From ec5933df1daa0ad24f7ef46f21b5fa95e8be7aa9 Mon Sep 17 00:00:00 2001
From: michael1011 <me@michael1011.at>
Date: Wed, 15 Jan 2025 23:01:42 +0100
Subject: [PATCH] refactor: always renegotiate overpaid chain swaps

---
 lib/swap/EthereumNursery.ts                 |  2 ++
 lib/swap/OverpaymentProtector.ts            | 25 +++++++++++++++-----
 lib/swap/UtxoNursery.ts                     |  2 ++
 test/unit/swap/OverpaymentProtector.spec.ts | 26 ++++++++++++++++++---
 4 files changed, 46 insertions(+), 9 deletions(-)

diff --git a/lib/swap/EthereumNursery.ts b/lib/swap/EthereumNursery.ts
index 3d06f499..e2e8a57b 100644
--- a/lib/swap/EthereumNursery.ts
+++ b/lib/swap/EthereumNursery.ts
@@ -229,6 +229,7 @@ class EthereumNursery extends TypedEventEmitter<{
 
       if (
         this.overpaymentProtector.isUnacceptableOverpay(
+          swap.type,
           expectedAmount,
           actualAmountSat,
         )
@@ -349,6 +350,7 @@ class EthereumNursery extends TypedEventEmitter<{
 
       if (
         this.overpaymentProtector.isUnacceptableOverpay(
+          swap.type,
           expectedAmount,
           actualAmount,
         )
diff --git a/lib/swap/OverpaymentProtector.ts b/lib/swap/OverpaymentProtector.ts
index 14de7816..884a2837 100644
--- a/lib/swap/OverpaymentProtector.ts
+++ b/lib/swap/OverpaymentProtector.ts
@@ -1,5 +1,6 @@
 import { OverPaymentConfig } from '../Config';
 import Logger from '../Logger';
+import { SwapType } from '../consts/Enums';
 
 class OverpaymentProtector {
   private static readonly defaultConfig = {
@@ -25,12 +26,24 @@ class OverpaymentProtector {
     );
   }
 
-  public isUnacceptableOverpay = (expected: number, actual: number): boolean =>
-    actual - expected >
-    Math.max(
-      this.overPaymentExemptAmount,
-      actual * this.overPaymentMaxPercentage,
-    );
+  public isUnacceptableOverpay = (
+    type: SwapType,
+    expected: number,
+    actual: number,
+  ): boolean => {
+    // For chain swaps we renegotiate overpayments
+    if (type === SwapType.Chain) {
+      return actual > expected;
+    } else {
+      return (
+        actual - expected >
+        Math.max(
+          this.overPaymentExemptAmount,
+          actual * this.overPaymentMaxPercentage,
+        )
+      );
+    }
+  };
 }
 
 export default OverpaymentProtector;
diff --git a/lib/swap/UtxoNursery.ts b/lib/swap/UtxoNursery.ts
index 211331fa..a0c6d87b 100644
--- a/lib/swap/UtxoNursery.ts
+++ b/lib/swap/UtxoNursery.ts
@@ -178,6 +178,7 @@ class UtxoNursery extends TypedEventEmitter<{
 
     if (
       this.overpaymentProtector.isUnacceptableOverpay(
+        swap.type,
         swap.receivingData.expectedAmount,
         outputValue,
       )
@@ -770,6 +771,7 @@ class UtxoNursery extends TypedEventEmitter<{
 
       if (
         this.overpaymentProtector.isUnacceptableOverpay(
+          swap.type,
           updatedSwap.expectedAmount,
           outputValue,
         )
diff --git a/test/unit/swap/OverpaymentProtector.spec.ts b/test/unit/swap/OverpaymentProtector.spec.ts
index c75d2094..bc2ce1cf 100644
--- a/test/unit/swap/OverpaymentProtector.spec.ts
+++ b/test/unit/swap/OverpaymentProtector.spec.ts
@@ -1,5 +1,6 @@
 import { OverPaymentConfig } from '../../../lib/Config';
 import Logger from '../../../lib/Logger';
+import { SwapType } from '../../../lib/consts/Enums';
 import OverpaymentProtector from '../../../lib/swap/OverpaymentProtector';
 
 describe('OverpaymentProtector', () => {
@@ -68,7 +69,7 @@ describe('OverpaymentProtector', () => {
           new OverpaymentProtector(
             Logger.disabledLogger,
             config,
-          ).isUnacceptableOverpay(expected, actual),
+          ).isUnacceptableOverpay(SwapType.Submarine, expected, actual),
         ).toEqual(false);
       },
     );
@@ -85,7 +86,7 @@ describe('OverpaymentProtector', () => {
           new OverpaymentProtector(
             Logger.disabledLogger,
             config,
-          ).isUnacceptableOverpay(expected, actual),
+          ).isUnacceptableOverpay(SwapType.Submarine, expected, actual),
         ).toEqual(false);
       },
     );
@@ -102,9 +103,28 @@ describe('OverpaymentProtector', () => {
           new OverpaymentProtector(
             Logger.disabledLogger,
             config,
-          ).isUnacceptableOverpay(expected, actual),
+          ).isUnacceptableOverpay(SwapType.Submarine, expected, actual),
         ).toEqual(true);
       },
     );
+
+    test.each`
+      expected | actual | expectedResult
+      ${100}   | ${101} | ${true}
+      ${100}   | ${105} | ${true}
+      ${100}   | ${110} | ${true}
+      ${100}   | ${100} | ${false}
+    `(
+      'should not allow overpayment for chain swaps',
+      ({ expected, actual, expectedResult }) => {
+        expect(
+          new OverpaymentProtector(Logger.disabledLogger).isUnacceptableOverpay(
+            SwapType.Chain,
+            expected,
+            actual,
+          ),
+        ).toEqual(expectedResult);
+      },
+    );
   });
 });