transfer hook: Add JS support for managing hook programs

[buffalojoec]

Problem

Currently, we've got some of the minimally necessary "extra account metas" support within @solana/spl-token. However, the toolset isn't complete for those who wish to create and test a transfer hook program against the interface.

For example, the instructions one would use to hit their hook program and initialize or update extra account metas is not present in @solana/spl-token, nor is there support for creating ExtraAccountMeta types with packed seed configurations, etc.

Solution

I believe the best way to do this is to roll a @solana/spl-transfer-hook package and provide all of the necessary off-chain tooling from the Rust libraries.

Then, @solana/spl-token can use this package to offer it's various tooling that matches Token2022's crate.

[deepto98]

@buffalojoec Can I work on this if its still open?

[buffalojoec]

Sure! But since this issue was opened we've added a good amount of transfer hook support to @solana/spl-token, so I don't think we need to do a new library like I laid out in the original description.

Right now, I'd say we need the two instructions for manipulating your program's list of extra account metas, and maybe some extra API sugar for serialization of extra metas. We can just add this stuff to the transfer-hook extension in Token JS.

What do you think?

[deepto98]

Sounds good, I'm new to Solana and would love to contribute. I looked at the code base and found these files:

• token/program-2022/src/extension/transfer_hook/instruction.rs
• token/js/src/extensions/transferHook/instructions.ts
  If I understand correctly, these are the base Rust and TS files for the instructions.
• token/js/src/extensions/transferHook/state.ts : This has some functions and types related to extraAccount - getExtraAccountMetaAddress,resolveExtraAccountMeta, etc. Is there any other file I need to look at?

[buffalojoec]

@deepto98 You're close, but there's also an interface that Transfer Hook programs are implementing, and in order to create/update that program's list of extra required metas, we're going to add the two client-side instructions.

That interface can be found here.

https://github.com/solana-labs/solana-program-library/tree/6edf3ecc3f51a9f7a6faba9a1a4d30f1e4857e69/token/transfer-hook/interface

What I would suggest is creating a file src/extensions/transferHook/interface.ts and writing helpers for the InitializeExtraAccountMetaList and UpdateExtraAccountMetaList instructions for the interface.

Like the Rust instructions, we can simply require a list of ExtraAccountMeta as input to the instruction helpers, but those helpers will need to serialize them into instruction data.

To do that, they'll leverage the layouts here.

solana-program-library/token/js/src/extensions/transferHook/state.ts

Lines 61 to 100 in 0ab6ed7

	/** ExtraAccountMeta as stored by the transfer hook program */
	export interface ExtraAccountMeta {
	discriminator: number;
	addressConfig: Uint8Array;
	isSigner: boolean;
	isWritable: boolean;
	}
	/** Buffer layout for de/serializing an ExtraAccountMeta */
	export const ExtraAccountMetaLayout = struct<ExtraAccountMeta>([
	u8('discriminator'),
	blob(32, 'addressConfig'),
	bool('isSigner'),
	bool('isWritable'),
	]);
	export interface ExtraAccountMetaList {
	count: number;
	extraAccounts: ExtraAccountMeta[];
	}
	/** Buffer layout for de/serializing a list of ExtraAccountMeta prefixed by a u32 length */
	export const ExtraAccountMetaListLayout = struct<ExtraAccountMetaList>([
	u32('count'),
	seq<ExtraAccountMeta>(ExtraAccountMetaLayout, greedy(ExtraAccountMetaLayout.span), 'extraAccounts'),
	]);
	/** Buffer layout for de/serializing a list of ExtraAccountMetaAccountData prefixed by a u32 length */
	export interface ExtraAccountMetaAccountData {
	instructionDiscriminator: bigint;
	length: number;
	extraAccountsList: ExtraAccountMetaList;
	}
	/** Buffer layout for de/serializing an ExtraAccountMetaAccountData */
	export const ExtraAccountMetaAccountDataLayout = struct<ExtraAccountMetaAccountData>([
	u64('instructionDiscriminator'),
	u32('length'),
	ExtraAccountMetaListLayout.replicate('extraAccountsList'),
	]);

[deepto98]

@buffalojoec Thanks for the pointers, I'll go through these and try to understand the architecture