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contracts: Allow indeterministic instructions off-chain (#12469)

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* Allow indetermistic instructions off-chain

* Apply suggestions from code review

Co-authored-by: Sasha Gryaznov <hi@agryaznov.com>

* fmt

Co-authored-by: Sasha Gryaznov <hi@agryaznov.com>
This commit is contained in:
Alexander Theißen
2022-10-24 19:48:04 +02:00
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parent d0dcf008ec
commit 3ae4be8662
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substrate/frame/contracts/README.md
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@@ -37,12 +37,37 @@ changes still persist.
One gas is equivalent to one [weight](https://docs.substrate.io/v3/runtime/weights-and-fees)
which is defined as one picosecond of execution time on the runtime's reference machine.
### Notable Scenarios
### Revert Behaviour
Contract call failures are not always cascading. When failures occur in a sub-call, they do not "bubble up",
Contract call failures are not cascading. When failures occur in a sub-call, they do not "bubble up",
and the call will only revert at the specific contract level. For example, if contract A calls contract B, and B
fails, A can decide how to handle that failure, either proceeding or reverting A's changes.
### Offchain Execution
In general, a contract execution needs to be deterministic so that all nodes come to the same
conclusion when executing it. To that end we disallow any instructions that could cause
indeterminism. Most notable are any floating point arithmetic. That said, sometimes contracts
are executed off-chain and hence are not subject to consensus. If code is only executed by a
single node and implicitly trusted by other actors is such a case. Trusted execution environments
come to mind. To that end we allow the execution of indeterminstic code for offchain usages
with the following constraints:
1. No contract can ever be instantiated from an indeterministic code. The only way to execute
the code is to use a delegate call from a deterministic contract.
2. The code that wants to use this feature needs to depend on `pallet-contracts` and use `bare_call`
directly. This makes sure that by default `pallet-contracts` does not expose any indeterminism.
## How to use
When setting up the `Schedule` for your runtime make sure to set `InstructionWeights::fallback`
to a non zero value. The default is `0` and prevents the upload of any non deterministic code.
An indeterministic code can be deployed on-chain by passing `Determinism::AllowIndeterministic`
to `upload_code`. A determinstic contract can then delegate call into it if and only if it
is ran by using `bare_call` and passing `Determinism::AllowIndeterministic` to it. **Never use
this argument when the contract is called from an on-chain transaction.**
## Interface
### Dispatchable functions