cosmos-sdk/x/ibc-transfer/keeper/relay.go

package keeper

import (
	sdk "github.com/cosmos/cosmos-sdk/types"
	sdkerrors "github.com/cosmos/cosmos-sdk/types/errors"
	"github.com/cosmos/cosmos-sdk/x/ibc-transfer/types"
	channeltypes "github.com/cosmos/cosmos-sdk/x/ibc/04-channel/types"
	host "github.com/cosmos/cosmos-sdk/x/ibc/24-host"
)

// SendTransfer handles transfer sending logic. There are 2 possible cases:
//
// 1. Sender chain is acting as the source zone. The coins are transferred
// to an escrow address (i.e locked) on the sender chain and then transferred
// to the receiving chain through IBC TAO logic. It is expected that the
// receiving chain will mint vouchers to the receiving address.
//
// 2. Sender chain is acting as the sink zone. The coins (vouchers) are burned
// on the sender chain and then transferred to the receiving chain though IBC
// TAO logic. It is expected that the receiving chain, which had previously
// sent the original denomination, will unescrow the fungible token and send
// it to the receiving address.
//
// Another way of thinking of source and sink zones is through the token's
// timeline. Each send to any chain other than the one it was previously
// received from is a movement forwards in the token's timeline. This causes
// trace to be added to the token's history and the destination port and
// destination channel to be prefixed to the denomination. In these instances
// the sender chain is acting as the source zone. When the token is sent back
// to the chain it previously received from, the prefix is removed. This is
// a backwards movement in the token's timeline and the sender chain
// is acting as the sink zone.
//
// Example:
// These steps of transfer occur: A -> B -> C -> A -> C -> B -> A
//
// 1. A -> B : sender chain is source zone. Denom upon receiving: 'B/denom'
// 2. B -> C : sender chain is source zone. Denom upon receiving: 'C/B/denom'
// 3. C -> A : sender chain is source zone. Denom upon receiving: 'A/C/B/denom'
// 4. A -> C : sender chain is sink zone. Denom upon receiving: 'C/B/denom'
// 5. C -> B : sender chain is sink zone. Denom upon receiving: 'B/denom'
// 6. B -> A : sender chain is sink zone. Denom upon receiving: 'denom'

func (k Keeper) SendTransfer(
	ctx sdk.Context,
	sourcePort,
	sourceChannel string,
	token sdk.Coin,
	sender sdk.AccAddress,
	receiver string,
	timeoutHeight,
	timeoutTimestamp uint64,
) error {
	sourceChannelEnd, found := k.channelKeeper.GetChannel(ctx, sourcePort, sourceChannel)
	if !found {
		return sdkerrors.Wrapf(channeltypes.ErrChannelNotFound, "port ID (%s) channel ID (%s)", sourcePort, sourceChannel)
	}

	destinationPort := sourceChannelEnd.GetCounterparty().GetPortID()
	destinationChannel := sourceChannelEnd.GetCounterparty().GetChannelID()

	// get the next sequence
	sequence, found := k.channelKeeper.GetNextSequenceSend(ctx, sourcePort, sourceChannel)
	if !found {
		return sdkerrors.Wrapf(
			channeltypes.ErrSequenceSendNotFound,
			"source port: %s, source channel: %s", sourcePort, sourceChannel,
		)
	}

	// begin createOutgoingPacket logic
	// See spec for this logic: https://github.com/cosmos/ics/tree/master/spec/ics-020-fungible-token-transfer#packet-relay

	channelCap, ok := k.scopedKeeper.GetCapability(ctx, host.ChannelCapabilityPath(sourcePort, sourceChannel))
	if !ok {
		return sdkerrors.Wrap(channeltypes.ErrChannelCapabilityNotFound, "module does not own channel capability")
	}

	// NOTE: SendTransfer simply sends the denomination as it exists on its own
	// chain inside the packet data. The receiving chain will perform denom
	// prefixing as necessary.

	if types.SenderChainIsSource(sourcePort, sourceChannel, token.Denom) {
		// create the escrow address for the tokens
		escrowAddress := types.GetEscrowAddress(sourcePort, sourceChannel)

		// escrow source tokens. It fails if balance insufficient.
		if err := k.bankKeeper.SendCoins(
			ctx, sender, escrowAddress, sdk.NewCoins(token),
		); err != nil {
			return err
		}

