Accessing blockchain data from state machine

[robert-zaremba]

MOVED

Moved to tendermint/tendermint#5977

Rationale

Currently, State Machine Programs (SMPs) [*] can't query blockchain data (transactions, block headers) from past blocks.
There are several use-cases for that:

• a smart-contract would like to see if a some voting stats
• smart-contract would like to examine transaction data
• some validator operations
• timestamping data: we make a transaction, and use calldata (message attributes which are not processed otherwise) - there is no need to copy that to a state, because messages are already stored in the block.

The workaround is to copy transaction data into smart-contract state... which is not ideal, because we essentially duplicate a data.

State Machine Program (SMP)

To avoid any confusion, State Machine Program is an on chain app which encapsulates on-chain state logic. This could be: SDK module, comswasm smart contract, agoric smart contract, state-machine module....

Goals

• Estimate the efforts to allow smart contracts accessing blockchain data
• See if there are any objections for that.

[robert-zaremba]

@ValarDragon . @sunnya97 - is this something you are also looking at?

[ValarDragon]

No, we're not looking at this. AFAICT this is about smart contracts

[tac0turtle]

The notion of smart contract is confusing here. You mean modules not a vm on top of the SDK right? If so, it may be good to reword the initial comment to use modules nomenclature.

I believe this is https://github.com/tendermint/spec/issues/203 similar to what you are looking for. Not sure this is a discussion for here but instead for Tendermint Core.

[robert-zaremba]

How about on-chain programs?

[aaronc]

Can we just say "state machine logic"?

[robert-zaremba]

then what about "state machine program"? (personally app sounds better for me).

[aaronc]

I have a strong opinion not to use smart contract to refer to modules and generally would prefer to avoid smart contract at all - VM code or script sounds better. I don’t care if the alternative is state machine logic or program, either is more clear to me

[robert-zaremba]

OK, so let's check about SM program / logic and if no objections we can coin it at least for the time being.

[ValarDragon]

I'm confused, these are all about APIs for smart contracts, not about state machine abstractions?

Timestamp data seems like it should be in read-only state that a contract can read from, its common to all contracts in a given block.

For not copying the rest, doesn't that depend on making the memory model for cosm wasm and golang/rust slices match up? (And having converters between the golang and rust slices?) Seems pretty complex, but this is not something I know much about

[robert-zaremba]

Both: update the sate machine abstraction to access tendermint data (even from past blocks) and API for smart contracts.

It's all read only, because nobody can change a finalized chain.

[okwme]

cosmwasm imports the staking module in order to allow for staking derivatives afaik. doesn't this address your concern?

[robert-zaremba]

No, I would like to have a read-only access to tendermint DB (probably through a sync API).

[tac0turtle]

@robert-zaremba would you like to open a discussion board in the Tendermint repo? There isn't much to discuss sdk side for these changes.

[robert-zaremba]

Yes. Moved to tendermint/tendermint#5977

[robert-zaremba]

I have also updated a description in Tendermint side to use State Machine Program (as discussed in one of the threads above).