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Shawn Tabrizi
762b4b25d0
* fix trigger fingers * more * Update frame/example-offchain-worker/README.md Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com> Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com> Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>
65 lines
3.0 KiB
Markdown
65 lines
3.0 KiB
Markdown
# Contract Module
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The Contract module provides functionality for the runtime to deploy and execute WebAssembly smart-contracts.
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- [`contract::Trait`](https://docs.rs/pallet-contracts/latest/pallet_contracts/trait.Trait.html)
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- [`Call`](https://docs.rs/pallet-contracts/latest/pallet_contracts/enum.Call.html)
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## Overview
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This module extends accounts based on the `Currency` trait to have smart-contract functionality. It can
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be used with other modules that implement accounts based on `Currency`. These "smart-contract accounts"
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have the ability to instantiate smart-contracts and make calls to other contract and non-contract accounts.
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The smart-contract code is stored once in a `code_cache`, and later retrievable via its `code_hash`.
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This means that multiple smart-contracts can be instantiated from the same `code_cache`, without replicating
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the code each time.
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When a smart-contract is called, its associated code is retrieved via the code hash and gets executed.
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This call can alter the storage entries of the smart-contract account, instantiate new smart-contracts,
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or call other smart-contracts.
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Finally, when an account is reaped, its associated code and storage of the smart-contract account
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will also be deleted.
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### Gas
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Senders must specify a gas limit with every call, as all instructions invoked by the smart-contract require gas.
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Unused gas is refunded after the call, regardless of the execution outcome.
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If the gas limit is reached, then all calls and state changes (including balance transfers) are only
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reverted at the current call's contract level. For example, if contract A calls B and B runs out of gas mid-call,
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then all of B's calls are reverted. Assuming correct error handling by contract A, A's other calls and state
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changes still persist.
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### Notable Scenarios
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Contract call failures are not always cascading. When failures occur in a sub-call, they do not "bubble up",
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and the call will only revert at the specific contract level. For example, if contract A calls contract B, and B
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fails, A can decide how to handle that failure, either proceeding or reverting A's changes.
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## Interface
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### Dispatchable functions
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* `put_code` - Stores the given binary Wasm code into the chain's storage and returns its `code_hash`.
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* `instantiate` - Deploys a new contract from the given `code_hash`, optionally transferring some balance.
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This instantiates a new smart contract account and calls its contract deploy handler to
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initialize the contract.
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* `call` - Makes a call to an account, optionally transferring some balance.
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## Usage
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The Contract module is a work in progress. The following examples show how this Contract module
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can be used to instantiate and call contracts.
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* [`ink`](https://github.com/paritytech/ink) is
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an [`eDSL`](https://wiki.haskell.org/Embedded_domain_specific_language) that enables writing
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WebAssembly based smart contracts in the Rust programming language. This is a work in progress.
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## Related Modules
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* [Balances](https://docs.rs/pallet-balances/latest/pallet_balances/)
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License: Apache-2.0
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