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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>
76 lines
2.7 KiB
Markdown
76 lines
2.7 KiB
Markdown
# System Module
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The System module provides low-level access to core types and cross-cutting utilities.
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It acts as the base layer for other pallets to interact with the Substrate framework components.
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- [`system::Trait`](https://docs.rs/frame-system/latest/frame_system/trait.Trait.html)
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## Overview
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The System module defines the core data types used in a Substrate runtime.
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It also provides several utility functions (see [`Module`](https://docs.rs/frame-system/latest/frame_system/struct.Module.html)) for other FRAME pallets.
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In addition, it manages the storage items for extrinsics data, indexes, event records, and digest items,
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among other things that support the execution of the current block.
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It also handles low-level tasks like depositing logs, basic set up and take down of
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temporary storage entries, and access to previous block hashes.
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## Interface
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### Dispatchable Functions
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The System module does not implement any dispatchable functions.
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### Public Functions
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See the [`Module`](https://docs.rs/frame-system/latest/frame_system/struct.Module.html) struct for details of publicly available functions.
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### Signed Extensions
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The System module defines the following extensions:
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- [`CheckWeight`]: Checks the weight and length of the block and ensure that it does not
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exceed the limits.
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- [`CheckNonce`]: Checks the nonce of the transaction. Contains a single payload of type
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`T::Index`.
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- [`CheckEra`]: Checks the era of the transaction. Contains a single payload of type `Era`.
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- [`CheckGenesis`]: Checks the provided genesis hash of the transaction. Must be a part of the
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signed payload of the transaction.
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- [`CheckSpecVersion`]: Checks that the runtime version is the same as the one used to sign the
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transaction.
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- [`CheckTxVersion`]: Checks that the transaction version is the same as the one used to sign the
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transaction.
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Lookup the runtime aggregator file (e.g. `node/runtime`) to see the full list of signed
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extensions included in a chain.
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## Usage
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### Prerequisites
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Import the System module and derive your module's configuration trait from the system trait.
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### Example - Get extrinsic count and parent hash for the current block
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```rust
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use frame_support::{decl_module, dispatch};
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use frame_system::{self as system, ensure_signed};
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pub trait Config: system::Config {}
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decl_module! {
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pub struct Module<T: Config> for enum Call where origin: T::Origin {
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#[weight = 0]
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pub fn system_module_example(origin) -> dispatch::DispatchResult {
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let _sender = ensure_signed(origin)?;
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let _extrinsic_count = <system::Module<T>>::extrinsic_count();
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let _parent_hash = <system::Module<T>>::parent_hash();
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Ok(())
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}
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}
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}
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```
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License: Apache-2.0
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