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Estimating Gas for Jumbochain Transactions in Go

This article delves into the crucial aspect of setting the gasLimit when sending transactions to a Jumbochain smart contract using Go.

We'll explore why hardcoding gas limits is risky and demonstrate how to use the EstimateGas function provided by the jumbochain-go library to dynamically determine the appropriate gas limit, thus preventing "out of gas" errors and optimizing transaction costs.

1. Understanding Gas and Gas Limit​

On Jumbochain, every operation performed on the blockchain, including executing smart contract functions, consumes a certain amount of computational effort, measured in units of "gas."

  • Gas Price: The amount of JNFTC (or the network's native currency) you are willing to pay per unit of gas.
  • Gas Limit: The maximum amount of gas you are willing to spend on a particular transaction. You set this limit when creating and signing the transaction.
  • Gas Used: The actual amount of gas consumed by the transaction upon execution.

If the gasUsed exceeds the gasLimit, the transaction will fail with an "out of gas" error, and you will still have to pay for the gas consumed up to that point. Setting an arbitrarily high gasLimit can lead to unnecessary costs if the transaction consumes far less gas.

2. The Pitfalls of Hardcoding gasLimit​

Hardcoding a gasLimit value (e.g., auth.GasLimit = uint64(100000)) might seem convenient initially, but it carries significant risks:

  • "Out of Gas" Errors: If the actual gas required by your transaction exceeds the hardcoded limit (due to changes in contract logic, state, or input parameters), your transaction will fail.
  • Wasted Gas: If you set a very high gasLimit that is much larger than what the transaction actually needs, you end up paying for unused gas.
warning

Avoid hardcoding gasLimit values in production applications. It makes your code brittle and prone to unexpected failures or increased costs.

3. Using EstimateGas for Dynamic Gas Limit Calculation​

The jumbochain-go library provides the EstimateGas function, which allows you to query the Jumbochain node to estimate the gas required for a specific transaction before you send it. This is the recommended approach for setting an appropriate gasLimit.

3.1. Importing Necessary Packages​

Ensure you have the following imports in your Go code:

main.go
import (
 // ... other imports
 "github.com/jumbochain/jumbochain-go"
 "github.com/jumbochain/jumbochain-go/accounts/abi/bind"
 "github.com/jumbochain/jumbochain-go/common"
 "github.com/jumbochain/jumbochain-go/jumboclient" // jumbochain client 

)

3.2. Implementing utility function with EstimateGas​

You can create similar to getTransactionAuthorizer function from the simple storage example to incorporate EstimateGas in your go codebase.

Check the highlighted part.

main.go

func getTransactionAuthorizer(client *jumboclient.Client,
  contractAddress common.Address,
  txData []byte) (*bind.TransactOpts, error) {
  privateKeyHex := os.Getenv("PRIVATE_KEY")
  if privateKeyHex == "" {
    return nil, fmt.Errorf("PRIVATE_KEY environment variable not set")
  }

  privateKey, err := crypto.HexToECDSA(privateKeyHex)
  if err != nil {
    return nil, err
  }

  address := crypto.PubkeyToAddress(privateKey.PublicKey)

  nonce, err := client.PendingNonceAt(context.Background(), address)
  if err != nil {
    return nil, err
  }

  chainID, err := client.ChainID(context.Background())
  if err != nil {
    return nil, err
  }

  auth, err := bind.NewKeyedTransactorWithChainID(privateKey, chainID)
  if err != nil {
    return nil, err
  }
  auth.Nonce = big.NewInt(int64(nonce))
  auth.Value = big.NewInt(0) // No Ether to send with this contract call

  // Estimate the gas required for the transaction.
  gas, err := client.EstimateGas(context.Background(), jumbochain.CallMsg{
    From: auth.From,
    To:   &contractAddress,
    Data: txData, // The encoded function call data
  })
  if err != nil {
    log.Printf("Error estimating gas: %v", err)
    // In case of an estimation error, you might want to fall back
    // to a slightly higher default gas limit or investigate the error.
    auth.GasLimit = uint64(300000) // Fallback gas limit (adjust as needed)
  } else {
    fmt.Println("Estimated gas:", gas)
    // It's often a good practice to add a small buffer (e.g., 10-20%)
    // to the estimated gas to account for minor variations during execution.
    auth.GasLimit = gas + 20000
  }

  return auth, nil
}

Code Explanation:

We call client.EstimateGas with a jumbochain.CallMsg struct.

This struct contains:

From: The address of the sender.
To: The address of the contract being called.
Data: The encoded data of the function call (obtained by packing 
the function name and arguments using the contract ABI).

The EstimateGas function returns the estimated gas required for the transaction. If there's an error during gas estimation, we log the error and fall back to a reasonable default gasLimit. If the estimation is successful, we set the auth.GasLimit to the estimated gas plus a small buffer.

3.3. Integrating utility in your codebase​

Now, following is a example how getTransactionAuthorizer utility is used before sending any state-changing transactions:

main.go

func main() {
 // ... (code for loading environment variables and connecting to the client) ...

 contractAddressStr := os.Getenv("CONTRACT_ADDRESS")
 // ... (error handling for contract address) ...
 contractAddress := common.HexToAddress(contractAddressStr)

 instance, err := contract.NewStorage(contractAddress, client)
 // ... (error handling for contract instance) ...

 contractABI, err := abi.JSON(strings.NewReader(contract.StorageABI))
 // ... (error handling for ABI parsing) ...

 // Setting a new value
 newValue := big.NewInt(200)
 txData, err := contractABI.Pack("set", newValue)
 // ... (error handling for packing arguments) ...

 // **Use the updated getTransactionAuthorizer to get the auth with estimated gas.**
 auth, err := getTransactionAuthorizer(client, contractAddress, txData)
 if err != nil {
  log.Fatal(err)
 }

 tx, err := instance.Set(auth, newValue)
 // ... (rest of the transaction sending and receipt handling) ...

 // Calling the 'add' function
 addValue := big.NewInt(50)
 txDataAdd, err := contractABI.Pack("add", addValue)
 // ... (error handling for packing arguments) ...

 // **Use the updated getTransactionAuthorizer again.**
 authAdd, err := getTransactionAuthorizer(client, contractAddress, txDataAdd)
 if err != nil {
  log.Fatal(err)
 }

 txAdd, err := instance.Add(authAdd, addValue)
 // ... (rest of the transaction sending and receipt handling) ...
}

4. Best Practices and Tips​

  • Always Estimate Gas for State-Changing Transactions: For functions that modify the blockchain state, always use EstimateGas to determine the appropriate gasLimit.

  • Add a Small Buffer: Include a small percentage or a fixed amount (e.g., 10-20% or a few thousand units) to the estimated gas to account for minor variations during transaction execution.

  • Handle Estimation Errors: Implement error handling for the EstimateGas function. You might want to log the error, retry the estimation, or fall back to a slightly higher default gasLimit after careful consideration.

  • Monitor Gas Usage: In production environments, consider monitoring the actual gas used by your transactions to fine-tune your buffer and ensure efficiency.

  • Consider Network Congestion: While EstimateGas provides a good approximation, high network congestion can sometimes lead to slightly higher gas usage. The buffer helps mitigate this.

By adopting the practice of estimating gas dynamically, you can build more robust and cost-effective applications that interact with smart contracts. This approach significantly reduces the risk of "out of gas" errors and avoids overpaying for transaction execution.