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https://github.com/pezkuwichain/pezkuwi-subxt.git
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Alexander Theißen
76 lines
3.7 KiB
Markdown
76 lines
3.7 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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- [`Call`](https://docs.rs/pallet-contracts/latest/pallet_contracts/enum.Call.html)
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- [`Config`](https://docs.rs/pallet-contracts/latest/pallet_contracts/trait.Config.html)
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- [`Error`](https://docs.rs/pallet-contracts/latest/pallet_contracts/enum.Error.html)
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- [`Event`](https://docs.rs/pallet-contracts/latest/pallet_contracts/enum.Event.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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One gas is equivalent to one [weight](https://substrate.dev/docs/en/knowledgebase/learn-substrate/weight)
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which is defined as one picosecond of execution time on the runtime's reference machine.
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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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Those are documented in the [reference documentation](https://docs.rs/pallet-contracts/latest/pallet_contracts/#dispatchable-functions).
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## Usage
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This module executes WebAssembly smart contracts. These can potentially be written in any language
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that compiles to web assembly. However, using a language that specifically targets this module
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will make things a lot easier. One such language is [`ink`](https://github.com/paritytech/ink)
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which is an [`eDSL`](https://wiki.haskell.org/Embedded_domain_specific_language) that enables
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writing WebAssembly based smart contracts in the Rust programming language.
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## Debugging
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Contracts can emit messages to the node console when run on a development chain through the
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`seal_println` API. This is exposed in ink! via
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[`ink_env::debug_println()`](https://docs.rs/ink_env/latest/ink_env/fn.debug_println.html).
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In order to see these messages the log level for the `runtime::contracts` target needs to be raised
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to at least the `info` level which is the default. However, those messages are easy to overlook
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because of the noise generated by block production. A good starting point for contract debugging
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could be:
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```bash
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cargo run --release -- --dev --tmp -lerror,runtime::contracts
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```
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License: Apache-2.0
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