# 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](#supply)
  * [Total Supply](#total-supply)
* [Module Accounts](#module-accounts)
  * [Permissions](#permissions)
* [State](#state)
* [Params](#params)
* [Keepers](#keepers)
* [Messages](#messages)
* [Events](#events)
  * [Message Events](#message-events)
  * [Keeper Events](#keeper-events)
* [Parameters](#parameters)
  * [SendEnabled](#sendenabled)
  * [DefaultSendEnabled](#defaultsendenabled)
* [Client](#client)
  * [CLI](#cli)
  * [Query](#query)
  * [Transactions](#transactions)
* [gRPC](#grpc)

## 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.Account`s 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:

```go
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 `ModuleAccount`s in order to be able to:

* Get and set `ModuleAccount`s by providing the `Name`.
* Send coins from and to other `ModuleAccount`s or standard `Account`s (`BaseAccount` or `VestingAccount`) by passing only the `Name`.
* `Mint` or `Burn` coins for a `ModuleAccount` (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:

1. Account balances
2. Denomination metadata
3. The total supply of all balances
4. 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)`

```protobuf
https://github.com/cosmos/cosmos-sdk/blob/v0.47.0-rc1/proto/cosmos/bank/v1beta1/bank.proto#L12-L23
```

## 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](https://ibc.cosmos.network).

### Common Types

#### Input

An input of a multiparty transfer

```protobuf
// Input models transaction input.
message Input {
  string   address                        = 1;
  repeated cosmos.base.v1beta1.Coin coins = 2;
}
```

#### Output

An output of a multiparty transfer.

```protobuf
// Output models transaction outputs.
message Output {
  string   address                        = 1;
  repeated cosmos.base.v1beta1.Coin coins = 2;
}
```

### 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).

```go
// Keeper defines a module interface that facilitates the transfer of coins
// between accounts.
type Keeper interface {
    SendKeeper
    WithMintCoinsRestriction(MintingRestrictionFn) BaseKeeper

    InitGenesis(context.Context, *types.GenesisState)
    ExportGenesis(context.Context) *types.GenesisState

    GetSupply(ctx context.Context, denom string) sdk.Coin
    HasSupply(ctx context.Context, denom string) bool
    GetPaginatedTotalSupply(ctx context.Context, pagination *query.PageRequest) (sdk.Coins, *query.PageResponse, error)
    IterateTotalSupply(ctx context.Context, cb func(sdk.Coin) bool)
    GetDenomMetaData(ctx context.Context, denom string) (types.Metadata, bool)
    HasDenomMetaData(ctx context.Context, denom string) bool
    SetDenomMetaData(ctx context.Context, denomMetaData types.Metadata)
    IterateAllDenomMetaData(ctx context.Context, cb func(types.Metadata) bool)

    SendCoinsFromModuleToAccount(ctx context.Context, senderModule string, recipientAddr sdk.AccAddress, amt sdk.Coins) error
    SendCoinsFromModuleToModule(ctx context.Context, senderModule, recipientModule string, amt sdk.Coins) error
    SendCoinsFromAccountToModule(ctx context.Context, senderAddr sdk.AccAddress, recipientModule string, amt sdk.Coins) error
    DelegateCoinsFromAccountToModule(ctx context.Context, senderAddr sdk.AccAddress, recipientModule string, amt sdk.Coins) error
    UndelegateCoinsFromModuleToAccount(ctx context.Context, senderModule string, recipientAddr sdk.AccAddress, amt sdk.Coins) error
    MintCoins(ctx context.Context, moduleName string, amt sdk.Coins) error
    BurnCoins(ctx context.Context, moduleName string, amt sdk.Coins) error

    DelegateCoins(ctx context.Context, delegatorAddr, moduleAccAddr sdk.AccAddress, amt sdk.Coins) error
    UndelegateCoins(ctx context.Context, moduleAccAddr, delegatorAddr sdk.AccAddress, amt sdk.Coins) error

    // GetAuthority gets the address capable of executing governance proposal messages. Usually the gov module account.
    GetAuthority() string

    types.QueryServer
}
```

### 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).

