03-request.md

Request a loan

Implement RequestLoan keeper method that will be called whenever a user requests a loan. RequestLoan creates a new loan with the provided data, sends the collateral from the borrower's account to a module account, and adds the loan to the blockchain's store.

Keeper method

package keeper

import (
	"context"

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

	"loan/x/loan/types"
)

func (k msgServer) RequestLoan(goCtx context.Context, msg *types.MsgRequestLoan) (*types.MsgRequestLoanResponse, error) {
	ctx := sdk.UnwrapSDKContext(goCtx)
	var loan = types.Loan{
		Amount:     msg.Amount,
		Fee:        msg.Fee,
		Collateral: msg.Collateral,
		Deadline:   msg.Deadline,
		State:      "requested",
		Borrower:   msg.Creator,
	}
	borrower, err := sdk.AccAddressFromBech32(msg.Creator)
	if err != nil {
		panic(err)
	}
	collateral, err := sdk.ParseCoinsNormalized(loan.Collateral)
	if err != nil {
		panic(err)
	}
	sdkError := k.bankKeeper.SendCoinsFromAccountToModule(ctx, borrower, types.ModuleName, collateral)
	if sdkError != nil {
		return nil, sdkError
	}
	k.AppendLoan(ctx, loan)
	return &types.MsgRequestLoanResponse{}, nil
}

The function takes in two arguments: a context.Context object and a pointer to a types.MsgRequestLoan struct. It returns a pointer to a types.MsgRequestLoanResponse struct and an error object.

The first thing the function does is create a new types.Loan struct with the data from the input types.MsgRequestLoan struct. It sets the State field of the types.Loan struct to "requested".

Next, the function gets the borrower's address from the msg.Creator field of the input types.MsgRequestLoan struct. It then parses the loan.Collateral field (which is a string) into sdk.Coins using the sdk.ParseCoinsNormalized function.

The function then sends the collateral from the borrower's account to a module account using the k.bankKeeper.SendCoinsFromAccountToModule function. Finally, it adds the new loan to a keeper using the k.AppendLoan function. The function returns a types.MsgRequestLoanResponse struct and a nil error if all goes well.

Basic message validation

When a loan is created, a certain message input validation is required. You want to throw error messages in case the end user tries impossible inputs.

package types

import (
	// highlight-next-line
	"strconv"

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

func (msg *MsgRequestLoan) ValidateBasic() error {
	_, err := sdk.AccAddressFromBech32(msg.Creator)
	if err != nil {
		return sdkerrors.Wrapf(sdkerrors.ErrInvalidAddress, "invalid creator address (%s)", err)
	}
	// highlight-start
	amount, _ := sdk.ParseCoinsNormalized(msg.Amount)
	if !amount.IsValid() {
		return sdkerrors.Wrap(sdkerrors.ErrInvalidRequest, "amount is not a valid Coins object")
	}
	if amount.Empty() {
		return sdkerrors.Wrap(sdkerrors.ErrInvalidRequest, "amount is empty")
	}
	fee, _ := sdk.ParseCoinsNormalized(msg.Fee)
	if !fee.IsValid() {
		return sdkerrors.Wrap(sdkerrors.ErrInvalidRequest, "fee is not a valid Coins object")
	}
	deadline, err := strconv.ParseInt(msg.Deadline, 10, 64)
	if err != nil {
		return sdkerrors.Wrap(sdkerrors.ErrInvalidRequest, "deadline is not an integer")
	}
	if deadline <= 0 {
		return sdkerrors.Wrap(sdkerrors.ErrInvalidRequest, "deadline should be a positive integer")
	}
	collateral, _ := sdk.ParseCoinsNormalized(msg.Collateral)
	if !collateral.IsValid() {
		return sdkerrors.Wrap(sdkerrors.ErrInvalidRequest, "collateral is not a valid Coins object")
	}
	if collateral.Empty() {
		return sdkerrors.Wrap(sdkerrors.ErrInvalidRequest, "collateral is empty")
	}
	// highlight-end
	return nil
}