Extending a deployed contract's TTL using code

When a smart contract is deployed on the Stellar network, its WebAssembly (Wasm) code has a Time To Live (TTL) that determines how long it remains accessible.

The TTL is the number of ledgers between the current ledger and the final ledger for which the contract data can still be accessed. If the TTL expires, the contract's code becomes archived and inaccessible. To prevent this, you need to periodically extend the TTL of the contract's Wasm code.

This guide will show you how to extend the TTL of a deployed contract's Wasm code using the Javascript and Rust SDKs.

Understanding TTL in Soroban

Before we demonstrate the TTL extension methods, you should note that in Soroban:

• Contract instances and code are stored in the instance storage
• TTL exists to prevent the blockchain from being cluttered with inactive contracts
• TTL extension can be done for both the contract instance and the contract code

Prerequisites

• Stellar SDK: npm install @stellar/stellar-sdk for Javascript
• A Stellar RPC endpoint (e.g., https://soroban-testnet.stellar.org)
• Basic knowledge of the SDK in use

Methods for Extending TTL

This guide will cover three ways to extend a contract's TTL:

1. Self-Extension: Extending the TTL from within the contract itself, in Rust.

   • Use case: When a contract needs to manage its own lifetime
   • Process: Directly accessing the contract's instance storage to extend its TTL

2. External Extension: Extending the TTL from another contract (the deployer), in Rust.

   • Use case: When managing multiple contract instances or implementing administrative control
   • Process: Using the deployer's authority to extend TTL for any contract it has deployed

3. Client Extension: Extending the TTL from an external client using Javascript.

   • Use Case: When you need to manage contract TTLs through an external application or automated system.
   • Process:
     • Get the contract's footprint
     • Set a reasonable resource fee (perhaps start at 10,000 stroops as this is a costly operation)
     • Set Soroban data as read-only
     • Set the desired ledger TTL to expire the contract
     • Create an operation StellarSdk.Operation.extendFootprintTtl

note

A resource fee and base fee are both charged in this operation.

Rust

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

#[contract]
pub struct ExtendTTLContract;

#[contractimpl]
impl ExtendTTLContract {
    // Self-extension
    pub fn extend_contract_ttl(env: Env, threshold: u32, extend_to: u32) {
        env.storage().instance().extend_ttl(threshold, extend_to);
    }

    // External extension
    pub fn extend_other_contract_ttl(env: Env, contract_address: Address, threshold: u32, extend_to: u32) {
        let deployer = env.deployer();
        deployer.extend_ttl(
            contract_address,
            threshold,
            extend_to
        );
    }
}

• env.storage().instance().extend_ttl(...) is called to extend the TTL of the current contract instance.
• threshold is a check that ensures that the current TTL of the contract instance is less than the set threshold value.
• extend_to is the number of ledgers to be added to the current TTL.
• contract_address is the address of the contract instance whose TTL we want to extend.
• env.deployer() accesses the deployer, which has methods for managing the contract's lifecycle.
• deployer.extend_ttl(...) extends the TTL of the specified contract instance.

JS

The code below uses Nodejs environment but same concept can also be applied in the browser using Freighter wallet or using any other Stellar SDK.

import * as StellarSdk from "@stellar/stellar-sdk";
import { Server } from "@stellar/stellar-sdk/rpc";

async function extendContractWasmTTL(contractId, sourceKeypair) {
  const server = new Server("https://soroban-testnet.stellar.org");

  // Create a new transaction builder
  const account = await server.getAccount(sourceKeypair.publicKey());
  const fee = "200100"; // Base fee plus resource fee

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

  // Set the Soroban data and create an operation to extend the contract's TTL
  const sorobanData = new StellarSdk.SorobanDataBuilder()
    .setResourceFee(200_000)
    .setReadOnly([instance])
    .build();
  const transaction = new StellarSdk.TransactionBuilder(account, {
    fee,
    networkPassphrase: StellarSdk.Networks.TESTNET, // Use appropriate network
  })
    .setSorobanData(sorobanData)
    .addOperation(
      StellarSdk.Operation.extendFootprintTtl({
        extendTo: 500_000,
      }),
    )
    .setTimeout(30)
    .build();

  // Sign and submit the transaction
  transaction.sign(sourceKeypair);
  const result = await server.sendTransaction(transaction);

  console.log(
    "Transaction submitted. Result:",
    JSON.stringify(result, null, 2),
  );
  return result;
}

// Usage
const contractId = "CC6MWZMG2JPQEENRL7XVICAY5RNMHJ2OORMUHXKRDID6MNGXSSOJZLLF";
const sourceKeypair = StellarSdk.Keypair.fromSecret(
  "SXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX",
);

extendContractWasmTTL(contractId, sourceKeypair)
  .then(console.log)
  .catch(console.error);

Breaking Down the Code

Let's walk through the key parts of this function:

1. Setting up the Soroban data: The SorobanDataBuilder() is where we prep the Soroban-specific info for our transaction.

• We set a resource fee with setResourceFee(200_000). This covers the extra costs for storage and execution.
• We use setReadOnly([instance]) to tell the network which contract stuff we need to access. We're using setReadOnly() instead of setReadWrite() because we're just extending the TTL, not changing any data.

Why setReadOnly()? A few reasons:

• It's faster and uses fewer resources
• It's safer - we can't accidentally change data we're not supposed to
• The ExtendFootprintTTLOp operation needs it

2. Adding the operation: After setting up the Soroban data, we add the extendFootprintTtl operation to our transaction. We're telling it to extend the TTL to 500,000 ledgers with extendTo: 500_000.

3. What's the point? This whole process is about keeping our contract's data alive in the ledger. It's like renewing a lease - we're telling the network "Hey, keep this stuff around longer, we're still using it!"

This is super important for contracts that need to stick around for a while. Without extending the TTL, the contract's data could expire and disappear from the ledger.

Learn how to test the TTL extension in this guide.

Want to dive deeper? Check out the docs on the Extend Footprint TTL operation.