Smart Contract Standardized Asset (Stellar Asset Contract) Extension: Memo

CAP: 0061
Title: Smart Contract Standardized Asset (Stellar Asset Contract) Extension: Memo
Working Group:
    Owner: Tomer Weller <@tomerweller>
    Authors: Leigh McCulloch <@leighmcculloch>, Tomer Weller <@tomerweller>
    Consulted: Nicolas Barry <@monsieurnicolas>, Alex Cordeiro <@accordeiro>, Dmytro Kozhevin <@dmkozh>
Status: Rejected
Created: 2024-08-26
Discussion: TBA

Simple Summary

Implement the SEP-44 for the Stellar Asset Contract.

Motivation

To support an unambiguous method by which contract wallets can transfer Stellar Assets to custodial wallets that require a memo to be associated with the transfer that is populated through to events used to track transfers.

Goals Alignment

This CAP is aligned with the following Stellar Network Goals:

• The Stellar Network should make it easy for developers of Stellar projects to create highly usable products
• The Stellar Network should enable cross-border payments, i.e. payments via exchange of assets, throughout the globe, enabling users to make payments between assets in a manner that is fast, cheap, and highly usable.

Abstract

This proposal introduces a built-in implementation for Stellar Assets of the SEP-44 standard for transferring with an associated memo.

This proposal disallows the subsequent use of the transaction memo field on smart contract transactions.

Specification

XDR Changes

None.

Transactions Changes

The memo field of Transaction must have value MEMO_NONE when SorobanTransactionData is present.

Extended Token Interface

The Stellar Asset Contract interface is extended with one function:

/// Transfer `amount` from `from` to `to`.
///
/// The memo annotates the transfer event.
///
/// # Arguments
///
/// - `from` - The address holding the balance of tokens which will be
/// withdrawn from.
/// - `to` - The address which will receive the transferred tokens.
/// - `amount` - The amount of tokens to be transferred.
/// - `memo` - The memo associated with the transfer.
///
/// # Events
///
/// Emits an event with topics `["transfer", from: Address, to: Address, sep0011_asset: String, memo: u64],
/// data = amount: i128`
fn transfer_memo(env: Env, from: Address, to: Address, amount: i128, memo: u64);

Design Rationale

See SEP-44 for the design rationale of the transfer_memo interface.

The memo field of transactions is disallowed on smart contract transactions to remove any ambiguity that arises by specifying different memos on the transaction vs within the smart contract invocation. An assessment of transaction memo usage today with smart contract transactions shows that their use are rare.

Protocol Upgrade Transition

Backwards Incompatibilities

This proposal introduces a breaking change into the Transaction structure where the memo cannot be set for transactions involving smart contracts.

This proposal is otherwise backwards compatible in regards to all existing functionality, however the introduction of the transfer event with the additional memo topic requires that existing applications be updated to handle the memo topic being present.

Resource Utilization

This proposal will lead to approximately the same resource usage as exists today.

Security Concerns

This proposal does not introduce any security concerns.

Test Cases

None yet.

Implementation

None yet.