Add `ERC7674` (draft) #5071

Amxx · 2024-06-07T14:49:32Z

Fixes #4959

ERC-7674 is still WIP, but having it implemented as a draft contract would be valuable for users

Pending discussions:

if (value > 0) {...} in ERC20._spendAllowance vs if (value > 0) super._spendAllowance(...) in ERC20TemporaryApproval
- remove _approve call when value is 0
- skip super call if temporary allowance covers everything
emit event when temporary allowance is set/updated ?

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changeset-bot · 2024-06-07T14:49:47Z

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.changeset/serious-carrots-provide.md

test/token/ERC20/extensions/ERC20TemporaryApproval.test.js

.changeset/serious-carrots-provide.md

contracts/interfaces/draft-IERC7674.sol

ernestognw · 2024-06-07T20:14:03Z

contracts/token/ERC20/ERC20.sol

+        if (value > 0) {
+            uint256 currentAllowance = allowance(owner, spender);
+            if (currentAllowance != type(uint256).max) {
+                if (currentAllowance < value) {
+                    revert ERC20InsufficientAllowance(spender, currentAllowance, value);
+                }
+                unchecked {
+                    _approve(owner, spender, currentAllowance - value, false);
+                }
            }
        }


Didn't we decide against address poisoning for similar reasons we would decide against filtering value == 0?

About address poisoning we decided to:

not revert if value is 0 (for many reason)

keep emitting the transfer event.

The changes here don't introduce a revert, and don't remove any event.

The logic here is the following:

if the temporary allowance is enough, we should not sload/sstore the persistent value (otherwize it break the point of gas savings). So we can do it in two ways:

in ERC20TemporaryApproval._spendAllowance only do the super call if value > 0

this is bad practice if someone else overrides _spendAllowance

in ERC20 change the semantics of _spendAllowance to mean "if there is nothing to spend, we are good anyway".

If we look at ERC20._spendAllowance, this has the following impact

if value = 0, currentAllowance cannot be smaller than value. ERC20InsufficientAllowance is never triggered, so the if doesn't change anything regarding the revert.

if value is 0, 5.0 code does:

load the allowance (from a potentially overridable function)

substract zero from it

set it as the new allowance, without emitting an event.

So there is a change, we are no longer calling _approve with the current value. It may be possible to create edge cases where the missed call to an overrident _approve has an effect. IMO its a non issue.

About address poisoning, it doesn't change the possibility of doing it (or not doing it). It makes it cheaper though, because the poisonning call would not read/write the zero allowance.

@frangio curious to having your opinion on this if in the core ERC20.

It may be possible to create edge cases where the missed call to an overrident _approve has an effect.

Hm, I have a vague memory that this actually was a concern for a project once... It does seem quite risky to change this in a minor version.

Could we implement this by overriding only allowance and _approve instead of _spendAllowance?

I have no idea how. In particular I'm not sure how to make transferFrom spend only temporary allowance, without touching the normal allowance, when the temporary allowance is enough

I think it's possible, but not without the same problem of not invoking super._approve. There seems to be no way around that.

in ERC20TemporaryApproval._spendAllowance only do the super call if value > 0

this is bad practice if someone else overrides _spendAllowance

This is true, but it may be preferable than changing the behavior of ERC20 in a minor version. I think it's worth considering.

Its what I used to do, before realizing there was a way to have the super call always happen.
I'm leanning toward the current version, but I'm open to re-using the old one

As discussed, I re-implemented the old one.

It negativelly affect the tests because the error emitted in some edge conditions depends on _approve being called (with spender = 0 and value = 0).
See 0490902

contracts/token/ERC20/README.adoc

contracts/token/ERC20/extensions/draft-ERC20TemporaryApproval.sol

test/token/ERC20/ERC20.behavior.js

contracts/token/ERC20/extensions/draft-ERC20TemporaryApproval.sol

test/token/ERC20/extensions/draft-ERC20TemporaryApproval.test.js

cairoeth

implementation lgtm. codecov is failing, rebasing should fix.

