Set correct blink min fee (#701)

* min fee

* fix tests

* amount_split test

cashu/core/split.py

@@ -3,6 +3,8 @@
 
 def amount_split(amount: int) -> List[int]:
     """Given an amount returns a list of amounts returned e.g. 13 is [1, 4, 8]."""
+    if amount <= 0:
+        return []
     bits_amt = bin(amount)[::-1][:-2]
     rv = []
     for pos, bit in enumerate(bits_amt):

cashu/lightning/blink.py

@@ -24,11 +24,13 @@
 
 # according to https://github.com/GaloyMoney/galoy/blob/7e79cc27304de9b9c2e7d7f4fdd3bac09df23aac/core/api/src/domain/bitcoin/index.ts#L59
 BLINK_MAX_FEE_PERCENT = 0.5
+# according to https://github.com/GaloyMoney/blink/blob/7e79cc27304de9b9c2e7d7f4fdd3bac09df23aac/core/api/src/domain/bitcoin/index.ts#L60C1-L60C41
+MINIMUM_FEE_MSAT = 10_000
 
 DIRECTION_SEND = "SEND"
 DIRECTION_RECEIVE = "RECEIVE"
 PROBE_FEE_TIMEOUT_SEC = 1
-MINIMUM_FEE_MSAT = 2000
+
 
 INVOICE_RESULT_MAP = {
     "PENDING": PaymentResult.PENDING,

cashu/mint/ledger.py

@@ -385,7 +385,11 @@ async def _generate_change_promises(
         # we make sure that the fee is positive
         overpaid_fee = fee_provided - fee_paid
 
-        if overpaid_fee == 0 or outputs is None:
+        if overpaid_fee <= 0 or outputs is None:
+            if overpaid_fee < 0:
+                logger.error(
+                    f"Overpaid fee is negative ({overpaid_fee}). This should not happen."
+                )
             return []
 
         logger.debug(

tests/test_core.py

@@ -8,6 +8,8 @@
 
 def test_get_output_split():
     assert amount_split(13) == [1, 4, 8]
+    assert amount_split(0) == []
+    assert amount_split(-8) == []
 
 
 def test_tokenv3_deserialize_get_attributes():

tests/test_mint_lightning_blink.py

@@ -190,7 +190,7 @@ async def test_blink_get_payment_status():
 @respx.mock
 @pytest.mark.asyncio
 async def test_blink_get_payment_quote():
-    # response says 1 sat fees but invoice (1000 sat) * 0.5% is 5 sat so we expect 5 sat
+    # response says 1 sat fees but invoice (1000 sat) * 0.5% is 5 sat so we expect MINIMUM_FEE_MSAT/1000 sat
     mock_response = {"data": {"lnInvoiceFeeProbe": {"amount": 1}}}
     respx.post(blink.endpoint).mock(return_value=Response(200, json=mock_response))
     melt_quote_request = PostMeltQuoteRequest(
@@ -199,7 +199,7 @@ async def test_blink_get_payment_quote():
     quote = await blink.get_payment_quote(melt_quote_request)
     assert quote.checking_id == payment_request
     assert quote.amount == Amount(Unit.sat, 1000)  # sat
-    assert quote.fee == Amount(Unit.sat, 5)  # sat
+    assert quote.fee == Amount(Unit.sat, MINIMUM_FEE_MSAT // 1000)  # msat
 
     # response says 10 sat fees but invoice (1000 sat) * 0.5% is 5 sat so we expect 10 sat
     mock_response = {"data": {"lnInvoiceFeeProbe": {"amount": 10}}}
@@ -238,7 +238,7 @@ async def test_blink_get_payment_quote():
 @respx.mock
 @pytest.mark.asyncio
 async def test_blink_get_payment_quote_backend_error():
-    # response says error but invoice (1000 sat) * 0.5% is 5 sat so we expect 10 sat
+    # response says error but invoice (1000 sat) * 0.5% is 5 sat so we expect 10 sat (MINIMUM_FEE_MSAT)
     mock_response = {"data": {"lnInvoiceFeeProbe": {"errors": [{"message": "error"}]}}}
     respx.post(blink.endpoint).mock(return_value=Response(200, json=mock_response))
     melt_quote_request = PostMeltQuoteRequest(
@@ -247,4 +247,4 @@ async def test_blink_get_payment_quote_backend_error():
     quote = await blink.get_payment_quote(melt_quote_request)
     assert quote.checking_id == payment_request
     assert quote.amount == Amount(Unit.sat, 1000)  # sat
-    assert quote.fee == Amount(Unit.sat, 5)  # sat
+    assert quote.fee == Amount(Unit.sat, MINIMUM_FEE_MSAT // 1000)  # msat