This document specifies the bank module of the Cosmos SDK.
The bank module is responsible for handling multi-asset coin transfers between accounts and tracking special-case pseudo-transfers which must work differently with particular kinds of accounts (notably delegating/undelegating for vesting accounts). It exposes several interfaces with varying capabilities for secure interaction with other modules which must alter user balances.
In addition, the bank module tracks and provides query support for the total supply of all assets used in the application.
This module will be used in the Cosmos Hub.
The supply functionality:
- passively tracks the total supply of coins within a chain,
- provides a pattern for modules to hold/interact with
Coins, and - introduces the invariant check to verify a chain's total supply.
The total Supply of the network is equal to the sum of all coins from the
account. The total supply is updated every time a Coin is minted (eg: as part
of the inflation mechanism) or burned (eg: due to slashing or if a governance
proposal is vetoed).
The supply functionality introduces a new type of auth.Account which can be used by
modules to allocate tokens and in special cases mint or burn tokens. At a base
level these module accounts are capable of sending/receiving tokens to and from
auth.Accounts and other module accounts. This design replaces previous
alternative designs where, to hold tokens, modules would burn the incoming
tokens from the sender account, and then track those tokens internally. Later,
in order to send tokens, the module would need to effectively mint tokens
within a destination account. The new design removes duplicate logic between
modules to perform this accounting.
The ModuleAccount interface is defined as follows:
type ModuleAccount interface {
auth.Account // same methods as the Account interface
GetName() string // name of the module; used to obtain the address
GetPermissions() []string // permissions of module account
HasPermission(string) bool
}WARNING! Any module or message handler that allows either direct or indirect sending of funds must explicitly guarantee those funds cannot be sent to module accounts (unless allowed).
The supply Keeper also introduces new wrapper functions for the auth Keeper
and the bank Keeper that are related to ModuleAccounts in order to be able
to:
- Get and set
ModuleAccounts by providing theName. - Send coins from and to other
ModuleAccounts or standardAccounts (BaseAccountorVestingAccount) by passing only theName. MintorBurncoins for aModuleAccount(restricted to its permissions).
Each ModuleAccount has a different set of permissions that provide different
object capabilities to perform certain actions. Permissions need to be
registered upon the creation of the supply Keeper so that every time a
ModuleAccount calls the allowed functions, the Keeper can lookup the
permissions to that specific account and perform or not the action.
The available permissions are:
Minter: allows for a module to mint a specific amount of coins.Burner: allows for a module to burn a specific amount of coins.Staking: allows for a module to delegate and undelegate a specific amount of coins.