Tutorial: custom bridges (also how do have SuperchainERC20 equivalence without using the same addresses)

pages/interop/tutorials/_meta.json

@@ -8,5 +8,6 @@
     "relay-messages-viem": "Relaying interop messages using `viem`",
     "contract-calls": "Making crosschain contract calls (ping pong)",
     "event-reads": "Making crosschain event reads (tic-tac-toe)",
-    "event-contests": "Deploying crosschain event composability (contests)"
+    "event-contests": "Deploying crosschain event composability (contests)",
+    "upgrade-to-superchain-erc20": "Upgrade to SuperchainERC20"
 }

pages/interop/tutorials/upgrade-to-superchain-erc20/_meta.json

@@ -0,0 +1,3 @@
+{
+    "custom-bridge": "Building a custom bridge"
+}

pages/interop/tutorials/upgrade-to-superchain-erc20/custom-bridge.mdx

@@ -0,0 +1,348 @@
+---
+title: Building a custom bridge
+lang: en-US
+description: Tutorial on how to create a custom interoperability bridge. The example is a bridge when the addresses of the ERC20 contracts are not the same.
+topic: Interoperability
+personas: [Developer]
+categories: [Tutorial, Interop]
+content_type: article
+---
+
+import { Steps, Callout, Tabs } from 'nextra/components'
+
+# Building a custom bridge
+
+## Overview
+
+Sometimes the address of an ERC20 contract is not available on a different chain.
+This means that the [SuperchainTokenBridge](/interop/superchain-erc20) is not an option.
+However, if the original ERC20 contract is behind a proxy (so we can add [ERC7802](https://eips.ethereum.org/EIPS/eip-7802) support), we can still use interop by writing our own bridge.
+
+<details>
+  <summary>About this tutorial</summary>
+
+  **What you'll learn**
+
+  *   How to use [interop message passing](/interop/tutorials/message-passing) to create a custom bridge.
+
+  **Prerequisite knowledge**
+
+  *   How to [deploy SuperchainERC20 tokens with custom code](/interop/tutorials/custom-superchain-erc20).
+  *   How to [transfer interop messages](/interop/tutorials/message-passing).
+</details>
+
+<Callout type="warning">
+  The code on the documentation site is sample code, *not* production code.
+  This means that we ran it, and it works as advertised.
+  However, it did not pass through the rigorous audit process that most Optimism code undergoes.
+  You're welcome to use it, but if you need it for production purposes you should get it audited first.
+</Callout>
+
+{/* 
+
+I put this warning here, when we don't have it on most pages, because this tutorial
+has code that is a lot more likely to be used in production. It doesn't just
+show what is possible, it does the exact job needed.
+
+*/}
+
+## How beacon proxies work
+
+```mermaid
+sequenceDiagram
+  Actor User
+  User->>BeaconProxy: transfer(<address>, <amount>)
+  BeaconProxy->>UpgradeableBeacon: What is the implementation address?
+  UpgradeableBeacon->>BeaconProxy: It is 0xBAD0...60A7
+  BeaconProxy->>0xBAD0...60A7: transfer(<address>, <amount>)
+```
+
+A [beacon proxy](https://docs.openzeppelin.com/contracts/3.x/api/proxy#BeaconProxy) uses two contracts.
+The [`UpgradeableBeacon`](https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/proxy/beacon/UpgradeableBeacon.sol) contract holds the address of the implementation contract.
+The [`BeaconProxy`](https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/proxy/beacon/BeaconProxy.sol) contract is the one called for the functionality, the one that holds the storage.
+When a user (or another contract) calls `BeaconProxy`, it asks `UpgradeableBeacon` for the implementation address and then uses [`delegatecall`](https://www.evm.codes/?fork=cancun#f4) to call that contract.
+
+```mermaid
+sequenceDiagram
+  Actor User
+  Actor Owner
+  Participant BeaconProxy
+  Participant 0x600D...60A7
+  Owner->>UpgradeableBeacon: Your new implementation address is 0x600D...60A7
+  User->>BeaconProxy: transfer(<address>, <amount>)
+  BeaconProxy->>UpgradeableBeacon: What is the implementation address?
+  UpgradeableBeacon->>BeaconProxy: It is 0x600D...60A7
+  BeaconProxy->>0x600D...60A7: transfer(<address>, <amount>)  
+```
+
+To upgrade the contract, an authorized address (typically the `Owner`) calls `UpgradeableBeacon` directly to specify the new implementation contract address.
+After that happens, all new calls are sent to the new implementation.
+
+## Instructions
+
+Some steps depend on whether you want to deploy on [Supersim](/interop/tools/supersim) or on the [development network](/interop/tools/devnet).
+
+<Steps>
+  ### Install and run Supersim
+
+  If you are going to use Supersim, [follow these instructions](/app-developers/tutorials/supersim/getting-started/installation) to install and run Supersim.
+
+  <Callout>
+    Make sure to run Supersim with autorelay on.
+
+    ```sh
+    ./supersim --interop.autorelay true
+    ```
+  </Callout>
+
+  ### Set up the ERC20 token on chain A
+
+  Download and run the setup script.
+
+  ```sh
+  curl https://docs.optimism.io/tutorials/setup-for-erc20-upgrade.sh > setup-for-erc20-upgrade.sh
+  chmod +x setup-for-erc20-upgrade.sh
+  ./setup-for-erc20-upgrade.sh
+  ```
+
+  If you want to deploy to the [development networks](/interop/tools/devnet), provide `setup-for-erc20-upgrade.sh` with the private key of an address with ETH on both devnets.
+
+  ```sh
+  ./setup-for-erc20-upgrade.sh <private key>
+  ```
+
+  ### Store the addresses
+
+  Execute the bottom two lines of the setup script output to store the ERC20 address and the address of the beacon contract.
+
+  ```sh
+  BEACON_ADDRESS=0xe7f1725E7734CE288F8367e1Bb143E90bb3F0512
+  export ERC20_ADDRESS=0x9fE46736679d2D9a65F0992F2272dE9f3c7fa6e0
+  ```
+
+  ### Specify environment variables
+
+  Specify these variables, which we use later:
+
+  <Tabs items={['Supersim', 'Devnets']}>
+    <Tabs.Tab>
+      Set these parameters for Supersim.
+
+      ```sh
+      PRIVATE_KEY=0xac0974bec39a17e36ba4a6b4d238ff944bacb478cbed5efcae784d7bf4f2ff80
+      USER_ADDRESS=0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266
+      URL_CHAIN_A=http://127.0.0.1:9545
+      URL_CHAIN_B=http://127.0.0.1:9546
+      ```
+    </Tabs.Tab>
+
+    <Tabs.Tab>
+      For Devnet, specify in `PRIVATE_KEY` the private key you used for the setup script and then these parameters.
+
+      ```sh
+      USER_ADDRESS=`cast wallet address --private-key $PRIVATE_KEY`
+      URL_CHAIN_A=https://interop-alpha-0.optimism.io
+      URL_CHAIN_B=https://interop-alpha-1.optimism.io
+      ```
+    </Tabs.Tab>
+  </Tabs>
+
+  ### Advance the user's nonce on chain B
+
+  This solution is necessary when the nonce on chain B is higher than it was on chain A when the proxy for the ERC-20 contract was installed.
+  To simulate this situation, we send a few meaningless transactions on chain B and then see that the nonce on B is higher than the nonce on A.
+
+  ```sh
+  cast send $USER_ADDRESS --private-key $PRIVATE_KEY --rpc-url $URL_CHAIN_B
+  cast send $USER_ADDRESS --private-key $PRIVATE_KEY --rpc-url $URL_CHAIN_B
+  cast send $USER_ADDRESS --private-key $PRIVATE_KEY --rpc-url $URL_CHAIN_B
+  cast send $USER_ADDRESS --private-key $PRIVATE_KEY --rpc-url $URL_CHAIN_B
+  echo -n Nonce on chain A:
+  cast nonce $USER_ADDRESS --rpc-url $URL_CHAIN_A
+  echo -n Nonce on chain B:
+  cast nonce $USER_ADDRESS --rpc-url $URL_CHAIN_B
+  ```
+
+  ### Create a Foundry project
+
+  Create a [Foundry](https://book.getfoundry.sh/) project and import the [OpenZeppelin](https://www.openzeppelin.com/solidity-contracts) contracts used for the original ERC20 and proxy deployment.
