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Create Sell Orders

In this chapter, you implement the logic for creating sell orders.

The packet proto file for a sell order is already generated. Add the seller information:

// proto/dex/packet.proto

message SellOrderPacketData {
// ...
string seller = 5;
}

Now, use Ignite CLI to build the proto files for the send-sell-order command. You used this command in a previous chapter.

ignite generate proto-go --yes

Message Handling in SendSellOrder

Sell orders are created using the send-sell-order command. This command creates a transaction with a SendSellOrder message that triggers the SendSellOrder keeper method.

The SendSellOrder command:

  • Checks that an order book for a specified denom pair exists.
  • Safely burns or locks token.
    • If the token is an IBC token, burn the token.
    • If the token is a native token, lock the token.
  • Saves the voucher that is received on the target chain to later resolve a denom.
  • Transmits an IBC packet to the target chain.
// x/dex/keeper/msg_server_sell_order.go

import (
"context"
"errors"

sdk "github.com/cosmos/cosmos-sdk/types"
clienttypes "github.com/cosmos/ibc-go/v3/modules/core/02-client/types"

"interchange/x/dex/types"
)

func (k msgServer) SendSellOrder(goCtx context.Context, msg *types.MsgSendSellOrder) (*types.MsgSendSellOrderResponse, error) {
ctx := sdk.UnwrapSDKContext(goCtx)

// If an order book doesn't exist, throw an error
pairIndex := types.OrderBookIndex(msg.Port, msg.ChannelID, msg.AmountDenom, msg.PriceDenom)
_, found := k.GetSellOrderBook(ctx, pairIndex)
if !found {
return &types.MsgSendSellOrderResponse{}, errors.New("the pair doesn't exist")
}

// Get sender's address
sender, err := sdk.AccAddressFromBech32(msg.Creator)
if err != nil {
return &types.MsgSendSellOrderResponse{}, err
}

// Use SafeBurn to ensure no new native tokens are minted
if err := k.SafeBurn(ctx, msg.Port, msg.ChannelID, sender, msg.AmountDenom, msg.Amount); err != nil {
return &types.MsgSendSellOrderResponse{}, err
}

// Save the voucher received on the other chain, to have the ability to resolve it into the original denom
k.SaveVoucherDenom(ctx, msg.Port, msg.ChannelID, msg.AmountDenom)

var packet types.SellOrderPacketData
packet.Seller = msg.Creator
packet.AmountDenom = msg.AmountDenom
packet.Amount = msg.Amount
packet.PriceDenom = msg.PriceDenom
packet.Price = msg.Price

// Transmit the packet
err = k.TransmitSellOrderPacket(ctx, packet, msg.Port, msg.ChannelID, clienttypes.ZeroHeight(), msg.TimeoutTimestamp)
if err != nil {
return nil, err
}

return &types.MsgSendSellOrderResponse{}, nil
}

On Receiving a Sell Order

When a "sell order" packet is received on the target chain, you want the module to:

  • Update the sell order book
  • Distribute sold token to the buyer
  • Send the sell order to chain A after the fill attempt
// x/dex/keeper/sell_order.go

func (k Keeper) OnRecvSellOrderPacket(ctx sdk.Context, packet channeltypes.Packet, data types.SellOrderPacketData) (packetAck types.SellOrderPacketAck, err error) {
if err := data.ValidateBasic(); err != nil {
return packetAck, err
}

pairIndex := types.OrderBookIndex(packet.SourcePort, packet.SourceChannel, data.AmountDenom, data.PriceDenom)
book, found := k.GetBuyOrderBook(ctx, pairIndex)
if !found {
return packetAck, errors.New("the pair doesn't exist")
}

// Fill sell order
remaining, liquidated, gain, _ := book.FillSellOrder(types.Order{
Amount: data.Amount,
Price: data.Price,
})

// Return remaining amount and gains
packetAck.RemainingAmount = remaining.Amount
packetAck.Gain = gain

// Before distributing sales, we resolve the denom
// First we check if the denom received comes from this chain originally
finalAmountDenom, saved := k.OriginalDenom(ctx, packet.DestinationPort, packet.DestinationChannel, data.AmountDenom)
if !saved {
// If it was not from this chain we use voucher as denom
finalAmountDenom = VoucherDenom(packet.SourcePort, packet.SourceChannel, data.AmountDenom)
}

// Dispatch liquidated buy orders
for _, liquidation := range liquidated {
liquidation := liquidation
addr, err := sdk.AccAddressFromBech32(liquidation.Creator)
if err != nil {
return packetAck, err
}

if err := k.SafeMint(ctx, packet.DestinationPort, packet.DestinationChannel, addr, finalAmountDenom, liquidation.Amount); err != nil {
return packetAck, err
}
}

// Save the new order book
k.SetBuyOrderBook(ctx, book)

return packetAck, nil
}

Implement a FillBuyOrder Function

The FillBuyOrder function tries to fill the sell order with the order book and returns all the side effects:

// x/dex/types/sell_order_book.go

func (s *SellOrderBook) FillBuyOrder(order Order) (
remainingBuyOrder Order,
liquidated []Order,
purchase int32,
filled bool,
) {
var liquidatedList []Order
totalPurchase := int32(0)
remainingBuyOrder = order

// Liquidate as long as there is match
for {
var match bool
var liquidation Order
remainingBuyOrder, liquidation, purchase, match, filled = s.LiquidateFromBuyOrder(
remainingBuyOrder,
)
if !match {
break
}

