Sway Standards

⌘K

Src 6 Vault

Icon LinkSRC-6: Vault

The following standard allows for the implementation of a standard API for asset vaults such as yield-bearing asset vaults or asset wrappers. This standard is an optional add-on to the SRC-20 standard.

Icon LinkMotivation

Asset vaults allow users to own shares of variable amounts of assets, such as lending protocols which may have growing assets due to profits from interest. This pattern is highly useful and would greatly benefit from standardization.

Icon LinkPrior Art

Asset vaults have been thoroughly explored on Ethereum and with EIP 4626 Icon Link they have their own standard for it. However as Fuel's Native Assets Icon Link are fundamentally different from Ethereum's ERC-20 tokens, the implementation will differ, but the interface may be used as a reference.

Icon LinkSpecification

Icon LinkRequired public functions

The following functions MUST be implemented to follow the SRC-6 standard. Any contract that implements the SRC-6 standard MUST implement the SRC-20 standard.

Icon Link`fn deposit(receiver: Identity, vault_sub_id: SubId) -> u64`

This function takes the receiver Identity and the SubId vault_sub_id of the sub-vault as an argument and returns the amount of shares minted to the receiver.

This function MUST allow for depositing of the underlying asset in exchange for pro-rata shares of the vault.
This function MAY reject arbitrary assets based on implementation and MUST revert if unaccepted assets are forwarded.
This function MAY reject any arbitrary receiver based on implementation and MUST revert in the case of a blacklisted or non-whitelisted receiver.
This function MUST mint an asset representing the pro-rata share of the vault, with the SubId of the sha256((underlying_asset, vault_sub_id)) digest, where underlying_asset is the AssetId of the deposited asset and the vault_sub_id is the id of the vault.
This function MUST emit a Deposit log.
This function MUST return the amount of minted shares.

Icon Link`fn withdraw(receiver: Identity, underlying_asset: AssetId, vault_sub_id: SubId) -> u64`

This function takes the receiver Identity, the underlying_asset AssetId, and the vault_sub_id of the sub vault, as arguments and returns the amount of assets transferred to the receiver.

This function MUST allow for redeeming of the vault shares in exchange for a pro-rata amount of the underlying assets.
This function MUST revert if any AssetId other than the AssetId representing the underlying asset's shares for the given sub vault at vault_sub_id is forwarded. (i.e. transferred share's AssetId must be equal to AssetId::new(ContractId::this(), sha256((underlying_asset, vault_sub_id)))
This function MUST burn the received shares.
This function MUST emit a Withdraw log.
This function MUST return amount of assets transferred to the receiver.

Icon Link`fn managed_assets(underlying_asset: AssetId, vault_sub_id: SubId) -> u64`

This function returns the total assets under management by vault. Includes assets controlled by the vault but not directly possessed by vault. It takes the underlying_asset AssetId and the vault_sub_id of the sub vault as arguments and returns the total amount of assets of AssetId under management by vault.

This function MUST return total amount of assets of underlying_asset AssetId under management by vault.
This function MUST return 0 if there are no assets of underlying_asset AssetId under management by vault.
This function MUST NOT revert under any circumstances.

Icon Link`fn max_depositable(receiver: Identity, underlying_asset: AssetId, vault_sub_id: SubId) -> Option<u64>`

This is a helper function for getting the maximum amount of assets that can be deposited. It takes the hypothetical receiver Identity, the underlying_asset AssetId, and the vault_sub_id SubId of the sub vault as an arguments and returns the maximum amount of assets that can be deposited into the contract, for the given asset.

This function MUST return the maximum amount of assets that can be deposited into the contract, for the given underlying_asset, if the given vault_sub_id vault exists.
This function MUST return an Some(amount) if the given vault_sub_id vault exists.
This function MUST return an None if the given vault_sub_id vault does not exist.
This function MUST account for both global and user specific limits. For example: if deposits are disabled, even temporarily, MUST return 0.

Icon Link`fn max_withdrawable(receiver: Identity, underlying_asset: AssetId, vault_sub_id: SubId) -> Option<u64>`

This is a helper function for getting maximum withdrawable. It takes the hypothetical receiver Identity, the underlying_asset AssetId, and the vault_sub_id SubId of the sub vault as an argument and returns the maximum amount of assets that can be withdrawn from the contract, for the given asset.

