Asynchronous transaction serializers prior to signing

[CedarMist]

Currently the transaction serializers are great, but they don't support async code prior to signing.

See the signTransaction function as an example.

• First it serializes the unsigned transaction, hashes then signs it (non-async)
• Then serializes the signed transaction (async)

This is messy, as sometimes the transaction serializer can be async and return a Promise, sometimes it can't. It would be good to be consistent and make it so the transaction serializer can always return a promise if it wants.

If the serializer returns a non-Promise object, the await will be a noop, so will not require modification of existing serializers.

The signEip712Transaction function passes a dummy signature to the transaction serializer, so is always async.

Suggested Fix

Modify signTransaction to keccak256(await serializer(signableTransaction))

Use Case

We are encrypting transactions prior to signing, to perform the encryption we need to fetch and validate a public key (if it hasn't already been fetched, or has expired). We cannot encrypt the transaction after signing (limitation of the protocol).

Locations Affected

signTransaction

viem/src/accounts/utils/signTransaction.ts

Lines 40 to 46 in 615d39c

	export async function signTransaction<
	serializer extends
	SerializeTransactionFn<TransactionSerializable> = SerializeTransactionFn<TransactionSerializable>,
	transaction extends Parameters<serializer>[0] = Parameters<serializer>[0],
	>(
	parameters: SignTransactionParameters<serializer, transaction>,
	): Promise<SignTransactionReturnType<serializer, transaction>> {

viem/src/accounts/utils/signTransaction.ts

Lines 64 to 72 in 615d39c

	const signature = await sign({
	hash: keccak256(serializer(signableTransaction)),
	privateKey,
	})
	return serializer(transaction, signature) as SignTransactionReturnType<
	serializer,
	transaction
	>
	}

signEip712Transaction

viem/src/accounts/utils/signTransaction.ts

Lines 40 to 46 in 615d39c

	export async function signTransaction<
	serializer extends
	SerializeTransactionFn<TransactionSerializable> = SerializeTransactionFn<TransactionSerializable>,
	transaction extends Parameters<serializer>[0] = Parameters<serializer>[0],
	>(
	parameters: SignTransactionParameters<serializer, transaction>,
	): Promise<SignTransactionReturnType<serializer, transaction>> {

viem/src/zksync/actions/signEip712Transaction.ts

Lines 141 to 149 in 615d39c

	return chain?.serializers?.transaction(
	{
	chainId,
	...transaction,
	customSignature,
	type: 'eip712' as any,
	},
	{ r: '0x0', s: '0x0', v: 0n },
	) as SignEip712TransactionReturnType