Assets Module

A simple, secure module for dealing with fungible assets.

Overview

The Assets module provides functionality for asset management of fungible asset classes with a fixed supply, including:

• Asset Issuance
• Asset Transfer
• Asset Destruction

To use it in your runtime, you need to implement the assets assets::Trait.

The supported dispatchable functions are documented in the assets::Call enum.

Terminology

• Asset issuance: The creation of a new asset, whose total supply will belong to the account that issues the asset.
• Asset transfer: The action of transferring assets from one account to another.
• Asset destruction: The process of an account removing its entire holding of an asset.
• Fungible asset: An asset whose units are interchangeable.
• Non-fungible asset: An asset for which each unit has unique characteristics.

Goals

The assets system in Substrate is designed to make the following possible:

• Issue a unique asset to its creator's account.
• Move assets between accounts.
• Remove an account's balance of an asset when requested by that account's owner and update the asset's total supply.

Interface

Dispatchable Functions

• issue - Issues the total supply of a new fungible asset to the account of the caller of the function.
• transfer - Transfers an amount of units of fungible asset id from the balance of the function caller's account (origin) to a target account.
• destroy - Destroys the entire holding of a fungible asset id associated with the account that called the function.

Please refer to the Call enum and its associated variants for documentation on each function.

Public Functions

• balance - Get the asset id balance of who.
• total_supply - Get the total supply of an asset id.

Please refer to the Module struct for details on publicly available functions.

Usage

The following example shows how to use the Assets module in your runtime by exposing public functions to:

• Issue a new fungible asset for a token distribution event (airdrop).
• Query the fungible asset holding balance of an account.
• Query the total supply of a fungible asset that has been issued.

Prerequisites

Import the Assets module and types and derive your runtime's configuration traits from the Assets module trait.

Simple Code Snippet

use pallet_assets as assets;
use frame_support::{decl_module, dispatch, ensure};
use frame_system::ensure_signed;
use sp_runtime::ArithmeticError;

pub trait Config: assets::Config { }

decl_module! {
	pub struct Module<T: Config> for enum Call where origin: T::Origin {
		pub fn issue_token_airdrop(origin) -> dispatch::DispatchResult {
			let sender = ensure_signed(origin).map_err(|e| e.as_str())?;

			const ACCOUNT_ALICE: u64 = 1;
			const ACCOUNT_BOB: u64 = 2;
			const COUNT_AIRDROP_RECIPIENTS: u64 = 2;
			const TOKENS_FIXED_SUPPLY: u64 = 100;

			ensure!(!COUNT_AIRDROP_RECIPIENTS.is_zero(), ArithmeticError::DivisionByZero);

			let asset_id = Self::next_asset_id();

			<NextAssetId<T>>::mutate(|asset_id| *asset_id += 1);
			<Balances<T>>::insert((asset_id, &ACCOUNT_ALICE), TOKENS_FIXED_SUPPLY / COUNT_AIRDROP_RECIPIENTS);
			<Balances<T>>::insert((asset_id, &ACCOUNT_BOB), TOKENS_FIXED_SUPPLY / COUNT_AIRDROP_RECIPIENTS);
			<TotalSupply<T>>::insert(asset_id, TOKENS_FIXED_SUPPLY);

			Self::deposit_event(RawEvent::Issued(asset_id, sender, TOKENS_FIXED_SUPPLY));
			Ok(())
		}
	}
}

Assumptions

Below are assumptions that must be held when using this module. If any of them are violated, the behavior of this module is undefined.

• The total count of assets should be less than Config::AssetId::max_value().

Related Modules

• System
• Support

License: Apache-2.0