This function MUST return the maximum amount of assets that can be withdrawn from the contract, for the given underlying_asset, if the given vault_sub_id vault exists.
This function MUST return an Some(amount) if the given vault_sub_id vault exists.
This function MUST return an None if the given vault_sub_id vault does not exist.
This function MUST account for global limits. For example: if withdrawals are disabled, even temporarily, MUST return 0.

Icon LinkRequired logs

The following logs MUST be emitted at the specified occasions.

Icon Link`Deposit`

caller has called the deposit() method sending deposited_amount assets of the underlying_asset Asset to the subvault of vault_sub_id, in exchange for minted_shares shares sent to the receiver receiver.

The Deposit struct MUST be logged whenever new shares are minted via the deposit() method.

The Deposit log SHALL have the following fields.

caller: Identity

The caller field MUST represent the Identity which called the deposit function.

receiver: Identity

The receiver field MUST represent the Identity which received the vault shares.

underlying_asset: AssetId

The underlying_asset field MUST represent the AssetId of the asset which was deposited into the vault.

vault_sub_id: SubId

The vault_sub_id field MUST represent the SubId of the vault which was deposited into.

deposited_amount: u64

The deposited_amount field MUST represent the u64 amount of assets deposited into the vault.

minted_shares: u64

The minted_shares field MUST represent the u64 amount of shares minted.

Icon Link`Withdraw`

caller has called the withdraw() method sending burned_shares shares in exchange for withdrawn_amount assets of the underlying_asset Asset from the subvault of vault_sub_id to the receiver receiver.

The Withdraw struct MUST be logged whenever shares are redeemed for assets via the withdraw() method.

The Withdraw log SHALL have the following fields.

caller: Identity

The caller field MUST represent the Identity which called the withdraw function.

receiver: Identity

The receiver field MUST represent the Identity which received the withdrawn assets.

underlying_asset: AssetId

The underlying_asset field MUST represent the AssetId of the asset that was withdrawn.

vault_sub_id: SubId

The vault_sub_id field MUST represent the SubId of the vault from which was withdrawn.

withdrawn_amount: u64

The withdrawn_amount field MUST represent the u64 amount of coins withdrawn.

burned_shares: u64

The burned_shares field MUST represent the u64 amount of shares burned.

Icon LinkRationale

The ABI discussed covers the known use cases of asset vaults while allowing safe implementations.

Icon LinkBackwards Compatibility

This standard is fully compatible with the SRC-20 standard .

Icon LinkSecurity Considerations

Incorrect implementation of asset vaults could allow attackers to steal underlying assets. It is recommended to properly audit any code using this standard to ensure exploits are not possible.

Icon LinkExample ABI

abi SRC6 {
    #[payable]
    #[storage(read, write)]
    fn deposit(receiver: Identity, vault_sub_id: SubId) -> u64;
 
    #[payable]
    #[storage(read, write)]
    fn withdraw(receiver: Identity, underlying_asset: AssetId, vault_sub_id: SubId) -> u64;
 
    #[storage(read)]
    fn managed_assets(underlying_asset: AssetId, vault_sub_id: SubId) -> u64;
    
    #[storage(read)]
    fn max_depositable(receiver: Identity, underlying_asset: AssetId, vault_sub_id: SubId) -> Option<u64>;
 
    #[storage(read)]
    fn max_withdrawable(underlying_asset: AssetId, vault_sub_id: SubId) -> Option<u64>;
}

Icon LinkExample Implementation

Icon LinkMulti Asset Vault

A basic implementation of the vault standard that supports any number of sub vaults being created for every AssetId.

contract;
 
use std::{
    asset::transfer,
    call_frames::msg_asset_id,
    context::msg_amount,
    hash::{
        Hash,
        sha256,
    },
    storage::storage_string::*,
    string::String,
};
 
use standards::{src20::SRC20, src6::{Deposit, SRC6, Withdraw}};
 
pub struct VaultInfo {
    /// Amount of assets currently managed by this vault
    managed_assets: u64,
    /// The vault_sub_id of this vault.
    vault_sub_id: SubId,
    /// The asset being managed by this vault
    asset: AssetId,
}
 
