Complete ICS20 ft-transfer implementation

[hu55a1n1]

Crate

ibc

Summary

This is an attempt to gather all requirements for a complete ICS20 implementation.

Problem Definition

• Complete ICS26 routing module implementation #60
• ICS20 Keeper - this would require access to an AccountReader/Keeper and a BankReader/Keeper, similar to the ibc-go's Keeper (see https://github.com/cosmos/ibc-go/blob/main/modules/apps/transfer/keeper/keeper.go) ->

type Keeper struct {
        // ...
	ics4Wrapper   types.ICS4Wrapper
	channelKeeper types.ChannelKeeper
	portKeeper    types.PortKeeper
	authKeeper    types.AccountKeeper
	bankKeeper    types.BankKeeper
}

The Keeper must additionally provide helper methods for port-binding, denom-traces, etc.

• ICS26 callbacks (See https://github.com/cosmos/ibc-go/blob/main/modules/apps/transfer/ibc_module.go)
• Relay code (See https://github.com/cosmos/ibc-go/blob/main/modules/apps/transfer/keeper/relay.go)

Proposal

I propose we design an API that doesn't make assumptions on the SDK stack. A detailed proposal can be discussed via a draft PR.

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[Wizdave97]

@hu55a1n1 @adizere put up a draft PR for the ICS 20 Keeper, please give a review informalsystems/hermes#1884