mint - check if melt quote already exists for invoice in request

cashu/cashu.go

@@ -430,6 +430,7 @@ var (
 	MeltQuotePending             = Error{Detail: "quote is pending", Code: MeltQuotePendingErrCode}
 	MeltQuoteAlreadyPaid         = Error{Detail: "quote already paid", Code: MeltQuoteAlreadyPaidErrCode}
 	MeltAmountExceededErr        = Error{Detail: "max amount for melting exceeded", Code: AmountLimitExceeded}
+	MeltQuoteForRequestExists    = Error{Detail: "melt quote for payment request already exists", Code: MeltQuoteErrCode}
 	InsufficientProofsAmount     = Error{
 		Detail: "amount of input proofs is below amount needed for transaction",
 		Code:   InsufficientProofAmountErrCode,

mint/mint.go

@@ -538,6 +538,12 @@ func (m *Mint) RequestMeltQuote(method, request, unit string) (storage.MeltQuote
 		}
 	}
 
+	// check if a melt quote for the invoice already exists
+	quote, _ := m.db.GetMeltQuoteByPaymentRequest(request)
+	if quote != nil {
+		return storage.MeltQuote{}, cashu.MeltQuoteForRequestExists
+	}
+
 	quoteId, err := cashu.GenerateRandomQuoteId()
 	if err != nil {
 		m.logErrorf("error generating random quote id: %v", err)

mint/mint_integration_test.go

@@ -390,6 +390,13 @@ func TestRequestMeltQuote(t *testing.T) {
 	if err != nil {
 		t.Fatalf("got unexpected error in melt request: %v", err)
 	}
+
+	// trying to create another melt quote with same invoice should throw error
+	_, err = testMint.RequestMeltQuote(testutils.BOLT11_METHOD, addInvoiceResponse.PaymentRequest, testutils.SAT_UNIT)
+	if !errors.Is(err, cashu.MeltQuoteForRequestExists) {
+		//if !errors.Is(err, cashu.PaymentMethodNotSupportedErr) {
+		t.Fatalf("expected error '%v' but got '%v' instead", cashu.MeltQuoteForRequestExists, err)
+	}
 }
 
 func TestMeltQuoteState(t *testing.T) {
@@ -518,6 +525,11 @@ func TestMelt(t *testing.T) {
 		t.Fatalf("expected error '%v' but got '%v' instead", cashu.MeltQuoteAlreadyPaid, err)
 	}
 
+	invoice = lnrpc.Invoice{Value: 6000}
+	addInvoiceResponse, err = lnd2.Client.AddInvoice(ctx, &invoice)
+	if err != nil {
+		t.Fatalf("error creating invoice: %v", err)
+	}
 	// test already used proofs
 	newQuote, err := testMint.RequestMeltQuote(testutils.BOLT11_METHOD, addInvoiceResponse.PaymentRequest, testutils.SAT_UNIT)
 	if err != nil {

mint/storage/sqlite/migrations/000006_melt_quote_request_idx.down.sql

@@ -0,0 +1,2 @@
+
+DROP INDEX IF EXISTS idx_melt_quotes_request;

mint/storage/sqlite/migrations/000006_melt_quote_request_idx.up.sql

@@ -0,0 +1,2 @@
+
+CREATE INDEX IF NOT EXISTS idx_melt_quotes_request ON melt_quotes(request);

mint/storage/sqlite/sqlite.go

@@ -444,6 +444,30 @@ func (sqlite *SQLiteDB) GetMeltQuote(quoteId string) (storage.MeltQuote, error)
 	return meltQuote, nil
 }
 
+func (sqlite *SQLiteDB) GetMeltQuoteByPaymentRequest(invoice string) (*storage.MeltQuote, error) {
+	row := sqlite.db.QueryRow("SELECT * FROM melt_quotes WHERE request = ?", invoice)
+
+	var meltQuote storage.MeltQuote
+	var state string
+
+	err := row.Scan(
+		&meltQuote.Id,
+		&meltQuote.InvoiceRequest,
+		&meltQuote.PaymentHash,
+		&meltQuote.Amount,
+		&meltQuote.FeeReserve,
+		&state,
+		&meltQuote.Expiry,
+		&meltQuote.Preimage,
+	)
+	if err != nil {
+		return nil, err
+	}
+	meltQuote.State = nut05.StringToState(state)
+
+	return &meltQuote, nil
+}
+
 func (sqlite *SQLiteDB) UpdateMeltQuote(quoteId, preimage string, state nut05.State) error {
 	updatedState := state.String()
 	result, err := sqlite.db.Exec(

mint/storage/storage.go

@@ -30,6 +30,8 @@ type MintDB interface {
 
 	SaveMeltQuote(MeltQuote) error
 	GetMeltQuote(string) (MeltQuote, error)
+	// used to check if a melt quote already exists for the passed invoice
+	GetMeltQuoteByPaymentRequest(string) (*MeltQuote, error)
 	UpdateMeltQuote(quoteId string, preimage string, state nut05.State) error
 
 	SaveBlindSignature(B_ string, blindSignature cashu.BlindedSignature) error