mukan-ignite/docs/versioned_docs/version-v0.27/02-guide/07-interchange/08-cancelling-orders.md

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8	Enable cancelling of buy and sell orders.

Cancelling Orders

You have implemented order books, buy and sell orders. In this chapter, you enable cancelling of buy and sell orders.

Cancel a Sell Order

To cancel a sell order, you have to get the ID of the specific sell order. Then you can use the function RemoveOrderFromID to remove the specific order from the order book and update the keeper accordingly.

Move to the keeper directory and edit the x/dex/keeper/msg_server_cancel_sell_order.go file:

// x/dex/keeper/msg_server_cancel_sell_order.go

package keeper

import (
	"context"
	"errors"

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

	"interchange/x/dex/types"
)

func (k msgServer) CancelSellOrder(goCtx context.Context, msg *types.MsgCancelSellOrder) (*types.MsgCancelSellOrderResponse, error) {
	ctx := sdk.UnwrapSDKContext(goCtx)

	// Retrieve the book
	pairIndex := types.OrderBookIndex(msg.Port, msg.Channel, msg.AmountDenom, msg.PriceDenom)
	s, found := k.GetSellOrderBook(ctx, pairIndex)
	if !found {
		return &types.MsgCancelSellOrderResponse{}, errors.New("the pair doesn't exist")
	}

	// Check order creator
	order, err := s.Book.GetOrderFromID(msg.OrderID)
	if err != nil {
		return &types.MsgCancelSellOrderResponse{}, err
	}

	if order.Creator != msg.Creator {
		return &types.MsgCancelSellOrderResponse{}, errors.New("canceller must be creator")
	}

	// Remove order
	if err := s.Book.RemoveOrderFromID(msg.OrderID); err != nil {
		return &types.MsgCancelSellOrderResponse{}, err
	}

	k.SetSellOrderBook(ctx, s)

	// Refund seller with remaining amount
	seller, err := sdk.AccAddressFromBech32(order.Creator)
	if err != nil {
		return &types.MsgCancelSellOrderResponse{}, err
	}

	if err := k.SafeMint(ctx, msg.Port, msg.Channel, seller, msg.AmountDenom, order.Amount); err != nil {
		return &types.MsgCancelSellOrderResponse{}, err
	}

	return &types.MsgCancelSellOrderResponse{}, nil
}

Implement the GetOrderFromID Function

The GetOrderFromID function gets an order from the book from its ID.

Add this function to the x/dex/types/order_book.go function in the types directory:

// x/dex/types/order_book.go

func (book OrderBook) GetOrderFromID(id int32) (Order, error) {
	for _, order := range book.Orders {
		if order.Id == id {
			return *order, nil
		}
	}

	return Order{}, ErrOrderNotFound
}

Implement the RemoveOrderFromID Function

The RemoveOrderFromID function removes an order from the book and keeps it ordered:

// x/dex/types/order_book.go

package types

// ...

func (book *OrderBook) RemoveOrderFromID(id int32) error {
	for i, order := range book.Orders {
		if order.Id == id {
			book.Orders = append(book.Orders[:i], book.Orders[i+1:]...)
			return nil
		}
	}

	return ErrOrderNotFound
}

Cancel a Buy Order

To cancel a buy order, you have to get the ID of the specific buy order. Then you can use the function RemoveOrderFromID to remove the specific order from the order book and update the keeper accordingly:

// x/dex/keeper/msg_server_cancel_buy_order.go

package keeper

import (
	"context"
	"errors"

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

	"interchange/x/dex/types"
)

func (k msgServer) CancelBuyOrder(goCtx context.Context, msg *types.MsgCancelBuyOrder) (*types.MsgCancelBuyOrderResponse, error) {
	ctx := sdk.UnwrapSDKContext(goCtx)

	// Retrieve the book
	pairIndex := types.OrderBookIndex(msg.Port, msg.Channel, msg.AmountDenom, msg.PriceDenom)
	b, found := k.GetBuyOrderBook(ctx, pairIndex)
	if !found {
		return &types.MsgCancelBuyOrderResponse{}, errors.New("the pair doesn't exist")
	}

	// Check order creator
	order, err := b.Book.GetOrderFromID(msg.OrderID)
	if err != nil {
		return &types.MsgCancelBuyOrderResponse{}, err
	}

	if order.Creator != msg.Creator {
		return &types.MsgCancelBuyOrderResponse{}, errors.New("canceller must be creator")
	}

	// Remove order
	if err := b.Book.RemoveOrderFromID(msg.OrderID); err != nil {
		return &types.MsgCancelBuyOrderResponse{}, err
	}

	k.SetBuyOrderBook(ctx, b)

	// Refund buyer with remaining price amount
	buyer, err := sdk.AccAddressFromBech32(order.Creator)
	if err != nil {
		return &types.MsgCancelBuyOrderResponse{}, err
	}

	if err := k.SafeMint(
		ctx,
		msg.Port,
		msg.Channel,
		buyer,
		msg.PriceDenom,
		order.Amount*order.Price,
	); err != nil {
		return &types.MsgCancelBuyOrderResponse{}, err
	}

	return &types.MsgCancelBuyOrderResponse{}, nil
}

Summary

You have completed implementing the functions that are required for the dex module. In this chapter, you have implemented the design for cancelling specific buy or sell orders.

To test if your Ignite CLI blockchain builds correctly, use the chain build command:

ignite chain build

Again, it is a good time (a great time!) to add your state to the local GitHub repository:

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

Finally, it's now time to write test files.