Avoid double-charging a LoanSet inner's counterparty in a Batch, since it is already counted among the BatchSigners

Author: kuan121

xrpl4j-core/src/main/java/org/xrpl/xrpl4j/model/client/fees/FeeUtils.java

@@ -197,7 +197,7 @@ public static ComputedNetworkFees computeFee(final FeeParams feeParams) {
     final long signatureUnits = signatureUnits(feeParams);
     final long feeUnits = transactionType == TransactionType.LOAN_PAY ?
       signatureUnits * feeParams.loanPaymentFeeIncrements().longValue() :
-      signatureUnits + surchargeUnits(feeParams, transaction);
+      signatureUnits + surchargeUnits(feeParams, transaction, false);
 
     return scaleByBaseFees(baseFees, feeUnits);
   }
@@ -229,7 +229,7 @@ private static ComputedNetworkFees computeFeeForBatch(
       } else {
         // An inner transaction never carries signatures or fee sponsorship, so it costs one base fee plus whatever
         // surcharge its type attracts.
-        feeUnits += 1L + surchargeUnits(feeParams, inner);
+        feeUnits += 1L + surchargeUnits(feeParams, inner, true);
       }
     }
 
@@ -284,10 +284,12 @@ private static long signatureUnits(final FeeParams feeParams) {
    * @param feeParams   The {@link FeeParams} being applied.
    * @param transaction The {@link Transaction} being priced, which may be an inner transaction of a Batch rather than
    *                    {@link FeeParams#transaction()} itself.
+   * @param isInner     {@code true} when {@code transaction} is a Batch inner, whose signatures are counted by the
+   *                    outer Batch rather than by the inner itself.
    *
    * @return A number of extra base fees, which is zero for most transaction types.
    */
-  private static long surchargeUnits(final FeeParams feeParams, final Transaction transaction) {
+  private static long surchargeUnits(final FeeParams feeParams, final Transaction transaction, final boolean isInner) {
     final TransactionType transactionType = transaction.transactionType();
 
     if (CONFIDENTIAL_MPT_TRANSACTION_TYPES.contains(transactionType)) {
@@ -297,7 +299,8 @@ private static long surchargeUnits(final FeeParams feeParams, final Transaction
       return fulfillmentUnits((EscrowFinish) transaction);
     }
     if (transactionType == TransactionType.LOAN_SET) {
-      return feeParams.counterpartySignatureCount().longValue();
+      // Charge the counterparty only for a standalone LoanSet; a Batch inner's is counted via the BatchSigners.
+      return isInner ? 0L : feeParams.counterpartySignatureCount().longValue();
     }
     return 0L;
   }

xrpl4j-core/src/test/java/org/xrpl/xrpl4j/model/client/fees/FeeUtilsTest.java

@@ -842,6 +842,15 @@ void batchPricesAMixOfConfidentialAndRegularInners() {
     );
   }
 
+  @Test
+  void batchDoesNotDoubleChargeALoanSetInnerCounterparty() {
+    // The counterparty is counted once among the batchSigners; the inner adds no counterparty surcharge, so 7 not 8.
+    // 2 outer + 3 batchSigners {bob, carol, dave} + (1 payment + 1 loanSet) inners
+    Batch batch = batch(ALICE, innerPayment(BOB, 1), innerLoanSet(CAROL, DAVE, 1));
+    assertThat(batch.requiredSigners()).containsExactlyInAnyOrder(BOB, CAROL, DAVE);
+    assertFeeUnits(paramsFor(batch), 7);
+  }
+
   @Test
   void standaloneConfidentialSendCostsTenBaseFees() {
     assertFeeUnits(paramsFor(innerConfidentialSend(ALICE, 1)), 10);
@@ -1057,6 +1066,19 @@ private LoanSet loanSet() {
       .build();
   }
 
+  private LoanSet innerLoanSet(final Address account, final Address counterparty, final int sequence) {
+    return LoanSet.builder()
+      .account(account)
+      .counterparty(counterparty)
+      .fee(XrpCurrencyAmount.ofDrops(0))
+      .sequence(UnsignedInteger.valueOf(sequence))
+      .flags(org.xrpl.xrpl4j.model.flags.LoanSetFlags.of(
+        org.xrpl.xrpl4j.model.flags.TransactionFlags.INNER_BATCH_TXN.getValue()))
+      .loanBrokerId(Hash256.of("C031EFE677CDEF1C5F43475B374A16F990EE184F76015CB7548D34B500F72BFB"))
+      .principalRequested(Amount.of("1000000"))
+      .build();
+  }
+
   private LoanPay loanPay() {
     return LoanPay.builder()
       .account(ALICE)