	} else {
		// transfer the coins to the module account and burn them
		if err := k.bankKeeper.SendCoinsFromAccountToModule(
			ctx, sender, types.ModuleName, sdk.NewCoins(token),
		); err != nil {
			return err
		}

		if err := k.bankKeeper.BurnCoins(
			ctx, types.ModuleName, sdk.NewCoins(token),
		); err != nil {
			// NOTE: should not happen as the module account was
			// retrieved on the step above and it has enough balace
			// to burn.
			return err
		}
	}

	packetData := types.NewFungibleTokenPacketData(
		token.Denom, token.Amount.Uint64(), sender.String(), receiver,
	)

	packet := channeltypes.NewPacket(
		packetData.GetBytes(),
		sequence,
		sourcePort,
		sourceChannel,
		destinationPort,
		destinationChannel,
		timeoutHeight,
		timeoutTimestamp,
	)

	return k.channelKeeper.SendPacket(ctx, channelCap, packet)
}

// OnRecvPacket processes a cross chain fungible token transfer. If the
// sender chain is the source of minted tokens then vouchers will be minted
// and sent to the receiving address. Otherwise if the sender chain is sending
// back tokens this chain originally transferred to it, the tokens are
// unescrowed and sent to the receiving address.
func (k Keeper) OnRecvPacket(ctx sdk.Context, packet channeltypes.Packet, data types.FungibleTokenPacketData) error {
	// NOTE: packet data type already checked in handler.go

	// decode the receiver address
	receiver, err := sdk.AccAddressFromBech32(data.Receiver)
	if err != nil {
		return err
	}

	// This is the prefix that would have been prefixed to the denomination
	// on sender chain IF and only if the token originally came from the
	// receiving chain.
	//
	// NOTE: We use SourcePort and SourceChannel here, because the counterparty
	// chain would have prefixed with DestPort and DestChannel when originally
	// receiving this coin as seen in the "sender chain is the source" condition.

	if types.ReceiverChainIsSource(packet.GetSourcePort(), packet.GetSourceChannel(), data.Denom) {
		// sender chain is not the source, unescrow tokens

		// remove prefix added by sender chain
		voucherPrefix := types.GetDenomPrefix(packet.GetSourcePort(), packet.GetSourceChannel())
		unprefixedDenom := data.Denom[len(voucherPrefix):]
		token := sdk.NewCoin(unprefixedDenom, sdk.NewIntFromUint64(data.Amount))

		// unescrow tokens
		escrowAddress := types.GetEscrowAddress(packet.GetDestPort(), packet.GetDestChannel())
		return k.bankKeeper.SendCoins(ctx, escrowAddress, receiver, sdk.NewCoins(token))
	}

	// sender chain is the source, mint vouchers

	// since SendPacket did not prefix the denomination, we must prefix denomination here
	sourcePrefix := types.GetDenomPrefix(packet.GetDestPort(), packet.GetDestChannel())
	// NOTE: sourcePrefix contains the trailing "/"
	prefixedDenom := sourcePrefix + data.Denom
	voucher := sdk.NewCoin(prefixedDenom, sdk.NewIntFromUint64(data.Amount))

	// mint new tokens if the source of the transfer is the same chain
	if err := k.bankKeeper.MintCoins(
		ctx, types.ModuleName, sdk.NewCoins(voucher),
	); err != nil {
		return err
	}

	// send to receiver
	return k.bankKeeper.SendCoinsFromModuleToAccount(
		ctx, types.ModuleName, receiver, sdk.NewCoins(voucher),
	)
}

// OnAcknowledgementPacket responds to the the success or failure of a packet
// acknowledgement written on the receiving chain. If the acknowledgement
// was a success then nothing occurs. If the acknowledgement failed, then
// the sender is refunded their tokens using the refundPacketToken function.
func (k Keeper) OnAcknowledgementPacket(ctx sdk.Context, packet channeltypes.Packet, data types.FungibleTokenPacketData, ack types.FungibleTokenPacketAcknowledgement) error {
	if !ack.Success {
		return k.refundPacketToken(ctx, packet, data)
	}
	return nil
}

// OnTimeoutPacket refunds the sender since the original packet sent was
// never received and has been timed out.
func (k Keeper) OnTimeoutPacket(ctx sdk.Context, packet channeltypes.Packet, data types.FungibleTokenPacketData) error {
	return k.refundPacketToken(ctx, packet, data)
}

// refundPacketToken will unescrow and send back the tokens back to sender
// if the sending chain was the source chain. Otherwise, the sent tokens
// were burnt in the original send so new tokens are minted and sent to
// the sending address.
func (k Keeper) refundPacketToken(ctx sdk.Context, packet channeltypes.Packet, data types.FungibleTokenPacketData) error {
	// NOTE: packet data type already checked in handler.go

	token := sdk.NewCoin(data.Denom, sdk.NewIntFromUint64(data.Amount))

	// decode the sender address
	sender, err := sdk.AccAddressFromBech32(data.Sender)
	if err != nil {
		return err
	}

	if types.SenderChainIsSource(packet.GetSourcePort(), packet.GetSourceChannel(), token.Denom) {
		// unescrow tokens back to sender
		escrowAddress := types.GetEscrowAddress(packet.GetSourcePort(), packet.GetSourceChannel())
		return k.bankKeeper.SendCoins(ctx, escrowAddress, sender, sdk.NewCoins(token))
	}

	// mint vouchers back to sender
	if err := k.bankKeeper.MintCoins(
		ctx, types.ModuleName, sdk.NewCoins(token),
	); err != nil {
		return err
	}

	return k.bankKeeper.SendCoinsFromModuleToAccount(ctx, types.ModuleName, sender, sdk.NewCoins(token))
}