SRC-4; Flash Mint Standard

[SwayStar123]

Abstract

The following standard allows for the implementation of a standard API for flash mints for native-assets using the Sway language. This standard is an optional add-on to the SRC-20 standard.

Motivation

Flash mints allow anyone to temporarily mint out a large number of tokens and use them for any purpose with the requirement that they be returned within the same transaction. This pattern is highly useful and would greatly benefit from standardisation

Prior Art

Flash mints have been thoroughly explored on Ethereum and with EIP 3156 they have their own standard for it. However as Fuel's native assets are fundamentally different to Ethereum's ERC-20 tokens, the implementation will differ, but the interface may be used as reference.

Specification

Required public functions

The following functions MUST be implemented (on top of the SRC-20 functions) to follow the SRC-4 standard

fn flash_mint(amount: u64, target: ContractId, calldata: Vec<u8>, gas_required: u64)

Calls the target ContractId forwarding gas_required gas and amount coins.

The target ContractId MUST implement the FlashBorrower abi.
The contract balance for the asset_id being minted MUST be greater than or equal to the balance prior to calling the target Contract + the flash fee to be charged for flash minting amount of coins

fn flash_fee(amount: u64)

Read only function that returns the fee that would be charged for a flashloan of the given amount

The parameters of the function may change depending on the implementation of native multi tokens on Fuel.

Required logs

The following logs MUST be emitted at the specified occasions

enum FlashLoanError {
    // The loan was not repaid. The missing amount is logged
    LoanNotRepaid: u64,
}

The LoanNotRepaid variant of this enum must be logged in the event that the entire expected amount is not repaid to the contract. The amount remaining to be paid must be the value associated.

Rationale

The ABI discussed is simple and covers the known use cases of flash mints while allowing safe implementations

Backwards compatibility

This standard is fully compatible with the SRC-20 standard

Security Considerations

Incorrect implementation of flashmints could allow attackers to gain very large number of tokens. It is recommended to properly audit any code using this standard to ensure exploits are not possible.

Reference implementation

Full reference implementation can be seen here

This is a draft standard

[dmihal]

Standard is ready for review, but we can't make a proper implementation without serialization, so tabling this for now