Exceptional ERC20s

Some ERC20s have unique behavior that may require extra handling. We document these here as they are discovered.

Assert vs Require

These ERC20’s use assert instead of require, which means that if the token reverts then (nearly) all of the gas from your transaction will be consumed. Specifically, you are left with 1/64 of the gas limit. Be mindful of this when implementing fallback logic; for example, if a call to transferFrom reverts then note you will only have 1/64 of the gas limit to handle the exception.

Known tokens:

• KNC

• LINK

• sUSD

• USDT

Tokens with Fees on Transfer

These tokens do not follow the ERC20 specification. As such the protocol expects the transfer to transfer the specified amount, or revert. Since tokens with transfer fees do not meet this criteria, the behaviour of the protocol with these tokens is unspecified. In most cases it will result in an overall transaction failure due to various slippage protections.