Icon LinkSRC-10: Native Bridge

The following standard allows for the implementation of a standard API for Native Bridges using the Sway Language. The standardized design has the bridge contract send a message to the origin chain to register which token it accepts to prevent a loss of funds.

Icon LinkMotivation

A standard interface for bridges intends to provide a safe and efficient bridge between the settlement or canonical chain and the Fuel Network.

Icon LinkPrior Art

The standard is centered on Fuel’s Bridge Architecture Icon Link. Fuel's bridge system is built on a message protocol that allows to send (and receive) messages between entities located in two different blockchains.

The following standard takes reference from the FungibleBridge Icon Link ABI defined in the fuel-bridge repository.

Icon LinkSpecification

The following functions MUST be implemented to follow the SRC-10; Native Bridge Standard:

Icon LinkRequired Functions

fn process_message(message_index: u64)

The process_message() function accepts incoming deposit messages from the canonical chain and issues the corresponding bridged asset.

• This function MUST parse a message at the given message_index index.
• This function SHALL mint an asset that follows the SRC-8; Bridged Asset Standard .
• This function SHALL issue a refund if there is an error in the bridging process.

fn withdraw(to_address: b256)

The withdraw() function accepts and burns a bridged Native Asset on Fuel and sends a message to the bridge contract on the canonical chain to release the originally deposited tokens to the to_address address.

• This function SHALL send a message to the bridge contract to release the bridged tokens to the to_address address on the canonical chain.
• This function MUST ensure the asset's AssetId sent in the transaction matches a bridged asset.
• This function SHALL burn all coins sent in the transaction.

fn claim_refund(to_address: b256, token_address: b256, token_id: b256, gateway_contract: b256)

The claim_refund() function is called if something goes wrong in the bridging process and an error occurs. It sends a message to the gateway_contract contract on the canonical chain to release the token_address token with token id token_id to the to_address address.

• This function SHALL send a message to the gateway_contract contract to release the token_address token with id token_id to the to_address address on the canonical chain.
• This function MUST ensure a refund was issued.

Icon LinkRequired Data Types

Icon LinkDepositType

The DepositType enum describes whether the bridged deposit is made to a address, contract, or contract and contains additional metadata. There MUST be the following variants in the DepositType enum:

Address: ()

The Address variant MUST represent when the deposit is made to an address on the Fuel chain.

Contract: ()

The Contract variant MUST represent when the deposit is made to an contract on the Fuel chain.

ContractWithData: ()

The ContractWithData variant MUST represent when the deposit is made to an contract and contains additional metadata for the Fuel chain.

Icon LinkExample Deposit Type

pub enum DepositType {
    Address: (),
    Contract: (),
    ContractWithData: (),
}

Icon LinkDepositMessage

The following describes a struct that encapsulates various deposit message metadata to a single type. There MUST be the following fields in the DepositMessage struct:

amount: u256

The amount field MUST represent the number of tokens.

from: b256

The from field MUST represent the bridging user’s address on the canonical chain.

to: Identity

The to field MUST represent the bridging target destination Address or ContractId on the Fuel Chain.

token_address: b256

The token_address field MUST represent the bridged token's address on the canonical chain.

token_id: b256

The token_id field MUST represent the token's ID on the canonical chain. The b256::zero() MUST be used if this is a fungible token and no token ID exists.

decimals: u8

The decimals field MUST represent the bridged token's decimals on the canonical chain.

deposit_type: DepositType

The deposit_type field MUST represent the type of bridge deposit made on the canonical chain.

Icon LinkExample Deposit Message

pub struct DepositMessage {
    pub amount: b256,
    pub from: b256,
    pub to: Identity,
    pub token_address: b256,
    pub token_id: b256,
    pub decimals: u8,
    pub deposit_type: DepositType,
}

Icon LinkMetadataMessage

The following describes a struct that encapsulates the metadata of token on the canonical chain to a single type. There MUST be the following fields in the MetadataMessage struct:

token_address: b256

The token_address field MUST represent the bridged token's address on the canonical chain.

token_id: b256

The token_id field MUST represent the token's ID on the canonical chain. The b256::zero() MUST be used if this is a fungible token and no token ID exists.

name: String

The name field MUST represent the bridged token's name field on the canonical chain.

symbol: String

The symbol field MUST represent the bridged token's symbol field on the canonical chain.

Icon LinkExample Metadata Message

pub struct MetadataMessage {
    pub token_address: b256,
    pub token_id: b256,
    pub name: String,
    pub symbol: String,
}

Icon LinkRequired Standards

Any contract that implements the SRC-10; Native Bridge Standard MUST implement the SRC-8; Bridged Asset Standard for all bridged assets.

Icon LinkRationale

The SRC-10; Native Bridge Standard is designed to standardize the native bridge interface between all Fuel instances.

Icon LinkBackwards Compatibility

This standard is compatible with the SRC-20 and SRC-8 standards.

Icon LinkExample ABI

abi SRC10 {
     fn process_message(message_index: u64);
     fn withdraw(to_address: b256);
     fn claim_refund(to_address: b256, token_address: b256, token_id: b256, gateway_contract: b256);
}