add bank hash to frozen slot update

[diman-io]

Problem

There is no easy way to get bank hashes as fast as possible

Summary of Changes

Added bank hash for frozen slot update

[mergify]

If this PR represents a change to the public RPC API:

1. Make sure it includes a complementary update to rpc-client/ (example)
2. Open a follow-up PR to update the JavaScript client @solana/web3.js (example)

Thank you for keeping the RPC clients in sync with the server API @diman-io.

[buffalojoec]

This lgtm. The bank is expected to be frozen at this point, so we know we'll get a valid hash from the hash() method.

[smcio]

Cool, we (Overclock) need this as well for the mithril project. Since the current RPC interface does not expose bankhashes, we've been using our own getBankHash method that we hacked into a test validator, so we'd love to see these changes land sooner rather than later. Thanks for this PR @diman-io.

[diman-io]

Just a kind reminder
I don’t have the merge button

[steviez]

I'm only just glancing at this PR, but is this change safe to make ? Assuming this lands in v2.2, what if a client running v2.2 (expecting new field) is subscribed to an RPC node running v2.1 (not supplying new field)

[steviez]

There is no easy way to get bank hashes as fast as possible

Hi @diman-io - I'm also curious what the use-case is for this; can you elaborate ? Ie, what do you need the bank hashes for ?

[buffalojoec]

I'm only just glancing at this PR, but is this change safe to make ? Assuming this lands in v2.2, what if a client running v2.2 (expecting new field) is subscribed to an RPC node running v2.1 (not supplying new field)

Yes you're right, a client subscribed to the wrong RPC API version would break. I figured clients should use an API version compatible with the server they're subscribed to, but we definitely shouldn't break the API on a minor bump.

I guess that leaves two options:

• Make the field an Option and let serde handle it.
• Add a new method and deprecate the old one.

Wdyt?

[diman-io]

@steviez

what do you need the bank hashes for ?

for a validator sidecar to filter transactions (I use my own, but the same can be done on jito relayer / anza vortexor / etc )

[diman-io]

Actually, I did some research after the initial question. However, I still haven’t come to any straightforward solution.

I would prefer the new method option with parameters. It provides scalability, and transaction statistics can be included there as well (not as an excluded option, which can be handled with the option option):

Frozen {
        slot: Slot,
        timestamp: u64,
        stats: SlotTransactionStats,
        hash: String,
    },

[steviez]

for a validator sidecar to filter transactions (I use my own, but the same can be done on jito relayer / anza vortexor / etc )

How does the bank hash come into play for filtering transactions ?

• For "user" transactions, a recent blockhash is included which is hashed into the bank hash, but not recoverable. So, I'm not seeing why bank hash is needed ?
• For votes, votes include the bank hash so I guess having bank hashes would allow you to compare what you've computed against what incoming votes have ?

[smcio]

There is no easy way to get bank hashes as fast as possible

Hi @diman-io - I'm also curious what the use-case is for this; can you elaborate ? Ie, what do you need the bank hashes for ?

I'd just like to add that we also need bank hashes for mithril, which is a project funded by a Solana Foundation grant, so we (Overclock) support the usefulness of these changes and/or any other RPC method that lets you retrieve bankhashes.

[steviez]

I'd just like to add that we also need bank hashes for mithril

I have some ideas but can you confirm what your desired use-case / workflow is for wanting bank hashes ?

[diman-io]

fixed while hanging my head in shame...

Of course, I meant the last blockhash. Now I’m extracting them from the sysvar

[steviez]

fixed while hanging my head in shame...

Of course, I meant the last blockhash. Now I’m extracting them from the sysvar

No worries! And I guess you can't use blockSubscribe since it does not support processed which is roughly equivalent to getting an update for "bank frozen":
https://solana.com/docs/rpc/websocket/blocksubscribe