From 8a4813aee674423e1adee555079bd5b5253601fd Mon Sep 17 00:00:00 2001
From: callebtc <93376500+callebtc@users.noreply.github.com>
Date: Wed, 18 Oct 2023 16:18:57 +0200
Subject: [PATCH] Zero amount invoices: throw error before attempting a payment
 (#349)

* Zero amount invoices: throw error before attempting a payment

* better naming of fee variables during melt
---
 cashu/mint/ledger.py | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/cashu/mint/ledger.py b/cashu/mint/ledger.py
index 179baad..8b1b804 100644
--- a/cashu/mint/ledger.py
+++ b/cashu/mint/ledger.py
@@ -445,16 +445,19 @@ class Ledger(LedgerVerification, LedgerSpendingConditions):
             # verify amounts
             total_provided = sum_proofs(proofs)
             invoice_obj = bolt11.decode(invoice)
+            assert invoice_obj.amount_msat, "invoice has no amount."
             invoice_amount = math.ceil(invoice_obj.amount_msat / 1000)
             if settings.mint_max_peg_out and invoice_amount > settings.mint_max_peg_out:
                 raise NotAllowedError(
                     f"Maximum melt amount is {settings.mint_max_peg_out} sat."
                 )
-            fees_sat = await self.get_melt_fees(invoice)
+            reserve_fees_sat = await self.get_melt_fees(invoice)
             # verify overspending attempt
-            assert total_provided >= invoice_amount + fees_sat, TransactionError(
+            assert (
+                total_provided >= invoice_amount + reserve_fees_sat
+            ), TransactionError(
                 "provided proofs not enough for Lightning payment. Provided:"
-                f" {total_provided}, needed: {invoice_amount + fees_sat}"
+                f" {total_provided}, needed: {invoice_amount + reserve_fees_sat}"
             )
 
             # verify spending inputs and their spending conditions
@@ -462,16 +465,17 @@ class Ledger(LedgerVerification, LedgerSpendingConditions):
 
             if settings.lightning:
                 logger.trace(f"paying lightning invoice {invoice}")
-                status, preimage, fee_msat = await self._pay_lightning_invoice(
-                    invoice, fees_sat * 1000
+                status, preimage, paid_fee_msat = await self._pay_lightning_invoice(
+                    invoice, reserve_fees_sat * 1000
                 )
                 preimage = preimage or ""
                 logger.trace("paid lightning invoice")
             else:
-                status, preimage, fee_msat = True, "preimage", 0
+                status, preimage, paid_fee_msat = True, "preimage", 0
 
             logger.debug(
-                f"Melt status: {status}: preimage: {preimage}, fee_msat: {fee_msat}"
+                f"Melt status: {status}: preimage: {preimage}, fee_msat:"
+                f" {paid_fee_msat}"
             )
 
             if not status:
@@ -482,11 +486,11 @@ class Ledger(LedgerVerification, LedgerSpendingConditions):
 
             # prepare change to compensate wallet for overpaid fees
             return_promises: List[BlindedSignature] = []
-            if outputs and fee_msat is not None:
+            if outputs and paid_fee_msat is not None:
                 return_promises = await self._generate_change_promises(
                     total_provided=total_provided,
                     invoice_amount=invoice_amount,
-                    ln_fee_msat=fee_msat,
+                    ln_fee_msat=paid_fee_msat,
                     outputs=outputs,
                 )