SIP-45: Deprecate ERC223 sUSD Deposits from Depot

Author	Clinton Ennis
Status	Implemented
Type	Governance
Implementor	TBD
Release	TBD
Discussions-To	https://discord.gg/DQ8ehX4
Created	2020-03-01

Simple Summary

Deploy a new Depot contract allowing ERC20 Deposits only and removing ERC223 support.

Abstract

ERC223 support was deprecated from Synthetix in sip-30. This disabled the MAINNET Synthetix Depot from being able to accept anymore sUSD deposits. A new ERC20 only version of the Depot is required to enable sUSD deposits again once this one sold its ~1M in sUSD desposits.

Motivation

Since the bZx attack on Feb 18 2020 the Synthetix Depot was drained of all its 943,837 sUSD in exchange for 2388 ETH rendering it empty and end of life. This occurred prematurely and a new version was quickly deployed in the Achernar release

Specification

Modify depositSynths to use the ERC20 transferFrom workflow, requiring users to perform an approve transaction first. Mintr to have the updated approve UX for sUSD deposits.

Rationale

ERC223 did provide a better UX for users to only perform and pay for 1 transaction to depoist sUSD into the Depot. However was the only use case for ERC223 within Synthetix and the gas overhead for each transaction was about an extra 100K gwei which was causing composability friction for protocols like Kyber where the tokens might transfer to 3 different addresses in an exchange causing an additional 300K overhead in gas.

It was always intedended to replace the Depot with an ERC20 version but the bZx attack brought this forward sooner than planned.

Test Cases

https://github.com/Synthetixio/synthetix/blob/v2.20.0/test/contracts/Depot.js

Implementation

Source https://github.com/Synthetixio/synthetix/blob/v2.20.0/contracts/Depot.sol

MAINNET Contract https://etherscan.io/address/0xE1f64079aDa6Ef07b03982Ca34f1dD7152AA3b86