Add back LoanSet counterparty logic

Author: kuan121

xrpl4j-core/src/main/java/org/xrpl/xrpl4j/model/transactions/Batch.java

@@ -149,8 +149,9 @@ default BatchFlags flags() {
    * extra one. xrpl4j's own construction-time validation ({@link #checkBatchSigners()}) enforces only that no
    * required signer is missing, deferring the stricter extra-signer check to the server. Each inner contributes:
    * <ul>
-   *   <li>its <em>initiator</em> — its {@code Delegate} when one is present, otherwise its {@code Account}; and</li>
-   *   <li>its {@code Sponsor}, when the inner also carries a {@code SponsorSignature}.</li>
+   *   <li>its <em>initiator</em> — its {@code Delegate} when one is present, otherwise its {@code Account};</li>
+   *   <li>its {@code Sponsor}, when the inner also carries a {@code SponsorSignature}; and</li>
+   *   <li>a {@code LoanSet}'s {@code Counterparty}, when present.</li>
    * </ul>
    * The outer {@link #account()} is excluded throughout, because it authorises its own inner transactions with the
    * signature it puts on the Batch itself.
@@ -171,6 +172,10 @@ default Set<Address> requiredSigners() {
         if (innerTransaction.sponsorSignature().isPresent()) {
           innerTransaction.sponsor().ifPresent(signers::add);
         }
+        // A LoanSet's Counterparty must also sign.
+        if (innerTransaction instanceof LoanSet) {
+          ((LoanSet) innerTransaction).counterparty().ifPresent(signers::add);
+        }
         return signers.build();
       })
       .filter(address -> !address.equals(outerAccount))
@@ -346,8 +351,9 @@ default Batch checkBatchSigners() {
     );
 
     // Check 4: When BatchSigners is non-empty, every account required to sign an inner transaction must have a
-    // corresponding BatchSigner entry. The required-signer set (initiator and sponsor, with the outer account
-    // excluded) is derived by requiredSigners(), which is the single source of truth shared with fee computation.
+    // corresponding BatchSigner entry. The required-signer set (initiator, sponsor, and LoanSet counterparty, with
+    // the outer account excluded) is derived by requiredSigners(), which is the single source of truth shared with
+    // fee computation.
     if (!this.batchSigners().isEmpty()) {
       final Set<Address> actualSignerAccounts = this.batchSigners().stream()
         .map(wrapper -> wrapper.batchSigner().account())

xrpl4j-core/src/test/java/org/xrpl/xrpl4j/model/transactions/BatchTest.java

@@ -31,6 +31,7 @@
 import org.xrpl.xrpl4j.crypto.keys.Seed;
 import org.xrpl.xrpl4j.crypto.signing.Signature;
 import org.xrpl.xrpl4j.model.flags.BatchFlags;
+import org.xrpl.xrpl4j.model.flags.LoanSetFlags;
 import org.xrpl.xrpl4j.model.flags.PaymentFlags;
 import org.xrpl.xrpl4j.model.flags.SponsorFlags;
 import org.xrpl.xrpl4j.model.flags.TransactionFlags;
@@ -516,6 +517,63 @@ void testBatchSignerFromAccountIsNotSufficientWhenDelegateIsSet() {
       .hasMessageContaining(delegateAccount.value());
   }
 
+  @Test
+  void testBatchSignerRequiredForLoanSetCounterparty() {
+    // A LoanSet inner's Counterparty must also sign the Batch (in addition to the LoanSet Account).
+    Address innerAccount = Seed.ed25519Seed().deriveKeyPair().publicKey().deriveAddress();
+    Address counterpartyAccount = Seed.ed25519Seed().deriveKeyPair().publicKey().deriveAddress();
+    PublicKey innerKey = Seed.ed25519Seed().deriveKeyPair().publicKey();
+    PublicKey counterpartyKey = Seed.ed25519Seed().deriveKeyPair().publicKey();
+
+    List<RawTransactionWrapper> transactions = Lists.newArrayList(
+      RawTransactionWrapper.of(createInnerLoanSet(innerAccount, counterpartyAccount, UnsignedInteger.ONE)),
+      RawTransactionWrapper.of(createInnerPayment(ACCOUNT, UnsignedInteger.valueOf(2)))
+    );
+
+    // Should fail because BatchSigners is missing a signature from the Counterparty.
+    assertThatThrownBy(() -> Batch.builder()
+      .account(ACCOUNT)
+      .fee(XrpCurrencyAmount.ofDrops(100))
+      .sequence(UnsignedInteger.ONE)
+      .flags(BatchFlags.ALL_OR_NOTHING)
+      .rawTransactions(transactions)
+      .batchSigners(Lists.newArrayList(
+        BatchSignerWrapper.of(BatchSigner.builder()
+          .account(innerAccount)
+          .signingPublicKey(innerKey)
+          .transactionSignature(Signature.fromBase16("00112233"))
+          .build()
+        )))
+      .build()
+    ).isInstanceOf(IllegalArgumentException.class)
+      .hasMessageContaining("BatchSigners must contain signatures from all accounts with inner transactions")
+      .hasMessageContaining(counterpartyAccount.value());
+
+    // Should succeed once BatchSigners includes both the Account and the Counterparty.
+    Batch batch = Batch.builder()
+      .account(ACCOUNT)
+      .fee(XrpCurrencyAmount.ofDrops(100))
+      .sequence(UnsignedInteger.ONE)
+      .flags(BatchFlags.ALL_OR_NOTHING)
+      .rawTransactions(transactions)
+      .batchSigners(Lists.newArrayList(
+        BatchSignerWrapper.of(BatchSigner.builder()
+          .account(innerAccount)
+          .signingPublicKey(innerKey)
+          .transactionSignature(Signature.fromBase16("00112233"))
+          .build()
+        ),
+        BatchSignerWrapper.of(BatchSigner.builder()
+          .account(counterpartyAccount)
+          .signingPublicKey(counterpartyKey)
+          .transactionSignature(Signature.fromBase16("44556677"))
+          .build()
+        )))
+      .build();
+
+    assertThat(batch.batchSigners()).hasSize(2);
+  }
+
   @Test
   void testBatchWithOuterSignerAsOnlyInnerAccount() {
     // Create inner transactions all from the outer signer account
@@ -1251,6 +1309,18 @@ private Payment createInnerPayment(Address account, Address delegate, UnsignedIn
       .build();
   }
 
+  private LoanSet createInnerLoanSet(Address account, Address counterparty, UnsignedInteger sequence) {
+    return LoanSet.builder()
+      .account(account)
+      .counterparty(counterparty)
+      .fee(XrpCurrencyAmount.ofDrops(0))
+      .sequence(sequence)
+      .flags(LoanSetFlags.of(TransactionFlags.INNER_BATCH_TXN.getValue()))
+      .loanBrokerId(Hash256.of("C031EFE677CDEF1C5F43475B374A16F990EE184F76015CB7548D34B500F72BFB"))
+      .principalRequested(Amount.of("1000000"))
+      .build();
+  }
+
   private List<RawTransactionWrapper> createInnerTransactions(int count) {
     return IntStream.range(0, count)
       .mapToObj(i -> RawTransactionWrapper.of(