From 186eda8fccc65e39d3ec40b2265b43bfad1f05a7 Mon Sep 17 00:00:00 2001
From: Scott Schurr <scott@ripple.com>
Date: Tue, 4 Jun 2024 16:03:16 -0700
Subject: [PATCH] [FOLD] Address review comments

---
 src/ripple/app/paths/impl/BookStep.cpp |  8 ++++++--
 src/test/app/Flow_test.cpp             | 23 +++++++++++++++++++++++
 2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/src/ripple/app/paths/impl/BookStep.cpp b/src/ripple/app/paths/impl/BookStep.cpp
index 1d7793625b8..e5e264761fb 100644
--- a/src/ripple/app/paths/impl/BookStep.cpp
+++ b/src/ripple/app/paths/impl/BookStep.cpp
@@ -670,8 +670,12 @@ limitStepIn(
         auto const inLmt =
             mulRatio(stpAmt.in, QUALITY_ONE, transferRateIn, /*roundUp*/ false);
         // It turns out we can prevent order book blocking by (strictly)
-        // rounding down the ceil_in() result.  This adjustment changes
-        // transaction outcomes, so it must be made under an amendment.
+        // rounding down the ceil_in() result.  By rounding down we guarantee
+        // that the quality of an offer left in the ledger is as good or
+        // better than the quality of the containing order book page.
+        //
+        // This adjustment changes transaction outcomes, so it must be made
+        // under an amendment.
         ofrAmt = offer.limitIn(ofrAmt, inLmt, rules, /* roundUp */ false);
         stpAmt.out = ofrAmt.out;
         ownerGives = mulRatio(
diff --git a/src/test/app/Flow_test.cpp b/src/test/app/Flow_test.cpp
index a4adecfa4cf..8884e490952 100644
--- a/src/test/app/Flow_test.cpp
+++ b/src/test/app/Flow_test.cpp
@@ -514,6 +514,7 @@ struct Flow_test : public beast::unit_test::suite
             env(pay(gw, alice, USD(1000)));
             env(pay(gw, bob, EUR(1000)));
 
+            Keylet const bobUsdOffer = keylet::offer(bob, env.seq(bob));
             env(offer(bob, USD(1), drops(2)), txflags(tfPassive));
             env(offer(bob, drops(1), EUR(1000)), txflags(tfPassive));
 
@@ -536,6 +537,28 @@ struct Flow_test : public beast::unit_test::suite
                 env.require(balance(carol, EUR(1)));
                 env.require(balance(bob, USD(0.4)));
                 env.require(balance(bob, EUR(999)));
+
+                // Show that bob's USD offer is now a blocker.
+                std::shared_ptr<SLE const> const usdOffer = env.le(bobUsdOffer);
+                if (BEAST_EXPECT(usdOffer))
+                {
+                    std::uint64_t const bookRate = [&usdOffer]() {
+                        // Extract the least significant 64 bits from the
+                        // book page.  That's where the quality is stored.
+                        std::string bookDirStr =
+                            to_string(usdOffer->at(sfBookDirectory));
+                        bookDirStr.erase(0, 48);
+                        return std::stoull(bookDirStr, nullptr, 16);
+                    }();
+                    std::uint64_t const actualRate = getRate(
+                        usdOffer->at(sfTakerGets), usdOffer->at(sfTakerPays));
+
+                    // We expect the actual rate of the offer to be worse
+                    // (larger) than the rate of the book page holding the
+                    // offer.  This is a defect which is corrected by
+                    // fixReducedOffersV2.
+                    BEAST_EXPECT(actualRate > bookRate);
+                }
             }
         }
     }