Repay a loan

The RepayLoan method is responsible for handling the repayment of a loan. This involves transferring the borrowed funds, along with any agreed upon fees, from the borrower to the lender. In addition, the collateral that was provided as part of the loan agreement will be released from the escrow account and returned to the borrower.

It is important to note that the RepayLoan method can only be called under certain conditions. Firstly, the transaction must be signed by the borrower of the loan. This ensures that only the borrower has the ability to initiate the repayment process. Secondly, the loan must be in an approved status. This means that the loan has received approval and is ready to be repaid.

To implement the RepayLoan method, we must ensure that these conditions are met before proceeding with the repayment process. Once the necessary checks have been performed, the method can then handle the transfer of funds and the release of the collateral from the escrow account.

Keeper method

x/loan/keeper/msg_server_repay_loan.go

package keeper

import (
    "context"

    errorsmod "cosmossdk.io/errors"
    sdk "github.com/cosmos/cosmos-sdk/types"
    sdkerrors "github.com/cosmos/cosmos-sdk/types/errors"

    "loan/x/loan/types"
)

func (k msgServer) RepayLoan(goCtx context.Context, msg *types.MsgRepayLoan) (*types.MsgRepayLoanResponse, error) {
    ctx := sdk.UnwrapSDKContext(goCtx)
    loan, found := k.GetLoan(ctx, msg.Id)
    if !found {
        return nil, errorsmod.Wrapf(sdkerrors.ErrKeyNotFound, "key %d doesn't exist", msg.Id)
    }
    if loan.State != "approved" {
        return nil, errorsmod.Wrapf(types.ErrWrongLoanState, "%v", loan.State)
    }
    lender, _ := sdk.AccAddressFromBech32(loan.Lender)
    borrower, _ := sdk.AccAddressFromBech32(loan.Borrower)
    if msg.Creator != loan.Borrower {
        return nil, errorsmod.Wrap(sdkerrors.ErrUnauthorized, "Cannot repay: not the borrower")
    }
    amount, _ := sdk.ParseCoinsNormalized(loan.Amount)
    fee, _ := sdk.ParseCoinsNormalized(loan.Fee)
    collateral, _ := sdk.ParseCoinsNormalized(loan.Collateral)
    err := k.bankKeeper.SendCoins(ctx, borrower, lender, amount)
    if err != nil {
        return nil, err
    }
    err = k.bankKeeper.SendCoins(ctx, borrower, lender, fee)
    if err != nil {
        return nil, err
    }
    err = k.bankKeeper.SendCoinsFromModuleToAccount(ctx, types.ModuleName, borrower, collateral)
    if err != nil {
        return nil, err
    }
    loan.State = "repayed"
    k.SetLoan(ctx, loan)
    return &types.MsgRepayLoanResponse{}, nil
}

RepayLoan takes in two arguments: a context and a pointer to a types.MsgRepayLoan type. It returns a pointer to a types.MsgRepayLoanResponse type and an error.

The method first retrieves a loan from storage by passing the provided loan ID to the k.GetLoan method. If the loan cannot be found, the method returns an error wrapped in a sdkerrors.ErrKeyNotFound error.

The method then checks that the state of the loan is "approved". If it is not, the method returns an error wrapped in a types.ErrWrongLoanState error.

Next, the method converts the lender and borrower addresses stored in the loan struct to sdk.AccAddress types using the sdk.AccAddressFromBech32 function. It then checks that the transaction is signed by the borrower of the loan by comparing the msg.Creator field to the borrower address stored in the loan struct. If these do not match, the method returns an error wrapped in a sdkerrors.ErrUnauthorized error.

The method then parses the loan amount, fee, and collateral stored in the loan struct as sdk.Coins using the sdk.ParseCoinsNormalized function. It then uses the k.bankKeeper.SendCoins function to transfer the loan amount and fee from the borrower to the lender. It then uses the k.bankKeeper.SendCoinsFromModuleToAccount function to transfer the collateral from the escrow account to the borrower.

Finally, the method updates the state of the loan to "repayed" and stores the updated loan in storage using the k.SetLoan method. The method returns a types.MsgRepayLoanResponse and a nil error to indicate that the repayment process was successful.