```go
// SendKeeper defines a module interface that facilitates the transfer of coins
// between accounts without the possibility of creating coins.
type SendKeeper interface {
    ViewKeeper

    InputOutputCoins(ctx context.Context, inputs types.Input, outputs []types.Output) error
    SendCoins(ctx context.Context, fromAddr sdk.AccAddress, toAddr sdk.AccAddress, amt sdk.Coins) error

    GetParams(ctx context.Context) types.Params
    SetParams(ctx context.Context, params types.Params) error

    IsSendEnabledDenom(ctx context.Context, denom string) bool
    SetSendEnabled(ctx context.Context, denom string, value bool)
    SetAllSendEnabled(ctx context.Context, sendEnableds []*types.SendEnabled)
    DeleteSendEnabled(ctx context.Context, denom string)
    IterateSendEnabledEntries(ctx context.Context, cb func(denom string, sendEnabled bool) (stop bool))
    GetAllSendEnabledEntries(ctx context.Context) []types.SendEnabled

    IsSendEnabledCoin(ctx context.Context, coin sdk.Coin) bool
    IsSendEnabledCoins(ctx context.Context, coins ...sdk.Coin) error

    BlockedAddr(addr sdk.AccAddress) bool
}
```

### 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)`.

```go
// ViewKeeper defines a module interface that facilitates read only access to
// account balances.
type ViewKeeper interface {
    ValidateBalance(ctx context.Context, addr sdk.AccAddress) error
    HasBalance(ctx context.Context, addr sdk.AccAddress, amt sdk.Coin) bool

    GetAllBalances(ctx context.Context, addr sdk.AccAddress) sdk.Coins
    GetAccountsBalances(ctx context.Context) []types.Balance
    GetBalance(ctx context.Context, addr sdk.AccAddress, denom string) sdk.Coin
    LockedCoins(ctx context.Context, addr sdk.AccAddress) sdk.Coins
    SpendableCoins(ctx context.Context, addr sdk.AccAddress) sdk.Coins
    SpendableCoin(ctx context.Context, addr sdk.AccAddress, denom string) sdk.Coin

    IterateAccountBalances(ctx context.Context, addr sdk.AccAddress, cb func(coin sdk.Coin) (stop bool))
    IterateAllBalances(ctx context.Context, cb func(address sdk.AccAddress, coin sdk.Coin) (stop bool))
}
```

## Messages

### MsgSend

Send coins from one address to another.

```protobuf
https://github.com/cosmos/cosmos-sdk/blob/v0.47.0-rc1/proto/cosmos/bank/v1beta1/tx.proto#L38-L53
```

The message will fail under the following conditions:

* The coins do not have sending enabled
* The `to` address 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.

```protobuf
https://github.com/cosmos/cosmos-sdk/blob/v0.47.0-rc1/proto/cosmos/bank/v1beta1/tx.proto#L58-L69
```

The message will fail under the following conditions:

* Any of the coins do not have sending enabled
* Any of the `to` addresses 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.

```protobuf
https://github.com/cosmos/cosmos-sdk/blob/v0.47.0-rc1/proto/cosmos/bank/v1beta1/tx.proto#L74-L88
```

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.

```protobuf
https://github.com/cosmos/cosmos-sdk/blob/v0.47.0-rc1/proto/cosmos/bank/v1beta1/tx.proto#L96-L117
```

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     | {recipientAddress} |
| transfer | amount        | {amount}           |
| message  | module        | bank               |
| message  | action        | send               |
| message  | sender        | {senderAddress}    |

#### MsgMultiSend

| Type     | Attribute Key | Attribute Value    |
| -------- | ------------- | ------------------ |
| transfer | recipient     | {recipientAddress} |
| transfer | amount        | {amount}           |
| message  | module        | bank               |
| message  | action        | multisend          |
| message  | sender        | {senderAddress}    |

### 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

```json
{
  "type": "coinbase",
  "attributes": [
    {
      "key": "minter",
      "value": "{{sdk.AccAddress of the module minting coins}}",
      "index": true
    },
    {
      "key": "amount",
      "value": "{{sdk.Coins being minted}}",
      "index": true
    }
  ]
}
```

