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check allowance expiration before increasing or decreasing it #17

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Merged
merged 1 commit into from
May 27, 2021
Merged

check allowance expiration before increasing or decreasing it #17

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28 changes: 23 additions & 5 deletions src/contract.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -993,9 +993,7 @@ fn use_allowance<S: Storage>(
) -> StdResult<()> {
let mut allowance = read_allowance(storage, owner, spender)?;

if allowance.expiration.map(|ex| ex < env.block.time) == Some(true) && allowance.amount != 0 {
allowance.amount = 0;
write_allowance(storage, owner, spender, allowance)?;
if allowance.is_expired_at(&env.block) {
return Err(insufficient_allowance(0, amount));
Comment on lines 995 to 997
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@reuvenpo reuvenpo May 27, 2021

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Note to reviewer: This code segment was expensive and unnecessary. There's no need to actively set the amount to 0 if the allowance query would make it clear to consumers that the allowance has expired anyway (so the amount isn't important)

}
if let Some(new_allowance) = allowance.amount.checked_sub(amount) {
Expand Down Expand Up @@ -1338,7 +1336,17 @@ fn try_increase_allowance<S: Storage, A: Api, Q: Querier>(
let spender_address = deps.api.canonical_address(&spender)?;

let mut allowance = read_allowance(&deps.storage, &owner_address, &spender_address)?;
allowance.amount = allowance.amount.saturating_add(amount.u128());

// If the previous allowance has expired, reset the allowance.
// Without this users can take advantage of an expired allowance given to
// them long ago.
if allowance.is_expired_at(&env.block) {
allowance.amount = amount.u128();
allowance.expiration = None;
} else {
allowance.amount = allowance.amount.saturating_add(amount.u128());
}

if expiration.is_some() {
allowance.expiration = expiration;
}
Expand Down Expand Up @@ -1373,7 +1381,17 @@ fn try_decrease_allowance<S: Storage, A: Api, Q: Querier>(
let spender_address = deps.api.canonical_address(&spender)?;

let mut allowance = read_allowance(&deps.storage, &owner_address, &spender_address)?;
allowance.amount = allowance.amount.saturating_sub(amount.u128());

// If the previous allowance has expired, reset the allowance.
// Without this users can take advantage of an expired allowance given to
// them long ago.
if allowance.is_expired_at(&env.block) {
allowance.amount = 0;
allowance.expiration = None;
} else {
allowance.amount = allowance.amount.saturating_sub(amount.u128());
}

if expiration.is_some() {
allowance.expiration = expiration;
}
Expand Down
9 changes: 9 additions & 0 deletions src/state.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -303,6 +303,15 @@ pub struct Allowance {
pub expiration: Option<u64>,
}

impl Allowance {
pub fn is_expired_at(&self, block: &cosmwasm_std::BlockInfo) -> bool {
match self.expiration {
Some(time) => block.time >= time,
None => false, // allowance has no expiration
}
}
}

pub fn read_allowance<S: Storage>(
store: &S,
owner: &CanonicalAddr,
Expand Down