aztec-nr - noir_aztec::messages::offchain_messages

Function emit_offchain_message

pub fn emit_offchain_message<T>(message: T, recipient: AztecAddress)

where
    T: Serialize

Emits a message that will be delivered offchain rather than through the data availability layer.

Sends data through an alternative app-specific channel without incurring data availability (DA) costs. After receiving the message, the recipient is expected to call the process_message function implemented on the contract that originally emitted the message.

Example use case

A typical use case would be a payment app where the notes and events do not need to be delivered via DA because the payment is considered successful by the recipient once he receives the notes and events offchain. Hence having the guaranteed delivery via DA is not necessary.

When not to use

This function should not be used when an onchain guarantee of successful delivery is required. This is the case when a smart contract (rather than a person) needs to make decisions based on the message. For example, consider a contract that escrows a privately-stored NFT (i.e. an NFT represented by a note) and releases it to a buyer only after receiving a payment in a specific token. Without onchain delivery, the buyer could potentially obtain the NFT without sending the payment token message (the note hash preimage) to the seller, rugging the seller.

To clarify the above, while the malicious buyer's payment token would still be deducted from their balance, they would obtain the NFT while the seller would be unable to spend the payment token, keeping the payment token note in limbo.

Arguments