```json
{
  "type": "coin_received",
  "attributes": [
    {
      "key": "receiver",
      "value": "{{sdk.AccAddress of the module minting coins}}",
      "index": true
    },
    {
      "key": "amount",
      "value": "{{sdk.Coins being received}}",
      "index": true
    }
  ]
}
```

#### BurnCoins

```json
{
  "type": "burn",
  "attributes": [
    {
      "key": "burner",
      "value": "{{sdk.AccAddress of the module burning coins}}",
      "index": true
    },
    {
      "key": "amount",
      "value": "{{sdk.Coins being burned}}",
      "index": true
    }
  ]
}
```

```json
{
  "type": "coin_spent",
  "attributes": [
    {
      "key": "spender",
      "value": "{{sdk.AccAddress of the module burning coins}}",
      "index": true
    },
    {
      "key": "amount",
      "value": "{{sdk.Coins being burned}}",
      "index": true
    }
  ]
}
```

#### addCoins

```json
{
  "type": "coin_received",
  "attributes": [
    {
      "key": "receiver",
      "value": "{{sdk.AccAddress of the address beneficiary of the coins}}",
      "index": true
    },
    {
      "key": "amount",
      "value": "{{sdk.Coins being received}}",
      "index": true
    }
  ]
}
```

#### subUnlockedCoins/DelegateCoins

```json
{
  "type": "coin_spent",
  "attributes": [
    {
      "key": "spender",
      "value": "{{sdk.AccAddress of the address which is spending coins}}",
      "index": true
    },
    {
      "key": "amount",
      "value": "{{sdk.Coins being spent}}",
      "index": true
    }
  ]
}
```

## 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.

```shell
emped query bank --help
```

**balances**

The `balances` command allows users to query account balances by address.

```shell
emped query bank balances [address] [flags]
```

Example:

```shell
emped query bank balances empe1..
```

Example Output:

```yml
balances:
- amount: "1000000000"
  denom: uempe
pagination:
  next_key: null
  total: "0"
```

**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.

```shell
emped query bank denom-metadata [flags]
```

Example:

```shell
emped query bank denom-metadata --denom stake
```

Example Output:

```yml
metadata:
  base: uempe
  denom_units:
  - aliases:
    - STAKE
    denom: uempe
  description: native staking token of simulation app
  display: uempe
  name: SimApp Token
  symbol: STK
```

**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.

```shell
emped query bank total [flags]
```

Example:

```shell
emped query bank total --denom stake
```

Example Output:

```yml
amount: "10000000000"
denom: uempe
```

**send-enabled**

The `send-enabled` command allows users to query for all or some SendEnabled entries.

```shell
emped query bank send-enabled [denom1 ...] [flags]
```

Example:

```shell
emped query bank send-enabled
```

Example output:

```yml
send_enabled:
- denom: foocoin
  enabled: true
- denom: barcoin
pagination:
  next-key: null
  total: 2 
```

#### Transactions

The `tx` commands allow users to interact with the `bank` module.

```shell
emped tx bank --help
```

**send**

The `send` command allows users to send funds from one account to another.

```shell
emped tx bank send [from_key_or_address] [to_address] [amount] [flags]
```

Example:

```shell
emped tx bank send empe1.. empe1.. 100stake
```

## 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.

```shell
cosmos.bank.v1beta1.Query/Balance
```

Example:

```shell
grpcurl -plaintext \
    -d '{"address":"empe1..","denom":"uempe"}' \
    localhost:9090 \
    cosmos.bank.v1beta1.Query/Balance
```

Example Output:

```json
{
  "balance": {
    "denom": "uempe",
    "amount": "1000000000"
  }
}
```

### AllBalances

The `AllBalances` endpoint allows users to query account balance by address for all denominations.

```shell
cosmos.bank.v1beta1.Query/AllBalances
```

Example:

```shell
grpcurl -plaintext \
    -d '{"address":"empe1.."}' \
    localhost:9090 \
    cosmos.bank.v1beta1.Query/AllBalances
```

Example Output:

```json
{
  "balances": [
    {
      "denom": "uempe",
      "amount": "1000000000"
    }
  ],
  "pagination": {
    "total": "1"
  }
}
```

### DenomMetadata

The `DenomMetadata` endpoint allows users to query metadata for a single coin denomination.

