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Steve Degosserie
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116 lines
4.1 KiB
Markdown
116 lines
4.1 KiB
Markdown
# Assets Module
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A simple, secure module for dealing with fungible assets.
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## Overview
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The Assets module provides functionality for asset management of fungible asset classes
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with a fixed supply, including:
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* Asset Issuance
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* Asset Transfer
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* Asset Destruction
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To use it in your runtime, you need to implement the assets [`Trait`](https://docs.rs/pallet-assets/latest/pallet_assets/trait.Trait.html).
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The supported dispatchable functions are documented in the [`Call`](https://docs.rs/pallet-assets/latest/pallet_assets/enum.Call.html) enum.
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### Terminology
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* **Asset issuance:** The creation of a new asset, whose total supply will belong to the
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account that issues the asset.
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* **Asset transfer:** The action of transferring assets from one account to another.
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* **Asset destruction:** The process of an account removing its entire holding of an asset.
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* **Fungible asset:** An asset whose units are interchangeable.
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* **Non-fungible asset:** An asset for which each unit has unique characteristics.
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### Goals
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The assets system in Substrate is designed to make the following possible:
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* Issue a unique asset to its creator's account.
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* Move assets between accounts.
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* Remove an account's balance of an asset when requested by that account's owner and update
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the asset's total supply.
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## Interface
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### Dispatchable Functions
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* `issue` - Issues the total supply of a new fungible asset to the account of the caller of the function.
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* `transfer` - Transfers an `amount` of units of fungible asset `id` from the balance of
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the function caller's account (`origin`) to a `target` account.
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* `destroy` - Destroys the entire holding of a fungible asset `id` associated with the account
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that called the function.
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Please refer to the [`Call`](https://docs.rs/pallet-assets/latest/pallet_assets/enum.Call.html) enum and its associated variants for documentation on each function.
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### Public Functions
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<!-- Original author of descriptions: @gavofyork -->
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* `balance` - Get the asset `id` balance of `who`.
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* `total_supply` - Get the total supply of an asset `id`.
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Please refer to the [`Module`](https://docs.rs/pallet-assets/latest/pallet_assets/struct.Module.html) struct for details on publicly available functions.
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## Usage
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The following example shows how to use the Assets module in your runtime by exposing public functions to:
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* Issue a new fungible asset for a token distribution event (airdrop).
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* Query the fungible asset holding balance of an account.
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* Query the total supply of a fungible asset that has been issued.
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### Prerequisites
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Import the Assets module and types and derive your runtime's configuration traits from the Assets module trait.
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### Simple Code Snippet
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```rust
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use pallet_assets as assets;
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use frame_support::{decl_module, dispatch, ensure};
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use frame_system::ensure_signed;
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pub trait Trait: assets::Trait { }
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decl_module! {
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pub struct Module<T: Trait> for enum Call where origin: T::Origin {
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pub fn issue_token_airdrop(origin) -> dispatch::DispatchResult {
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let sender = ensure_signed(origin).map_err(|e| e.as_str())?;
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const ACCOUNT_ALICE: u64 = 1;
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const ACCOUNT_BOB: u64 = 2;
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const COUNT_AIRDROP_RECIPIENTS: u64 = 2;
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const TOKENS_FIXED_SUPPLY: u64 = 100;
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ensure!(!COUNT_AIRDROP_RECIPIENTS.is_zero(), "Divide by zero error.");
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let asset_id = Self::next_asset_id();
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<NextAssetId<T>>::mutate(|asset_id| *asset_id += 1);
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<Balances<T>>::insert((asset_id, &ACCOUNT_ALICE), TOKENS_FIXED_SUPPLY / COUNT_AIRDROP_RECIPIENTS);
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<Balances<T>>::insert((asset_id, &ACCOUNT_BOB), TOKENS_FIXED_SUPPLY / COUNT_AIRDROP_RECIPIENTS);
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<TotalSupply<T>>::insert(asset_id, TOKENS_FIXED_SUPPLY);
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Self::deposit_event(RawEvent::Issued(asset_id, sender, TOKENS_FIXED_SUPPLY));
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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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## Assumptions
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Below are assumptions that must be held when using this module. If any of
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them are violated, the behavior of this module is undefined.
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* The total count of assets should be less than
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`Trait::AssetId::max_value()`.
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## Related Modules
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* [`System`](https://docs.rs/frame-system/latest/frame_system/)
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* [`Support`](https://docs.rs/frame-support/latest/frame_support/)
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License: Apache-2.0 |