Integration

This document provides instructions on integrating and configuring the Packet Forward Middleware (PFM) within your existing chain implementation.

This document provides instructions on integrating and configuring the Packet Forward Middleware (PFM) within your existing chain implementation. The integration steps include the following:

1. Import the PFM, initialize the PFM Module & Keeper, initialize the store keys, and initialize the Begin/End Block logic and InitGenesis order
2. Configure the IBC application stack including the transfer module
3. Configuration of additional options such as timeout period and number of retries on timeout

Integration of the PFM should take approximately 20 minutes.

Example integration of the Packet Forward Middleware

// app.go

// Import the packet forward middleware
import (
    packetforward "github.com/cosmos/ibc-go/v11/modules/apps/packet-forward-middleware"
    packetforwardkeeper "github.com/cosmos/ibc-go/v11/modules/apps/packet-forward-middleware/keeper"
    packetforwardtypes "github.com/cosmos/ibc-go/v11/modules/apps/packet-forward-middleware/types"
)

...

// Add packet forward middleware Keeper
type App struct {
    ...
    PFMKeeper *packetforwardkeeper.Keeper
    ...
}

...

// Create store keys
keys := storetypes.NewKVStoreKeys(
    ...
    packetforwardtypes.StoreKey,
    ...
)

...

// Initialize the transfer module Keeper first (PFM Keeper requires it)
app.TransferKeeper = ibctransferkeeper.NewKeeper(...)

// Initialize the packet forward middleware Keeper
app.PFMKeeper = packetforwardkeeper.NewKeeper(
    appCodec,
    app.AccountKeeper.AddressCodec(),
    runtime.NewKVStoreService(keys[packetforwardtypes.StoreKey]),
    app.TransferKeeper,
    app.IBCKeeper.ChannelKeeper,
    app.BankKeeper,
    authtypes.NewModuleAddress(govtypes.ModuleName).String(),
)

// See the section below for configuring an application stack with the packet forward middleware

...

// Register packet forward middleware AppModule
app.moduleManager = module.NewManager(
    ...
    packetforward.NewAppModule(app.PFMKeeper),
)

...

// Add packet forward middleware to begin blocker logic
app.moduleManager.SetOrderBeginBlockers(
    ...
    packetforwardtypes.ModuleName,
    ...
)

// Add packet forward middleware to end blocker logic
app.moduleManager.SetOrderEndBlockers(
    ...
    packetforwardtypes.ModuleName,
    ...
)

// Add packet forward middleware to init genesis logic
app.moduleManager.SetOrderInitGenesis(
    ...
    packetforwardtypes.ModuleName,
    ...
)

Configuring the transfer application stack with Packet Forward Middleware

Here is an example of how to create an application stack using transfer and packet-forward-middleware. The following transferStack is configured in app/app.go and added to the IBC Router. The in-line comments describe the execution flow of packets between the application stack and IBC core.

For more information on configuring an IBC application stack see the middleware development guide.

// Create Transfer Stack
// SendPacket, since it is originating from the application to core IBC:
// transferKeeper.SendPacket -> packetforward.SendPacket -> channel.SendPacket

// RecvPacket, message that originates from core IBC and goes down to app, the flow is the other way
// channel.RecvPacket -> packetforward.OnRecvPacket -> transfer.OnRecvPacket

// transfer stack contains (from top to bottom):
// - Packet Forward Middleware
// - Transfer

// create IBC module from bottom to top of stack
transferStack := porttypes.NewIBCStackBuilder(app.IBCKeeper.ChannelKeeper)
transferStack.Base(transfer.NewIBCModule(app.TransferKeeper)).
    Next(packetforward.NewIBCMiddleware(
        app.PFMKeeper,
        0, // retries on timeout
        packetforwardkeeper.DefaultForwardTransferPacketTimeoutTimestamp, // forward timeout
    ))

// Add transfer stack to IBC Router
ibcRouter.AddRoute(ibctransfertypes.ModuleName, transferStack.Build())

Configurable options in the Packet Forward Middleware

The Packet Forward Middleware has several configurable options available when initializing the IBC application stack. You can see these passed in as arguments to packetforward.NewIBCMiddleware and they include the number of retries that will be performed on a forward timeout, and the timeout period that will be used for a forward.

• Retries On Timeout - how many times will a forward be re-attempted in the case of a timeout.
• Timeout Period - how long can a forward be in progress before giving up.