From 2189728771e318f6e8431303bc3c7af45ce2db11 Mon Sep 17 00:00:00 2001
From: callebtc <93376500+callebtc@users.noreply.github.com>
Date: Mon, 19 Feb 2024 16:30:44 +0100
Subject: [PATCH] blink: round up fees to next satoshi (#445)

---
 cashu/lightning/blink.py           | 14 ++++++++---
 tests/test_mint_lightning_blink.py | 39 +++++++++++++++++++++++++++---
 2 files changed, 47 insertions(+), 6 deletions(-)

diff --git a/cashu/lightning/blink.py b/cashu/lightning/blink.py
index eb78ed29..83348d5f 100644
--- a/cashu/lightning/blink.py
+++ b/cashu/lightning/blink.py
@@ -393,10 +393,18 @@ async def get_payment_quote(self, bolt11: str) -> PaymentQuoteResponse:
 
         amount_msat = int(invoice_obj.amount_msat)
 
-        # we take the highest: fee_msat_response, or BLINK_MAX_FEE_PERCENT, or 2000 msat
-        fees_msat = max(
+        # we take the highest: fee_msat_response, or BLINK_MAX_FEE_PERCENT, or MINIMUM_FEE_MSAT msat
+        # Note: fees with BLINK_MAX_FEE_PERCENT are rounded to the nearest 1000 msat
+        fees_amount_msat: int = (
+            math.ceil(amount_msat / 100 * BLINK_MAX_FEE_PERCENT / 1000) * 1000
+        )
+
+        fees_msat: int = max(
             fees_response_msat,
-            max(math.ceil(amount_msat / 100 * BLINK_MAX_FEE_PERCENT), MINIMUM_FEE_MSAT),
+            max(
+                fees_amount_msat,
+                MINIMUM_FEE_MSAT,
+            ),
         )
 
         fees = Amount(unit=Unit.msat, amount=fees_msat)
diff --git a/tests/test_mint_lightning_blink.py b/tests/test_mint_lightning_blink.py
index 393829ad..64777d6e 100644
--- a/tests/test_mint_lightning_blink.py
+++ b/tests/test_mint_lightning_blink.py
@@ -4,7 +4,7 @@
 
 from cashu.core.base import Amount, MeltQuote, Unit
 from cashu.core.settings import settings
-from cashu.lightning.blink import BlinkWallet
+from cashu.lightning.blink import MINIMUM_FEE_MSAT, BlinkWallet
 
 settings.mint_blink_key = "123"
 blink = BlinkWallet()
@@ -12,6 +12,23 @@
     "lnbc10u1pjap7phpp50s9lzr3477j0tvacpfy2ucrs4q0q6cvn232ex7nt2zqxxxj8gxrsdpv2phhwetjv4jzqcneypqyc6t8dp6xu6twva2xjuzzda6qcqzzsxqrrsss"
     "p575z0n39w2j7zgnpqtdlrgz9rycner4eptjm3lz363dzylnrm3h4s9qyyssqfz8jglcshnlcf0zkw4qu8fyr564lg59x5al724kms3h6gpuhx9xrfv27tgx3l3u3cyf6"
     "3r52u0xmac6max8mdupghfzh84t4hfsvrfsqwnuszf"
+)  # 1000 sat
+
+payment_request_10k = (
+    "lnbc100u1pjaxuyzpp5wn37d3mx38haqs7nd5he4j7pq4r806e6s83jdksxrd77pnanm3zqdpv2phhwetjv4jzqcneypqyc6t8dp6xu6twva2xjuzzda6qcqzzsxqrrss"
+    "sp5ayy0uuhwgy8hwphvy7ptzpg2dfn8vt3vlgsk53rsvj76jvafhujs9qyyssqc8aj03s5au3tgu6pj0rm0ws4a838s8ffe3y3qkj77esh7qmgsz7qlvdlzgj6dvx7tx7"
+    "zn6k352z85rvdqvlszrevvzakp96a4pvyn2cpgaaks6"
+)
+
+payment_request_4973 = (
+    "lnbc49730n1pjaxuxnpp5zw0ry2w2heyuv7wk4r6z38vvgnaudfst0hl2p5xnv0mjkxtavg2qdpv2phhwetjv4jzqcneypqyc6t8dp6xu6twva2xjuzzda6qcqzzsxqrr"
+    "sssp5x8tv2ka0m95hgek25kauw540m0dx727stqqr07l8h37v5283sn5q9qyyssqeevcs6vxcdnerk5w5mwfmntsf8nze7nxrf97dywmga7v0742vhmxtjrulgu3kah4f"
+    "2r6025j974jpjg4mkqhv2gdls5k7e5cvwdf4wcp3ytsvx"
+)
+payment_request_1 = (
+    "lnbc10n1pjaxujrpp5sqehn6h5p8xpa0c0lvj5vy3a537gxfk5e7h2ate2alfw3y5cm6xqdpv2phhwetjv4jzqcneypqyc6t8dp6xu6twva2xjuzzda6qcqzzsxqrrsss"
+    "p5fkxsvyl0r32mvnhv9cws4rp986v0wjl2lp93zzl8jejnuwzvpynq9qyyssqqmsnatsz87qrgls98c97dfa6l2z3rzg2x6kxmrvpz886rwjylmd56y3qxzfulrq03kkh"
+    "hwk6r32wes6pjt2zykhnsjn30c6uhuk0wugp3x74al"
 )
 
 
@@ -132,7 +149,7 @@ 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 * 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 5 sat
     mock_response = {"data": {"lnInvoiceFeeProbe": {"amount": 1}}}
     respx.post(blink.endpoint).mock(return_value=Response(200, json=mock_response))
     quote = await blink.get_payment_quote(payment_request)
@@ -140,10 +157,26 @@ async def test_blink_get_payment_quote():
     assert quote.amount == Amount(Unit.msat, 1000000)  # msat
     assert quote.fee == Amount(Unit.msat, 5000)  # msat
 
-    # response says 10 sat fees but invoice * 0.5% is 5 sat so we expect 10 sat
+    # 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}}}
     respx.post(blink.endpoint).mock(return_value=Response(200, json=mock_response))
     quote = await blink.get_payment_quote(payment_request)
     assert quote.checking_id == payment_request
     assert quote.amount == Amount(Unit.msat, 1000000)  # msat
     assert quote.fee == Amount(Unit.msat, 10000)  # msat
+
+    # response says 10 sat fees but invoice (4973 sat) * 0.5% is 24.865 sat so we expect 25 sat
+    mock_response = {"data": {"lnInvoiceFeeProbe": {"amount": 10}}}
+    respx.post(blink.endpoint).mock(return_value=Response(200, json=mock_response))
+    quote = await blink.get_payment_quote(payment_request_4973)
+    assert quote.checking_id == payment_request_4973
+    assert quote.amount == Amount(Unit.msat, 4973000)  # msat
+    assert quote.fee == Amount(Unit.msat, 25000)  # msat
+
+    # response says 0 sat fees but invoice (1 sat) * 0.5% is 0.005 sat so we expect MINIMUM_FEE_MSAT/1000 sat
+    mock_response = {"data": {"lnInvoiceFeeProbe": {"amount": 0}}}
+    respx.post(blink.endpoint).mock(return_value=Response(200, json=mock_response))
+    quote = await blink.get_payment_quote(payment_request_1)
+    assert quote.checking_id == payment_request_1
+    assert quote.amount == Amount(Unit.msat, 1000)  # msat
+    assert quote.fee == Amount(Unit.msat, MINIMUM_FEE_MSAT)  # msat