fix(swaps): failed payment for completed swap

This handles an edge case described below that causes xud to crash due
to an assertion error when a payment fails as taker for a swap that has
already completed, as described below.

1. Taker sends payment.
2. Maker sees payment, and sends payment to Taker.
3. Taker receives payment, and marks the swap as complete.
4. Maker fails to claim payment, so the attempt to send payment (from
step 1) fails.
5. Error handling logic when Taker's payment attempt doesn't go through
causes it to "fail" the deal.
6. But the swap actually succeeded - from Taker's perspective - in step
3, and Taker hits an assertion error trying to fail a deal that has
completed.

Fixes #1569.

Author: sangaman

Diff for: lib/swaps/Swaps.ts

@@ -759,6 +759,13 @@ class Swaps extends EventEmitter {
     try {
       await makerSwapClient.sendPayment(deal);
     } catch (err) {
+      // first we must handle the edge case where the maker has paid us but failed to claim our payment
+      // in this case, we've already marked the swap as having been paid and completed
+      if (deal.state !== SwapState.Completed) {
+        this.logger.warn(`maker was unable to claim payment for ${deal.rHash} but has already paid us`);
+        return;
+      }
+
       if (err.code === errorCodes.PAYMENT_REJECTED) {
         // if the maker rejected our payment, the swap failed due to an error on their side
         // and we don't need to send them a SwapFailedPacket
@@ -776,7 +783,6 @@ class Swaps extends EventEmitter {
           errorMessage: err.message,
         });
       }
-      return;
     }
   }
 

Diff for: test/simulation/custom-xud.patch

@@ -1,5 +1,5 @@
 diff --git a/lib/Xud.ts b/lib/Xud.ts
-index 810345d90..9585a2761 100644
+index b50acec47..bfd7a86d6 100644
 --- a/lib/Xud.ts
 +++ b/lib/Xud.ts
 @@ -87,6 +87,11 @@ class Xud extends EventEmitter {
@@ -36,7 +36,7 @@ index f077b3ca4..7398a97b4 100644
    }
 
 diff --git a/lib/swaps/Swaps.ts b/lib/swaps/Swaps.ts
-index fd7024fa2..d469ce7ac 100644
+index 5ee168fa9..f0a3b879d 100644
 --- a/lib/swaps/Swaps.ts
 +++ b/lib/swaps/Swaps.ts
 @@ -205,9 +205,28 @@ class Swaps extends EventEmitter {
@@ -110,9 +110,9 @@ index fd7024fa2..d469ce7ac 100644
 +        return;
 +      }
      } catch (err) {
-       if (err.code === errorCodes.PAYMENT_REJECTED) {
-         // if the maker rejected our payment, the swap failed due to an error on their side
-@@ -933,12 +972,29 @@ class Swaps extends EventEmitter {
+       // first we must handle the edge case where the maker has paid us but failed to claim our payment
+       // in this case, we've already marked the swap as having been paid and completed
+@@ -939,12 +978,29 @@ class Swaps extends EventEmitter {
 
        this.logger.debug('Executing maker code to resolve hash');
 
@@ -142,7 +142,7 @@ index fd7024fa2..d469ce7ac 100644
          deal.rPreimage = await swapClient.sendPayment(deal);
          return deal.rPreimage;
        } catch (err) {
-@@ -968,6 +1024,16 @@ class Swaps extends EventEmitter {
+@@ -974,6 +1030,16 @@ class Swaps extends EventEmitter {
        assert(htlcCurrency === undefined || htlcCurrency === deal.takerCurrency, 'incoming htlc does not match expected deal currency');
        this.logger.debug('Executing taker code to resolve hash');