Integration

Synopsis

Learn how to integrate IBC to your application and send data packets to other chains.

This document outlines the required steps to integrate and configure the IBC module to your Cosmos SDK application and send fungible token transfers to other chains.

Integrating the IBC module

Integrating the IBC module to your SDK-based application is straightforward. The general changes can be summarized in the following steps:

• Define additional Keeper fields for the new modules on the App type.
• Add the module's StoreKeys and initialize their Keepers.
• Set up IBC router and add route for the transfer module.
• Grant permissions to transfer's ModuleAccount.
• Add the modules to the module Manager.
• Update the module SimulationManager to enable simulations.
• Integrate light client modules (e.g. 07-tendermint).
• Add modules to Begin/EndBlockers and InitGenesis.

Add application fields to App

We need to register the core ibc and transfer Keepers as follows:

app.go

import (
  // other imports
  // ...
  capabilitykeeper "github.com/cosmos/ibc-go/modules/capability/keeper"
  ibckeeper "github.com/cosmos/ibc-go/v9/modules/core/keeper"
  ibctransferkeeper "github.com/cosmos/ibc-go/v9/modules/apps/transfer/keeper"
)

type App struct {
  // baseapp, keys and subspaces definitions

  // other keepers
  // ...
  IBCKeeper        *ibckeeper.Keeper // IBC Keeper must be a pointer in the app, so we can SetRouter on it correctly
  TransferKeeper   ibctransferkeeper.Keeper // for cross-chain fungible token transfers

  // make scoped keepers public for test purposes
  ScopedIBCKeeper      capabilitykeeper.ScopedKeeper
  ScopedTransferKeeper capabilitykeeper.ScopedKeeper

  // ...
  // module and simulation manager definitions
}

Configure the Keepers

During initialization, besides initializing the IBC Keepers (for core ibc and transfer modules), we need to grant specific capabilities through the capability module ScopedKeepers so that we can authenticate the object-capability permissions for each of the IBC channels.

import (
  // other imports
  // ...
  authtypes "github.com/cosmos/cosmos-sdk/x/auth/types"

  capabilitykeeper "github.com/cosmos/ibc-go/modules/capability/keeper"
  capabilitytypes "github.com/cosmos/ibc-go/modules/capability/types"
  ibcexported "github.com/cosmos/ibc-go/v9/modules/core/exported"
  ibckeeper "github.com/cosmos/ibc-go/v9/modules/core/keeper"
  "github.com/cosmos/ibc-go/v9/modules/apps/transfer"
  ibctransfertypes "github.com/cosmos/ibc-go/v9/modules/apps/transfer/types"
  ibctm "github.com/cosmos/ibc-go/v9/modules/light-clients/07-tendermint"
)

func NewApp(...args) *App {
  // define codecs and baseapp

  // add capability keeper and ScopeToModule for ibc module
  app.CapabilityKeeper = capabilitykeeper.NewKeeper(
    appCodec,
    keys[capabilitytypes.StoreKey],
    memKeys[capabilitytypes.MemStoreKey],
  )

  // grant capabilities for the ibc and transfer modules
  scopedIBCKeeper := app.CapabilityKeeper.ScopeToModule(ibcexported.ModuleName)
  scopedTransferKeeper := app.CapabilityKeeper.ScopeToModule(ibctransfertypes.ModuleName)

  // ... other module keepers

  // Create IBC Keeper
  app.IBCKeeper = ibckeeper.NewKeeper(
    appCodec,
    keys[ibcexported.StoreKey],
    app.GetSubspace(ibcexported.ModuleName),
    ibctm.NewConsensusHost(app.StakingKeeper),
    app.UpgradeKeeper,
    scopedIBCKeeper,
    authtypes.NewModuleAddress(govtypes.ModuleName).String(),
  )

  // Create Transfer Keeper
  app.TransferKeeper = ibctransferkeeper.NewKeeper(
    appCodec,
    keys[ibctransfertypes.StoreKey],
    app.GetSubspace(ibctransfertypes.ModuleName),
    app.IBCKeeper.ChannelKeeper,
    app.IBCKeeper.ChannelKeeper,
    app.IBCKeeper.PortKeeper,
    app.AccountKeeper,
    app.BankKeeper,
    scopedTransferKeeper,
    authtypes.NewModuleAddress(govtypes.ModuleName).String(),
  )
  transferModule := transfer.NewIBCModule(app.TransferKeeper)

  // ... continues
}

Register module routes in the IBC Router

IBC needs to know which module is bound to which port so that it can route packets to the appropriate module and call the appropriate callbacks. The port to module name mapping is handled by IBC's port Keeper. However, the mapping from module name to the relevant callbacks is accomplished by the port Router on the ibc module.

Adding the module routes allows the IBC handler to call the appropriate callback when processing a channel handshake or a packet.

