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// This file is part of Substrate.
// Copyright (C) 2019-2022 Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: Apache-2.0
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//! `Inspect` and `Mutate` traits for working with regular balances.
use sp_std::marker::PhantomData;
use crate::{
dispatch::DispatchError,
ensure,
traits::{
tokens::{
misc::{
Balance, DepositConsequence,
Fortitude::{self, Force, Polite},
Precision::{self, BestEffort, Exact},
Preservation::{self, Expendable},
Provenance::{self, Extant},
WithdrawConsequence,
},
AssetId,
},
SameOrOther, TryDrop,
},
};
use sp_arithmetic::traits::{CheckedAdd, CheckedSub, One};
use sp_runtime::{traits::Saturating, ArithmeticError, TokenError};
use super::{Credit, Debt, HandleImbalanceDrop, Imbalance};
/// Trait for providing balance-inspection access to a set of named fungible assets.
pub trait Inspect<AccountId>: Sized {
/// Means of identifying one asset class from another.
type AssetId: AssetId;
/// Scalar type for representing balance of an account.
type Balance: Balance;
/// The total amount of issuance in the system.
fn total_issuance(asset: Self::AssetId) -> Self::Balance;
/// The total amount of issuance in the system excluding those which are controlled by the
/// system.
fn active_issuance(asset: Self::AssetId) -> Self::Balance {
Self::total_issuance(asset)
}
/// The minimum balance any single account may have.
fn minimum_balance(asset: Self::AssetId) -> Self::Balance;
/// Get the total amount of funds whose ultimate beneficial ownership can be determined as
/// `who`.
///
/// This may include funds which are wholly inaccessible to `who`, either temporarily or even
/// indefinitely.
///
/// For the amount of the balance which is currently free to be removed from the account without
/// error, use `reducible_balance`.
///
/// For the amount of the balance which may eventually be free to be removed from the account,
/// use `balance()`.
fn total_balance(asset: Self::AssetId, who: &AccountId) -> Self::Balance;
/// Get the balance of `who` which does not include funds which are exclusively allocated to
/// subsystems of the chain ("on hold" or "reserved").
///
/// In general this isn't especially useful outside of tests, and for practical purposes, you'll
/// want to use `reducible_balance()`.
fn balance(asset: Self::AssetId, who: &AccountId) -> Self::Balance;
/// Get the maximum amount that `who` can withdraw/transfer successfully based on whether the
/// account should be kept alive (`preservation`) or whether we are willing to force the
/// transfer and potentially go below user-level restrictions on the minimum amount of the
/// account.
///
/// Always less than `free_balance()`.
fn reducible_balance(
asset: Self::AssetId,
who: &AccountId,
preservation: Preservation,
force: Fortitude,
) -> Self::Balance;
/// Returns `true` if the `asset` balance of `who` may be increased by `amount`.
///
/// - `asset`: The asset that should be deposited.
/// - `who`: The account of which the balance should be increased by `amount`.
/// - `amount`: How much should the balance be increased?
/// - `mint`: Will `amount` be minted to deposit it into `account`?
fn can_deposit(
asset: Self::AssetId,
who: &AccountId,
amount: Self::Balance,
provenance: Provenance,
) -> DepositConsequence;
/// Returns `Failed` if the `asset` balance of `who` may not be decreased by `amount`, otherwise
/// the consequence.
fn can_withdraw(
asset: Self::AssetId,
who: &AccountId,
amount: Self::Balance,
) -> WithdrawConsequence<Self::Balance>;
/// Returns `true` if an `asset` exists.
fn asset_exists(asset: Self::AssetId) -> bool;
}
/// Special dust type which can be type-safely converted into a `Credit`.
#[must_use]
pub struct Dust<A, T: Unbalanced<A>>(pub T::AssetId, pub T::Balance);
impl<A, T: Balanced<A>> Dust<A, T> {
/// Convert `Dust` into an instance of `Credit`.
pub fn into_credit(self) -> Credit<A, T> {
Credit::<A, T>::new(self.0, self.1)
}
}
/// A fungible token class where the balance can be set arbitrarily.
///
/// **WARNING**
/// Do not use this directly unless you want trouble, since it allows you to alter account balances
/// without keeping the issuance up to date. It has no safeguards against accidentally creating
/// token imbalances in your system leading to accidental inflation or deflation. It's really just
/// for the underlying datatype to implement so the user gets the much safer `Balanced` trait to
/// use.
pub trait Unbalanced<AccountId>: Inspect<AccountId> {
/// Create some dust and handle it with `Self::handle_dust`. This is an unbalanced operation
/// and it must only be used when an account is modified in a raw fashion, outside of the entire
/// fungibles API. The `amount` is capped at `Self::minimum_balance() - 1`.
