Creating Buy Orders

In this chapter, you implement the creation of buy orders. The logic is very similar to the sell order logic you implemented in the previous chapter.

Modify the Proto Definition

Add the buyer to the proto file definition:

// proto/interchange/dex/packet.proto

message BuyOrderPacketData {
  // ...
  string buyer = 5;
}

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

ignite generate proto-go --yes

IBC Message Handling in SendBuyOrder

• Check if the pair exists on the order book
• If the token is an IBC token, burn the tokens
• If the token is a native token, lock the tokens
• Save the voucher received on the target chain to later resolve a denom

// x/dex/keeper/msg_server_buy_order.go

package keeper

import (
    "context"
    "errors"

    sdk "github.com/cosmos/cosmos-sdk/types"

    "interchange/x/dex/types"
)

func (k msgServer) SendBuyOrder(goCtx context.Context, msg *types.MsgSendBuyOrder) (*types.MsgSendBuyOrderResponse, error) {
    ctx := sdk.UnwrapSDKContext(goCtx)

    // Cannot send a order if the pair doesn't exist
    pairIndex := types.OrderBookIndex(msg.Port, msg.ChannelID, msg.AmountDenom, msg.PriceDenom)
    _, found := k.GetBuyOrderBook(ctx, pairIndex)
    if !found {
        return &types.MsgSendBuyOrderResponse{}, errors.New("the pair doesn't exist")
    }

    // Lock the token to send
    sender, err := sdk.AccAddressFromBech32(msg.Creator)
    if err != nil {
        return &types.MsgSendBuyOrderResponse{}, err
    }

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

    // Construct the packet
    var packet types.BuyOrderPacketData

    packet.Buyer = msg.Creator
    packet.AmountDenom = msg.AmountDenom
    packet.Amount = msg.Amount
    packet.PriceDenom = msg.PriceDenom
    packet.Price = msg.Price

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

    // Transmit an IBC packet...
    return &types.MsgSendBuyOrderResponse{}, nil
}

On Receiving a Buy Order

• Update the buy order book
• Distribute sold token to the buyer
• Send the sell order to chain A after the fill attempt

// x/dex/keeper/buy_order.go

package keeper

// ...

func (k Keeper) OnRecvBuyOrderPacket(ctx sdk.Context, packet channeltypes.Packet, data types.BuyOrderPacketData) (packetAck types.BuyOrderPacketAck, err error) {
    // validate packet data upon receiving
    if err := data.ValidateBasic(); err != nil {
        return packetAck, err
    }

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

    // Fill buy order
    remaining, liquidated, purchase, _ := book.FillBuyOrder(types.Order{
        Amount: data.Amount,
        Price:  data.Price,
    })

    // Return remaining amount and gains
    packetAck.RemainingAmount = remaining.Amount
    packetAck.Purchase = purchase

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

    // Dispatch liquidated buy order
    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,
            finalPriceDenom,
            liquidation.Amount*liquidation.Price,
        ); err != nil {
            return packetAck, err
        }
    }

    // Save the new order book
    k.SetSellOrderBook(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

package types

// ...

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

package types

// ...

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
}

Receiving a Buy Order Acknowledgment

After a buy order acknowledgement is received, chain Mars:

• Stores the remaining sell order in the sell order book.
• Distributes sold marscoin to the buyers.
• Distributes to the seller the price of the amount sold.
• On error, mints back the burned tokens.

// x/dex/keeper/buy_order.go

package keeper

// ...

func (k Keeper) OnAcknowledgementBuyOrderPacket(ctx sdk.Context, packet channeltypes.Packet, data types.BuyOrderPacketData, 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.Buyer)
        if err != nil {
            return err
        }

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

        return nil
    case *channeltypes.Acknowledgement_Result:
        // Decode the packet acknowledgment
        var packetAck types.BuyOrderPacketAck

        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.GetBuyOrderBook(ctx, pairIndex)
        if !found {
            panic("buy order book must exist")
        }

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

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

        // Mint the purchase
        if packetAck.Purchase > 0 {
            receiver, err := sdk.AccAddressFromBech32(data.Buyer)
            if err != nil {
                return err
            }

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

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

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

AppendOrder appends an order in the buy order book. Add the following function to the x/dex/types/buy_order_book.go file in the types directory.

// x/dex/types/buy_order_book.go

package types

// ...

func (b *BuyOrderBook) AppendOrder(creator string, amount int32, price int32) (int32, error) {
    return b.Book.appendOrder(creator, amount, price, Increasing)
}

OnTimeout of a Buy Order Packet

If a timeout occurs, mint back the native token:

// x/dex/keeper/buy_order.go

package keeper

// ...

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

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

    return nil
}

Summary

Congratulations, you implemented the buy order logic.

Again, it's a good time to save your current state to your local GitHub repository:

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