07-cancel.md

Cancel a loan

As a borrower, you have the option to cancel a loan you have created if you no longer want to proceed with it. However, this action is only possible if the loan's current status is marked as "requested".

If you decide to cancel the loan, the collateral tokens that were being held as security for the loan will be transferred back to your account from the module account. This means that you will regain possession of the collateral tokens you had originally put up for the loan.

package keeper

import (
	"context"

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

	"loan/x/loan/types"
)

func (k msgServer) CancelLoan(goCtx context.Context, msg *types.MsgCancelLoan) (*types.MsgCancelLoanResponse, error) {
	ctx := sdk.UnwrapSDKContext(goCtx)
	loan, found := k.GetLoan(ctx, msg.Id)
	if !found {
		return nil, sdkerrors.Wrapf(sdkerrors.ErrKeyNotFound, "key %d doesn't exist", msg.Id)
	}
	if loan.Borrower != msg.Creator {
		return nil, sdkerrors.Wrap(sdkerrors.ErrUnauthorized, "Cannot cancel: not the borrower")
	}
	if loan.State != "requested" {
		return nil, sdkerrors.Wrapf(types.ErrWrongLoanState, "%v", loan.State)
	}
	borrower, _ := sdk.AccAddressFromBech32(loan.Borrower)
	collateral, _ := sdk.ParseCoinsNormalized(loan.Collateral)
	err := k.bankKeeper.SendCoinsFromModuleToAccount(ctx, types.ModuleName, borrower, collateral)
	if err != nil {
		return nil, err
	}
	loan.State = "cancelled"
	k.SetLoan(ctx, loan)
	return &types.MsgCancelLoanResponse{}, nil
}

CancelLoan takes in two arguments: a context.Context named goCtx and a pointer to a types.MsgCancelLoan named msg. It returns a pointer to a types.MsgCancelLoanResponse and an error.

The function begins by using the sdk.UnwrapSDKContext method to get the sdk.Context from the context.Context object. It then uses the GetLoan method of the msgServer type to retrieve a loan identified by the Id field of the msg argument. If the loan is not found, the function returns an error using the sdk.ErrKeyNotFound error wrapped with the sdk.Wrap method.

Next, the function checks if the Creator field of the msg argument is the same as the Borrower field of the loan. If they are not the same, the function returns an error using the sdk.ErrUnauthorized error wrapped with the sdk.Wrap method.

The function then checks if the State field of the loan is equal to the string "requested". If it is not, the function returns an error using the types.ErrWrongLoanState error wrapped with the sdk.Wrapf method.

If the loan has the correct state and the creator of the message is the borrower of the loan, the function proceeds to send the collateral coins held in the Collateral field of the loan back to the borrower's account using the SendCoinsFromModuleToAccount method of the bankKeeper. The function then updates the State field of the loan to the string "cancelled" and sets the updated loan using the SetLoan method. Finally, the function returns a types.MsgCancelLoanResponse object and a nil error.