storage {
    /// Vault share AssetId -> VaultInfo.
    vault_info: StorageMap<AssetId, VaultInfo> = StorageMap {},
    /// Number of different assets managed by this contract.
    total_assets: u64 = 0,
    /// Total supply of shares for each asset.
    total_supply: StorageMap<AssetId, u64> = StorageMap {},
    /// Asset name.
    name: StorageMap<AssetId, StorageString> = StorageMap {},
    /// Asset symbol.
    symbol: StorageMap<AssetId, StorageString> = StorageMap {},
    /// Asset decimals.
    decimals: StorageMap<AssetId, u8> = StorageMap {},
}
 
impl SRC6 for Contract {
    #[payable]
    #[storage(read, write)]
    fn deposit(receiver: Identity, vault_sub_id: SubId) -> u64 {
        let asset_amount = msg_amount();
        require(asset_amount != 0, "ZERO_ASSETS");
 
        let underlying_asset = msg_asset_id();
        let (shares, share_asset, share_asset_vault_sub_id) = preview_deposit(underlying_asset, vault_sub_id, asset_amount);
 
        _mint(receiver, share_asset, share_asset_vault_sub_id, shares);
 
        let mut vault_info = storage.vault_info.get(share_asset).read();
        vault_info.managed_assets = vault_info.managed_assets + asset_amount;
        storage.vault_info.insert(share_asset, vault_info);
 
        log(Deposit {
            caller: msg_sender().unwrap(),
            receiver,
            underlying_asset,
            vault_sub_id,
            deposited_amount: asset_amount,
            minted_shares: shares,
        });
 
        shares
    }
 
    #[payable]
    #[storage(read, write)]
    fn withdraw(
        receiver: Identity,
        underlying_asset: AssetId,
        vault_sub_id: SubId,
    ) -> u64 {
        let shares = msg_amount();
        require(shares != 0, "ZERO_SHARES");
 
        let (share_asset_id, share_asset_vault_sub_id) = vault_asset_id(underlying_asset, vault_sub_id);
 
        require(msg_asset_id() == share_asset_id, "INVALID_ASSET_ID");
        let assets = preview_withdraw(share_asset_id, shares);
 
        _burn(share_asset_id, share_asset_vault_sub_id, shares);
 
        transfer(receiver, underlying_asset, assets);
 
        log(Withdraw {
            caller: msg_sender().unwrap(),
            receiver,
            underlying_asset,
            vault_sub_id,
            withdrawn_amount: assets,
            burned_shares: shares,
        });
 
        assets
    }
    #[storage(read)]
    fn managed_assets(underlying_asset: AssetId, vault_sub_id: SubId) -> u64 {
        let vault_share_asset = vault_asset_id(underlying_asset, vault_sub_id).0;
        // In this implementation managed_assets and max_withdrawable are the same. However in case of lending out of assets, managed_assets should be greater than max_withdrawable.
        managed_assets(vault_share_asset)
    }
 
    #[storage(read)]
    fn max_depositable(
        receiver: Identity,
        underlying_asset: AssetId,
        vault_sub_id: SubId,
    ) -> Option<u64> {
        // This is the max value of u64 minus the current managed_assets. Ensures that the sum will always be lower than u64::MAX.
        Some(u64::max() - managed_assets(underlying_asset))
    }
 
    #[storage(read)]
    fn max_withdrawable(underlying_asset: AssetId, vault_sub_id: SubId) -> Option<u64> {
        // In this implementation total_assets and max_withdrawable are the same. However in case of lending out of assets, total_assets should be greater than max_withdrawable.
        Some(managed_assets(underlying_asset))
    }
}
 
impl SRC20 for Contract {
    #[storage(read)]
    fn total_assets() -> u64 {
        storage.total_assets.try_read().unwrap_or(0)
    }
 
    #[storage(read)]
    fn total_supply(asset: AssetId) -> Option<u64> {
        storage.total_supply.get(asset).try_read()
    }
 
    #[storage(read)]
    fn name(asset: AssetId) -> Option<String> {
        storage.name.get(asset).read_slice()
    }
 
    #[storage(read)]
    fn symbol(asset: AssetId) -> Option<String> {
        storage.symbol.get(asset).read_slice()
    }
 
    #[storage(read)]
    fn decimals(asset: AssetId) -> Option<u8> {
        storage.decimals.get(asset).try_read()
    }
}
 
/// Returns the vault shares assetid and subid for the given assets assetid and the vaults sub id
fn vault_asset_id(asset: AssetId, vault_sub_id: SubId) -> (AssetId, SubId) {
    let share_asset_vault_sub_id = sha256((asset, vault_sub_id));
    let share_asset_id = AssetId::new(ContractId::this(), share_asset_vault_sub_id);
    (share_asset_id, share_asset_vault_sub_id)
}
 
