&DataKey::HighestBid, &0);
    }

    /// Place a bid and extend the TTL of the highest bid data entry.
    pub fn place_bid(env: Env, bid: u64) {
        let highest_bid: u64 = env.storage().temporary().get(&DataKey::HighestBid).unwrap_or(0);
        if bid > highest_bid {
            env.storage().temporary().set(&DataKey::HighestBid, &bid);
            env.storage().temporary().extend_ttl(&DataKey::HighestBid, 1000, 5000);
        }
    }
}

2. Restoring archived data​

When developing a dapp on Stellar, you may encounter situations where contract data or the contract instance has been archived due to inactivity. Let's walk through the process of restoring archived data using the JavaScript SDK and Freighter wallet.

Prerequisites​

  • Stellar SDK: npm install @stellar/stellar-sdk
  • Freighter API: npm install @stellar/freighter-api
  • A Stellar RPC endpoint (e.g., https://soroban-testnet.stellar.org)

Step 1: Set up the SDK and Freighter​

First, import the necessary components:

import * as StellarSdk from "@stellar/stellar-sdk";
import {
  isConnected,
  setAllowed,
  getPublicKey,
  signTransaction,
} from "@stellar/freighter-api";

import { Api } from "@stellar/stellar-sdk/rpc";
const rpcUrl = "https://soroban-testnet.stellar.org";
const server = new StellarSdk.SorobanRpc.Server(rpcUrl);
const networkPassphrase = StellarSdk.Networks.TESTNET; // Use PUBLIC for production

This setup provides the foundation for interacting with the Stellar network and Freighter wallet.

Step 2: Create a helper function for restoration​

Let's create a helper function that attempts to submit a transaction, and if it fails due to archived data, it will restore the data and retry:

async function submitOrRestoreAndRetry(contractId, method, ...args) {
  try {
    let hasFreighter = await isConnected();
    if (!hasFreighter) {
      return alert("Freighter wallet is required for transactions");
    }

    const isAllowed = await setAllowed();
    if (!isAllowed) {
      return alert("Please allow the transaction in Freighter wallet");
    }

    const accountId = await getPublicKey();
    const contract = new StellarSdk.Contract(contractId);
    const account = await server.getAccount(accountId);
    const fee = StellarSdk.BASE_FEE;

    const transaction = new StellarSdk.TransactionBuilder(account, {
      fee,
      networkPassphrase,
    })
      .addOperation(contract.call(method, ...args))
      .setTimeout(30)
      .build();

    let preparedTransaction = await server.prepareTransaction(transaction);

    let signedXDR = await signTransaction(preparedTransaction.toXDR());
    let signedTransaction = StellarSdk.TransactionBuilder.fromXDR(
      signedXDR,
      networkPassphrase,
    );

    // Try to send the transaction
    const sim = await server.simulateTransaction(signedTransaction);

    // Other failures are out of scope of this tutorial.
    if (!Api.isSimulationSuccess(sim)) {
      throw sim;
    }

    // If simulation didn't fail, we don't need to restore anything! Just send it.
    if (Api.isSimulationRestore(sim)) {
      console.log("Data archived. Attempting restoration...");

      // Prepare restoration transaction
      const restoreTx = new StellarSdk.TransactionBuilder(account, { fee })
        .setNetworkPassphrase(networkPassphrase)
        .addOperation(StellarSdk.Operation.restoreFootprint({}))
        .setTimeout(30)
        .build();

      let preparedRestoreTx = await server.prepareTransaction(restoreTx);
      let signedRestoreXDR = await signTransaction(preparedRestoreTx.toXDR());
      let signedRestoreTx = StellarSdk.TransactionBuilder.fromXDR(
        signedRestoreXDR,
        networkPassphrase,
      );

      await server.sendTransaction(signedRestoreTx);
      console.log("Restoration complete. Retrying original transaction...");

      // Retry the original transaction
      return submitOrRestoreAndRetry(contractId, method, ...args);
    }

    const result = await server.sendTransaction(signedTransaction);

    return result;
  } catch (error) {
    console.error("Transaction failed:", error);
    throw error;
  }
}

This function now uses Freighter for signing transactions. It first checks if Freighter is connected and authorized, then proceeds with the transaction. If restoration is needed (indicated by a HostStorageError), it creates a separate restoration transaction, signs it with Freighter, and submits it before retrying the original transaction.