///
/// This should not be reimplemented.
fn handle_raw_dust(asset: Self::AssetId, amount: Self::Balance) {
Self::handle_dust(Dust(
asset.clone(),
amount.min(Self::minimum_balance(asset).saturating_sub(One::one())),
))
}
/// Do something with the dust which has been destroyed from the system. `Dust` can be converted
/// into a `Credit` with the `Balanced` trait impl.
fn handle_dust(dust: Dust<AccountId, Self>);
/// Forcefully set the balance of `who` to `amount`.
///
/// If this call executes successfully, you can `assert_eq!(Self::balance(), amount);`.
///
/// For implementations which include one or more balances on hold, then these are *not*
/// included in the `amount`.
///
/// This function does its best to force the balance change through, but will not break system
/// invariants such as any Existential Deposits needed or overflows/underflows.
/// If this cannot be done for some reason (e.g. because the account cannot be created, deleted
/// or would overflow) then an `Err` is returned.
fn write_balance(
asset: Self::AssetId,
who: &AccountId,
amount: Self::Balance,
) -> Result<Option<Self::Balance>, DispatchError>;
/// Set the total issuance to `amount`.
fn set_total_issuance(asset: Self::AssetId, amount: Self::Balance);
/// Reduce the balance of `who` by `amount`.
///
/// If `precision` is `Exact` and it cannot be reduced by that amount for
/// some reason, return `Err` and don't reduce it at all. If `precision` is `BestEffort`, then
/// reduce the balance of `who` by the most that is possible, up to `amount`.
///
/// In either case, if `Ok` is returned then the inner is the amount by which is was reduced.
/// Minimum balance will be respected and thus the returned amount may be up to
/// `Self::minimum_balance() - 1` greater than `amount` in the case that the reduction caused
/// the account to be deleted.
fn decrease_balance(
asset: Self::AssetId,
who: &AccountId,
mut amount: Self::Balance,
precision: Precision,
preservation: Preservation,
force: Fortitude,
) -> Result<Self::Balance, DispatchError> {
let old_balance = Self::balance(asset.clone(), who);
let free = Self::reducible_balance(asset.clone(), who, preservation, force);
if let BestEffort = precision {
amount = amount.min(free);
}
let new_balance = old_balance.checked_sub(&amount).ok_or(TokenError::FundsUnavailable)?;
if let Some(dust) = Self::write_balance(asset.clone(), who, new_balance)? {
Self::handle_dust(Dust(asset, dust));
}
Ok(old_balance.saturating_sub(new_balance))
}
/// Increase the balance of `who` by `amount`.
///
/// If it cannot be increased by that amount for some reason, return `Err` and don't increase
/// it at all. If Ok, return the imbalance.
/// Minimum balance will be respected and an error will be returned if
/// `amount < Self::minimum_balance()` when the account of `who` is zero.
fn increase_balance(
asset: Self::AssetId,
who: &AccountId,
amount: Self::Balance,
precision: Precision,
) -> Result<Self::Balance, DispatchError> {
let old_balance = Self::balance(asset.clone(), who);
let new_balance = if let BestEffort = precision {
old_balance.saturating_add(amount)
} else {
old_balance.checked_add(&amount).ok_or(ArithmeticError::Overflow)?
};
if new_balance < Self::minimum_balance(asset.clone()) {
// Attempt to increase from 0 to below minimum -> stays at zero.
if let BestEffort = precision {
Ok(Self::Balance::default())
} else {
Err(TokenError::BelowMinimum.into())
}
} else {
if new_balance == old_balance {
Ok(Self::Balance::default())
} else {
if let Some(dust) = Self::write_balance(asset.clone(), who, new_balance)? {
Self::handle_dust(Dust(asset, dust));
}
Ok(new_balance.saturating_sub(old_balance))
}
}
}
/// Reduce the active issuance by some amount.
fn deactivate(_asset: Self::AssetId, _: Self::Balance) {}
/// Increase the active issuance by some amount, up to the outstanding amount reduced.
fn reactivate(_asset: Self::AssetId, _: Self::Balance) {}
}
/// Trait for providing a basic fungible asset.
pub trait Mutate<AccountId>: Inspect<AccountId> + Unbalanced<AccountId> {
/// Increase the balance of `who` by exactly `amount`, minting new tokens. If that isn't
/// possible then an `Err` is returned and nothing is changed.