Currently, a Router is static so it must be initialized and set correctly on app initialization. Once the Router has been set, no new routes can be added.

app.go

import (
  // other imports
  // ...
  porttypes "github.com/cosmos/ibc-go/v9/modules/core/05-port/types" 
  ibctransfertypes "github.com/cosmos/ibc-go/v9/modules/apps/transfer/types"
)

func NewApp(...args) *App {
  // .. continuation from above

  // Create static IBC router, add transfer module route, then set and seal it
  ibcRouter := porttypes.NewRouter()
  ibcRouter.AddRoute(ibctransfertypes.ModuleName, transferModule)
  // Setting Router will finalize all routes by sealing router
  // No more routes can be added
  app.IBCKeeper.SetRouter(ibcRouter)

  // ... continues

Module Manager and SimulationManager

In order to use IBC, we need to add the new modules to the module Manager and to the SimulationManager, in case your application supports simulations.

app.go

import (
  // other imports
  // ...
  "github.com/cosmos/cosmos-sdk/types/module"

  ibc "github.com/cosmos/ibc-go/v9/modules/core"
  "github.com/cosmos/ibc-go/modules/capability"
  "github.com/cosmos/ibc-go/v9/modules/apps/transfer"
)

func NewApp(...args) *App {
  // ... continuation from above

  app.ModuleManager = module.NewManager(
    // other modules
    // ...
+   capability.NewAppModule(appCodec, *app.CapabilityKeeper, false),
+   ibc.NewAppModule(app.IBCKeeper),
+   transfer.NewAppModule(app.TransferKeeper),
  )

  // ...

  app.simulationManager = module.NewSimulationManagerFromAppModules(
    // other modules
    // ...
    app.ModuleManager.Modules,
    map[string]module.AppModuleSimulation{},
  )

  // ... continues

Module account permissions

After that, we need to grant Minter and Burner permissions to the transfer ModuleAccount to mint and burn relayed tokens.

app.go

import (
  // other imports
  // ...
  "github.com/cosmos/cosmos-sdk/types/module"
  authtypes "github.com/cosmos/cosmos-sdk/x/auth/types"

+ ibctransfertypes "github.com/cosmos/ibc-go/v9/modules/apps/transfer/types"
)

// app.go
var (
  // module account permissions
  maccPerms = map[string][]string{
    // other module accounts permissions
    // ...
    ibctransfertypes.ModuleName: {authtypes.Minter, authtypes.Burner},
  }
)

Integrating light clients

Note that from v9 onwards, all light clients are expected to implement the LightClientInterface interface defined by core IBC, and have to be explicitly registered in a chain's app.go. This is in contrast to earlier versions of ibc-go when 07-tendermint and 06-solomachine were added out of the box. Follow the steps below to integrate the 07-tendermint light client.

All light clients must be registered with module.Manager in a chain's app.go file.

The following code example shows how to instantiate 07-tendermint light client module and register its ibctm.AppModule.

app.go

import (
  // other imports
  // ...
  "github.com/cosmos/cosmos-sdk/types/module"
+ ibctm "github.com/cosmos/ibc-go/v9/modules/light-clients/07-tendermint"
)

// app.go
// after sealing the IBC router

storeProvider := app.IBCKeeper.ClientKeeper.GetStoreProvider()

tmLightClientModule := ibctm.NewLightClientModule(appCodec, storeProvider)
app.IBCKeeper.ClientKeeper.AddRoute(ibctm.ModuleName, &tmLightClientModule)
app.ModuleManager = module.NewManager(
  // ...
  capability.NewAppModule(appCodec, *app.CapabilityKeeper, false),
  ibc.NewAppModule(app.IBCKeeper),
  transfer.NewAppModule(app.TransferKeeper), // i.e ibc-transfer module

  // register light clients on IBC
+ ibctm.NewAppModule(tmLightClientModule),
)

Application ABCI ordering

One addition from IBC is the concept of HistoricalInfo which is stored in the Cosmos SDK x/staking module. The number of records stored by x/staking is controlled by the HistoricalEntries parameter which stores HistoricalInfo on a per height basis. Each entry contains the historical information for the Header and ValidatorSet of this chain which is stored at each height during the BeginBlock call. The HistoricalInfo is required to introspect a blockchain's prior state at a given height in order to verify the light client ConsensusState during the connection handshake.

app.go

import (
  // other imports
  // ...
  stakingtypes "github.com/cosmos/cosmos-sdk/x/staking/types"
  capabilitytypes "github.com/cosmos/ibc-go/modules/capability/types"
  ibcexported "github.com/cosmos/ibc-go/v9/modules/core/exported"
  ibckeeper "github.com/cosmos/ibc-go/v9/modules/core/keeper"
  ibctransfertypes "github.com/cosmos/ibc-go/v9/modules/apps/transfer/types"
)

func NewApp(...args) *App {
  // ... continuation from above

  // add x/staking, ibc and transfer modules to BeginBlockers
  // capability module's Beginblocker must come before any
  // modules using capabilities (e.g. IBC)
  app.ModuleManager.SetOrderBeginBlockers(
    // other modules ...
    capabilitytypes.ModuleName,
    stakingtypes.ModuleName,
    ibcexported.ModuleName,
    ibctransfertypes.ModuleName,
  )
  app.ModuleManager.SetOrderEndBlockers(
    // other modules ...
    stakingtypes.ModuleName,
    ibcexported.ModuleName,
    ibctransfertypes.ModuleName,
    capabilitytypes.ModuleName,
  )

  // ...

  // NOTE: Capability module must occur first so that it can initialize any capabilities
  // so that other modules that want to create or claim capabilities afterwards in InitChain
  // can do so safely.
  genesisModuleOrder := []string{
    capabilitytypes.ModuleName,
    // other modules
    // ...
    ibcexported.ModuleName,
    ibctransfertypes.ModuleName,
  }
  app.ModuleManager.SetOrderInitGenesis(genesisModuleOrder...)

  // ... continues

warning

IMPORTANT: The capability module must be declared first in SetOrderBeginBlockers and SetOrderInitGenesis.

That's it! You have now wired up the IBC module and the transfer module, and are now able to send fungible tokens across different chains. If you want to have a broader view of the changes take a look into the SDK's SimApp.