Multiple OP-Return Outputs in One Transaction

When it comes to Ethereum, the concept of
OP-Return and its usage is crucial for developers building decentralized applications (dApps). In this article, we’ll explore whether you can inject multiple OP-Return outputs in one transaction.

What are OP-Returns?

OP-Returns allow a user to send Ether (ETH) from a transaction without explicitly using the eth_sendTransaction function. Instead, they can create a transaction that includes an empty value field, followed by any number of outputs with different
signatures, known as
addresses.

In essence, OP-Return outputs are used to specify which addresses should receive Ether in exchange for performing certain actions (like calling smart contracts). These actions can be complex or involve multiple steps.

Can I have multiple OP-Return outputs in one transaction?

While it’s technically possible to create a single transaction with multiple OP-Return outputs, there are some limitations and considerations:

• Transaction size: Each OP-Return output requires an additional field (the value field) that exceeds the maximum allowed transaction size. This can lead to significant space constraints for transactions.

• Chain ID: The chainId field in a transaction is hardcoded to 0x1, which means that only one chain ID can be used at a time. When you add multiple OP-Return outputs, each output must have its own unique chainId, leading to additional complexity and potential conflicts.

• Smart contract interactions: If your smart contracts are designed to receive Ether from OP-Return outputs, you’ll need to ensure that the smart contracts can handle multiple signers or different addresses. This may require significant changes to your codebase.

When might it be feasible?

While having multiple OP-Return outputs in one transaction is not straightforward, there are scenarios where it might make sense:

• Batching: If you’re building a system that requires sending Ether from multiple users simultaneously (e.g., for a batch processing scenario), using OP-Returns could help reduce the number of transactions needed.

• Smart contract simplification: In certain cases, having fewer OP-Return outputs might make your smart contracts simpler and easier to maintain.

In conclusion

While it’s not necessarily impossible to have multiple OP-Return outputs in one transaction, it requires careful consideration of several factors, including transaction size constraints, chain ID uniqueness, and potential conflicts. Unless you’re working with a specific use case that demands this functionality (e.g., batching or smart contract simplification), it may be more efficient to explore alternative approaches.

Best practices:

To minimize the complexity and costs associated with OP-Return outputs in your transaction:

• Optimize transaction size: Use a smaller value field for each output, as large values can increase the transaction size.

• Use chain ID uniqueness: Ensure that each OP-Return output has its own unique chainId.

• Consider smart contract complexity: Plan ahead and design your smart contracts to handle multiple signers or different addresses.

By understanding the limitations and potential pitfalls of using OP-Returns in transactions, you can make informed decisions about how best to implement this feature in your applications.