fn mint_into(
asset: Self::AssetId,
who: &AccountId,
amount: Self::Balance,
) -> Result<Self::Balance, DispatchError> {
Self::total_issuance(asset.clone())
.checked_add(&amount)
.ok_or(ArithmeticError::Overflow)?;
let actual = Self::increase_balance(asset.clone(), who, amount, Exact)?;
Self::set_total_issuance(
asset.clone(),
Self::total_issuance(asset.clone()).saturating_add(actual),
);
Self::done_mint_into(asset, who, amount);
Ok(actual)
}
/// Decrease the balance of `who` by at least `amount`, possibly slightly more in the case of
/// minimum-balance requirements, burning the tokens. If that isn't possible then an `Err` is
/// returned and nothing is changed. If successful, the amount of tokens reduced is returned.
fn burn_from(
asset: Self::AssetId,
who: &AccountId,
amount: Self::Balance,
precision: Precision,
force: Fortitude,
) -> Result<Self::Balance, DispatchError> {
let actual = Self::reducible_balance(asset.clone(), who, Expendable, force).min(amount);
ensure!(actual == amount || precision == BestEffort, TokenError::FundsUnavailable);
Self::total_issuance(asset.clone())
.checked_sub(&actual)
.ok_or(ArithmeticError::Overflow)?;
let actual =
Self::decrease_balance(asset.clone(), who, actual, BestEffort, Expendable, force)?;
Self::set_total_issuance(
asset.clone(),
Self::total_issuance(asset.clone()).saturating_sub(actual),
);
Self::done_burn_from(asset, who, actual);
Ok(actual)
}
/// Attempt to decrease the `asset` balance of `who` by `amount`.
///
/// Equivalent to `burn_from`, except with an expectation that within the bounds of some
/// universal issuance, the total assets `suspend`ed and `resume`d will be equivalent. The
/// implementation may be configured such that the total assets suspended may never be less than
/// the total assets resumed (which is the invariant for an issuing system), or the reverse
/// (which the invariant in a non-issuing system).
///
/// Because of this expectation, any metadata associated with the asset is expected to survive
/// the suspect-resume cycle.
fn shelve(
asset: Self::AssetId,
who: &AccountId,
amount: Self::Balance,
) -> Result<Self::Balance, DispatchError> {
let actual = Self::reducible_balance(asset.clone(), who, Expendable, Polite).min(amount);
ensure!(actual == amount, TokenError::FundsUnavailable);
Self::total_issuance(asset.clone())
.checked_sub(&actual)
.ok_or(ArithmeticError::Overflow)?;
let actual =
Self::decrease_balance(asset.clone(), who, actual, BestEffort, Expendable, Polite)?;
Self::set_total_issuance(
asset.clone(),
Self::total_issuance(asset.clone()).saturating_sub(actual),
);
Self::done_shelve(asset, who, actual);
Ok(actual)
}
/// Attempt to increase the `asset` balance of `who` by `amount`.
///
/// Equivalent to `mint_into`, except with an expectation that within the bounds of some
/// universal issuance, the total assets `suspend`ed and `resume`d will be equivalent. The
/// implementation may be configured such that the total assets suspended may never be less than
/// the total assets resumed (which is the invariant for an issuing system), or the reverse
/// (which the invariant in a non-issuing system).
///
/// Because of this expectation, any metadata associated with the asset is expected to survive
/// the suspect-resume cycle.
fn restore(
asset: Self::AssetId,
who: &AccountId,
amount: Self::Balance,
) -> Result<Self::Balance, DispatchError> {
Self::total_issuance(asset.clone())
.checked_add(&amount)
.ok_or(ArithmeticError::Overflow)?;
let actual = Self::increase_balance(asset.clone(), who, amount, Exact)?;
Self::set_total_issuance(
asset.clone(),
Self::total_issuance(asset.clone()).saturating_add(actual),
);
Self::done_restore(asset, who, amount);
Ok(actual)
}
/// Transfer funds from one account into another.
fn transfer(
asset: Self::AssetId,
source: &AccountId,
dest: &AccountId,
amount: Self::Balance,
preservation: Preservation,
) -> Result<Self::Balance, DispatchError> {
let _extra = Self::can_withdraw(asset.clone(), source, amount)
.into_result(preservation != Expendable)?;
Self::can_deposit(asset.clone(), dest, amount, Extant).into_result()?;
Self::decrease_balance(asset.clone(), source, amount, BestEffort, preservation, Polite)?;
// This should never fail as we checked `can_deposit` earlier. But we do a best-effort
// anyway.
let _ = Self::increase_balance(asset.clone(), dest, amount, BestEffort);
Self::done_transfer(asset, source, dest, amount);
Ok(amount)
}
/// Simple infallible function to force an account to have a particular balance, good for use
/// in tests and benchmarks but not recommended for production code owing to the lack of
/// error reporting.
///
/// Returns the new balance.
fn set_balance(asset: Self::AssetId, who: &AccountId, amount: Self::Balance) -> Self::Balance {
let b = Self::balance(asset.clone(), who);
if b > amount {
Self::burn_from(asset, who, b - amount, BestEffort, Force).map(|d| b.saturating_sub(d))
} else {
Self::mint_into(asset, who, amount - b).map(|d| b.saturating_add(d))
}
.unwrap_or(b)
}
fn done_mint_into(_asset: Self::AssetId, _who: &AccountId, _amount: Self::Balance) {}
fn done_burn_from(_asset: Self::AssetId, _who: &AccountId, _amount: Self::Balance) {}
fn done_shelve(_asset: Self::AssetId, _who: &AccountId, _amount: Self::Balance) {}
fn done_restore(_asset: Self::AssetId, _who: &AccountId, _amount: Self::Balance) {}
fn done_transfer(
_asset: Self::AssetId,
_source: &AccountId,
_dest: &AccountId,
_amount: Self::Balance,
) {
}
}
/// Simple handler for an imbalance drop which increases the total issuance of the system by the
/// imbalance amount. Used for leftover debt.
pub struct IncreaseIssuance<AccountId, U>(PhantomData<(AccountId, U)>);
impl<AccountId, U: Unbalanced<AccountId>> HandleImbalanceDrop<U::AssetId, U::Balance>
for IncreaseIssuance<AccountId, U>
{
fn handle(asset: U::AssetId, amount: U::Balance) {
U::set_total_issuance(asset.clone(), U::total_issuance(asset).saturating_add(amount))
}
}
/// Simple handler for an imbalance drop which decreases the total issuance of the system by the
/// imbalance amount. Used for leftover credit.
pub struct DecreaseIssuance<AccountId, U>(PhantomData<(AccountId, U)>);
impl<AccountId, U: Unbalanced<AccountId>> HandleImbalanceDrop<U::AssetId, U::Balance>
for DecreaseIssuance<AccountId, U>
{
fn handle(asset: U::AssetId, amount: U::Balance) {
U::set_total_issuance(asset.clone(), U::total_issuance(asset).saturating_sub(amount))
}
}
/// A fungible token class where any creation and deletion of tokens is semi-explicit and where the
/// total supply is maintained automatically.
///
/// This is auto-implemented when a token class has `Unbalanced` implemented.
pub trait Balanced<AccountId>: Inspect<AccountId> + Unbalanced<AccountId> {
/// The type for managing what happens when an instance of `Debt` is dropped without being used.
type OnDropDebt: HandleImbalanceDrop<Self::AssetId, Self::Balance>;
/// The type for managing what happens when an instance of `Credit` is dropped without being
/// used.
type OnDropCredit: HandleImbalanceDrop<Self::AssetId, Self::Balance>;
/// Reduce the total issuance by `amount` and return the according imbalance. The imbalance will
/// typically be used to reduce an account by the same amount with e.g. `settle`.
///
/// This is infallible, but doesn't guarantee that the entire `amount` is burnt, for example
/// in the case of underflow.
fn rescind(asset: Self::AssetId, amount: Self::Balance) -> Debt<AccountId, Self> {
let old = Self::total_issuance(asset.clone());
let new = old.saturating_sub(amount);
Self::set_total_issuance(asset.clone(), new);
let delta = old - new;
Self::done_rescind(asset.clone(), delta);
Imbalance::<Self::AssetId, Self::Balance, Self::OnDropDebt, Self::OnDropCredit>::new(
asset, delta,
)
}
/// Increase the total issuance by `amount` and return the according imbalance. The imbalance
/// will typically be used to increase an account by the same amount with e.g.
/// `resolve_into_existing` or `resolve_creating`.
///
/// This is infallible, but doesn't guarantee that the entire `amount` is issued, for example
/// in the case of overflow.
fn issue(asset: Self::AssetId, amount: Self::Balance) -> Credit<AccountId, Self> {
let old = Self::total_issuance(asset.clone());
let new = old.saturating_add(amount);
Self::set_total_issuance(asset.clone(), new);
let delta = new - old;
Self::done_issue(asset.clone(), delta);
Imbalance::<Self::AssetId, Self::Balance, Self::OnDropCredit, Self::OnDropDebt>::new(
asset, delta,
)
}
/// Produce a pair of imbalances that cancel each other out exactly.