#[storage(read)]
fn managed_assets(share_asset: AssetId) -> u64 {
    match storage.vault_info.get(share_asset).try_read() {
        Some(vault_info) => vault_info.managed_assets,
        None => 0,
    }
}
 
#[storage(read)]
fn preview_deposit(
    underlying_asset: AssetId,
    vault_sub_id: SubId,
    assets: u64,
) -> (u64, AssetId, SubId) {
    let (share_asset_id, share_asset_vault_sub_id) = vault_asset_id(underlying_asset, vault_sub_id);
 
    let shares_supply = storage.total_supply.get(share_asset_id).try_read().unwrap_or(0);
    if shares_supply == 0 {
        (assets, share_asset_id, share_asset_vault_sub_id)
    } else {
        (
            assets * shares_supply / managed_assets(share_asset_id),
            share_asset_id,
            share_asset_vault_sub_id,
        )
    }
}
 
#[storage(read)]
fn preview_withdraw(share_asset_id: AssetId, shares: u64) -> u64 {
    let supply = storage.total_supply.get(share_asset_id).read();
    if supply == shares {
        managed_assets(share_asset_id)
    } else {
        shares * (managed_assets(share_asset_id) / supply)
    }
}
 
#[storage(read, write)]
pub fn _mint(
    recipient: Identity,
    asset_id: AssetId,
    vault_sub_id: SubId,
    amount: u64,
) {
    use std::asset::mint_to;
 
    let supply = storage.total_supply.get(asset_id).try_read();
    // Only increment the number of assets minted by this contract if it hasn't been minted before.
    if supply.is_none() {
        storage.total_assets.write(storage.total_assets.read() + 1);
    }
    storage
        .total_supply
        .insert(asset_id, supply.unwrap_or(0) + amount);
    mint_to(recipient, vault_sub_id, amount);
}
 
#[storage(read, write)]
pub fn _burn(asset_id: AssetId, vault_sub_id: SubId, amount: u64) {
    use std::{asset::burn, context::this_balance};
 
    require(
        this_balance(asset_id) >= amount,
        "BurnError::NotEnoughCoins",
    );
    // If we pass the check above, we can assume it is safe to unwrap.
    let supply = storage.total_supply.get(asset_id).try_read().unwrap();
    storage.total_supply.insert(asset_id, supply - amount);
    burn(vault_sub_id, amount);
}

Icon LinkSingle Asset Vault

A basic implementation of the vault standard demonstrating how to restrict deposits and withdrawals to a single AssetId.

contract;
 
use std::{
    asset::transfer,
    call_frames::msg_asset_id,
    context::msg_amount,
    hash::{
        Hash,
        sha256,
    },
    storage::storage_string::*,
    string::String,
};
 
use standards::{src20::SRC20, src6::{Deposit, SRC6, Withdraw}};
 
pub struct VaultInfo {
    /// Amount of assets currently managed by this vault
    managed_assets: u64,
    /// The vault_sub_id of this vault.
    vault_sub_id: SubId,
    /// The asset being managed by this vault
    asset: AssetId,
}
 
storage {
    /// Vault share AssetId -> VaultInfo.
    vault_info: StorageMap<AssetId, VaultInfo> = StorageMap {},
    /// Number of different assets managed by this contract.
    total_assets: u64 = 0,
    /// Total supply of shares.
    total_supply: StorageMap<AssetId, u64> = StorageMap {},
    /// Asset name.
    name: StorageMap<AssetId, StorageString> = StorageMap {},
    /// Asset symbol.
    symbol: StorageMap<AssetId, StorageString> = StorageMap {},
    /// Asset decimals.
    decimals: StorageMap<AssetId, u8> = StorageMap {},
}
 
impl SRC6 for Contract {
    #[payable]
    #[storage(read, write)]
    fn deposit(receiver: Identity, vault_sub_id: SubId) -> u64 {
        let asset_amount = msg_amount();
        let underlying_asset = msg_asset_id();
 
        require(underlying_asset == AssetId::base(), "INVALID_ASSET_ID");
        let (shares, share_asset, share_asset_vault_sub_id) = preview_deposit(underlying_asset, vault_sub_id, asset_amount);
        require(asset_amount != 0, "ZERO_ASSETS");
 
