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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 legacy 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.

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 all accounts within a chain. 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:

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 interface also introduces new wrapper functions for the auth Keeper and the bank SendKeeper in order to be able to:

  • Get ModuleAccounts by providing its Name.
  • Send coins from and to other ModuleAccounts by passing only the Name or standard Accounts (BaseAccount or legacy VestingAccount).
  • 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
  • Send enabled Denoms: 0x4 | string -> bool

Params​

The bank module stores its params in state with the prefix of 0x05, it can be updated with governance or the address with authority.

  • Params: 0x05 | ProtocolBuffer(Params)
https://github.com/cosmos/cosmos-sdk/blob/v0.52.0-beta.1/x/bank/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 expected.

Denied Addresses​

The x/bank module accepts a map of addresses (blockedAddrs) 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.

Common Types​

Input​

An input of a multi-send transaction

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

Output​

An output of a multi-send transaction.

// 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).

// 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) error
    ExportGenesis(context.Context) (*types.GenesisState, error)

    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, address []byte, 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

    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).

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

    AppendSendRestriction(restriction SendRestrictionFn)
    PrependSendRestriction(restriction SendRestrictionFn)
    ClearSendRestriction()

    InputOutputCoins(ctx context.Context, input types.Input, outputs []types.Output) error
    SendCoins(ctx context.Context, fromAddr, 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
}

Send Restrictions​

The SendKeeper applies a SendRestrictionFn before each transfer of funds.

// A SendRestrictionFn can restrict sends and/or provide a new receiver address.
type SendRestrictionFn func(ctx context.Context, fromAddr, toAddr sdk.AccAddress, amt sdk.Coins) (newToAddr sdk.AccAddress, err error)

After the SendKeeper (or BaseKeeper) has been created, send restrictions can be added to it using the AppendSendRestriction or PrependSendRestriction functions. Both functions compose the provided restriction with any previously provided restrictions. AppendSendRestriction adds the provided restriction to be run after any previously provided send restrictions. PrependSendRestriction adds the restriction to be run before any previously provided send restrictions. The composition will short-circuit when an error is encountered. I.e. if the first one returns an error, the second is not run. Send restrictions can also be cleared by using ClearSendRestriction.

During SendCoins, the send restriction is applied before coins are removed from the from_address and adding them to the to_address. During InputOutputCoins, the send restriction is applied before the input coins are removed, once for each output before the funds are added.

Send Restrictions are not placed on ModuleToAccount or ModuleToModule transfers. This is done due to modules needing to move funds to user accounts and other module accounts. This is a design decision to allow for more flexibility in the state machine. The state machine should be able to move funds between module accounts and user accounts without restrictions.

Secondly this limitation would limit the usage of the state machine even for itself. users would not be able to receive rewards, not be able to move funds between module accounts. In the case that a user sends funds from a user account to the community pool and then a governance proposal is used to get those tokens into the users account this would fall under the discretion of the app chain developer to what they would like to do here. We can not make strong assumptions here.

Thirdly, this issue could lead into a chain halt if a token is disabled and the token is moved in the begin/endblock. This is the last reason we see the current change as they are more damaging then beneficial for users.

A send restriction function should make use of a custom value in the context to allow bypassing that specific restriction. For example, in your module's keeper package, you'd define the send restriction function:

var _ banktypes.SendRestrictionFn = Keeper{}.SendRestrictionFn

func (k Keeper) SendRestrictionFn(ctx context.Context, fromAddr, toAddr sdk.AccAddress, amt sdk.Coins) (sdk.AccAddress, error) {
    // Bypass if the context says to.
    if mymodule.HasBypass(ctx) {
        return toAddr, nil
    }

    // Your custom send restriction logic goes here.
    return nil, errors.New("not implemented")
}

The bank keeper should be provided to your keeper's constructor so the send restriction can be added to it:

func NewKeeper(cdc codec.BinaryCodec, storeKey storetypes.StoreKey, bankKeeper mymodule.BankKeeper) Keeper {
    rv := Keeper{/*...*/}
    bankKeeper.AppendSendRestriction(rv.SendRestrictionFn)
    return rv
}

Then, in the mymodule package, define the context helpers:

const bypassKey = "bypass-mymodule-restriction"

// WithBypass returns a new context that will cause the mymodule bank send restriction to be skipped.
func WithBypass(ctx context.Context) context.Context {
    return sdk.UnwrapSDKContext(ctx).WithValue(bypassKey, true)
}

// WithoutBypass returns a new context that will cause the mymodule bank send restriction to not be skipped.
func WithoutBypass(ctx context.Context) context.Context {
    return sdk.UnwrapSDKContext(ctx).WithValue(bypassKey, false)
}

// HasBypass checks the context to see if the mymodule bank send restriction should be skipped.
func HasBypass(ctx context.Context) bool {
    bypassValue := ctx.Value(bypassKey)
    if bypassValue == nil {
        return false
    }
    bypass, isBool := bypassValue.(bool)
    return isBool && bypass
}

Now, anywhere where you want to use SendCoins or InputOutputCoins but you don't want your send restriction applied you just need to apply custom value in the context:

func (k Keeper) DoThing(ctx context.Context, fromAddr, toAddr sdk.AccAddress, amt sdk.Coins) error {
    return k.bankKeeper.SendCoins(mymodule.WithBypass(ctx), fromAddr, toAddr, amt)
}

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).

