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Payment paths with a zero output step are dry (RIPD-1749):

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A tiny input amount to a payment step can cause this step to output zero. For
example, if a previous steps outputs a dust amount of 10^-80, and this step is a
IOU -> XRP offer, the offer may output zero drops. In this case, call the strand
dry. Before this patch, an error would be logged, the strand would be called
dry; in debug mode an assert triggered.

Note, this patch is not transaction breaking, as the caller did not user the ter
code. The caller only checked for success or failuer.

This patch addresses github issue issue reported here:
https://github.com/ripple/rippled/issues/2929
This commit is contained in:
seelabs
2019-05-09 10:16:06 -04:00
committed by Manoj doshi
parent 6f9e8dc720
commit 79a0cb096b
3 changed files with 87 additions and 9 deletions
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12
src/ripple/app/paths/impl/AmountSpec.h
View File

@@ -105,6 +105,18 @@ struct EitherAmount
else
iou = a.iou;
}
#ifndef NDEBUG
friend std::ostream&
operator<<(std::ostream& stream, EitherAmount const& amt)
{
if (amt.native)
stream << to_string(amt.xrp);
else
stream << to_string(amt.iou);
return stream;
}
#endif
};
template <class T>

49
src/ripple/app/paths/impl/StrandFlow.h
View File

@@ -144,14 +144,21 @@ flow (
*sb, *afView, ofrsToRm, EitherAmount (*maxIn));
limitStepOut = r.second;
if (strand[i]->isZero (r.second) ||
get<TInAmt> (r.first) != *maxIn)
if (strand[i]->isZero(r.second))
{
JLOG(j.trace()) << "First step found dry";
return {tecPATH_DRY, std::move(ofrsToRm)};
}
if (get<TInAmt> (r.first) != *maxIn)
{
// Something is very wrong
// throwing out the sandbox can only increase liquidity
// yet the limiting is still limiting
JLOG (j.fatal()) << "Re-executed limiting step failed";
assert (0);
JLOG(j.fatal())
<< "Re-executed limiting step failed. r.first: "
<< to_string(get<TInAmt>(r.first))
<< " maxIn: " << to_string(*maxIn);
assert(0);
return {telFAILED_PROCESSING, std::move (ofrsToRm)};
}
}
@@ -168,13 +175,25 @@ flow (
r = strand[i]->rev (*sb, *afView, ofrsToRm, stepOut);
limitStepOut = r.second;
if (strand[i]->isZero (r.second) ||
!strand[i]->equalOut (r.second, stepOut))
if (strand[i]->isZero(r.second))
{
// A tiny input amount can cause this step to output zero.
// I.e. 10^-80 IOU into an IOU -> XRP offer.
JLOG(j.trace()) << "Limiting step found dry";
return {tecPATH_DRY, std::move(ofrsToRm)};
}
if (!strand[i]->equalOut (r.second, stepOut))
{
// Something is very wrong
// throwing out the sandbox can only increase liquidity
// yet the limiting is still limiting
#ifndef NDEBUG
JLOG(j.fatal())
<< "Re-executed limiting step failed. r.second: "
<< r.second << " stepOut: " << stepOut;
#else
JLOG (j.fatal()) << "Re-executed limiting step failed";
#endif
assert (0);
return {telFAILED_PROCESSING, std::move (ofrsToRm)};
}
@@ -189,13 +208,25 @@ flow (
EitherAmount stepIn (limitStepOut);
for (auto i = limitingStep + 1; i < s; ++i)
{
auto const r = strand[i]->fwd (*sb, *afView, ofrsToRm, stepIn);
if (strand[i]->isZero (r.second) ||
!strand[i]->equalIn (r.first, stepIn))
auto const r = strand[i]->fwd(*sb, *afView, ofrsToRm, stepIn);
if (strand[i]->isZero(r.second))
{
// A tiny input amount can cause this step to output zero.
// I.e. 10^-80 IOU into an IOU -> XRP offer.
JLOG(j.trace()) << "Non-limiting step found dry";
return {tecPATH_DRY, std::move(ofrsToRm)};
}
if (!strand[i]->equalIn (r.first, stepIn))
{
// The limits should already have been found, so executing a strand forward
// from the limiting step should not find a new limit
#ifndef NDEBUG
JLOG(j.fatal())
<< "Re-executed forward pass failed. r.first: "
<< r.first << " stepIn: " << stepIn;
#else
JLOG (j.fatal()) << "Re-executed forward pass failed";
#endif
assert (0);
return {telFAILED_PROCESSING, std::move (ofrsToRm)};
}

35
src/test/app/Flow_test.cpp
View File

@@ -1248,6 +1248,40 @@ struct Flow_test : public beast::unit_test::suite
ter(temBAD_PATH));
}
void
testZeroOutputStep()
{
testcase("Zero Output Step");
using namespace jtx;
auto const alice = Account("alice");
auto const bob = Account("bob");
auto const carol = Account("carol");
auto const gw = Account("gw");
auto const USD = gw["USD"];
auto const EUR = gw["EUR"];
auto const features = supported_amendments();
Env env(*this, features);
env.fund(XRP(10000), alice, bob, carol, gw);
env.trust(USD(1000), alice, bob, carol);
env.trust(EUR(1000), alice, bob, carol);
env(pay(gw, alice, USD(100)));
env(pay(gw, bob, USD(100)));
env(pay(gw, bob, EUR(100)));
env.close();
env(offer(bob, USD(100), EUR(100)));
env(offer(bob, EUR(100), XRP(0.000001)));
env.close();
env(pay(alice, carol, XRP(1)),
path(~EUR, ~XRP),
sendmax(USD(1)),
txflags(tfPartialPayment),
ter(tecPATH_DRY));
}
void testWithFeats(FeatureBitset features)
{
using namespace jtx;
@@ -1276,6 +1310,7 @@ struct Flow_test : public beast::unit_test::suite
void run() override
{
testLimitQuality();
testZeroOutputStep();
testRIPD1443(true);
testRIPD1443(false);
testRIPD1449(true);