The SuperchainERC20 standard is ready for production deployments. Please note that the OP Stack interoperability upgrade, required for crosschain messaging, is currently still in active development.
Relaying interop messages using cast
This tutorial walks through how to form a message identifier (opens in a new tab) to relay a L2ToL2CrossDomainMessenger (opens in a new tab) cross-chain call.
We'll perform the SuperchainERC20 interop transfer in Supersim first steps by manually relaying the message without the autorelayer.
Contracts used
- L2NativeSuperchainERC20 (opens in a new tab)
0x420beeF000000000000000000000000000000001
- L2ToL2CrossDomainMessenger (opens in a new tab)
0x4200000000000000000000000000000000000023
High level steps
Sending an interop message using the L2ToL2CrossDomainMessenger:
On source chain (OPChainA 901)
- Invoke
L2NativeSuperchainERC20.sendERC20to bridge funds- this leverages
L2ToL2CrossDomainMessenger.sendMessageto make the cross chain call
- this leverages
- Retrieve the log identifier and the message payload for the
SentMessageevent.
On destination chain (OPChainB 902)
- Relay the message with
L2ToL2CrossDomainMessenger.relayMessage- which then calls
L2NativeSuperchainERC20.relayERC20
- which then calls
Message identifier
A message identifier uniquely identifies a log emitted on a chain. The sequencer and smart contracts (CrossL2Inbox) use the identifier to perform invariant checks (opens in a new tab) to confirm that the message is valid.
struct Identifier {
address origin; // Account (contract) that emits the log
uint256 blocknumber; // Block number in which the log was emitted
uint256 logIndex; // Index of the log in the array of all logs emitted in the block
uint256 timestamp; // Timestamp that the log was emitted
uint256 chainid; // Chain ID of the chain that emitted the log
}Steps
Start supersim
supersimMint tokens to transfer on chain 901
Run the following command to mint 1000 L2NativeSuperchainERC20 tokens to the recipient address:
cast send 0x420beeF000000000000000000000000000000001 "mint(address _to, uint256 _amount)" 0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266 1000 --rpc-url http://127.0.0.1:9545 --private-key 0xac0974bec39a17e36ba4a6b4d238ff944bacb478cbed5efcae784d7bf4f2ff80Initiate the send transaction on chain 901
Send the tokens from Chain 901 to Chain 902 using the following command:
cast send 0x4200000000000000000000000000000000000028 "sendERC20(address _token, address _to, uint256 _amount, uint256 _chainId)" 0x420beeF000000000000000000000000000000001 0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266 1000 902 --rpc-url http://127.0.0.1:9545 --private-key 0xac0974bec39a17e36ba4a6b4d238ff944bacb478cbed5efcae784d7bf4f2ff80Get the log emitted by the L2ToL2CrossDomainMessenger
The token contract calls the L2ToL2CrossDomainMessenger (opens in a new tab), which emits a message (log) that can be relayed on the destination chain.
cast logs --address 0x4200000000000000000000000000000000000023 --rpc-url http://127.0.0.1:9545Sample output:
address: 0x4200000000000000000000000000000000000023
blockHash: 0x311f8ccea3fc121aa3af18e0a87766ae56ed3f1d08cae91ec29f34a9919abcc0
blockNumber: 14
data: 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
logIndex: 2
removed: false
topics: [
0x382409ac69001e11931a28435afef442cbfd20d9891907e8fa373ba7d351f320
0x0000000000000000000000000000000000000000000000000000000000000386
0x0000000000000000000000004200000000000000000000000000000000000028
0x0000000000000000000000000000000000000000000000000000000000000000
]
transactionHash: 0x746a3e8a3a0ed0787367c3476269fa3050a2f9113637b563a4579fbc03efe5c4
transactionIndex: 0Retrieve the block timestamp the log was emitted in
Since the message identifier requires the block timestamp, fetch the block info to get the timestamp. 0xREPLACE_WITH_CORRECT_BLOCKHASH should be replaced with the blockHash from the output of the previous step.
cast block 0xREPLACE_WITH_CORRECT_BLOCKHASH --rpc-url http://127.0.0.1:9545Sample output:
// (truncated for brevity)
timestamp 1743801675
// ...Prepare the message identifier & payload
Now we have all the information needed for the message (log) identifier.
| Parameter | Value | Note |
|---|---|---|
| origin | 0x4200000000000000000000000000000000000023 | L2ToL2CrossDomainMessenger |
| blocknumber | 4 | from step 4 |
| logIndex | 1 | from step 4 |
| timestamp | 1728507703 | from step 5 |
| chainid | 901 | OPChainA chainID |
The message payload is the concatenation of the [...topics, data] in order.
