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// https://github.com/ethereum-optimism/optimism/blob/c84d3450225306abbb39b4e7d6d82424341df2be/packages/contracts/contracts/optimistic-ethereum/OVM/predeploys/OVM_L2ToL1MessagePasser.sol#L23
// You can read more about how Solidity storage slots are computed for mappings here:
// https://docs.soliditylang.org/en/v0.8.4/internals/layout_in_storage.html#mappings-and-dynamic-arrays
const messageSlot = ethers.utils.keccak256(
ethers.utils.keccak256(
encodeCrossDomainMessage(message) +
remove0x(l2CrossDomainMessengerAddress)
) + '00'.repeat(32)
)
// We need a Merkle trie proof for the given storage slot. This allows us to prove to L1 that
// the message was actually sent on L2.
const stateTrieProof = await getStateTrieProof(
l2RpcProvider,
l2Transaction.blockNumber,
predeploys.OVM_L2ToL1MessagePasser,
messageSlot
)
// State roots are published in batches to L1 and correspond 1:1 to transactions. We compute a
// Merkle root for these state roots so that we only need to store the minimum amount of
// information on-chain. So we need to create a Merkle proof for the specific state root that
// corresponds to this transaction.
const stateRootMerkleProof = getMerkleTreeProof(
batch.stateRoots,
txIndexInBatch
)
// We now have enough information to create the message proof.
const proof: CrossDomainMessageProof = {
stateRoot: batch.stateRoots[txIndexInBatch],
stateRootBatchHeader: batch.header,