ARCHIVE/rippled
1
0
Fork 0
mirror of https://github.com/XRPLF/rippled.git synced 2026-04-29 15:37:57 +00:00
Code Issues Packages Projects Releases Wiki Activity

fixReducedOffersV2: prevent offers from blocking order books: (#5032)

Browse Source 
Fixes issue #4937.

The fixReducedOffersV1 amendment fixed certain forms of offer
modification that could lead to blocked order books.  Reduced
offers can block order books if the effective quality of the
reduced offer is worse than the quality of the original offer
(from the perspective of the taker). It turns out that, for
small values, the quality of the reduced offer can be
significantly affected by the rounding mode used during
scaling computations.

Issue #4937 identified an additional code path that modified
offers in a way that could lead to blocked order books.  This
commit changes the rounding in that newly located code path so
the quality of the modified offer is never worse than the
quality of the offer as it was originally placed.

It is possible that additional ways of producing blocking
offers will come to light.  Therefore there may be a future
need for a V3 amendment.
This commit is contained in:
Scott Schurr
2024-06-13 14:57:12 -07:00
committed by GitHub
parent 263e984bf4
commit ae7ea33b75
12 changed files with 532 additions and 157 deletions
Download Patch File Download Diff File Expand all files Collapse all files

46
src/test/app/Flow_test.cpp
View File

@@ -506,7 +506,6 @@ struct Flow_test : public beast::unit_test::suite
// Without limits, the 0.4 USD would produce 1000 EUR in the forward
// pass. This test checks that the payment produces 1 EUR, as
// expected.
Env env(*this, features);
env.fund(XRP(10000), alice, bob, carol, gw);
env.trust(USD(1000), alice, bob, carol);
@@ -515,17 +514,52 @@ 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));
bool const reducedOffersV2 = features[fixReducedOffersV2];
// With reducedOffersV2, it is not allowed to accept less than
// USD(0.5) of bob's USD offer. If we provide 1 drop for less
// than USD(0.5), then the remaining fractional offer would
// block the order book.
TER const expectedTER =
reducedOffersV2 ? TER(tecPATH_DRY) : TER(tesSUCCESS);
env(pay(alice, carol, EUR(1)),
path(~XRP, ~EUR),
sendmax(USD(0.4)),
txflags(tfNoRippleDirect | tfPartialPayment));
txflags(tfNoRippleDirect | tfPartialPayment),
ter(expectedTER));
env.require(balance(carol, EUR(1)));
env.require(balance(bob, USD(0.4)));
env.require(balance(bob, EUR(999)));
if (!reducedOffersV2)
{
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);
}
}
}
}
@@ -1375,9 +1409,11 @@ struct Flow_test : public beast::unit_test::suite
{
using namespace jtx;
FeatureBitset const ownerPaysFee{featureOwnerPaysFee};
FeatureBitset const reducedOffersV2(fixReducedOffersV2);
testLineQuality(features);
testFalseDry(features);
testBookStep(features - reducedOffersV2);
testDirectStep(features);
testBookStep(features);
testDirectStep(features | ownerPaysFee);