---
title: Keeper
sidebar_label: Keeper
sidebar_position: 4
slug: /ibc/apps/keeper
---

# Keeper

:::note Synopsis
Learn how to implement the IBC Module keeper.
:::

:::note

## Pre-requisite readings

- [IBC Overview](../01-overview.md)
- [IBC default integration](../02-integration.md)

:::
In the previous sections, on channel handshake callbacks and port binding in `InitGenesis`, a reference was made to keeper methods that need to be implemented when creating a custom IBC module. Below is an overview of how to define an IBC module's keeper.

> Note that some code has been left out for clarity, to get a full code overview, please refer to [the transfer module's keeper in the ibc-go repo](https://github.com/cosmos/ibc-go/blob/main/modules/apps/transfer/keeper/keeper.go).

```go
// Keeper defines the IBC app module keeper
type Keeper struct {
	storeKey   sdk.StoreKey
	cdc        codec.BinaryCodec
	paramSpace paramtypes.Subspace

	channelKeeper types.ChannelKeeper
	portKeeper    types.PortKeeper
	scopedKeeper  capabilitykeeper.ScopedKeeper

    // ... additional according to custom logic
}

// NewKeeper creates a new IBC app module Keeper instance
func NewKeeper(
	// args
) Keeper {
	// ...

	return Keeper{
		cdc:           cdc,
		storeKey:      key,
		paramSpace:    paramSpace,

		channelKeeper: channelKeeper,
		portKeeper:    portKeeper,
		scopedKeeper:  scopedKeeper,

        // ... additional according to custom logic
	}
}

// IsBound checks if the IBC app module is already bound to the desired port
func (k Keeper) IsBound(ctx sdk.Context, portID string) bool {
	_, ok := k.scopedKeeper.GetCapability(ctx, host.PortPath(portID))
	return ok
}

// BindPort defines a wrapper function for the port Keeper's function in
// order to expose it to module's InitGenesis function
func (k Keeper) BindPort(ctx sdk.Context, portID string) error {
	cap := k.portKeeper.BindPort(ctx, portID)
	return k.ClaimCapability(ctx, cap, host.PortPath(portID))
}

// GetPort returns the portID for the IBC app module. Used in ExportGenesis
func (k Keeper) GetPort(ctx sdk.Context) string {
	store := ctx.KVStore(k.storeKey)
	return string(store.Get(types.PortKey))
}

// SetPort sets the portID for the IBC app module. Used in InitGenesis
func (k Keeper) SetPort(ctx sdk.Context, portID string) {
	store := ctx.KVStore(k.storeKey)
	store.Set(types.PortKey, []byte(portID))
}

// AuthenticateCapability wraps the scopedKeeper's AuthenticateCapability function
func (k Keeper) AuthenticateCapability(ctx sdk.Context, cap *capabilitytypes.Capability, name string) bool {
	return k.scopedKeeper.AuthenticateCapability(ctx, cap, name)
}

// ClaimCapability allows the IBC app module to claim a capability that core IBC
// passes to it
func (k Keeper) ClaimCapability(ctx sdk.Context, cap *capabilitytypes.Capability, name string) error {
	return k.scopedKeeper.ClaimCapability(ctx, cap, name)
}

// ... additional according to custom logic
```
