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Taiko nodes

Taiko nodes are minimally modified Ethereum execution clients that consist of two parts:

You can think of it like an Ethereum mainnet node, except replacing the consensus client with taiko-client. taiko-client then drives taiko-geth over the Engine API. This is a modular design that allows easily plugging in other execution clients.

Taiko nodes diagram

taiko-geth

The taiko-geth software is a fork of go-ethereum with some changes made according to the Taiko protocol.

Like Ethereum mainnet execution engines, taiko-geth listens to new L2 transactions broadcasted in the L2 network, executes them in the EVM, and holds the latest state and database of all current L2 data.

You can see all the changes made in the taiko-geth fork at geth.taiko.xyz!

taiko-client

The taiko-client software replaces the consensus client piece of an Ethereum mainnet node. It connects to taiko-geth, and the compiled binary includes three sub-commands:

driver

The driver serves as an L2 consensus client. It listens for new L2 blocks from the TaikoL1 protocol contract, then directs the connected L2 execution engine to insert them or reorganize its local chain through the Engine API.

proposer

The proposer fetches pending transactions from the L2 execution engine’s mempool intervally pool, then tries to propose them to the TaikoL1 protocol contract.

prover

The prover requests validity proofs from the ZK-EVM and sends transactions to prove the proposed blocks are valid or invalid.

Chain synchronization process

The Taiko protocol allows a block’s timestamp to be equal to its parent block’s timestamp, which differs from the original Ethereum protocol. So it’s fine that there are two TaikoL1.proposeBlock transactions included in one L1 block.

Taiko client’s driver informs the L2 execution engine about Taiko protocol contract’s latest verified L2 head and tries to let it catch up with the latest verified L2 block through P2P at first.

The driver monitors the execution engine’s sync progress: If it’s unable to make any new sync progress in a period of time, the driver switches to inserting the verified blocks into its local chain through the Engine API one by one.

After the L2 execution engine catches up with the latest verified L2 head, the driver subscribes to TaikoL1.BlockProposed events. When a new pending block is proposed, the driver:

  1. Gets the corresponding TaikoL1.proposeBlock L1 transaction.
  2. Decodes the txList and block metadata from the transaction’s calldata.
  3. Checks whether the txList is valid based on the rules defined in the Taiko protocol.

If the txList is valid, the driver:

  1. Assembles a deterministic TaikoL2.anchor transaction based on the rules defined in the protocol and puts it as the first transaction in the proposed txList.
  2. Uses this txList and the decoded block metadata to assemble a deterministic L2 block.
  3. Directs the L2 execution engine to insert this assembled block and sets it as the current canonical chain’s head via the Engine API.

If the txList is invalid, the driver:

  1. Assembles an empty L2 block with only the anchor transaction.

Process of proposing a block

To propose a block, the proposer:

  1. Fetches the pending transactions from the L2 execution engine through the txpool_content RPC method.
  2. If there are too many pending transactions in the L2 execution engine, splits them into several smaller txLists. This is because the Taiko protocol restricts the max size of each proposed txList.
  3. Proposes all split txLists by sending TaikoL1.proposeBlock transactions.

Process of proving a block

When a new block is proposed, the prover:

  1. Gets the TaikoL1.proposeBlock L1 transaction calldata, decodes it, and validates the txList, just like what the driver software does.
  2. Waits until the corresponding block is inserted by the L2 execution engine’s driver software.
  3. Generates a validity proof for that block asynchronously.

If the proposed block has a valid or invalid txList, the prover:

  1. Generates a Merkle proof of the block’s TaikoL2.anchor transaction to prove its existence in the block.txRoot’s MPT and this transaction receipt’s Merkle proof in the block.receiptRoot’s MPT from the L2 execution engine.
  2. Submits the TaikoL2.anchor transaction’s RLP encoded bytes, its receipt’s RLP encoded bytes, the generated Merkle proofs, and a validity proof to prove this block valid by sending a TaikoL1.proveBlock transaction (the block is valid even for an invalid txList because we prove the invalid txList maps to an empty block with only the anchor transaction).