        _mint(receiver, share_asset, share_asset_vault_sub_id, shares);
 
        let mut vault_info = storage.vault_info.get(share_asset).read();
        vault_info.managed_assets = vault_info.managed_assets + asset_amount;
        storage.vault_info.insert(share_asset, vault_info);
 
        log(Deposit {
            caller: msg_sender().unwrap(),
            receiver: receiver,
            underlying_asset,
            vault_sub_id: vault_sub_id,
            deposited_amount: asset_amount,
            minted_shares: shares,
        });
 
        shares
    }
 
    #[payable]
    #[storage(read, write)]
    fn withdraw(
        receiver: Identity,
        underlying_asset: AssetId,
        vault_sub_id: SubId,
    ) -> u64 {
        let shares = msg_amount();
        require(shares != 0, "ZERO_SHARES");
 
        let (share_asset_id, share_asset_vault_sub_id) = vault_asset_id(underlying_asset, vault_sub_id);
 
        require(msg_asset_id() == share_asset_id, "INVALID_ASSET_ID");
        let assets = preview_withdraw(share_asset_id, shares);
 
        _burn(share_asset_id, share_asset_vault_sub_id, shares);
 
        transfer(receiver, underlying_asset, assets);
 
        log(Withdraw {
            caller: msg_sender().unwrap(),
            receiver: receiver,
            underlying_asset,
            vault_sub_id: vault_sub_id,
            withdrawn_amount: assets,
            burned_shares: shares,
        });
 
        assets
    }
 
    #[storage(read)]
    fn managed_assets(underlying_asset: AssetId, vault_sub_id: SubId) -> u64 {
        if underlying_asset == AssetId::base() {
            let vault_share_asset = vault_asset_id(underlying_asset, vault_sub_id).0;
            // In this implementation managed_assets and max_withdrawable are the same. However in case of lending out of assets, managed_assets should be greater than max_withdrawable.
            managed_assets(vault_share_asset)
        } else {
            0
        }
    }
 
    #[storage(read)]
    fn max_depositable(
        receiver: Identity,
        underlying_asset: AssetId,
        vault_sub_id: SubId,
    ) -> Option<u64> {
        if underlying_asset == AssetId::base() {
            // This is the max value of u64 minus the current managed_assets. Ensures that the sum will always be lower than u64::MAX.
            Some(u64::max() - managed_assets(underlying_asset))
        } else {
            None
        }
    }
 
    #[storage(read)]
    fn max_withdrawable(underlying_asset: AssetId, vault_sub_id: SubId) -> Option<u64> {
        if underlying_asset == AssetId::base() {
            // In this implementation total_assets and max_withdrawable are the same. However in case of lending out of assets, total_assets should be greater than max_withdrawable.
            Some(managed_assets(underlying_asset))
        } else {
            None
        }
    }
}
 
impl SRC20 for Contract {
    #[storage(read)]
    fn total_assets() -> u64 {
        storage.total_assets.try_read().unwrap_or(0)
    }
 
    #[storage(read)]
    fn total_supply(asset: AssetId) -> Option<u64> {
        storage.total_supply.get(asset).try_read()
    }
 
    #[storage(read)]
    fn name(asset: AssetId) -> Option<String> {
        storage.name.get(asset).read_slice()
    }
 
    #[storage(read)]
    fn symbol(asset: AssetId) -> Option<String> {
        storage.symbol.get(asset).read_slice()
    }
 
    #[storage(read)]
    fn decimals(asset: AssetId) -> Option<u8> {
        storage.decimals.get(asset).try_read()
    }
}
 
/// Returns the vault shares assetid and subid for the given assets assetid and the vaults sub id
fn vault_asset_id(underlying_asset: AssetId, vault_sub_id: SubId) -> (AssetId, SubId) {
    let share_asset_vault_sub_id = sha256((underlying_asset, vault_sub_id));
    let share_asset_id = AssetId::new(ContractId::this(), share_asset_vault_sub_id);
    (share_asset_id, share_asset_vault_sub_id)
}
 
#[storage(read)]
fn managed_assets(share_asset: AssetId) -> u64 {
    match storage.vault_info.get(share_asset).try_read() {
        Some(vault_info) => vault_info.managed_assets,
        None => 0,
    }
}
 
