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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.
//! The traits for putting holds within a single fungible token class.
use crate::{
ensure,
traits::tokens::{
DepositConsequence::Success,
Fortitude::{self, Force},
Precision::{self, BestEffort, Exact},
Preservation::{self, Protect},
Provenance::Extant,
Restriction::{self, Free, OnHold},
},
};
use scale_info::TypeInfo;
use sp_arithmetic::{
traits::{CheckedAdd, CheckedSub, Zero},
ArithmeticError,
};
use sp_runtime::{DispatchError, DispatchResult, Saturating, TokenError};
use super::*;
/// Trait for inspecting a fungible asset whose accounts support partitioning and slashing.
pub trait Inspect<AccountId>: super::Inspect<AccountId> {
/// An identifier for a hold. Used for disambiguating different holds so that
/// they can be individually replaced or removed and funds from one hold don't accidentally
/// become unreserved or slashed for another.
type Reason: codec::Encode + TypeInfo + 'static;
/// Amount of funds on hold (for all hold reasons) of `who`.
fn total_balance_on_hold(asset: Self::AssetId, who: &AccountId) -> Self::Balance;
/// Get the maximum amount that the `total_balance_on_hold` of `who` can be reduced successfully
/// based on whether we are willing to force the reduction and potentially go below user-level
/// restrictions on the minimum amount of the account. Note: This cannot bring the account into
/// an inconsistent state with regards any required existential deposit.
///
/// Never more than `total_balance_on_hold()`.
fn reducible_total_balance_on_hold(
asset: Self::AssetId,
who: &AccountId,
_force: Fortitude,
) -> Self::Balance {
Self::total_balance_on_hold(asset, who)
}
/// Amount of funds on hold (for the given reason) of `who`.
fn balance_on_hold(
asset: Self::AssetId,
reason: &Self::Reason,
who: &AccountId,
) -> Self::Balance;
/// Returns `true` if it's possible to place (additional) funds under a hold of a given
/// `reason`. This may fail if the account has exhausted a limited number of concurrent
/// holds or if it cannot be made to exist (e.g. there is no provider reference).
///
/// NOTE: This does not take into account changes which could be made to the account of `who`
/// (such as removing a provider reference) after this call is made. Any usage of this should
/// therefore ensure the account is already in the appropriate state prior to calling it.
fn hold_available(_asset: Self::AssetId, _reason: &Self::Reason, _who: &AccountId) -> bool {
true
}
/// Check to see if some `amount` of funds of `who` may be placed on hold with the given
/// `reason`. Reasons why this may not be true:
///
/// - The implementor supports only a limited number of concurrent holds on an account which is
/// the possible values of `reason`;
/// - The total balance of the account is less than `amount`;
/// - Removing `amount` from the total balance would kill the account and remove the only
/// provider reference.
///
/// Note: we pass `Fortitude::Force` as the last argument to `reducible_balance` since we assume
/// that if needed the balance can slashed. If we are using a simple non-forcing
/// reserve-transfer, then we really ought to check that we are not reducing the funds below the
/// freeze-limit (if any).
///
/// NOTE: This does not take into account changes which could be made to the account of `who`
/// (such as removing a provider reference) after this call is made. Any usage of this should
/// therefore ensure the account is already in the appropriate state prior to calling it.
fn ensure_can_hold(
asset: Self::AssetId,
reason: &Self::Reason,
who: &AccountId,
amount: Self::Balance,
) -> DispatchResult {
ensure!(Self::hold_available(asset.clone(), reason, who), TokenError::CannotCreateHold);
ensure!(
amount <= Self::reducible_balance(asset, who, Protect, Force),
TokenError::FundsUnavailable
);
Ok(())
}
/// Check to see if some `amount` of funds of `who` may be placed on hold for the given
/// `reason`. Reasons why this may not be true:
///
/// - The implementor supports only a limited number of concurrent holds on an account which is
/// the possible values of `reason`;
/// - The main balance of the account is less than `amount`;
/// - Removing `amount` from the main balance would kill the account and remove the only
/// provider reference.
