From f8a8c2301cb4386ae1d9302fe7530f8ba92a0280 Mon Sep 17 00:00:00 2001
From: tequ <git@tequ.dev>
Date: Thu, 19 Mar 2026 14:33:55 +0900
Subject: [PATCH] fix M2

---
 .../tx/transactors/Sponsor/SponsorshipSet.cpp | 10 +++++--
 src/test/app/Sponsor_test.cpp                 | 29 +++++++++++++++++++
 2 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/src/libxrpl/tx/transactors/Sponsor/SponsorshipSet.cpp b/src/libxrpl/tx/transactors/Sponsor/SponsorshipSet.cpp
index 15e8d3b1b3..6a1d1822c6 100644
--- a/src/libxrpl/tx/transactors/Sponsor/SponsorshipSet.cpp
+++ b/src/libxrpl/tx/transactors/Sponsor/SponsorshipSet.cpp
@@ -210,9 +210,6 @@ SponsorshipSet::doApply()
 
     auto reserveSponsorAccSle = getTxReserveSponsor(view(), ctx_.tx);
 
-    if (feeAmount && (*feeAmount).xrp() > (*sponsorAccSle)[sfBalance])
-        return tecUNFUNDED;
-
     if (!sponsorObjSle)
     {
         // Create
@@ -225,6 +222,9 @@ SponsorshipSet::doApply()
 
         (*newSle)[sfOwner] = sponsorAccountID;
         (*newSle)[sfSponsee] = sponseeAccountID;
+        if (feeAmount && (*feeAmount).xrp() > (*sponsorAccSle)[sfBalance])
+            return tecUNFUNDED;
+
         if (feeAmount && *feeAmount > XRPAmount(0))
         {
             (*sponsorAccSle)[sfBalance] -= *feeAmount;
@@ -267,6 +267,10 @@ SponsorshipSet::doApply()
         auto const currentFeeAmount = (*sponsorObjSle)[~sfFeeAmount].value_or(XRPAmount(0));
         auto feeAmountDelta = XRPAmount(*feeAmount - currentFeeAmount);
 
+        if (feeAmountDelta > beast::zero &&
+            feeAmountDelta > (*sponsorAccSle)[sfBalance])
+            return tecUNFUNDED;
+
         // transfer feeAmount to ledger entry
         if (feeAmountDelta != beast::zero)
         {
diff --git a/src/test/app/Sponsor_test.cpp b/src/test/app/Sponsor_test.cpp
index 890e232487..a83362258b 100644
--- a/src/test/app/Sponsor_test.cpp
+++ b/src/test/app/Sponsor_test.cpp
@@ -214,6 +214,35 @@ public:
             fee(XRP(1)),
             ter(tesSUCCESS));
         env.close();
+
+        // delta-based balance check
+        // After create: sponsor balance ~ 0, feeAmount = XRP(1000)
+
+        // Decreasing feeAmount should succeed (refund, negative delta)
+        adjustAccountXRPBalance(env, sponsor, XRP(500));
+        env(sponsor::set_fee(sponsor, 0, XRP(800)),
+            sponsor::sponseeAcc(alice),
+            fee(XRP(1)),
+            ter(tesSUCCESS));
+        env.close();
+        // balance was 500, delta = 800-1000 = -200 (refund), balance = 500+200-1 = 699
+
+        // Increasing feeAmount within delta budget should succeed
+        adjustAccountXRPBalance(env, sponsor, XRP(500));
+        env(sponsor::set_fee(sponsor, 0, XRP(850)),
+            sponsor::sponseeAcc(alice),
+            fee(XRP(1)),
+            ter(tesSUCCESS));
+        env.close();
+        // balance was 500, delta = 850-800 = 50, balance = 500-50-1 = 449
+
+        // Increasing feeAmount where delta exceeds balance should fail
+        adjustAccountXRPBalance(env, sponsor, XRP(310));
+        env(sponsor::set_fee(sponsor, 0, XRP(1200)),
+            sponsor::sponseeAcc(alice),
+            fee(XRP(1)),
+            ter(tecUNFUNDED));
+        env.close();
     }
 
     void