Custom USDC bridge

[fedealconada]

We want to use the canonical zkSync Bridge with a custom bridge implementation that works only for USDC (since we want to use the native USDC and not the ERC20 that the zksync bridge deploys by default).

The PR is a little bit large but the key contracts to review are:

• src/L1SharedBridge.sol
• src/L2SharedBridge.sol

Bridge/Withdrawal flow

The flow to bridge and withdraw using custom bridges is the same as when bridging with any token except for the fact that when Bridgehub is called, you need specify the address of the custom L1 bridge.

To bridge USDC from L1 (Ethereum) -> L2 (Sophon):

• Call bridgehub.requestL2TransactionTwoBridges (same as normally) but you set the secondBridgeAddress with the custom shared bridge deployed on L1. This way, the bridgehub contracts knows which contract to ping to.
• requestL2TransactionTwoBridges makes a call to the custom shared bridge customBridgeL1.bridgehubDeposit function and transfers USDC from the user to this contract and emits an event.
• sequencers will pick this event and automatically make a call to customL2Bridge.finalizeDeposit on the custom bridge deployed on L2 (on Sophon).
• finalizeDeposit is the one that calls usdc.mint() to mint USDC on L2 (note this custom bridge must have MINTER role on the USDC contract).

To withdraw USDC from L2 (Sophon) -> L1 (Etheruem):

• User makes a call to customBridgeL2.withdraw (same as normally except for the fact that you're calling the custom bridge contract)
• Once the batch is sealed, user needs to call customL1Bridge.finalizeWithdrawal to finalise the withdrawal

Fixes #SOP-53
Fixes #SOP-54
Fixes #SOP-88
Fixes #SOP-89

[linear]

SOP-54 Create L2SharedBridge.sol

Create a custom L2SharedBridge.sol that works with the native USDC

SOP-53 Create L1SharedBridge.sol

Create a custom L1SharedBridge.sol that works with the USDC implementation

SOP-88 Create unit tests

[federava]

This looks great! The implementation is clear, and the test coverage is thorough.

[kelemeno]

Look good overall I think, the main is a direct clone of one of era_contracts repo right?

I would get rid of even more of the legacy code, I don't think you need it, modifying the interfaces is ok.

But the approach/security/code looks good!

[fedealconada]

Look good overall I think, the main is a direct clone of one of era_contracts repo right?

I would get rid of even more of the legacy code, I don't think you need it, modifying the interfaces is ok.

But the approach/security/code looks good!

Thanks for the comments!

[fedealconada]

I would get rid of even more of the legacy code, I don't think you need it, modifying the interfaces is ok.

would you point me to which are the other legacy things that we are safe to remove?

[fedealconada]

@kelemeno do we need this? or it's safe to be removed?

[kelemeno]

yes you can remove.

[fedealconada]

Btw, which commit did you branch off from in era-contracts? It is the audited one right? Could you include it somewhere please?

this is the commit we've forked from https://github.com/matter-labs/era-contracts.git#bce4b2d0f34bd87f1aaadd291772935afb1c3bd6