///
/// NOTE: This does not take into account changes which could be made to the account of `who`
/// (such as removing a provider reference) after this call is made. Any usage of this should
/// therefore ensure the account is already in the appropriate state prior to calling it.
fn can_hold(
asset: Self::AssetId,
reason: &Self::Reason,
who: &AccountId,
amount: Self::Balance,
) -> bool {
Self::ensure_can_hold(asset, reason, who, amount).is_ok()
}
}
/// A fungible, holdable token class where the balance on hold 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> {
/// Forcefully set the balance on hold of `who` to `amount`. This is independent of any other
/// balances on hold or the main ("free") balance.
///
/// If this call executes successfully, you can `assert_eq!(Self::balance_on_hold(), 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 doesn't exist) then an
/// `Err` is returned.
// Implementation note: This should increment the consumer refs if it moves total on hold from
// zero to non-zero and decrement in the opposite direction.
//
// Since this was not done in the previous logic, this will need either a migration or a
// state item which tracks whether the account is on the old logic or new.
fn set_balance_on_hold(
asset: Self::AssetId,
reason: &Self::Reason,
who: &AccountId,
amount: Self::Balance,
) -> DispatchResult;
/// Reduce the balance on hold of `who` by `amount`.
///
/// If `precision` is `Precision::Exact` and it cannot be reduced by that amount for
/// some reason, return `Err` and don't reduce it at all. If `precision` is
/// `Precision::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.
fn decrease_balance_on_hold(
asset: Self::AssetId,
reason: &Self::Reason,
who: &AccountId,
mut amount: Self::Balance,
precision: Precision,
) -> Result<Self::Balance, DispatchError> {
let old_balance = Self::balance_on_hold(asset.clone(), reason, who);
if let BestEffort = precision {
amount = amount.min(old_balance);
}
let new_balance = old_balance.checked_sub(&amount).ok_or(TokenError::FundsUnavailable)?;
Self::set_balance_on_hold(asset, reason, who, new_balance)?;
Ok(amount)
}
/// Increase the balance on hold 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.
fn increase_balance_on_hold(
asset: Self::AssetId,
reason: &Self::Reason,
who: &AccountId,
amount: Self::Balance,
precision: Precision,
) -> Result<Self::Balance, DispatchError> {
let old_balance = Self::balance_on_hold(asset.clone(), reason, who);
let new_balance = if let BestEffort = precision {
old_balance.saturating_add(amount)
} else {
old_balance.checked_add(&amount).ok_or(ArithmeticError::Overflow)?
};
let amount = new_balance.saturating_sub(old_balance);
if !amount.is_zero() {
Self::set_balance_on_hold(asset, reason, who, new_balance)?;
}
Ok(amount)
}
}
/// Trait for slashing a fungible asset which can be place on hold.
pub trait Balanced<AccountId>: super::Balanced<AccountId> + Unbalanced<AccountId> {
/// Reduce the balance of some funds on hold in an account.
///
/// The resulting imbalance is the first item of the tuple returned.
///
/// As much funds that are on hold up to `amount` will be deducted as possible. If this is less
/// than `amount`, then a non-zero second item will be returned.
fn slash(
asset: Self::AssetId,
reason: &Self::Reason,
who: &AccountId,
amount: Self::Balance,
) -> (Credit<AccountId, Self>, Self::Balance) {
let decrease =
Self::decrease_balance_on_hold(asset.clone(), reason, who, amount, BestEffort)
.unwrap_or(Default::default());
let credit =
Imbalance::<Self::AssetId, Self::Balance, Self::OnDropCredit, Self::OnDropDebt>::new(
asset.clone(),
decrease,
);
Self::done_slash(asset, reason, who, decrease);
(credit, amount.saturating_sub(decrease))
}
fn done_slash(
_asset: Self::AssetId,
_reason: &Self::Reason,
_who: &AccountId,
_amount: Self::Balance,
) {
}
}
/// Trait for mutating a fungible asset which can be placed on hold.
pub trait Mutate<AccountId>:
Inspect<AccountId> + super::Unbalanced<AccountId> + Unbalanced<AccountId>
{
/// Hold some funds in an account. If a hold for `reason` is already in place, then this
/// will increase it.
fn hold(
asset: Self::AssetId,
reason: &Self::Reason,
who: &AccountId,
amount: Self::Balance,
) -> DispatchResult {
// NOTE: This doesn't change the total balance of the account so there's no need to
// check liquidity.
