From 754f59707822bd84dde86baad0100e977380b767 Mon Sep 17 00:00:00 2001
From: tequ <git@tequ.dev>
Date: Tue, 7 Oct 2025 16:02:02 +0900
Subject: [PATCH] Support sfSponsorSignature autofilling in Simulate RPC

---
 src/test/rpc/Simulate_test.cpp      | 85 +++++++++++++++++++++++++++++
 src/xrpld/rpc/handlers/Simulate.cpp |  7 +++
 2 files changed, 92 insertions(+)

diff --git a/src/test/rpc/Simulate_test.cpp b/src/test/rpc/Simulate_test.cpp
index 0a36a8a841..b5c5a8428c 100644
--- a/src/test/rpc/Simulate_test.cpp
+++ b/src/test/rpc/Simulate_test.cpp
@@ -592,6 +592,91 @@ class Simulate_test : public beast::unit_test::suite
             // test without autofill
             testTx(env, tx, validateOutput);
         }
+
+        {
+            // autofill sponsor signature
+
+            auto validateOutput = [&](Json::Value const& resp,
+                                      Json::Value const& tx) {
+                auto result = resp[jss::result];
+                checkBasicReturnValidity(
+                    result, tx, 2, env.current()->fees().base);
+
+                BEAST_EXPECT(result[jss::engine_result] == "tesSUCCESS");
+                BEAST_EXPECT(result[jss::engine_result_code] == 0);
+                BEAST_EXPECT(
+                    result[jss::engine_result_message] ==
+                    "The simulated transaction would have been applied.");
+
+                if (BEAST_EXPECT(
+                        result.isMember(jss::meta) ||
+                        result.isMember(jss::meta_blob)))
+                {
+                    Json::Value const metadata = getJsonMetadata(result);
+
+                    if (BEAST_EXPECT(
+                            metadata.isMember(sfAffectedNodes.jsonName)))
+                    {
+                        BEAST_EXPECT(
+                            metadata[sfAffectedNodes.jsonName].size() == 2);
+
+                        auto node = metadata[sfAffectedNodes.jsonName][0u];
+                        if (BEAST_EXPECT(
+                                node.isMember(sfModifiedNode.jsonName)))
+                        {
+                            auto modifiedNode = node[sfModifiedNode];
+                            BEAST_EXPECT(
+                                modifiedNode[sfLedgerEntryType] ==
+                                "AccountRoot");
+                            auto previousFields =
+                                modifiedNode[sfPreviousFields];
+                            BEAST_EXPECT(
+                                !previousFields.isMember(sfBalance.jsonName));
+                        }
+
+                        auto node2 = metadata[sfAffectedNodes.jsonName][1u];
+                        if (BEAST_EXPECT(
+                                node2.isMember(sfModifiedNode.jsonName)))
+                        {
+                            auto modifiedNode = node2[sfModifiedNode];
+                            BEAST_EXPECT(
+                                modifiedNode[sfLedgerEntryType] ==
+                                "AccountRoot");
+
+                            auto previousFields =
+                                modifiedNode[sfPreviousFields];
+                            BEAST_EXPECT(
+                                previousFields.isMember(sfBalance.jsonName));
+                        }
+                    }
+                    BEAST_EXPECT(metadata[sfTransactionIndex.jsonName] == 0);
+                    BEAST_EXPECT(
+                        metadata[sfTransactionResult.jsonName] == "tesSUCCESS");
+                }
+            };
+
+            Account const sponsor("sponsor");
+            env.fund(XRP(10000), sponsor);
+            env.close();
+
+            Json::Value tx;
+
+            tx[jss::Account] = env.master.human();
+            tx[jss::TransactionType] = jss::AccountSet;
+            tx[sfDomain] = newDomain;
+            tx[sfSponsor.jsonName][sfAccount.jsonName] = sponsor.human();
+            tx[sfSponsor.jsonName][sfFlags.jsonName] = tfSponsorFee;
+            tx[sfSponsorSignature.jsonName] = Json::objectValue;
+
+            // test with autofill
+            testTx(env, tx, validateOutput);
+
+            tx[sfSponsorSignature.jsonName][sfTxnSignature.jsonName] = "";
+            tx[sfSponsorSignature.jsonName][sfSigningPubKey.jsonName] = "";
+
+            // test without autofill
+            testTx(env, tx, validateOutput);
+        }
     }
 
     void
diff --git a/src/xrpld/rpc/handlers/Simulate.cpp b/src/xrpld/rpc/handlers/Simulate.cpp
index 35cb7587d4..56e87d3d29 100644
--- a/src/xrpld/rpc/handlers/Simulate.cpp
+++ b/src/xrpld/rpc/handlers/Simulate.cpp
@@ -149,6 +149,13 @@ autofillTx(Json::Value& tx_json, RPC::JsonContext& context)
     if (auto error = autofillSignature(tx_json))
         return *error;
 
+    if (tx_json.isMember(sfSponsorSignature.jsonName))
+    {
+        if (auto error =
+                autofillSignature(tx_json[sfSponsorSignature.jsonName]))
+            return *error;
+    }
+
     if (!tx_json.isMember(jss::Sequence))
     {
         auto const seq = getAutofillSequence(tx_json, context);