#[storage(read)]
fn preview_deposit(
    underlying_asset: AssetId,
    vault_sub_id: SubId,
    assets: u64,
) -> (u64, AssetId, SubId) {
    let (share_asset_id, share_asset_vault_sub_id) = vault_asset_id(underlying_asset, vault_sub_id);
 
    let shares_supply = storage.total_supply.get(share_asset_id).try_read().unwrap_or(0);
    if shares_supply == 0 {
        (assets, share_asset_id, share_asset_vault_sub_id)
    } else {
        (
            assets * shares_supply / managed_assets(share_asset_id),
            share_asset_id,
            share_asset_vault_sub_id,
        )
    }
}
 
#[storage(read)]
fn preview_withdraw(share_asset_id: AssetId, shares: u64) -> u64 {
    let supply = storage.total_supply.get(share_asset_id).read();
    if supply == shares {
        managed_assets(share_asset_id)
    } else {
        shares * (managed_assets(share_asset_id) / supply)
    }
}
 
#[storage(read, write)]
pub fn _mint(
    recipient: Identity,
    asset_id: AssetId,
    vault_sub_id: SubId,
    amount: u64,
) {
    use std::asset::mint_to;
 
    let supply = storage.total_supply.get(asset_id).try_read();
    // Only increment the number of assets minted by this contract if it hasn't been minted before.
    if supply.is_none() {
        storage.total_assets.write(storage.total_assets.read() + 1);
    }
    let current_supply = supply.unwrap_or(0);
    storage
        .total_supply
        .insert(asset_id, current_supply + amount);
    mint_to(recipient, vault_sub_id, amount);
}
 
#[storage(read, write)]
pub fn _burn(asset_id: AssetId, vault_sub_id: SubId, amount: u64) {
    use std::{asset::burn, context::this_balance};
 
    require(
        this_balance(asset_id) >= amount,
        "BurnError::NotEnoughCoins",
    );
    // If we pass the check above, we can assume it is safe to unwrap.
    let supply = storage.total_supply.get(asset_id).try_read().unwrap();
    storage.total_supply.insert(asset_id, supply - amount);
    burn(vault_sub_id, amount);
}

Icon LinkSingle Asset Single Sub Vault

A basic implementation of the vault standard demonstrating how to restrict deposits and withdrawals to a single AssetId, and to a single Sub vault.

contract;
 
use std::{
    asset::transfer,
    call_frames::msg_asset_id,
    context::msg_amount,
    hash::{
        Hash,
        sha256,
    },
    storage::storage_string::*,
    string::String,
};
 
use standards::{src20::SRC20, src6::{Deposit, SRC6, Withdraw}};
 
configurable {
    /// The only sub vault that can be deposited and withdrawn from this vault.
    ACCEPTED_SUB_VAULT: SubId = SubId::zero(),
    PRE_CALCULATED_SHARE_VAULT_SUB_ID: SubId = 0xf5a5fd42d16a20302798ef6ed309979b43003d2320d9f0e8ea9831a92759fb4b,
}
 
storage {
    /// The total amount of assets managed by this vault.
    managed_assets: u64 = 0,
    /// The total amount of shares minted by this vault.
    total_supply: u64 = 0,
    /// Whether the vault shares have been minted.
    minted: bool = false,
}
 
impl SRC6 for Contract {
    #[payable]
    #[storage(read, write)]
    fn deposit(receiver: Identity, vault_sub_id: SubId) -> u64 {
        require(vault_sub_id == ACCEPTED_SUB_VAULT, "INVALID_vault_sub_id");
 
        let underlying_asset = msg_asset_id();
        require(underlying_asset == AssetId::base(), "INVALID_ASSET_ID");
 
        let asset_amount = msg_amount();
        require(asset_amount != 0, "ZERO_ASSETS");
        let shares = preview_deposit(asset_amount);
 
        _mint(receiver, shares);
 
        storage
            .managed_assets
            .write(storage.managed_assets.read() + asset_amount);
 
        log(Deposit {
            caller: msg_sender().unwrap(),
            receiver,
            underlying_asset,
            vault_sub_id,
            deposited_amount: asset_amount,
            minted_shares: shares,
        });
 
        shares
    }
 
    #[payable]
    #[storage(read, write)]
    fn withdraw(
        receiver: Identity,
        underlying_asset: AssetId,
        vault_sub_id: SubId,
    ) -> u64 {
        require(underlying_asset == AssetId::base(), "INVALID_ASSET_ID");
        require(vault_sub_id == ACCEPTED_SUB_VAULT, "INVALID_vault_sub_id");
 
        let shares = msg_amount();
        require(shares != 0, "ZERO_SHARES");
 
        let share_asset_id = vault_assetid();
 
        require(msg_asset_id() == share_asset_id, "INVALID_ASSET_ID");
        let assets = preview_withdraw(shares);
 