```shell
cosmos.bank.v1beta1.Query/DenomMetadata
```

Example:

```shell
grpcurl -plaintext \
    -d '{"denom":"uempe"}' \
    localhost:9090 \
    cosmos.bank.v1beta1.Query/DenomMetadata
```

Example Output:

```json
{
  "metadata": {
    "description": "native staking token of simulation app",
    "denomUnits": [
      {
        "denom": "uempe",
        "aliases": [
          "STAKE"
        ]
      }
    ],
    "base": "uempe",
    "display": "uempe",
    "name": "SimApp Token",
    "symbol": "STK"
  }
}
```

### DenomsMetadata

The `DenomsMetadata` endpoint allows users to query metadata for all coin denominations.

```shell
cosmos.bank.v1beta1.Query/DenomsMetadata
```

Example:

```shell
grpcurl -plaintext \
    localhost:9090 \
    cosmos.bank.v1beta1.Query/DenomsMetadata
```

Example Output:

```json
{
  "metadatas": [
    {
      "description": "native staking token of simulation app",
      "denomUnits": [
        {
          "denom": "uempe",
          "aliases": [
            "STAKE"
          ]
        }
      ],
      "base": "uempe",
      "display": "uempe",
      "name": "SimApp Token",
      "symbol": "STK"
    }
  ],
  "pagination": {
    "total": "1"
  }
}
```

### DenomOwners

The `DenomOwners` endpoint allows users to query metadata for a single coin denomination.

```shell
cosmos.bank.v1beta1.Query/DenomOwners
```

Example:

```shell
grpcurl -plaintext \
    -d '{"denom":"uempe"}' \
    localhost:9090 \
    cosmos.bank.v1beta1.Query/DenomOwners
```

Example Output:

```json
{
  "denomOwners": [
    {
      "address": "empe1..",
      "balance": {
        "denom": "uempe",
        "amount": "5000000000"
      }
    },
    {
      "address": "empe1..",
      "balance": {
        "denom": "uempe",
        "amount": "5000000000"
      }
    },
  ],
  "pagination": {
    "total": "2"
  }
}
```

### TotalSupply

The `TotalSupply` endpoint allows users to query the total supply of all coins.

```shell
cosmos.bank.v1beta1.Query/TotalSupply
```

Example:

```shell
grpcurl -plaintext \
    localhost:9090 \
    cosmos.bank.v1beta1.Query/TotalSupply
```

Example Output:

```json
{
  "supply": [
    {
      "denom": "uempe",
      "amount": "10000000000"
    }
  ],
  "pagination": {
    "total": "1"
  }
}
```

### SupplyOf

The `SupplyOf` endpoint allows users to query the total supply of a single coin.

```shell
cosmos.bank.v1beta1.Query/SupplyOf
```

Example:

```shell
grpcurl -plaintext \
    -d '{"denom":"uempe"}' \
    localhost:9090 \
    cosmos.bank.v1beta1.Query/SupplyOf
```

Example Output:

```json
{
  "amount": {
    "denom": "uempe",
    "amount": "10000000000"
  }
}
```

### Params

The `Params` endpoint allows users to query the parameters of the `bank` module.

```shell
cosmos.bank.v1beta1.Query/Params
```

Example:

```shell
grpcurl -plaintext \
    localhost:9090 \
    cosmos.bank.v1beta1.Query/Params
```

Example Output:

```json
{
  "params": {
    "defaultSendEnabled": true
  }
}
```

### SendEnabled

The `SendEnabled` enpoints allows users to query the SendEnabled entries of the `bank` module.

Any denominations NOT returned, use the `Params.DefaultSendEnabled` value.

```shell
cosmos.bank.v1beta1.Query/SendEnabled
```

Example:

```shell
grpcurl -plaintext \
    localhost:9090 \
    cosmos.bank.v1beta1.Query/SendEnabled
```

Example Output:

```json
{
  "send_enabled": [
    {
      "denom": "foocoin",
      "enabled": true
    },
    {
      "denom": "barcoin"
    }
  ],
  "pagination": {
    "next-key": null,
    "total": 2
  }
}
```