Self::ensure_can_hold(asset.clone(), reason, who, amount)?;
// Should be infallible now, but we proceed softly anyway.
Self::decrease_balance(asset.clone(), who, amount, Exact, Protect, Force)?;
Self::increase_balance_on_hold(asset.clone(), reason, who, amount, BestEffort)?;
Self::done_hold(asset, reason, who, amount);
Ok(())
}
/// Release up to `amount` held funds in an account.
///
/// The actual amount released is returned with `Ok`.
///
/// If `precision` is `BestEffort`, then the amount actually unreserved and returned as the
/// inner value of `Ok` may be smaller than the `amount` passed.
fn release(
asset: Self::AssetId,
reason: &Self::Reason,
who: &AccountId,
amount: Self::Balance,
precision: Precision,
) -> Result<Self::Balance, DispatchError> {
// NOTE: This doesn't change the total balance of the account so there's no need to
// check liquidity.
// We want to make sure we can deposit the amount in advance. If we can't then something is
// very wrong.
ensure!(
Self::can_deposit(asset.clone(), who, amount, Extant) == Success,
TokenError::CannotCreate
);
// Get the amount we can actually take from the hold. This might be less than what we want
// if we're only doing a best-effort.
let amount = Self::decrease_balance_on_hold(asset.clone(), reason, who, amount, precision)?;
// Increase the main balance by what we took. We always do a best-effort here because we
// already checked that we can deposit before.
let actual = Self::increase_balance(asset.clone(), who, amount, BestEffort)?;
Self::done_release(asset, reason, who, actual);
Ok(actual)
}
/// Attempt to decrease the balance of `who` which is held for the given `reason` by `amount`.
///
/// If `precision` is true, then as much as possible is reduced, up to `amount`, and the
/// amount of tokens reduced is returned. Otherwise, if the total amount can be reduced, then it
/// is and the amount returned, and if not, then nothing changes and `Err` is returned.
///
/// If `force` is `Force`, then locks/freezes will be ignored. This should only be used when
/// conducting slashing or other activity which materially disadvantages the account holder
/// since it could provide a means of circumventing freezes.
fn burn_held(
asset: Self::AssetId,
reason: &Self::Reason,
who: &AccountId,
mut amount: Self::Balance,
precision: Precision,
force: Fortitude,
) -> Result<Self::Balance, DispatchError> {
// We must check total-balance requirements if `!force`.
let liquid = Self::reducible_total_balance_on_hold(asset.clone(), who, force);
if let BestEffort = precision {
amount = amount.min(liquid);
} else {
ensure!(amount <= liquid, TokenError::Frozen);
}
let amount = Self::decrease_balance_on_hold(asset.clone(), reason, who, amount, precision)?;
Self::set_total_issuance(
asset.clone(),
Self::total_issuance(asset.clone()).saturating_sub(amount),
);
Self::done_burn_held(asset, reason, who, amount);
Ok(amount)
}
/// Transfer held funds into a destination account.
///
/// If `mode` is `OnHold`, then the destination account must already exist and the assets
/// transferred will still be on hold in the destination account. If not, then the destination
/// account need not already exist, but must be creatable.
///
/// If `precision` is `BestEffort`, then an amount less than `amount` may be transferred without
/// error.
///
/// If `force` is `Force`, then other fund-locking mechanisms may be disregarded. It should be
/// left as `Regular` in most circumstances, but when you want the same power as a `slash`, it
/// may be `Force`.
