bug: Tx delayer hashes do not match when submitting blob txs

[spalladino]

The tx delayer computes the hash of a tx manually to return it to the caller. However, the hash it computes and the hash it receives from anvil once it's actually submitted do not match. Tested it with the latest version of anvil and still happens, need to figure out whether this is an issue with viem, anvil, or how we're computing the hash manually.

For reference, we're computing tx hash using the input from sendRawTx directly:

const { serializedTransaction } = args[0];
const txHash = keccak256(serializedTransaction);

And that txHash does not match the response from anvil when we actually call sendRawTx on it with the serializedTransaction.

See here for a run where it happens consistently.

[spalladino]

Comment by @MirandaWood:

I think it's viem's serialisation. It appends the blobs, commitments, and proofs if they are available to the serialized tx, but those are not included in the tx hash AFAIK. I managed to recreate one correct tx hash by manually serialising it without the extra bits and hashing it. If viem's version of these extras are fixed size, we can probably just cut off the end of serializedTransaction in tx delayer to find the tx hash, otherwise it might get tricky (edited)

[spalladino]

Confirmed that tx hash for blob txs is computed omitting the blob. From alloy-consensus-0.9.1/src/transaction/eip4844.rs:

fn tx_hash_with_type(&self, signature: &Signature, ty: u8) -> alloy_primitives::TxHash {
    // eip4844 tx_hash is always based on the non-sidecar encoding
    self.tx.tx_hash_with_type(signature, ty)
}

Where the encoded fields are:

fn rlp_encode_fields(&self, out: &mut dyn alloy_rlp::BufMut) {
    self.chain_id.encode(out);
    self.nonce.encode(out);
    self.max_priority_fee_per_gas.encode(out);
    self.max_fee_per_gas.encode(out);
    self.gas_limit.encode(out);
    self.to.encode(out);
    self.value.encode(out);
    self.input.0.encode(out);
    self.access_list.encode(out);
    self.max_fee_per_blob_gas.encode(out);
    self.blob_versioned_hashes.encode(out);
}