Revive Pallet

This is an experimental module that provides functionality for the runtime to deploy and execute PolkaVM smart-contracts. It is a heavily modified pallet_contracts fork.

Overview

This module extends accounts based on the [frame_support::traits::fungible] traits to have smart-contract functionality. It can be used with other modules that implement accounts based on [frame_support::traits::fungible]. These "smart-contract accounts" have the ability to instantiate smart-contracts and make calls to other contract and non-contract accounts.

The smart-contract code is stored once, and later retrievable via its code_hash. This means that multiple smart-contracts can be instantiated from the same code, without replicating the code each time.

When a smart-contract is called, its associated code is retrieved via the code hash and gets executed. This call can alter the storage entries of the smart-contract account, instantiate new smart-contracts, or call other smart-contracts.

Finally, when an account is reaped, its associated code and storage of the smart-contract account will also be deleted.

Weight

Senders must specify a Weight limit with every call, as all instructions invoked by the smart-contract require weight. Unused weight is refunded after the call, regardless of the execution outcome.

If the weight limit is reached, then all calls and state changes (including balance transfers) are only reverted at the current call's contract level. For example, if contract A calls B and B runs out of weight mid-call, then all of B's calls are reverted. Assuming correct error handling by contract A, A's other calls and state changes still persist.

One ref_time Weight is defined as one picosecond of execution time on the runtime's reference machine.

Revert Behaviour

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.

Interface

Dispatchable functions

Those are documented in the reference documentation.

Usage

This module executes PolkaVM smart contracts. These can potentially be written in any language that compiles to RISC-V. For now, the only officially supported languages are Solidity (via revive) and Rust (check the fixtures directory for Rust examples).

Debugging

Contracts can emit messages to the client when called as RPC through the debug_message API.

Those messages are gathered into an internal buffer and sent to the RPC client. It is up to the individual client if and how those messages are presented to the user.

This buffer is also printed as a debug message. In order to see these messages on the node console the log level for the runtime::revive target needs to be raised to at least the debug level. However, those messages are easy to overlook because of the noise generated by block production. A good starting point for observing them on the console is using this command line in the root directory of the Substrate repository:

cargo run --release -- --dev -lerror,runtime::revive=debug

This raises the log level of runtime::revive to debug and all other targets to error in order to prevent them from spamming the console.

--dev: Use a dev chain spec --tmp: Use temporary storage for chain data (the chain state is deleted on exit)

Host function tracing

For contract authors, it can be a helpful debugging tool to see which host functions are called, with which arguments, and what the result was.

In order to see these messages on the node console, the log level for the runtime::revive::strace target needs to be raised to the trace level.

Example:

cargo run --release -- --dev -lerror,runtime::revive::strace=trace,runtime::revive=debug

Unstable Interfaces

Driven by the desire to have an iterative approach in developing new contract interfaces this pallet contains the concept of an unstable interface. Akin to the rust nightly compiler it allows us to add new interfaces but mark them as unstable so that contract languages can experiment with them and give feedback before we stabilize those.

In order to access interfaces which don't have a stable #[api_version(x)] in runtime.rs one need to set pallet_revive::Config::UnsafeUnstableInterface to ConstU32<true>. It should be obvious that any production runtime should never be compiled with this feature: In addition to be subject to change or removal those interfaces might not have proper weights associated with them and are therefore considered unsafe.

New interfaces are generally added as unstable and might go through several iterations before they are promoted to a stable interface.

License: Apache-2.0

Release

Polkadot SDK stable2409