Add ZEIP 35

[hysz]

Preamble

ZEIP: 35
Title: Permissive Order Cancellations
Author: 0x Core Team
Type: Standard Track
Category: Core
Status: Final
Created: 2019-10-29

Discussion: #35

Summary

The current batchCancelOrders function is difficult to use because the caller runs the risk of the entire transaction reverting if only a single cancellation fails. This is difficult to prevent because a cancellation may fail for non-deterministic reasons (such as the order being expired). This can be improved by doing a no-op instead of reverting for noncritical errors.

The proposed change would alter the logic of cancelOrder and batchCancelOrders, but would not affect the interface.

Motivation

This will improve the reliability of cancelling batches of specific orders.

Specification

The table below compares how failure scenarios are handled when cancelling an order.

Scenario	Current Action	Proposed Action
Reentrancy	Revert	Revert
Sender Not Authorized	Revert	Revert
Order Expired	Revert	No-op
Order Already Cancelled	Revert	No-op
Order Already Filled	Revert	No-op
Order Invalid	Revert	No-op

Copyright

Copyright and related rights waived via CC0.