+
+  ```sh
+  mkdir custom-bridge
+  cd custom-bridge
+  forge init
+  forge install OpenZeppelin/openzeppelin-contracts
+  forge install OpenZeppelin/openzeppelin-contracts-upgradeable
+  forge install ethereum-optimism/interop-lib
+  ```
+
+  ### Deploy proxies
+
+  We need two contracts on each chain: an ERC20 and a bridge, and to enable future upgrades, we want to install each of those contracts behind a proxy.
+  You already have one contract—the ERC20 on chain A—but need to create the other three.
+
+  There's an interesting [chicken-and-egg](https://en.wikipedia.org/wiki/Chicken_or_the_egg) issue here.
+  To create a proxy, we need the address of the implementation contract, the one with the actual code.
+  However, the bridge and ERC20 code needs to have the proxy addresses.
+  One possible solution is to choose a pre-existing contract, and use that as the implementation contract until we can upgrade.
+  Every OP Stack chain has [predeploys](https://specs.optimism.io/protocol/predeploys.html) we can use for this purpose.
+
+  ```sh
+  DUMMY_ADDRESS=0x4200000000000000000000000000000000000000
+  UPGRADE_BEACON_CONTRACT=lib/openzeppelin-contracts-upgradeable/lib/openzeppelin-contracts/contracts/proxy/beacon/UpgradeableBeacon.sol:UpgradeableBeacon
+  PROXY_CONTRACT=lib/openzeppelin-contracts-upgradeable/lib/openzeppelin-contracts/contracts/proxy/beacon/BeaconProxy.sol:BeaconProxy
+  BRIDGE_BEACON_ADDRESS_A=`forge create $UPGRADE_BEACON_CONTRACT --broadcast --rpc-url $URL_CHAIN_A --private-key $PRIVATE_KEY --constructor-args $DUMMY_ADDRESS $USER_ADDRESS | awk '/Deployed to:/ {print $3}'`
+  BRIDGE_ADDRESS_A=`forge create $PROXY_CONTRACT --broadcast --rpc-url $URL_CHAIN_A --private-key $PRIVATE_KEY --constructor-args $BRIDGE_BEACON_ADDRESS_A 0x | awk '/Deployed to:/ {print $3}'`
+  BRIDGE_BEACON_ADDRESS_B=`forge create $UPGRADE_BEACON_CONTRACT --broadcast --rpc-url $URL_CHAIN_B --private-key $PRIVATE_KEY --constructor-args $DUMMY_ADDRESS $USER_ADDRESS | awk '/Deployed to:/ {print $3}'`
+  BRIDGE_ADDRESS_B=`forge create $PROXY_CONTRACT --broadcast --rpc-url $URL_CHAIN_B --private-key $PRIVATE_KEY --constructor-args $BRIDGE_BEACON_ADDRESS_B 0x | awk '/Deployed to:/ {print $3}'`
+  ERC20_BEACON_ADDRESS_A=$BEACON_ADDRESS
+  ERC20_ADDRESS_A=$ERC20_ADDRESS
+  ERC20_BEACON_ADDRESS_B=`forge create $UPGRADE_BEACON_CONTRACT --broadcast --rpc-url $URL_CHAIN_B --private-key $PRIVATE_KEY --constructor-args $DUMMY_ADDRESS $USER_ADDRESS | awk '/Deployed to:/ {print $3}'`
+  ERC20_ADDRESS_B=`forge create $PROXY_CONTRACT --broadcast --rpc-url $URL_CHAIN_B --private-key $PRIVATE_KEY --constructor-args $ERC20_BEACON_ADDRESS_B 0x | awk '/Deployed to:/ {print $3}'`  
+  ```
+
+  ### Deploy ERC7802 contracts
+
+  Replace the ERC20 contracts with contracts that:
+
+  *   Support [ERC7802](https://eips.ethereum.org/EIPS/eip-7802) and [ERC165](https://eips.ethereum.org/EIPS/eip-165).