// Update gains
totalPurchase += purchase

// Update liquidated
liquidatedList = append(liquidatedList, liquidation)

if filled {
break
}
}

return remainingBuyOrder, liquidatedList, totalPurchase, filled
}

Implement a LiquidateFromBuyOrder Function

The LiquidateFromBuyOrder function liquidates the first buy order of the book from the sell order. If no match is found, return false for match:

// x/dex/types/sell_order_book.go

func (s *SellOrderBook) LiquidateFromBuyOrder(order Order) (
remainingBuyOrder Order,
liquidatedSellOrder Order,
purchase int32,
match bool,
filled bool,
) {
remainingBuyOrder = order

// No match if no order
orderCount := len(s.Book.Orders)
if orderCount == 0 {
return order, liquidatedSellOrder, purchase, false, false
}

// Check if match
lowestAsk := s.Book.Orders[orderCount-1]
if order.Price < lowestAsk.Price {
return order, liquidatedSellOrder, purchase, false, false
}

liquidatedSellOrder = *lowestAsk

// Check if buy order can be entirely filled
if lowestAsk.Amount >= order.Amount {
remainingBuyOrder.Amount = 0
liquidatedSellOrder.Amount = order.Amount
purchase = order.Amount

// Remove lowest ask if it has been entirely liquidated
lowestAsk.Amount -= order.Amount
if lowestAsk.Amount == 0 {
s.Book.Orders = s.Book.Orders[:orderCount-1]
} else {
s.Book.Orders[orderCount-1] = lowestAsk
}

return remainingBuyOrder, liquidatedSellOrder, purchase, true, true
}

// Not entirely filled
purchase = lowestAsk.Amount
s.Book.Orders = s.Book.Orders[:orderCount-1]
remainingBuyOrder.Amount -= lowestAsk.Amount

return remainingBuyOrder, liquidatedSellOrder, purchase, true, false
}

Implement the OnAcknowledgement Function for Sell Order Packets

After an IBC packet is processed on the target chain, an acknowledgement is returned to the source chain and processed by the OnAcknowledgementSellOrderPacket function.

The dex module on the source chain:

  • Stores the remaining sell order in the sell order book.
  • Distributes sold tokens to the buyers.
  • Distributes the price of the amount sold to the seller.
  • On error, mints the burned tokens.
// x/dex/keeper/sell_order.go

func (k Keeper) OnAcknowledgementSellOrderPacket(ctx sdk.Context, packet channeltypes.Packet, data types.SellOrderPacketData, ack channeltypes.Acknowledgement) error {
switch dispatchedAck := ack.Response.(type) {
case *channeltypes.Acknowledgement_Error:
// In case of error we mint back the native token
receiver, err := sdk.AccAddressFromBech32(data.Seller)
if err != nil {
return err
}

if err := k.SafeMint(ctx, packet.SourcePort, packet.SourceChannel, receiver, data.AmountDenom, data.Amount); err != nil {
return err
}

return nil
case *channeltypes.Acknowledgement_Result:
// Decode the packet acknowledgment
var packetAck types.SellOrderPacketAck
if err := types.ModuleCdc.UnmarshalJSON(dispatchedAck.Result, &packetAck); err != nil {
// The counter-party module doesn't implement the correct acknowledgment format
return errors.New("cannot unmarshal acknowledgment")
}

// Get the sell order book
pairIndex := types.OrderBookIndex(packet.SourcePort, packet.SourceChannel, data.AmountDenom, data.PriceDenom)
book, found := k.GetSellOrderBook(ctx, pairIndex)
if !found {
panic("sell order book must exist")
}

// Append the remaining amount of the order
if packetAck.RemainingAmount > 0 {
_, err := book.AppendOrder(data.Seller, packetAck.RemainingAmount, data.Price)
if err != nil {
return err
}

// Save the new order book
k.SetSellOrderBook(ctx, book)
}

// Mint the gains
if packetAck.Gain > 0 {
receiver, err := sdk.AccAddressFromBech32(data.Seller)
if err != nil {
return err
}

finalPriceDenom, saved := k.OriginalDenom(ctx, packet.SourcePort, packet.SourceChannel, data.PriceDenom)
if !saved {
// If it was not from this chain we use voucher as denom
finalPriceDenom = VoucherDenom(packet.DestinationPort, packet.DestinationChannel, data.PriceDenom)
}

if err := k.SafeMint(ctx, packet.SourcePort, packet.SourceChannel, receiver, finalPriceDenom, packetAck.Gain); err != nil {
return err
}
}

return nil
default:
// The counter-party module doesn't implement the correct acknowledgment format
return errors.New("invalid acknowledgment format")
}
}
// x/dex/types/sell_order_book.go

func (s *SellOrderBook) AppendOrder(creator string, amount int32, price int32) (int32, error) {
return s.Book.appendOrder(creator, amount, price, Decreasing)
}

Add the OnTimeout of a Sell Order Packet Function

If a timeout occurs, mint back the native token:

// x/dex/keeper/sell_order.go

func (k Keeper) OnTimeoutSellOrderPacket(ctx sdk.Context, packet channeltypes.Packet, data types.SellOrderPacketData) error {
// In case of error we mint back the native token
receiver, err := sdk.AccAddressFromBech32(data.Seller)
if err != nil {
return err
}

if err := k.SafeMint(ctx, packet.SourcePort, packet.SourceChannel, receiver, data.AmountDenom, data.Amount); err != nil {
return err
}

return nil
}

Summary

Great, you have completed the sell order logic.

It is a good time to make another git commit again to save the state of your work:

git add .
git commit -m "Add Sell Orders"