.changeset/serious-carrots-provide.md

contracts/interfaces/draft-IERC7674.sol

cairoeth · 2024-07-16T14:05:49Z

contracts/interfaces/draft-IERC7674.sol

+     * @dev Set the temporary allowance, allowing allows `spender` to withdraw (within the same transaction) assets
+     * held by the caller.


https://github.com/OpenZeppelin/openzeppelin-contracts/pull/5071/files#diff-7b0f1795668241cd100ce0a5728fc598e10533cf7bd2846a8b5c86b8a7ac6fa5R60-R71 is much clearer imo. for consistency (and to not duplicate), shouldn't we have these comments in the interface, and point to the interface in the implementation function comments? as in here https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC20/ERC20.sol#L118

contracts/interfaces/draft-IERC7674.sol

Co-authored-by: Ernesto García <ernestognw@gmail.com>

Co-authored-by: cairo <cairoeth@protonmail.com>

cairoeth

lgtm!

ernestognw

Looking good for a draft. Thanks all!

Amxx added this to the 5.1 milestone Jun 7, 2024

Amxx commented Jun 7, 2024

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Amxx force-pushed the feature/erc-7674 branch 2 times, most recently from 80261e2 to 036ed54 Compare June 10, 2024 11:33

Amxx changed the title ~~Add ERC20TemporaryApproval~~ Add ERC7674 Jun 10, 2024

Amxx changed the title ~~Add ERC7674~~ Add ERC7674 (draft) Jun 10, 2024

Amxx force-pushed the feature/erc-7674 branch from bac03e6 to 0490902 Compare June 13, 2024 14:05

Amxx commented Jun 13, 2024

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Amxx added 11 commits July 16, 2024 16:49

Add ERC20TemporaryApproval

bbf64d3

Update .changeset/serious-carrots-provide.md

4f94434

testing

119f718

update

76f1745

coverage

1e6911e

doc

28402a6

Update draft-IERC7674.sol

43ee727

Update test/token/ERC20/extensions/ERC20TemporaryApproval.test.js

e729394

rename events in helper

2bbd0b2

update

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update

f48694c

Amxx and others added 8 commits July 16, 2024 16:49

rename ERC20TemporaryApproval -> ERC7674

8119a6e

rename

b8fa057

if value greater than zero check in ERC20TemporaryApproval

5bb7662

fix tests

fc031f1

spelling

112c22b

Update test/token/ERC20/ERC20.behavior.js

6f3df41

Apply suggestions from code review

352f56c

Update contracts/token/ERC20/extensions/draft-ERC20TemporaryApproval.sol

a18f963

Co-authored-by: Ernesto García <ernestognw@gmail.com>

cairoeth force-pushed the feature/erc-7674 branch from 19c414a to a18f963 Compare July 16, 2024 14:49

Amxx and others added 4 commits July 17, 2024 18:15

Apply suggestions from code review

17f3410

Co-authored-by: cairo <cairoeth@protonmail.com>

Update draft-IERC7674.sol

461d527

Update draft-IERC7674.sol

12a79e7

fix override

887121c

Amxx requested review from ernestognw and cairoeth July 19, 2024 06:40

cairoeth approved these changes Jul 19, 2024

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ernestognw approved these changes Jul 22, 2024

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Amxx merged commit e30b390 into OpenZeppelin:master Jul 22, 2024
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Amxx deleted the feature/erc-7674 branch July 22, 2024 15:23

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Add `ERC7674` (draft) #5071

Add `ERC7674` (draft) #5071

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		* @dev Set the temporary allowance, allowing allows `spender` to withdraw (within the same transaction) assets
		* held by the caller.

Add ERC7674 (draft) #5071

Add ERC7674 (draft) #5071

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Add `ERC7674` (draft) #5071

Add `ERC7674` (draft) #5071

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