Step 3: Use the helper function in your dapp​

You can now use this function to make contract calls that automatically handle restoration:

async function performContractAction(contractId, method, ...args) {
  try {
    const result = await submitOrRestoreAndRetry(contractId, method, ...args);
    console.log("Transaction successful:", result);
    return result;
  } catch (error) {
    console.error("Error performing contract action:", error);
    // Handle the error appropriately in your UI
  }
}

Step 4: Handling contract instance restoration​

For restoring an entire contract instance, you might need a separate function:

Here we will be using the getLedgerEntries method to get the WASM code of the contract and also the restoreFootprint operation to restore the contract instance.

async function restoreContractInstance(contractId) {
  try {
    let hasFreighter = await isConnected();
    if (!hasFreighter) {
      return alert("Freighter wallet is required for transactions");
    }

    const isAllowed = await setAllowed();
    if (!isAllowed) {
      return alert("Please allow the transaction in Freighter wallet");
    }

    const accountId = await getPublicKey();
    const account = await server.getAccount(accountId);
    const fee = StellarSdk.BASE_FEE;

    const contract = new StellarSdk.Contract(contractId);
    const instance = contract.getFootprint();

    window.ins = instance;

    // Fetch the WASM entry from the ledger

    const wasmEntry = await server.getLedgerEntries(instance);

    const restoreTx = new StellarSdk.TransactionBuilder(account, {
      fee: StellarSdk.BASE_FEE,
    })
      .setNetworkPassphrase(StellarSdk.Networks.TESTNET)
      .setSorobanData(
        // Set the restoration footprint (remember, it should be in the
        // read-write part!)
        new StellarSdk.SorobanDataBuilder()
          .setReadWrite([
            instance,
            ...wasmEntry.entries.map((entry) => entry.key),
          ])
          .build(),
      )
      .setTimebounds(0, Date.now() + 10000)
      .addOperation(StellarSdk.Operation.restoreFootprint({}))
      .build();

    let preparedTx = await server.prepareTransaction(restoreTx);
    let signedXDR = await signTransaction(preparedTx.toXDR(), {
      networkPassphrase: networkPassphrase,
    });
    let signedTx = StellarSdk.TransactionBuilder.fromXDR(
      signedXDR,
      networkPassphrase,
    );

    return server.sendTransaction(signedTx);
  } catch (error) {
    console.error("Error restoring contract instance:", error);
    throw error;
  }
}

// Helper function to get the ledger key for the WASM entry
function getWasmLedgerKey(entry) {
  return StellarSdk.xdr.LedgerKey.contractCode(
    new StellarSdk.xdr.LedgerKeyContractCode({
      hash: entry.val().instance().wasmHash(),
    }),
  );
}
info

This function specifically restores a contract instance and its associated Wasm code. It retrieves the contract's footprint and Wasm entry, creates a restoration transaction, which is then signed using Freighter and submitted to the network.

When to use these functions​

  1. performContractAction helper can be used when trying to invoke a smart contract function. It can help to restore persistent data associated with the call.
  2. restoreContractInstance helper can be used during app initialization after the app has not been used for a long time. Using an indexer to get this info (when last app was used) is a great approach.

Conclusion​

By implementing these state archival and restoration techniques, your dapp will be able to handle situations where contract data or instances have been archived, ensuring a smoother user experience even after periods of inactivity. The use of wallets like Freighter for transaction signing provides a secure and user-friendly way for users to interact with your dapp.

Remember to handle errors appropriately and provide clear feedback to users throughout the restoration process. You may also want to implement a loading indicator in your UI while restoration is in progress, as it may take a moment to complete.

Understanding and effectively managing state archival is crucial for creating robust and efficient Stellar-based dapps that can maintain functionality and data integrity over time.

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