cosmos-sdk/docs/spec/ibc/mvp/mvp1.md

IBC Spec

This is a living document and should be edited as the IBC spec and implementation change

MVP1

The initial implementation of IBC will include just enough for simple coin transfers between chains, with safety features such as ACK messages being added later.

It is a complete stand-alone module. It includes the commands to send IBC packets as well as to post them to the destination chain.

IBC Module

// User facing API

type IBCPacket struct {
    SrcAddr   sdk.Address
    DestAddr  sdk.Address
    Coins     sdk.Coins
    SrcChain  string
    DestChain string
}

// Implements sdk.Msg
type IBCTransferMsg struct {
    IBCPacket
}

// Implements sdk.Msg
type IBCReceiveMsg struct {
    IBCPacket
    Relayer  sdk.Address
    Sequence int64
}

// Internal API

type IBCMapper struct {
    ibcKey sdk.StoreKey // IngressKey / EgressKey             => Value
                        // Ingress: Source Chain ID           => last income msg's sequence
                        // Egress: (Dest chain ID, Msg index) => length / indexed msg
}

type IngressKey struct {
    SrcChain string
}

type EgressKey struct {
    DestChain   string
    Index       int64
}

egressKey stores the outgoing IBCTransfers as a list. Its getter takes an EgressKey and returns the length if egressKey.Index == -1, an element if egressKey.Index > 0.

ingressKey stores the latest income IBCTransfer's sequence. It's getter takes an IngressKey.

Relayer

Packets

• Connect to 2 Tendermint RPC endpoints
• Query for IBC outgoing IBCOutMsg queue (can poll on a certain time interval, or check after each new block, etc)
• For any new IBCOutMsg, build IBCInMsg and post to destination chain

CLI

• Load relay process
• Execute IBCOutMsg