        _burn(share_asset_id, shares);
 
        transfer(receiver, underlying_asset, assets);
 
        log(Withdraw {
            caller: msg_sender().unwrap(),
            receiver,
            underlying_asset,
            vault_sub_id,
            withdrawn_amount: assets,
            burned_shares: shares,
        });
 
        assets
    }
 
    #[storage(read)]
    fn managed_assets(underlying_asset: AssetId, vault_sub_id: SubId) -> u64 {
        if underlying_asset == AssetId::base() && vault_sub_id == ACCEPTED_SUB_VAULT {
            // In this implementation managed_assets and max_withdrawable are the same. However in case of lending out of assets, managed_assets should be greater than max_withdrawable.
            storage.managed_assets.read()
        } else {
            0
        }
    }
 
    #[storage(read)]
    fn max_depositable(
        receiver: Identity,
        underlying_asset: AssetId,
        vault_sub_id: SubId,
    ) -> Option<u64> {
        if underlying_asset == AssetId::base() {
            // This is the max value of u64 minus the current managed_assets. Ensures that the sum will always be lower than u64::MAX.
            Some(u64::max() - storage.managed_assets.read())
        } else {
            None
        }
    }
 
    #[storage(read)]
    fn max_withdrawable(underlying_asset: AssetId, vault_sub_id: SubId) -> Option<u64> {
        if underlying_asset == AssetId::base() {
            // In this implementation managed_assets and max_withdrawable are the same. However in case of lending out of assets, managed_assets should be greater than max_withdrawable.
            Some(storage.managed_assets.read())
        } else {
            None
        }
    }
}
 
impl SRC20 for Contract {
    #[storage(read)]
    fn total_assets() -> u64 {
        1
    }
 
    #[storage(read)]
    fn total_supply(asset: AssetId) -> Option<u64> {
        if asset == vault_assetid() {
            Some(storage.total_supply.read())
        } else {
            None
        }
    }
 
    #[storage(read)]
    fn name(asset: AssetId) -> Option<String> {
        Some(String::from_ascii_str("Vault Shares"))
    }
 
    #[storage(read)]
    fn symbol(asset: AssetId) -> Option<String> {
        Some(String::from_ascii_str("VLTSHR"))
    }
 
    #[storage(read)]
    fn decimals(asset: AssetId) -> Option<u8> {
        Some(9_u8)
    }
}
 
/// Returns the vault shares assetid for the given assets assetid and the vaults sub id
fn vault_assetid() -> AssetId {
    let share_asset_id = AssetId::new(ContractId::this(), PRE_CALCULATED_SHARE_VAULT_SUB_ID);
    share_asset_id
}
 
#[storage(read)]
fn preview_deposit(assets: u64) -> u64 {
    let shares_supply = storage.total_supply.try_read().unwrap_or(0);
    if shares_supply == 0 {
        assets
    } else {
        assets * shares_supply / storage.managed_assets.try_read().unwrap_or(0)
    }
}
 
#[storage(read)]
fn preview_withdraw(shares: u64) -> u64 {
    let supply = storage.total_supply.read();
    if supply == shares {
        storage.managed_assets.read()
    } else {
        shares * (storage.managed_assets.read() / supply)
    }
}
 
#[storage(read, write)]
pub fn _mint(recipient: Identity, amount: u64) {
    use std::asset::mint_to;
 
    let supply = storage.total_supply.read();
    storage.total_supply.write(supply + amount);
    mint_to(recipient, PRE_CALCULATED_SHARE_VAULT_SUB_ID, amount);
}
 
#[storage(read, write)]
pub fn _burn(asset_id: AssetId, amount: u64) {
    use std::{asset::burn, context::this_balance};
 
    require(
        this_balance(asset_id) >= amount,
        "BurnError::NotEnoughCoins",
    );
    // If we pass the check above, we can assume it is safe to unwrap.
    let supply = storage.total_supply.read();
    storage.total_supply.write(supply - amount);
    burn(PRE_CALCULATED_SHARE_VAULT_SUB_ID, amount);
}