[FIX] Wallet sort outputs before swapping (#648)

* sort proofs

* outputs-ordering

* mypy fix

* clean up

* test if output amounts are sorted

* clean up test

---------

Co-authored-by: callebtc <93376500+callebtc@users.noreply.github.com>

cashu/wallet/wallet.py

@@ -456,7 +456,7 @@ class Wallet(
         # sort by increasing amount
         amounts_we_want.sort()
 
-        logger.debug(
+        logger.trace(
             f"Amounts we have: {[(a, amounts_we_have.count(a)) for a in set(amounts_we_have)]}"
         )
         amounts: list[int] = []
@@ -470,7 +470,7 @@ class Wallet(
             amounts += amount_split(remaining_amount)
         amounts.sort()
 
-        logger.debug(f"Amounts we want: {amounts}")
+        logger.trace(f"Amounts we want: {amounts}")
         if sum(amounts) != amount:
             raise Exception(f"Amounts do not sum to {amount}.")
 
@@ -643,7 +643,7 @@ class Wallet(
         proofs = self.add_witnesses_to_proofs(proofs)
 
         input_fees = self.get_fees_for_proofs(proofs)
-        logger.debug(f"Input fees: {input_fees}")
+        logger.trace(f"Input fees: {input_fees}")
         # create a suitable amounts to keep and send.
         keep_outputs, send_outputs = self.determine_output_amounts(
             proofs,
@@ -674,8 +674,22 @@ class Wallet(
         # potentially add witnesses to outputs based on what requirement the proofs indicate
         outputs = self.add_witnesses_to_outputs(proofs, outputs)
 
+        # sort outputs by amount, remember original order
+        sorted_outputs_with_indices = sorted(
+            enumerate(outputs), key=lambda p: p[1].amount
+        )
+        original_indices, sorted_outputs = zip(*sorted_outputs_with_indices)
+
         # Call swap API
-        promises = await super().split(proofs, outputs)
+        sorted_promises = await super().split(proofs, sorted_outputs)
+
+        # sort promises back to original order
+        promises = [
+            promise
+            for _, promise in sorted(
+                zip(original_indices, sorted_promises), key=lambda x: x[0]
+            )
+        ]
 
         # Construct proofs from returned promises (i.e., unblind the signatures)
         new_proofs = await self._construct_proofs(

tests/test_wallet_requests.py

@@ -0,0 +1,57 @@
+import json
+
+import pytest
+import pytest_asyncio
+import respx
+from httpx import Request, Response
+
+from cashu.core.base import BlindedSignature
+from cashu.core.crypto.b_dhke import hash_to_curve
+from cashu.wallet.wallet import Wallet
+from cashu.wallet.wallet import Wallet as Wallet1
+from tests.conftest import SERVER_ENDPOINT
+from tests.helpers import pay_if_regtest
+
+
+@pytest_asyncio.fixture(scope="function")
+async def wallet1(mint):
+    wallet1 = await Wallet1.with_db(
+        url=SERVER_ENDPOINT,
+        db="test_data/wallet1",
+        name="wallet1",
+    )
+    await wallet1.load_mint()
+    yield wallet1
+
+
+@pytest.mark.asyncio
+async def test_swap_outputs_are_sorted(wallet1: Wallet):
+    await wallet1.load_mint()
+    mint_quote = await wallet1.request_mint(16)
+    await pay_if_regtest(mint_quote.request)
+    await wallet1.mint(16, quote_id=mint_quote.quote, split=[16])
+    assert wallet1.balance == 16
+
+    test_url = f"{wallet1.url}/v1/swap"
+    key = hash_to_curve("test".encode("utf-8"))
+    mock_blind_signature = BlindedSignature(
+        id=wallet1.keyset_id,
+        amount=8,
+        C_=key.serialize().hex(),
+    )
+    mock_response_data = {"signatures": [mock_blind_signature.dict()]}
+    with respx.mock() as mock:
+        route = mock.post(test_url).mock(
+            return_value=Response(200, json=mock_response_data)
+        )
+        await wallet1.select_to_send(wallet1.proofs, 5)
+
+        assert route.called
+        assert route.call_count == 1
+        request: Request = route.calls[0].request
+        assert request.method == "POST"
+        assert request.url == test_url
+        request_data = json.loads(request.content.decode("utf-8"))
+        output_amounts = [o["amount"] for o in request_data["outputs"]]
+        # assert that output amounts are sorted
+        assert output_amounts == sorted(output_amounts)