Add EIP-5568: Required Action Signals Using Revert Reasons

EIPS/eip-5568.md

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+---
+eip: 5568
+title: Required Action Signals Using Revert Reasons
+description: Signal to wallets that an action is needed by returning a custom revert code
+author: Pandapip1 (@Pandapip1)
+discussions-to: https://ethereum-magicians.org/t/eip-5568-revert-signals/10622
+status: Draft
+type: Standards Track
+category: Interface
+created: 2022-08-31
+requires: 140
+---
+
+## Abstract
+
+This EIP introduces a minimalistic machine-readable (binary) format to signal to wallets that an action needs to be taken by the user using a well-known revert reason. This custom revert reason contains just enough data to be extendable by future EIPs and to take in arbitrary parameters (up to 64 kB of data). Example use cases could include approving a token for an exchange, sending an HTTP request, or requesting the user to rotate their keys after a certain period of time to enforce good hygiene.
+
+## Motivation
+
+Oftentimes, a smart contract needs to signal to a wallet that an action needs to be taken, such as to sign a transaction or send an HTTP request to a URL. Traditionally, this has been done by hard-coding the logic into the frontend, but this EIP allows the smart contract itself to request the action.
+
+This means that, for example, an exchange or a market can directly tell the wallet to approve the smart contract to spend the token, vastly simplifying the front-end code.
+
+## Specification
+
+The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in RFC 2119.
+
+### Custom Revert Reason
+
+To send a signal to a wallet, a compliant smart contract MUST revert with the following error:
+
+```solidity
+error WalletSignal24(uint8 number_hint, uint24 instruction_id, bytes instruction_data)
+```
+
+The `number_hint` is an estimate of the number of signals that will be sent after the current signal. If a guess is availabe, `number_hint` MUST be that estimate. If a guess is unavailable, `number_hint` MUST be `0`.
+
+The `instruction_id` of an instruction defined by an EIP MUST be its EIP number unless there are exceptional circumstances (be reasonable). An EIP MUST define exactly zero or one `instruction_id`. The structure of the instruction data for any `instruction_id` MUST be defined by the EIP that defines the `instruction_id`.
+
+### Signal Response
+
+Before submitting a transaction to the mempool, it MUST be evaluated locally. If it reverts and the revert signature matches the custom error, then it MUST be treated as a signal. (It is RECOMMENDED for wallets to show a warning if the transaction reverts, even if the revert is not a signal).
+
+The `number_hint`, `instruction_id`, and `instruction_data` MUST be parsed from the revert data. It is RECOMMENDED for wallets to show a progress indicator using the `number_hint`. The instruction SHOULD be evaluated as per the relevant EIP. If the instruction is not supported by the wallet, it MUST display an error to the user indicating that is the case. The wallet MUST then re-evaluate the transaction, except if an instruction explicitly states that the transaction MUST NOT be re-evaluated.
+
+If an instruction is invalid, or the `number_hint`, `instruction_id`, and `instruction_data` cannot be parsed, then an error MUST be displayed to the user indicating that is the case.
+
+## Rationale
+
+This EIP was explicitly optimized for deployment gas cost and simplicity. It is expected that libraries will eventually be developed that makes sending and receiving signals more developer-friendly.
+
+## Backwards Compatibility
+
+### Human-Readable Revert Messages
+
+See [Revert Reason Collisions](#revert-reason-collisions).
+
+### [EIP-3668](./eip-3668.md)
+
+EIP-3668 can be used alongside this EIP, but it uses a different mechanism than this EIP.
+
+## Security Considerations
+
+### Revert Reason Collisions
+
+It is unlikely that the signature of the custom error matches any custom errors in the wild. In the case that it does, no harm is caused unless the data happen to be a valid instruction, which is even more unlikely.
+
+## Copyright
+
+Copyright and related rights waived via [CC0](../LICENSE.md).