+  *   Allow the bridge address to mint and burn tokens.
+      Normally this is `PredeployAddresses.SUPERCHAIN_TOKEN_BRIDGE`, but in our case it would be the bridge proxy address, which we'll store in `bridgeAddress`.
+  *   Have the same storage layout as the ERC20 contracts they replace (in the case of chain A).
+
+  1.  Create a file, `src/InteropToken.sol`.
+
+      ```solidity file=<rootDir>/public/tutorials/InteropToken.sol hash=5e728534c265028c94d60dcb6550699d filename="src/InteropToken.sol"
+      ```
+
+  2.  This `src/InteropToken.sol` is used for contract upgrades when the ERC20 contracts are at the same address.
+      Here we need to edit it to allow our custom bridge to mint and burn tokens instead of the predeployed superchain token bridge.
+
+      *   On lines 20 and 31 replace ~~`PredeployAddresses.SUPERCHAIN_TOKEN_BRIDGE`~~ with `bridgeAddress`.
+
+          ```solidity
+          require(msg.sender == bridgeAddress, "Unauthorized");
+          ```
+
+      *   Add these lines anywhere in the contract:
+
+          ```solidity
+              address public immutable bridgeAddress;
+
+              constructor(address bridgeAddress_) {
+                  bridgeAddress = bridgeAddress_;
+              }
+          ```
+
+  3.  Deploy `InteropToken` on both chains, with the bridge address.
+
+      ```sh
+      INTEROP_TOKEN_A=`forge create InteropToken --private-key $PRIVATE_KEY --broadcast --rpc-url $URL_CHAIN_A --constructor-args $BRIDGE_ADDRESS_A | awk '/Deployed to:/ {print $3}'`
+      INTEROP_TOKEN_B=`forge create InteropToken --private-key $PRIVATE_KEY --broadcast --rpc-url $URL_CHAIN_B --constructor-args $BRIDGE_ADDRESS_B | awk '/Deployed to:/ {print $3}'`
+      ```
+
+  4.  Update the proxies to the new implementations.
+
+      ```sh
+      cast send $ERC20_BEACON_ADDRESS_A "upgradeTo(address)" $INTEROP_TOKEN_A --private-key $PRIVATE_KEY --rpc-url $URL_CHAIN_A
+      cast send $ERC20_BEACON_ADDRESS_B "upgradeTo(address)" $INTEROP_TOKEN_B --private-key $PRIVATE_KEY --rpc-url $URL_CHAIN_B
+      ```
+
+  ### Deploy the actual bridge
+
+  1.  Create a file, `src/CustomBridge.sol`.
+      This file is based on the standard `SuperchainERC20`  [`SuperchainTokenBridge.sol`](https://github.com/ethereum-optimism/optimism/blob/develop/packages/contracts-bedrock/src/L2/SuperchainTokenBridge.sol).
+
+      ```solidity file=<rootDir>/public/tutorials/CustomBridge.sol hash=fc6cb08b40b7cf5bfb2b0c5793e4795e filename="src/CustomBridge.sol"
+      ```
+
+      <details>
+          <summary>Explanation</summary>
+
+          These are the main differences between the generic bridge and our implementation.
+
+          ```solidity file=<rootDir>/public/tutorials/CustomBridge.sol#L14-L18 hash=fd42623685f26046337ea6d105f27e4a
+          ```
+
+          The configuration is [`immutable`](https://docs.soliditylang.org/en/latest/contracts.html#immutable).
+          We are deploying the contract behind a proxy, so if we need to change it we can deploy a different contract.
+
+          These parameters assume there are only two chains in the interop cluster.
+          If there are more, change the `There` variables to array.
+
+          ```solidity file=<rootDir>/public/tutorials/CustomBridge.sol#L48-L65 hash=87edfdbb21fe11f573eff932d6f36d82
+          ```
+
+          The constructor writes the configuration parameters.