///
/// This is just the same as burning and issuing the same amount and has no effect on the
/// total issuance.
fn pair(
asset: Self::AssetId,
amount: Self::Balance,
) -> (Debt<AccountId, Self>, Credit<AccountId, Self>) {
(Self::rescind(asset.clone(), amount), Self::issue(asset, amount))
}
/// Mints `value` into the account of `who`, creating it as needed.
///
/// If `precision` is `BestEffort` and `value` in full could not be minted (e.g. due to
/// overflow), then the maximum is minted, up to `value`. If `precision` is `Exact`, then
/// exactly `value` must be minted into the account of `who` or the operation will fail with an
/// `Err` and nothing will change.
///
/// If the operation is successful, this will return `Ok` with a `Debt` of the total value
/// added to the account.
fn deposit(
asset: Self::AssetId,
who: &AccountId,
value: Self::Balance,
precision: Precision,
) -> Result<Debt<AccountId, Self>, DispatchError> {
let increase = Self::increase_balance(asset.clone(), who, value, precision)?;
Self::done_deposit(asset.clone(), who, increase);
Ok(Imbalance::<Self::AssetId, Self::Balance, Self::OnDropDebt, Self::OnDropCredit>::new(
asset, increase,
))
}
/// Removes `value` balance from `who` account if possible.
///
/// If `precision` is `BestEffort` and `value` in full could not be removed (e.g. due to
/// underflow), then the maximum is removed, up to `value`. If `precision` is `Exact`, then
/// exactly `value` must be removed from the account of `who` or the operation will fail with an
/// `Err` and nothing will change.
///
/// If the removal is needed but not possible, then it returns `Err` and nothing is changed.
/// If the account needed to be deleted, then slightly more than `value` may be removed from the
/// account owning since up to (but not including) minimum balance may also need to be removed.
///
/// If the operation is successful, this will return `Ok` with a `Credit` of the total value
/// removed from the account.
fn withdraw(
asset: Self::AssetId,
who: &AccountId,
value: Self::Balance,
precision: Precision,
preservation: Preservation,
force: Fortitude,
) -> Result<Credit<AccountId, Self>, DispatchError> {
let decrease =
Self::decrease_balance(asset.clone(), who, value, precision, preservation, force)?;
Self::done_withdraw(asset.clone(), who, decrease);
Ok(Imbalance::<Self::AssetId, Self::Balance, Self::OnDropCredit, Self::OnDropDebt>::new(
asset, decrease,
))
}
/// The balance of `who` is increased in order to counter `credit`. If the whole of `credit`
/// cannot be countered, then nothing is changed and the original `credit` is returned in an
/// `Err`.
///
/// Please note: If `credit.peek()` is less than `Self::minimum_balance()`, then `who` must
/// already exist for this to succeed.
fn resolve(
who: &AccountId,
credit: Credit<AccountId, Self>,
) -> Result<(), Credit<AccountId, Self>> {
let v = credit.peek();
let debt = match Self::deposit(credit.asset(), who, v, Exact) {
Err(_) => return Err(credit),
Ok(d) => d,
};
if let Ok(result) = credit.offset(debt) {
let result = result.try_drop();
debug_assert!(result.is_ok(), "ok deposit return must be equal to credit value; qed");
} else {
debug_assert!(false, "debt.asset is credit.asset; qed");
}
Ok(())
}
/// The balance of `who` is decreased in order to counter `debt`. If the whole of `debt`
/// cannot be countered, then nothing is changed and the original `debt` is returned in an
/// `Err`.
fn settle(
who: &AccountId,
debt: Debt<AccountId, Self>,
preservation: Preservation,
) -> Result<Credit<AccountId, Self>, Debt<AccountId, Self>> {
let amount = debt.peek();
let asset = debt.asset();
let credit = match Self::withdraw(asset.clone(), who, amount, Exact, preservation, Polite) {
Err(_) => return Err(debt),
Ok(d) => d,
};
match credit.offset(debt) {
Ok(SameOrOther::None) => Ok(Credit::<AccountId, Self>::zero(asset)),
Ok(SameOrOther::Same(dust)) => Ok(dust),
Ok(SameOrOther::Other(rest)) => {
debug_assert!(false, "ok withdraw return must be at least debt value; qed");
Err(rest)
},
Err(_) => {
debug_assert!(false, "debt.asset is credit.asset; qed");
Ok(Credit::<AccountId, Self>::zero(asset))
},
}
}
fn done_rescind(_asset: Self::AssetId, _amount: Self::Balance) {}
fn done_issue(_asset: Self::AssetId, _amount: Self::Balance) {}
fn done_deposit(_asset: Self::AssetId, _who: &AccountId, _amount: Self::Balance) {}
fn done_withdraw(_asset: Self::AssetId, _who: &AccountId, _amount: Self::Balance) {}
}