Contract Rust Template

This is a minimal template for a Rust contract targeting pallet_revive. This is a low- level way to write contracts, so we don't expect it to be used for implementing high-level contract logic. Instead, we expect that Rust will be used to implement libraries that are then called by Solidity, similar to Python, where performance-critical code is written in C.

Components

In terms of code, this template is very bare bones. main.rs is just a few lines of code. Most of the files in this repo deal with compiling the code to PolkaVM in a rust-analyzer-friendly way. We included a rust-toolchain.toml and a .cargo/config.toml so that all tools automatically select the correct target and toolchain (we need a relatively new nightly).

The call_from_sol.sol file demonstrates how to call the example in main.rs from Solidity.

Memory Allocation

The contract depends on the pallet-revive-uapi crate, which is a thin (but safe) wrapper around all available host functions. It only includes the absolute minimum. This means we also don't include a memory allocator. If you want to use alloc, you need to define a global allocator. Note that we don't support dynamic memory allocations in pallet_revive yet. Therefore, the allocator would need to operate on a static buffer.

How to Build

You can build this project with cargo build. However, to generate a valid contract, you also need to link it. Linking means taking the ELF file outputted by the Rust compiler and transforming it into a PolkaVM module.

# Make sure to have the latest polkatool installed
$ cargo install polkatool

# This will build the project and then use polkatool to link it
$ make

The build result is placed as contract.polkavm in the repository root. This is the final artifact that can be deployed as-is.

How to Deploy and Call

The easiest way, is to use cast from the Foundry test-suite.

# Define the RPC URL (default to http://localhost:8545)
export ETH_RPC_URL="https://westend-asset-hub-eth-rpc.polkadot.io"

# Define the account that will use to call and deploy the contract
# Make sure to fund the account with some tokens (e.g. using the faucet https://contracts.polkadot.io/connect-to-asset-hub)
export ETH_FROM=0xf24FF3a9CF04c71Dbc94D0b566f7A27B94566cac
cast wallet import dev-account --private-key 5fb92d6e98884f76de468fa3f6278f8807c48bebc13595d45af5bdc4da702133

# Deploy the contract
cast send --account evm-dev --create "$(xxd -p -c 99999 contract.polkavm)"

# output
# ...
# contractAddress      0xc01Ee7f10EA4aF4673cFff62710E1D7792aBa8f3
# ...

# or to get the address

RUST_ADDRESS=$(cast send --account dev-account --create "$(xxd -p -c 99999 contract.polkavm)" --json | jq -r .contractAddress)

# Call the contract
cast call $RUST_ADDRESS "fibonacci(uint32) public pure returns (uint32)" "4"

# Build the solidity contract
npx @parity/revive@latest --bin call_from_sol.sol

# Deploy the solidity contract
SOL_ADDRESS=$(cast send --account dev-account --create "$(xxd -p -c 99999 call_from_sol_sol_CallRust.polkavm)" --json | jq -r .contractAddress)

# Compare the gas estimates
cast estimate $RUST_ADDRESS "fibonacci(uint32) public pure returns (uint32)" 4
cast estimate $SOL_ADDRESS "fibonacci(uint32) public pure returns (uint32)" 4

# Call the rust contract from solidity
cast call $SOL_ADDRESS "fibonacciRust(uint32, address) external pure returns (uint32)" 4 $RUST_ADDRESS

How to Inspect the Contract

polkatool stats contract.polkavm
polkatool disassemble contract.polkavm

Examples

The test fixtures for pallet_revive are written in the same way as this template and might be useful as examples.