+
+          ```solidity file=<rootDir>/public/tutorials/CustomBridge.sol#L72-L75 hash=01ac207764b0d944ec4a005c7c3f01a8
+          ```
+
+          We don't need to specify the token address, or the chain ID on the other side, because they are hardwired in this bridge.
+
+          ```solidity file=<rootDir>/public/tutorials/CustomBridge.sol#L86 hash=d4ccbac2c6ce01bce65bc75242741f6e
+          ```
+
+          Emit the same log entry that would be emitted by the standard bridge.
+
+          ```solidity file=<rootDir>/public/tutorials/CustomBridge.sol#L100-L101 hash=142a487e877cc2cbeba8e07fce451c88
+          ```
+
+          Make sure any relay requests come from the correct contract on the correct chain.
+      </details>
+
+  2.  Get the chainID values.
+
+      ```sh
+      CHAINID_A=`cast chain-id --rpc-url $URL_CHAIN_A`
+      CHAINID_B=`cast chain-id --rpc-url $URL_CHAIN_B`
+      ```
+
+  3.  Deploy the bridges with the correct configuration.
+
+      ```sh
+      BRIDGE_IMPLEMENTATION_ADDRESS_A=`forge create CustomBridge --broadcast --rpc-url $URL_CHAIN_A --private-key $PRIVATE_KEY --constructor-args  $ERC20_ADDRESS_A $ERC20_ADDRESS_B $CHAINID_B $BRIDGE_ADDRESS_B | awk '/Deployed to:/ {print $3}'`
+      BRIDGE_IMPLEMENTATION_ADDRESS_B=`forge create CustomBridge --broadcast --rpc-url $URL_CHAIN_B --private-key $PRIVATE_KEY --constructor-args  $ERC20_ADDRESS_B $ERC20_ADDRESS_A $CHAINID_A $BRIDGE_ADDRESS_A | awk '/Deployed to:/ {print $3}'`      
+      ```
+
+  4.  Inform the proxy beacons about the new addresses of the bridge implementation contracts.
+
+      ```sh
+      cast send $BRIDGE_BEACON_ADDRESS_A "upgradeTo(address)" $BRIDGE_IMPLEMENTATION_ADDRESS_A --private-key $PRIVATE_KEY --rpc-url $URL_CHAIN_A
+      cast send $BRIDGE_BEACON_ADDRESS_B "upgradeTo(address)" $BRIDGE_IMPLEMENTATION_ADDRESS_B --private-key $PRIVATE_KEY --rpc-url $URL_CHAIN_B
+      ```
+
+  ### Verification
+
+  1.  See your balance on chain A.
+
+      ```sh
+      cast call $ERC20_ADDRESS_A "balanceOf(address)" $USER_ADDRESS --rpc-url $URL_CHAIN_A | cast from-wei
+      ```
+
+  2.  See your balance on chain B.
+
+      ```sh
+      cast call $ERC20_ADDRESS_B "balanceOf(address)" $USER_ADDRESS --rpc-url $URL_CHAIN_B | cast from-wei
+      ```
+
+  3.  Transfer 0.1 token.
+
+      ```sh
+      AMOUNT=`echo 0.1 | cast to-wei`
+      cast send $BRIDGE_ADDRESS_A --rpc-url $URL_CHAIN_A --private-key $PRIVATE_KEY "sendERC20(address,uint256)" $USER_ADDRESS $AMOUNT
+      ```
+
+  4.  See the new balances. The A chain should have 0.9 tokens, and the B chain should have 0.1 tokens.
+
+      ```sh
+      cast call $ERC20_ADDRESS_A "balanceOf(address)" $USER_ADDRESS --rpc-url $URL_CHAIN_A | cast from-wei
+      cast call $ERC20_ADDRESS_B "balanceOf(address)" $USER_ADDRESS --rpc-url $URL_CHAIN_B | cast from-wei
+      ```
+</Steps>
+
+## Next steps
+
+*   Deploy a [SuperchainERC20](/interop/tutorials/deploy-superchain-erc20) to the Superchain
+*   [Learn more about SuperchainERC20](/interop/superchain-erc20)
+*   Build a [revolutionary app](/app-developers/get-started) that uses multiple blockchains within the Superchain