0x + 382409ac69001e11931a28435afef442cbfd20d9891907e8fa373ba7d351f320
+ 0000000000000000000000000000000000000000000000000000000000000386
+ 0000000000000000000000004200000000000000000000000000000000000028
+ 0000000000000000000000000000000000000000000000000000000000000000
+ 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: 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
Construct the access list for the message
An access list must be passed along with the relay message transaction. There are two admin RPC methods that can be used to construct the access list: admin_getAccessListByMsgHash and admin_getAccessListForIdentifier.
a. To get the access list using the admin_getAccessListByMsgHash RPC method, call the method with the message hash.
- Retrieve the message hash from the supersim logs
INFO [04-04|14:21:15.587] L2ToL2CrossChainMessenger#SentMessage sourceChainID=901 destinationChainID=902 nonce=0 sender=0x4200000000000000000000000000000000000028 target=0x4200000000000000000000000000000000000028 msgHash=0xccff97c17ef11d659d319cbc5780235ea03ef34b0fa34f40b208a9519f257379 txHash=0x746a3e8a3a0ed0787367c3476269fa3050a2f9113637b563a4579fbc03efe5c4- Call
admin_getAccessListByMsgHashwith the message hash.
cast rpc admin_getAccessListByMsgHash 0xccff97c17ef11d659d319cbc5780235ea03ef34b0fa34f40b208a9519f257379 --rpc-url http://localhost:8420Sample output:
{
"accessList": [
{
"address": "0x4200000000000000000000000000000000000022",
"storageKeys": [
"0x010000000000000000000385000000000000000e0000000067f04d4b00000002",
"0x03c6d2648cef120ce1d7ccf9f8d4042d6b25ff30a02e22d9ea2a47d2677ccb8d"
]
}
]
}b. To get the access list using the admin_getAccessListForIdentifier RPC method, call the method with the identifier and the message payload.
cast rpc admin_getAccessListForIdentifier \
'{
"origin": "0x4200000000000000000000000000000000000023",
"blockNumber": "14",
"logIndex": "2",
"timestamp": "1743801675",
"chainId": "901",
"payload": "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"
}' \
--rpc-url http://localhost:8420Sample output:
{
"accessList": [
{
"address": "0x4200000000000000000000000000000000000022",
"storageKeys": [
"0x010000000000000000000385000000000000000e0000000067f04d4b00000002",
"0x03c6d2648cef120ce1d7ccf9f8d4042d6b25ff30a02e22d9ea2a47d2677ccb8d"
]
}
]
}Send the relayMessage transaction
Call relayMessage on the L2ToL2CrossDomainMessenger (opens in a new tab) with the access list.
// L2ToL2CrossDomainMessenger.sol (truncated for brevity)
contract L2ToL2CrossDomainMessenger {
// ...
function relayMessage(
ICrossL2Inbox.Identifier calldata _id,
bytes calldata _sentMessage
) payable
// ...
}relayMessage parameters
ICrossL2Inbox.Identifier calldata _id: identifier pointing to theSentMessagelog on the source chainbytes memory _sentMessage: encoding of the log topics & data
Below is an example call, but make sure to replace them with the correct values you received in previous steps.
cast send 0x4200000000000000000000000000000000000023 \
"relayMessage((address, uint256, uint256, uint256, uint256), bytes)" \
"(0x4200000000000000000000000000000000000023, 14, 2, 1743801675, 901)" \
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 \
--access-list '[{"address":"0x4200000000000000000000000000000000000022","storageKeys":["0x010000000000000000000385000000000000000e0000000067f04d4b00000002", "0x03c6d2648cef120ce1d7ccf9f8d4042d6b25ff30a02e22d9ea2a47d2677ccb8d"]}]' \
--rpc-url http://127.0.0.1:9546 \
--private-key 0xac0974bec39a17e36ba4a6b4d238ff944bacb478cbed5efcae784d7bf4f2ff80Check the balance on chain 902
Verify that the balance of the L2NativeSuperchainERC20 on chain 902 has increased:
cast balance --erc20 0x420beeF000000000000000000000000000000001 0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266 --rpc-url http://127.0.0.1:9546Alternatives
This is obviously very tedious to do by hand 😅. Here are some alternatives:
- use
supersim --interop.autorelay- this only works on supersim, but relayers for the testnet/prod environment will be available soon! - use
viembindings/actions - if you're using typescript, we have bindings available to make fetching identifiers and relaying messages easy
Next steps
- Check out the collection of Supersim tutorials for more resources on building with Interop.
- Use the SuperchainERC20 Starter Kit to deploy your token across the Superchain.
- Review the Superchain Interop Explainer for answers to common questions about interoperability.