taler-typescript-core

commit 017c67f81cb2ee4a67144fc3bc593a2188e690b5
parent 32122aae69e5d2712f29ea0df97ec77d9ca3a87e
Author: Florian Dold <florian@dold.me>
Date:   Fri,  7 Feb 2025 14:46:49 +0100

wallet-core: don't overspend when there is still a deposit fee allowance

Thanks for Theodor Straube for finding this bug and contributing a test
case.

Diffstat:
M
packages/taler-wallet-core/src/coinSelection.test.ts
 | 
47
+++++++++++++++++++++++++++++++++++++++++++++++
M
packages/taler-wallet-core/src/coinSelection.ts
 | 
6
+++++-

2 files changed, 52 insertions(+), 1 deletion(-)
diff --git a/packages/taler-wallet-core/src/coinSelection.test.ts b/packages/taler-wallet-core/src/coinSelection.test.ts
@@ -181,6 +181,7 @@ test("pay: select one coin to pay with fee", (t) => {
     customerWireFees: Amounts.parse("LOCAL:0.1"),
     wireFeeCoveredForExchange: new Set(["http://exchange.localhost/"]),
     lastDepositFee: Amounts.parse("LOCAL:0.1"),
+    totalDepositFees: Amounts.parse("LOCAL:0.1"),
   });
 });
 
@@ -452,3 +453,49 @@ test("demo: deposit max after withdraw raw 13", (t) => {
 
   // current wallet impl fee 0.14
 });
+
+test("overpay when remaining < depositFee", (t) => {
+  const instructedAmount = Amounts.parseOrThrow("LOCAL:2.1");
+  const tally = emptyTallyForPeerPayment({
+    instructedAmount,
+  });
+  tally.amountDepositFeeLimitRemaining = Amounts.parseOrThrow("LOCAL:0.5");
+
+  const coins = testing_selectGreedy(
+    {
+      wireFeesPerExchange: {},
+    },
+    createCandidates([
+      {
+        amount: "LOCAL:2" as AmountString,
+        numAvailable: 1,
+        depositFee: "LOCAL:0.2" as AmountString,
+        fromExchange: "http://exchange.localhost/",
+      },
+      {
+        amount: "LOCAL:1" as AmountString,
+        numAvailable: 1,
+        depositFee: "LOCAL:0.2" as AmountString,
+        fromExchange: "http://exchange.localhost/",
+      },
+    ]),
+    tally,
+  );
+
+  t.assert(coins != null);
+
+  t.deepEqual(coins, {
+    "hash0;32;http://exchange.localhost/": {
+      exchangeBaseUrl: "http://exchange.localhost/",
+      denomPubHash: "hash0",
+      maxAge: 32,
+      contributions: [Amounts.parseOrThrow("LOCAL:2")],
+    },
+    "hash1;32;http://exchange.localhost/": {
+      exchangeBaseUrl: "http://exchange.localhost/",
+      denomPubHash: "hash1",
+      maxAge: 32,
+      contributions: [Amounts.parseOrThrow("LOCAL:0.1")],
+    },
+  });
+});
diff --git a/packages/taler-wallet-core/src/coinSelection.ts b/packages/taler-wallet-core/src/coinSelection.ts
@@ -650,6 +650,9 @@ function selectGreedy(
       i < denom.numAvailable && Amounts.isNonZero(tally.amountPayRemaining);
       i++
     ) {
+      // Save the allowance *before* tallying.
+      const depositFeeAllowance = tally.amountDepositFeeLimitRemaining;
+
       tallyFees(
         tally,
         req.wireFeesPerExchange,
@@ -659,7 +662,8 @@ function selectGreedy(
 
       const coinSpend = Amounts.max(
         Amounts.min(tally.amountPayRemaining, denom.value),
-        denom.feeDeposit,
+        // Underflow saturates to zero
+        Amounts.sub(denom.feeDeposit, depositFeeAllowance).amount,
       );
 
       tally.amountPayRemaining = Amounts.sub(