///
/// The actual amount transferred is returned, or `Err` in the case of error and nothing is
/// changed.
fn transfer_on_hold(
asset: Self::AssetId,
reason: &Self::Reason,
source: &AccountId,
dest: &AccountId,
mut amount: Self::Balance,
precision: Precision,
mode: Restriction,
force: Fortitude,
) -> Result<Self::Balance, DispatchError> {
// We must check total-balance requirements if `!force`.
let have = Self::balance_on_hold(asset.clone(), reason, source);
let liquid = Self::reducible_total_balance_on_hold(asset.clone(), source, force);
if let BestEffort = precision {
amount = amount.min(liquid).min(have);
} else {
ensure!(amount <= liquid, TokenError::Frozen);
ensure!(amount <= have, TokenError::FundsUnavailable);
}
// We want to make sure we can deposit the amount in advance. If we can't then something is
// very wrong.
ensure!(
Self::can_deposit(asset.clone(), dest, amount, Extant) == Success,
TokenError::CannotCreate
);
ensure!(
mode == Free || Self::hold_available(asset.clone(), reason, dest),
TokenError::CannotCreateHold
);
let amount =
Self::decrease_balance_on_hold(asset.clone(), reason, source, amount, precision)?;
let actual = if mode == OnHold {
Self::increase_balance_on_hold(asset.clone(), reason, dest, amount, precision)?
} else {
Self::increase_balance(asset.clone(), dest, amount, precision)?
};
Self::done_transfer_on_hold(asset, reason, source, dest, actual);
Ok(actual)
}
/// Transfer some `amount` of free balance from `source` to become owned by `dest` but on hold
/// for `reason`.
/// for `reason`.
///
/// If `precision` is `BestEffort`, then an amount less than `amount` may be transferred without
/// error.
///
/// `source` must obey the requirements of `keep_alive`.
///
/// If `force` is `Force`, then other fund-locking mechanisms may be disregarded. It should be
/// left as `Regular` in most circumstances, but when you want the same power as a `slash`, it
/// may be `Force`.
///
/// The amount placed on hold is returned or `Err` in the case of error and nothing is changed.
///
/// WARNING: This may return an error after a partial storage mutation. It should be used only
/// inside a transactional storage context and an `Err` result must imply a storage rollback.
fn transfer_and_hold(
asset: Self::AssetId,
reason: &Self::Reason,
source: &AccountId,
dest: &AccountId,
amount: Self::Balance,
precision: Precision,
expendability: Preservation,
force: Fortitude,
) -> Result<Self::Balance, DispatchError> {
ensure!(Self::hold_available(asset.clone(), reason, dest), TokenError::CannotCreateHold);
ensure!(
Self::can_deposit(asset.clone(), dest, amount, Extant) == Success,
TokenError::CannotCreate
);
let actual =
Self::decrease_balance(asset.clone(), source, amount, precision, expendability, force)?;
Self::increase_balance_on_hold(asset.clone(), reason, dest, actual, precision)?;
Self::done_transfer_on_hold(asset, reason, source, dest, actual);
Ok(actual)
}
fn done_hold(
_asset: Self::AssetId,
_reason: &Self::Reason,
_who: &AccountId,
_amount: Self::Balance,
) {
}
fn done_release(
_asset: Self::AssetId,
_reason: &Self::Reason,
_who: &AccountId,
_amount: Self::Balance,
) {
}
fn done_burn_held(
_asset: Self::AssetId,
_reason: &Self::Reason,
_who: &AccountId,
_amount: Self::Balance,
) {
}
fn done_transfer_on_hold(
_asset: Self::AssetId,
_reason: &Self::Reason,
_source: &AccountId,
_dest: &AccountId,
_amount: Self::Balance,
) {
}
fn done_transfer_and_hold(
_asset: Self::AssetId,
_reason: &Self::Reason,
_source: &AccountId,
_dest: &AccountId,
_transferred: Self::Balance,
) {
}
}