Cosmos SDK

# Integration

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 (opens new window) 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 straighforward. The general changes can be summarized in the following steps:

Add required modules to the module.BasicManager
Define additional Keeper fields for the new modules on the App type
Add the module's StoreKeys and initialize their Keepers
Set up corresponding routers and routes for the ibc and evidence modules
Add the modules to the module Manager
Add modules to Begin/EndBlockers and InitGenesis
Update the module SimulationManager to enable simulations

# Module `BasicManager` and `ModuleAccount` permissions

The first step is to add the following modules to the BasicManager: x/capability, x/ibc, x/evidence and x/ibc-transfer. After that, we need to grant Minter and Burner permissions to the ibc-transfer ModuleAccount to mint and burn relayed tokens.

// app.go var ( ModuleBasics = module.NewBasicManager( // ... capability.AppModuleBasic{}, ibc.AppModuleBasic{}, evidence.AppModuleBasic{}, transfer.AppModuleBasic{}, // i.e ibc-transfer module ) // module account permissions maccPerms = map[string][]string{ // other module accounts permissions // ... ibctransfertypes.ModuleName: {authtypes.Minter, authtypes.Burner}, )

# Application fields

Then, we need to register the Keepers as follows:

// app.go 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 EvidenceKeeper evidencekeeper.Keeper // required to set up the client misbehaviour route 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 the x/ibc, and x/ibc-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.

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 ibc-transfer modules scopedIBCKeeper := app.CapabilityKeeper.ScopeToModule(ibchost.ModuleName) scopedTransferKeeper := app.CapabilityKeeper.ScopeToModule(ibctransfertypes.ModuleName) // ... other modules keepers // Create IBC Keeper app.IBCKeeper = ibckeeper.NewKeeper( appCodec, keys[ibchost.StoreKey], app.StakingKeeper, scopedIBCKeeper, ) // Create Transfer Keepers app.TransferKeeper = ibctransferkeeper.NewKeeper( appCodec, keys[ibctransfertypes.StoreKey], app.IBCKeeper.ChannelKeeper, &app.IBCKeeper.PortKeeper, app.AccountKeeper, app.BankKeeper, scopedTransferKeeper, ) transferModule := transfer.NewAppModule(app.TransferKeeper) // Create evidence Keeper for to register the IBC light client misbehaviour evidence route evidenceKeeper := evidencekeeper.NewKeeper( appCodec, keys[evidencetypes.StoreKey], &app.StakingKeeper, app.SlashingKeeper, ) // .. continues }

# Register `Routers`

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 (opens new window) 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.

The second Router that is required is the evidence module router. This router handles genenal evidence submission and routes the business logic to each registered evidence handler. In the case of IBC, it is required to submit evidence for light client misbehaviour (opens new window) in order to freeze a client and prevent further data packets from being sent/received.

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 func NewApp(...args) *App { // .. continuation from above // Create static IBC router, add ibc-tranfer module route, then set and seal it ibcRouter := port.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) // create static Evidence routers evidenceRouter := evidencetypes.NewRouter(). // add IBC ClientMisbehaviour evidence handler AddRoute(ibcclient.RouterKey, ibcclient.HandlerClientMisbehaviour(app.IBCKeeper.ClientKeeper)) // Setting Router will finalize all routes by sealing router // No more routes can be added evidenceKeeper.SetRouter(evidenceRouter) // set the evidence keeper from the section above app.EvidenceKeeper = *evidenceKeeper // .. continues

# Module Managers

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 func NewApp(...args) *App { // .. continuation from above app.mm = module.NewManager( // other modules // ... capability.NewAppModule(appCodec, *app.CapabilityKeeper), evidence.NewAppModule(app.EvidenceKeeper), ibc.NewAppModule(app.IBCKeeper), transferModule, ) // ... app.sm = module.NewSimulationManager( // other modules // ... capability.NewAppModule(appCodec, *app.CapabilityKeeper), evidence.NewAppModule(app.EvidenceKeeper), ibc.NewAppModule(app.IBCKeeper), transferModule, ) // .. continues

# Application ABCI Ordering

One addition from IBC is the concept of HistoricalEntries which are stored on the staking module. 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 historical info is required to introspect the past historical info at any given height in order to verify the light client ConsensusState during the connection handhake.

The IBC module also has BeginBlock (opens new window) logic as well. This is optional as it is only required if your application uses the localhost client (opens new window) to connect two different modules from the same chain.

Only register the ibc module to the SetOrderBeginBlockers if your application will use the localhost (aka loopback) client.

// app.go func NewApp(...args) *App { // .. continuation from above // add evidence, staking and ibc modules to BeginBlockers app.mm.SetOrderBeginBlockers( // other modules ... evidencetypes.ModuleName, stakingtypes.ModuleName, ibchost.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. app.mm.SetOrderInitGenesis( capabilitytypes.ModuleName, // other modules ... ibchost.ModuleName, evidencetypes.ModuleName, ibctransfertypes.ModuleName, ) // .. continues

IMPORTANT: The capability module must be declared first in SetOrderInitGenesis

That's it! You have now wired up the IBC 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 (opens new window).