// 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.

https://github.com/cosmos/cosmos-sdk/blob/v0.52.0-beta.1/x/bank/proto/cosmos/bank/v1beta1/tx.proto#L44-L59

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.

https://github.com/cosmos/cosmos-sdk/blob/v0.52.0-beta.1/x/bank/proto/cosmos/bank/v1beta1/tx.proto#L65-L75

The message will fail under the following conditions:

  • Any of the coins do not have sending enabled
  • Any of the to_address are restricted
  • Any of the coins are locked
  • The inputs and outputs do not correctly correspond to one another (eg: total_in not equal to total_out)

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. 

https://github.com/cosmos/cosmos-sdk/blob/v0.52.0-beta.1/x/bank/proto/cosmos/bank/v1beta1/tx.proto#L81-L93

The message handling can fail if:

  • signer is not the gov module account address.

MsgSetSendEnabled​

Used with the x/gov module to create or edit SendEnabled entries.

https://github.com/cosmos/cosmos-sdk/blob/v0.52.0-beta.1/x/bank/proto/cosmos/bank/v1beta1/tx.proto#L106-L122

The message will fail under the following conditions:

  • The authority is not a decodable 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

MsgBurn​

Used to burn coins from an account. The coins are removed from the account and the total supply is reduced.

https://github.com/cosmos/cosmos-sdk/blob/v0.52.0-beta.1/x/bank/proto/cosmos/bank/v1beta1/tx.proto#L130-L139

This message will fail under the following conditions:

  • The from_address is not a decodable address
  • The coins are not spendable
  • The coins are not positive
  • The coins are not valid

Events​

The bank module emits the following events:

Message Events​

MsgSend​

TypeAttribute KeyAttribute Value
transferrecipient{recipientAddress}
transfersender{senderAddress}
transferamount{amount}
messagemodulebank
messageactionsend

MsgMultiSend​

TypeAttribute KeyAttribute Value
transferrecipient{recipientAddress}
transfersender{senderAddress}
transferamount{amount}
messagemodulebank
messageactionmultisend

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​

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

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

{
  "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​

{
  "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​

SendEnabled is depreacted and only kept for backward compatibility. For genesis, use the newly added send_enabled field in the genesis object. Storage, lookup, and manipulation of this information is now in the keeper.

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.

simd query bank --help
balance​

The balance command allows users to query account balance by specific denom.

simd query bank balance [address] [denom] [flags]

Example:

simd query bank balance cosmos1.. stake
balances​

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

simd query bank balances [address] [flags]

Example:

simd query bank balances cosmos1..
spendable balances​

The spendable-balances command allows users to query account spendable balances by address.

simd query spendable-balances [address] [flags]

Example:

simd query bank spendable-balances cosmos1..
spendable balance by denom​

The spendable-balance command allows users to query account spendable balance by address for a specific denom.

simd query spendable-balance [address] [denom] [flags]

Example:

simd query bank spendable-balance cosmos1.. stake
denom-metadata​

The denom-metadata command allows users to query metadata for coin denominations. 

simd query bank denom-metadata [denom]

Example:

simd query bank denom-metadata stake
denoms-metadata​

The denoms-metadata command allows users to query metadata for all coin denominations.

simd query bank denoms-metadata [flags]

Example:

simd query bank denoms-metadata
total supply​

The total-supply (or total for short) command allows users to query the total supply of coins.

simd query bank total [flags]

Example:

simd query bank total --denom stake
total supply of​

The total-supply-of command allows users to query the total supply for a specific coin denominations.

simd query bank total-supply-of [denom]

Example:

simd query bank total-supply-of stake
send-enabled​

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

simd query bank send-enabled [denom1 ...] [flags]

Example:

simd query bank send-enabled
params​

The params command allows users to query for the current bank parameters.

simd query bank params [flags]
denom owners​

The denom-owners command allows users to query for all account addresses that own a particular token denomination.

simd query bank denom-owners [denom] [flags]

Example:

simd query bank denom-owners stake

Transactions​

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

simd tx bank --help
send​

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

simd tx bank send [from_key_or_address] [to_address] [amount] [flags]

Example:

simd tx bank send cosmos1.. cosmos1.. 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.

cosmos.bank.v1beta1.Query/Balance

Example:

grpcurl -plaintext \
    -d '{"address":"cosmos1..","denom":"stake"}' \
    localhost:9090 \
    cosmos.bank.v1beta1.Query/Balance

AllBalances​

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

cosmos.bank.v1beta1.Query/AllBalances

Example:

grpcurl -plaintext \
    -d '{"address":"cosmos1.."}' \
    localhost:9090 \
    cosmos.bank.v1beta1.Query/AllBalances

DenomMetadata​

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

cosmos.bank.v1beta1.Query/DenomMetadata

Example:

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

DenomsMetadata​

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

cosmos.bank.v1beta1.Query/DenomsMetadata

Example:

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

DenomOwners​

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

cosmos.bank.v1beta1.Query/DenomOwners

Example:

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

TotalSupply​

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

cosmos.bank.v1beta1.Query/TotalSupply

Example:

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

SupplyOf​

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

cosmos.bank.v1beta1.Query/SupplyOf

Example:

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

Params​

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

cosmos.bank.v1beta1.Query/Params

Example:

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

SendEnabled​

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

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

cosmos.bank.v1beta1.Query/SendEnabled

Example:

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