transfer-hook: Add update instruction

[joncinque]

Problem

A program implementing the transfer-hook interface only absolutely requires one instruction, the execute hook which is called by token-2022.

However, the interface does also include an initialization function, which is needed in some form to write data to the extra-account-metas account. An implementer may choose to do something else for that instruction.

Similarly, there's no way to update the extra-account-metas account with just the interface.

Solution

This behavior is fine as is, but it would be nicer to have a recommended-but-not-required update instruction for devs looking to implement the transfer hook.

cc @buffalojoec

[gdutk007]

would it be possible for me to work on this issue? I'm a bit of a newcomer to this domain but wouldn't mind tackling it.

[buffalojoec]

would it be possible for me to work on this issue? I'm a bit of a newcomer to this domain but wouldn't mind tackling it.

Of course! I’d start with the interface change, then in separate PRs we can address the different clients.

Feel free to request my review.

[tonton-sol]

I am also trying to implement this. I have added the new instruction to the interface and example program. I have also added a subcommand to the CLI. When testing with the CLI, the RPC simulation fails with custom program error: 0x47af3bc1.

How can I decode this? Also is there an easy way to show logs of the failed RPC simulation?

[tonton-sol]

I figured out the error, it is TlvError::TypeAlreadyExists.

I thought I could simply just create a new TransferHookInstruction::UpdateExtraAccountMetaList in the interface similar to TransferHookInstruction::InitializeExtraAccountMetaList, then change the example program to handle this instruction.

The error arises when:

ExtraAccountMetaList::init::<ExecuteInstruction>(&mut data, extra_account_metas)?;

is called in the new update instruction in the example program. Also why is the TLV instruction type ExecuteInstuction and not InitializeExtraAccountMetaListInstruction or UpdateExtraAccountMetaListInstruction?

[buffalojoec]

The error arises when:

ExtraAccountMetaList::init::<ExecuteInstruction>(&mut data, extra_account_metas)?;

is called in the new update instruction in the example program.

This is going to try to initialize a new TLV entry and it will error if it exists, so it's not appropriate for updating an existing one! You'll have to add an update method to ExtraAccountMetaList and inside of it drive TlvStateMut and realloc_and_pack_* or something similar.

Also why is the TLV instruction type ExecuteInstuction and not InitializeExtraAccountMetaListInstruction or UpdateExtraAccountMetaListInstruction?

This is because the instructions' discriminator is used to identify which set of extra accounts are required for a particular instruction. For example:

----------------------------------------------------------
| <ExecuteInstruction>  | <extra accounts for execute>[] |
| <OtherInstruction>    | <extra accounts for other>[]   |
----------------------------------------------------------

The confusing bit here is that besides "initializing extra required accounts", Transfer Hook has only one instruction: execute the transfer.

[tonton-sol]

Thank you! I have a working implementation now, that updates tlv-account-resolution, the transfer-hook-interface, and the example program. How can I let you review it?

[buffalojoec]

Thank you! I have a working implementation now, that updates tlv-account-resolution, the transfer-hook-interface, and the example program. How can I let you review it?

I saw! If you can't request my review just tag me in a comment or the PR description.

[buffalojoec]

Done as of #5894 !