Fees Module

[shawntabrizi]

Custom Documentation:

• The purpose of the module
• Explanation of the real world users and their role/interactions with the module
• Key logic, processes, or assumptions that happen within the module
• Details on how a module easily integrates with other associated modules

Rust Docs:

• Available storage items and what they hold
• Public Functions
• Internal Functions

[4meta5]

fees

The fees module handles transaction fee related operations.

Overview

The fees module provides functions for:

• Getting and setting the base and per-byte transaction fee
• Tracking the overall charged fees for each transaction
• Charging and refunding transaction fees

The dispatchable function on_finalise deposits a Charged event if a transaction fee is charged. When using the publicly exposed functions, it is important to emit events in the body of functions dependent on a transaction's finality (in the context of irreversible storage).

Public Interface

Types

• TransferAsset
• AssetOf

Dispatchable Function

• on_finalise - Deposit an event if a transaction fee is charged for any extrinsics in the <system::Module<T>>::extrinsic_count()

Usage

The following example demonstrates how to use the fees module in your custom module.

1. Import the fees module and derive your module configuration trait with the balances trait.

use fees;

pub trait Trait: fees::Trait {}

2. Set the config fields (example in srml/contract)

// set the base per-byte fee for a transaction
let base_fee = fees::transaction_base_fee();
let byte_fee = fees::transaction_byte_fee();

3. Charge the base bytes transaction fee (example in srml/executive)

System::set_extrinsic_index(0);
fees::charge_base_bytes_fee(sender, 0).map_err(|_| internal::ApplyError::CantPay)?;

Dependencies

The fees module depends on the system and srml_support modules as well as Substrate Core libraries and the Rust standard library.

Genesis Config

Configuration is in <your-node-name>/src/chain_spec.rs. The following storage items are configurable:

• transaction_base_fee
• transaction_byte_fee

[4meta5]

Added a few comments but the code is short and easy to read (relative to other modules), but Monday I'll review these with someone to make sure I'm not missing any important.

[shawntabrizi]

@amarrsingh can you reach out to @xlc on GitHub (Bryan on Riot) since he wrote this module to ensure accuracy or any suggestions he may have about the documentation?

paritytech/substrate#1648

[shawntabrizi]

@amarrsingh I think Gav is going to remove the fees module, so this doc may not be needed anymore :(

So de-prioritize it if you are still working on it at all.