# x/bank
# Abstract
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 is used in the Cosmos Hub.
# Contents
# Supply
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.
# 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).
# Module Accounts
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:
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).
# 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 perform 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.
# State
The x/bank module keeps state of the following primary objects:
- Account balances
- Denomination metadata
- The total supply of all balances
- Information on which denominations are allowed to be sent.
In addition, the x/bank module keeps the following indexes to manage the
aforementioned state:
- Supply Index:
0x0 | byte(denom) -> byte(amount) - Denom Metadata Index:
0x1 | byte(denom) -> ProtocolBuffer(Metadata) - Balances Index:
0x2 | byte(address length) | []byte(address) | []byte(balance.Denom) -> ProtocolBuffer(balance) - Reverse Denomination to Address Index:
0x03 | byte(denom) | 0x00 | []byte(address) -> 0
# Params
The bank module stores it's params in state with the prefix of 0x05,
it can be updated with governance or the address with authority.
- Params:
0x05 | ProtocolBuffer(Params)
# Keepers
The bank module provides these exported keeper interfaces that can be passed to other modules that read or update account balances. Modules should use the least-permissive interface that provides the functionality they require.
Best practices dictate careful review of bank module code to ensure that
permissions are limited in the way that you expect.
# Denied Addresses
The x/bank module accepts a map of addresses that are considered blocklisted
from directly and explicitly receiving funds through means such as MsgSend and
MsgMultiSend and direct API calls like SendCoinsFromModuleToAccount.
Typically, these addresses are module accounts. If these addresses receive funds outside the expected rules of the state machine, invariants are likely to be broken and could result in a halted network.
By providing the x/bank module with a blocklisted set of addresses, an error occurs for the operation if a user or client attempts to directly or indirectly send funds to a blocklisted account, for example, by using IBC (opens new window).
# Common Types
# Input
An input of a multiparty transfer
# Output
An output of a multiparty transfer.
# BaseKeeper
The base keeper provides full-permission access: the ability to arbitrary modify any account's balance and mint or burn coins.
Restricted permission to mint per module could be achieved by using baseKeeper with WithMintCoinsRestriction to give specific restrictions to mint (e.g. only minting certain denom).
# SendKeeper
The send keeper provides access to account balances and the ability to transfer coins between accounts. The send keeper does not alter the total supply (mint or burn coins).
# ViewKeeper
The view keeper provides read-only access to account balances. The view keeper does not have balance alteration functionality. All balance lookups are O(1).
# Messages
# MsgSend
Send coins from one address to another.
The message will fail under the following conditions:
- The coins do not have sending enabled
- The
toaddress is restricted
# MsgMultiSend
Send coins from one sender and to a series of different address. If any of the receiving addresses do not correspond to an existing account, a new account is created.
The message will fail under the following conditions:
- Any of the coins do not have sending enabled
- Any of the
toaddresses are restricted - Any of the coins are locked
- The inputs and outputs do not correctly correspond to one another
# MsgUpdateParams
The bank module params can be updated through MsgUpdateParams, which can be done using governance proposal. The signer will always be the gov module account address.
The message handling can fail if:
- signer is not the gov module account address.
# MsgSetSendEnabled
Used with the x/gov module to set create/edit SendEnabled entries.
The message will fail under the following conditions:
- The authority is not a bech32 address.
- The authority is not x/gov module's address.
- There are multiple SendEnabled entries with the same Denom.
- One or more SendEnabled entries has an invalid Denom.
# Events
The bank module emits the following events:
# Message Events
# MsgSend
| Type | Attribute Key | Attribute Value |
|---|---|---|
| transfer | recipient | |
| transfer | amount | |
| message | module | bank |
| message | action | send |
| message | sender |
# MsgMultiSend
| Type | Attribute Key | Attribute Value |
|---|---|---|
| transfer | recipient | |
| transfer | amount | |
| message | module | bank |
| message | action | multisend |
| message | sender |
# Keeper Events
In addition to message events, the bank keeper will produce events when the following methods are called (or any method which ends up calling them)
# MintCoins
# BurnCoins
# addCoins
# subUnlockedCoins/DelegateCoins
# Parameters
The bank module contains the following parameters
# SendEnabled
The SendEnabled parameter is now deprecated and not to be use. It is replaced with state store records.
# DefaultSendEnabled
The default send enabled value controls send transfer capability for all
coin denominations unless specifically included in the array of SendEnabled
parameters.
# Client
# CLI
A user can query and interact with the bank module using the CLI.
# Query
The query commands allow users to query bank state.
# balances
The balances command allows users to query account balances by address.
Example:
Example Output:
# denom-metadata
The denom-metadata command allows users to query metadata for coin denominations. A user can query metadata for a single denomination using the --denom flag or all denominations without it.
Example:
Example Output:
# total
The total command allows users to query the total supply of coins. A user can query the total supply for a single coin using the --denom flag or all coins without it.
Example:
Example Output:
# send-enabled
The send-enabled command allows users to query for all or some SendEnabled entries.
Example:
Example output:
# Transactions
The tx commands allow users to interact with the bank module.
# send
The send command allows users to send funds from one account to another.
Example:
# gRPC
A user can query the bank module using gRPC endpoints.
# Balance
The Balance endpoint allows users to query account balance by address for a given denomination.
Example:
Example Output:
# AllBalances
The AllBalances endpoint allows users to query account balance by address for all denominations.
Example:
Example Output:
# DenomMetadata
The DenomMetadata endpoint allows users to query metadata for a single coin denomination.
Example:
Example Output:
# DenomsMetadata
The DenomsMetadata endpoint allows users to query metadata for all coin denominations.
Example:
Example Output:
# DenomOwners
The DenomOwners endpoint allows users to query metadata for a single coin denomination.
Example:
Example Output:
# TotalSupply
The TotalSupply endpoint allows users to query the total supply of all coins.
Example:
Example Output:
# SupplyOf
The SupplyOf endpoint allows users to query the total supply of a single coin.
Example:
Example Output:
# Params
The Params endpoint allows users to query the parameters of the bank module.
Example:
Example Output:
# SendEnabled
The SendEnabled enpoints allows users to query the SendEnabled entries of the bank module.
Any denominations NOT returned, use the Params.DefaultSendEnabled value.
Example:
Example Output: