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BallotProtocol.cpp
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BallotProtocol.cpp
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// Copyright 2014 Stellar Development Foundation and contributors. Licensed
// under the Apache License, Version 2.0. See the COPYING file at the root
// of this distribution or at http://www.apache.org/licenses/LICENSE-2.0
#include "BallotProtocol.h"
#include "Slot.h"
#include "crypto/Hex.h"
#include "crypto/SHA.h"
#include "lib/json/json.h"
#include "scp/LocalNode.h"
#include "scp/QuorumSetUtils.h"
#include "util/GlobalChecks.h"
#include "util/Logging.h"
#include "util/XDROperators.h"
#include "xdrpp/marshal.h"
#include <functional>
namespace stellar
{
using namespace std::placeholders;
// max number of transitions that can occur from processing one message
static const int MAX_ADVANCE_SLOT_RECURSION = 50;
BallotProtocol::BallotProtocol(Slot& slot)
: mSlot(slot)
, mHeardFromQuorum(false)
, mPhase(SCP_PHASE_PREPARE)
, mCurrentMessageLevel(0)
{
}
bool
BallotProtocol::isNewerStatement(NodeID const& nodeID, SCPStatement const& st)
{
auto oldp = mLatestEnvelopes.find(nodeID);
bool res = false;
if (oldp == mLatestEnvelopes.end())
{
res = true;
}
else
{
res = isNewerStatement(oldp->second.statement, st);
}
return res;
}
bool
BallotProtocol::isNewerStatement(SCPStatement const& oldst,
SCPStatement const& st)
{
bool res = false;
// total ordering described in SCP paper.
auto t = st.pledges.type();
// statement type (PREPARE < CONFIRM < EXTERNALIZE)
if (oldst.pledges.type() != t)
{
res = (oldst.pledges.type() < t);
}
else
{
// can't have duplicate EXTERNALIZE statements
if (t == SCPStatementType::SCP_ST_EXTERNALIZE)
{
res = false;
}
else if (t == SCPStatementType::SCP_ST_CONFIRM)
{
// sorted by (b, p, p', h) (p' = 0 implicitely)
auto const& oldC = oldst.pledges.confirm();
auto const& c = st.pledges.confirm();
int compBallot = compareBallots(oldC.ballot, c.ballot);
if (compBallot < 0)
{
res = true;
}
else if (compBallot == 0)
{
if (oldC.nPrepared == c.nPrepared)
{
res = (oldC.nH < c.nH);
}
else
{
res = (oldC.nPrepared < c.nPrepared);
}
}
}
else
{
// Lexicographical order between PREPARE statements:
// (b, p, p', h)
auto const& oldPrep = oldst.pledges.prepare();
auto const& prep = st.pledges.prepare();
int compBallot = compareBallots(oldPrep.ballot, prep.ballot);
if (compBallot < 0)
{
res = true;
}
else if (compBallot == 0)
{
compBallot = compareBallots(oldPrep.prepared, prep.prepared);
if (compBallot < 0)
{
res = true;
}
else if (compBallot == 0)
{
compBallot = compareBallots(oldPrep.preparedPrime,
prep.preparedPrime);
if (compBallot < 0)
{
res = true;
}
else if (compBallot == 0)
{
res = (oldPrep.nH < prep.nH);
}
}
}
}
}
return res;
}
void
BallotProtocol::recordEnvelope(SCPEnvelope const& env)
{
auto const& st = env.statement;
auto oldp = mLatestEnvelopes.find(st.nodeID);
if (oldp == mLatestEnvelopes.end())
{
mLatestEnvelopes.insert(std::make_pair(st.nodeID, env));
}
else
{
oldp->second = env;
}
mSlot.recordStatement(env.statement);
}
SCP::EnvelopeState
BallotProtocol::processEnvelope(SCPEnvelope const& envelope, bool self)
{
SCP::EnvelopeState res = SCP::EnvelopeState::INVALID;
dbgAssert(envelope.statement.slotIndex == mSlot.getSlotIndex());
SCPStatement const& statement = envelope.statement;
NodeID const& nodeID = statement.nodeID;
if (!isStatementSane(statement, self))
{
if (self)
{
CLOG(ERROR, "SCP") << "not sane statement from self, skipping "
<< " e: " << mSlot.getSCP().envToStr(envelope);
}
return SCP::EnvelopeState::INVALID;
}
if (!isNewerStatement(nodeID, statement))
{
if (self)
{
CLOG(ERROR, "SCP") << "stale statement from self, skipping "
<< " e: " << mSlot.getSCP().envToStr(envelope);
}
else
{
CLOG(TRACE, "SCP") << "stale statement, skipping "
<< " i: " << mSlot.getSlotIndex();
}
return SCP::EnvelopeState::INVALID;
}
auto validationRes = validateValues(statement);
if (validationRes != SCPDriver::kInvalidValue)
{
bool processed = false;
if (mPhase != SCP_PHASE_EXTERNALIZE)
{
if (validationRes == SCPDriver::kMaybeValidValue)
{
mSlot.setFullyValidated(false);
}
recordEnvelope(envelope);
processed = true;
advanceSlot(statement);
res = SCP::EnvelopeState::VALID;
}
if (!processed)
{
// note: this handles also our own messages
// in particular our final EXTERNALIZE message
if (mPhase == SCP_PHASE_EXTERNALIZE &&
mCommit->value == getWorkingBallot(statement).value)
{
recordEnvelope(envelope);
res = SCP::EnvelopeState::VALID;
}
else
{
if (self)
{
CLOG(ERROR, "SCP")
<< "externalize statement with invalid value from "
"self, skipping "
<< " e: " << mSlot.getSCP().envToStr(envelope);
}
res = SCP::EnvelopeState::INVALID;
}
}
}
else
{
// If the value is not valid, we just ignore it.
if (self)
{
CLOG(ERROR, "SCP") << "invalid value from self, skipping "
<< " e: " << mSlot.getSCP().envToStr(envelope);
}
else
{
CLOG(TRACE, "SCP") << "invalid value "
<< " i: " << mSlot.getSlotIndex();
}
res = SCP::EnvelopeState::INVALID;
}
return res;
}
bool
BallotProtocol::isStatementSane(SCPStatement const& st, bool self)
{
auto qSet = mSlot.getQuorumSetFromStatement(st);
const char* reason = nullptr;
bool res = qSet != nullptr && isQuorumSetSane(*qSet, false, &reason);
if (!res)
{
CLOG(DEBUG, "SCP") << "Invalid quorum set received";
if (reason != nullptr)
{
std::string msg(reason);
CLOG(DEBUG, "SCP") << msg;
}
return false;
}
switch (st.pledges.type())
{
case SCPStatementType::SCP_ST_PREPARE:
{
auto const& p = st.pledges.prepare();
// self is allowed to have b = 0 (as long as it never gets emitted)
bool isOK = self || p.ballot.counter > 0;
isOK = isOK &&
((!p.preparedPrime || !p.prepared) ||
(areBallotsLessAndIncompatible(*p.preparedPrime, *p.prepared)));
isOK =
isOK && (p.nH == 0 || (p.prepared && p.nH <= p.prepared->counter));
// c != 0 -> c <= h <= b
isOK = isOK && (p.nC == 0 || (p.nH != 0 && p.ballot.counter >= p.nH &&
p.nH >= p.nC));
if (!isOK)
{
CLOG(TRACE, "SCP") << "Malformed PREPARE message";
res = false;
}
}
break;
case SCPStatementType::SCP_ST_CONFIRM:
{
auto const& c = st.pledges.confirm();
// c <= h <= b
res = c.ballot.counter > 0;
res = res && (c.nH <= c.ballot.counter);
res = res && (c.nCommit <= c.nH);
if (!res)
{
CLOG(TRACE, "SCP") << "Malformed CONFIRM message";
}
}
break;
case SCPStatementType::SCP_ST_EXTERNALIZE:
{
auto const& e = st.pledges.externalize();
res = e.commit.counter > 0;
res = res && e.nH >= e.commit.counter;
if (!res)
{
CLOG(TRACE, "SCP") << "Malformed EXTERNALIZE message";
}
}
break;
default:
dbgAbort();
}
return res;
}
bool
BallotProtocol::abandonBallot(uint32 n)
{
CLOG(TRACE, "SCP") << "BallotProtocol::abandonBallot";
bool res = false;
Value v = mSlot.getLatestCompositeCandidate();
if (v.empty())
{
if (mCurrentBallot)
{
v = mCurrentBallot->value;
}
}
if (!v.empty())
{
if (n == 0)
{
res = bumpState(v, true);
}
else
{
res = bumpState(v, n);
}
}
return res;
}
bool
BallotProtocol::bumpState(Value const& value, bool force)
{
uint32 n;
if (!force && mCurrentBallot)
{
return false;
}
n = mCurrentBallot ? (mCurrentBallot->counter + 1) : 1;
return bumpState(value, n);
}
bool
BallotProtocol::bumpState(Value const& value, uint32 n)
{
if (mPhase != SCP_PHASE_PREPARE && mPhase != SCP_PHASE_CONFIRM)
{
return false;
}
SCPBallot newb;
newb.counter = n;
if (mValueOverride)
{
// we use the value that we saw confirmed prepared
// or that we at least voted to commit to
newb.value = *mValueOverride;
}
else
{
newb.value = value;
}
if (Logging::logTrace("SCP"))
CLOG(TRACE, "SCP") << "BallotProtocol::bumpState"
<< " i: " << mSlot.getSlotIndex()
<< " v: " << mSlot.getSCP().ballotToStr(newb);
bool updated = updateCurrentValue(newb);
if (updated)
{
emitCurrentStateStatement();
checkHeardFromQuorum();
}
return updated;
}
// updates the local state based to the specified ballot
// (that could be a prepared ballot) enforcing invariants
bool
BallotProtocol::updateCurrentValue(SCPBallot const& ballot)
{
if (mPhase != SCP_PHASE_PREPARE && mPhase != SCP_PHASE_CONFIRM)
{
return false;
}
bool updated = false;
if (!mCurrentBallot)
{
bumpToBallot(ballot, true);
updated = true;
}
else
{
dbgAssert(compareBallots(*mCurrentBallot, ballot) <= 0);
if (mCommit && !areBallotsCompatible(*mCommit, ballot))
{
return false;
}
int comp = compareBallots(*mCurrentBallot, ballot);
if (comp < 0)
{
bumpToBallot(ballot, true);
updated = true;
}
else if (comp > 0)
{
// this code probably changes with the final version
// of the conciliator
// this case may happen if the other nodes are not
// following the protocol (and we end up with a smaller value)
// not sure what is the best way to deal
// with this situation
CLOG(ERROR, "SCP")
<< "BallotProtocol::updateCurrentValue attempt to bump to "
"a smaller value";
// can't just bump to the value as we may already have
// statements at counter+1
return false;
}
}
if (updated)
{
CLOG(TRACE, "SCP") << "BallotProtocol::updateCurrentValue updated";
}
checkInvariants();
return updated;
}
void
BallotProtocol::bumpToBallot(SCPBallot const& ballot, bool check)
{
if (Logging::logTrace("SCP"))
CLOG(TRACE, "SCP") << "BallotProtocol::bumpToBallot"
<< " i: " << mSlot.getSlotIndex()
<< " b: " << mSlot.getSCP().ballotToStr(ballot);
// `bumpToBallot` should be never called once we committed.
dbgAssert(mPhase != SCP_PHASE_EXTERNALIZE);
if (check)
{
// We should move mCurrentBallot monotonically only
dbgAssert(!mCurrentBallot ||
compareBallots(ballot, *mCurrentBallot) >= 0);
}
bool gotBumped =
!mCurrentBallot || (mCurrentBallot->counter != ballot.counter);
if (!mCurrentBallot)
{
mSlot.getSCPDriver().startedBallotProtocol(mSlot.getSlotIndex(),
ballot);
}
mCurrentBallot = std::make_unique<SCPBallot>(ballot);
// invariant: h.value = b.value
if (mHighBallot && !areBallotsCompatible(*mCurrentBallot, *mHighBallot))
{
mHighBallot.reset();
}
if (gotBumped)
{
mHeardFromQuorum = false;
}
}
void
BallotProtocol::startBallotProtocolTimer()
{
std::chrono::milliseconds timeout =
mSlot.getSCPDriver().computeTimeout(mCurrentBallot->counter);
std::shared_ptr<Slot> slot = mSlot.shared_from_this();
std::function<void()>* func = new std::function<void()>;
*func = [slot]() { slot->getBallotProtocol().ballotProtocolTimerExpired(); };
mSlot.getSCPDriver().setupTimer(
mSlot.getSlotIndex(), Slot::BALLOT_PROTOCOL_TIMER, timeout, func);
}
void
BallotProtocol::stopBallotProtocolTimer()
{
std::shared_ptr<Slot> slot = mSlot.shared_from_this();
mSlot.getSCPDriver().setupTimer(mSlot.getSlotIndex(),
Slot::BALLOT_PROTOCOL_TIMER,
std::chrono::seconds::zero(), nullptr);
}
void
BallotProtocol::ballotProtocolTimerExpired()
{
abandonBallot(0);
}
SCPStatement
BallotProtocol::createStatement(SCPStatementType const& type)
{
SCPStatement statement;
checkInvariants();
statement.pledges.type(type);
switch (type)
{
case SCPStatementType::SCP_ST_PREPARE:
{
auto& p = statement.pledges.prepare();
p.quorumSetHash = getLocalNode()->getQuorumSetHash();
if (mCurrentBallot)
{
p.ballot = *mCurrentBallot;
}
if (mCommit)
{
p.nC = mCommit->counter;
}
if (mPrepared)
{
p.prepared.activate() = *mPrepared;
}
if (mPreparedPrime)
{
p.preparedPrime.activate() = *mPreparedPrime;
}
if (mHighBallot)
{
p.nH = mHighBallot->counter;
}
}
break;
case SCPStatementType::SCP_ST_CONFIRM:
{
auto& c = statement.pledges.confirm();
c.quorumSetHash = getLocalNode()->getQuorumSetHash();
c.ballot = *mCurrentBallot;
c.nPrepared = mPrepared->counter;
c.nCommit = mCommit->counter;
c.nH = mHighBallot->counter;
}
break;
case SCPStatementType::SCP_ST_EXTERNALIZE:
{
auto& e = statement.pledges.externalize();
e.commit = *mCommit;
e.nH = mHighBallot->counter;
e.commitQuorumSetHash = getLocalNode()->getQuorumSetHash();
}
break;
default:
dbgAbort();
}
return statement;
}
void
BallotProtocol::emitCurrentStateStatement()
{
SCPStatementType t;
switch (mPhase)
{
case SCP_PHASE_PREPARE:
t = SCP_ST_PREPARE;
break;
case SCP_PHASE_CONFIRM:
t = SCP_ST_CONFIRM;
break;
case SCP_PHASE_EXTERNALIZE:
t = SCP_ST_EXTERNALIZE;
break;
default:
dbgAbort();
}
SCPStatement statement = createStatement(t);
SCPEnvelope envelope = mSlot.createEnvelope(statement);
bool canEmit = (mCurrentBallot != nullptr);
// if we generate the same envelope, don't process it again
// this can occur when updating h in PREPARE phase
// as statements only keep track of h.n (but h.x could be different)
auto lastEnv = mLatestEnvelopes.find(mSlot.getSCP().getLocalNodeID());
if (lastEnv == mLatestEnvelopes.end() || !(lastEnv->second == envelope))
{
if (mSlot.processEnvelope(envelope, true) == SCP::EnvelopeState::VALID)
{
if (canEmit &&
(!mLastEnvelope || isNewerStatement(mLastEnvelope->statement,
envelope.statement)))
{
mLastEnvelope = std::make_shared<SCPEnvelope>(envelope);
// this will no-op if invoked from advanceSlot
// as advanceSlot consolidates all messages sent
sendLatestEnvelope();
}
}
else
{
// there is a bug in the application if it queued up
// a statement for itself that it considers invalid
throw std::runtime_error("moved to a bad state (ballot protocol)");
}
}
}
void
BallotProtocol::checkInvariants()
{
if (mCurrentBallot)
{
dbgAssert(mCurrentBallot->counter != 0);
}
if (mPrepared && mPreparedPrime)
{
dbgAssert(areBallotsLessAndIncompatible(*mPreparedPrime, *mPrepared));
}
if (mHighBallot)
{
dbgAssert(mCurrentBallot);
dbgAssert(areBallotsLessAndCompatible(*mHighBallot, *mCurrentBallot));
}
if (mCommit)
{
dbgAssert(mCurrentBallot);
dbgAssert(areBallotsLessAndCompatible(*mCommit, *mHighBallot));
dbgAssert(areBallotsLessAndCompatible(*mHighBallot, *mCurrentBallot));
}
switch (mPhase)
{
case SCP_PHASE_PREPARE:
break;
case SCP_PHASE_CONFIRM:
dbgAssert(mCommit);
break;
case SCP_PHASE_EXTERNALIZE:
dbgAssert(mCommit);
dbgAssert(mHighBallot);
break;
default:
dbgAbort();
}
}
std::set<SCPBallot>
BallotProtocol::getPrepareCandidates(SCPStatement const& hint)
{
std::set<SCPBallot> hintBallots;
switch (hint.pledges.type())
{
case SCP_ST_PREPARE:
{
auto const& prep = hint.pledges.prepare();
hintBallots.insert(prep.ballot);
if (prep.prepared)
{
hintBallots.insert(*prep.prepared);
}
if (prep.preparedPrime)
{
hintBallots.insert(*prep.preparedPrime);
}
}
break;
case SCP_ST_CONFIRM:
{
auto const& con = hint.pledges.confirm();
hintBallots.insert(SCPBallot(con.nPrepared, con.ballot.value));
hintBallots.insert(SCPBallot(UINT32_MAX, con.ballot.value));
}
break;
case SCP_ST_EXTERNALIZE:
{
auto const& ext = hint.pledges.externalize();
hintBallots.insert(SCPBallot(UINT32_MAX, ext.commit.value));
}
break;
default:
abort();
};
std::set<SCPBallot> candidates;
while (!hintBallots.empty())
{
auto last = --hintBallots.end();
SCPBallot topVote = *last;
hintBallots.erase(last);
auto const& val = topVote.value;
// find candidates that may have been prepared
for (auto const& e : mLatestEnvelopes)
{
SCPStatement const& st = e.second.statement;
switch (st.pledges.type())
{
case SCP_ST_PREPARE:
{
auto const& prep = st.pledges.prepare();
if (areBallotsLessAndCompatible(prep.ballot, topVote))
{
candidates.insert(prep.ballot);
}
if (prep.prepared &&
areBallotsLessAndCompatible(*prep.prepared, topVote))
{
candidates.insert(*prep.prepared);
}
if (prep.preparedPrime &&
areBallotsLessAndCompatible(*prep.preparedPrime, topVote))
{
candidates.insert(*prep.preparedPrime);
}
}
break;
case SCP_ST_CONFIRM:
{
auto const& con = st.pledges.confirm();
if (areBallotsCompatible(topVote, con.ballot))
{
candidates.insert(topVote);
if (con.nPrepared < topVote.counter)
{
candidates.insert(SCPBallot(con.nPrepared, val));
}
}
}
break;
case SCP_ST_EXTERNALIZE:
{
auto const& ext = st.pledges.externalize();
if (areBallotsCompatible(topVote, ext.commit))
{
candidates.insert(topVote);
}
}
break;
default:
abort();
}
}
}
return candidates;
}
bool
BallotProtocol::updateCurrentIfNeeded(SCPBallot const& h)
{
bool didWork = false;
if (!mCurrentBallot || compareBallots(*mCurrentBallot, h) < 0)
{
bumpToBallot(h, true);
didWork = true;
}
return didWork;
}
bool
BallotProtocol::attemptPreparedAccept(SCPStatement const& hint)
{
if (mPhase != SCP_PHASE_PREPARE && mPhase != SCP_PHASE_CONFIRM)
{
return false;
}
auto candidates = getPrepareCandidates(hint);
// see if we can accept any of the candidates, starting with the highest
for (auto cur = candidates.rbegin(); cur != candidates.rend(); cur++)
{
SCPBallot ballot = *cur;
if (mPhase == SCP_PHASE_CONFIRM)
{
// only consider the ballot if it may help us increase
// p (note: at this point, p ~ c)
if (!areBallotsLessAndCompatible(*mPrepared, ballot))
{
continue;
}
dbgAssert(areBallotsCompatible(*mCommit, ballot));
}
// if we already prepared this ballot, don't bother checking again
// if ballot <= p' ballot is neither a candidate for p nor p'
if (mPreparedPrime && compareBallots(ballot, *mPreparedPrime) <= 0)
{
continue;
}
if (mPrepared)
{
// if ballot is already covered by p, skip
if (areBallotsLessAndCompatible(ballot, *mPrepared))
{
continue;
}
// otherwise, there is a chance it increases p'
}
bool accepted = federatedAccept(
// checks if any node is voting for this ballot
[&ballot](SCPStatement const& st) {
bool res;
switch (st.pledges.type())
{
case SCP_ST_PREPARE:
{
auto const& p = st.pledges.prepare();
res = areBallotsLessAndCompatible(ballot, p.ballot);
}
break;
case SCP_ST_CONFIRM:
{
auto const& c = st.pledges.confirm();
res = areBallotsCompatible(ballot, c.ballot);
}
break;
case SCP_ST_EXTERNALIZE:
{
auto const& e = st.pledges.externalize();
res = areBallotsCompatible(ballot, e.commit);
}
break;
default:
res = false;
dbgAbort();
}
return res;
},
std::bind(&BallotProtocol::hasPreparedBallot, ballot, _1));
if (accepted)
{
return setPreparedAccept(ballot);
}
}
return false;
}
bool
BallotProtocol::setPreparedAccept(SCPBallot const& ballot)
{
if (Logging::logTrace("SCP"))
CLOG(TRACE, "SCP") << "BallotProtocol::setPreparedAccept"
<< " i: " << mSlot.getSlotIndex()
<< " b: " << mSlot.getSCP().ballotToStr(ballot);
// update our state
bool didWork = setPrepared(ballot);
// check if we also need to clear 'c'
if (mCommit && mHighBallot)
{
if ((mPrepared &&
areBallotsLessAndIncompatible(*mHighBallot, *mPrepared)) ||
(mPreparedPrime &&
areBallotsLessAndIncompatible(*mHighBallot, *mPreparedPrime)))
{
dbgAssert(mPhase == SCP_PHASE_PREPARE);
mCommit.reset();
didWork = true;
}
}
if (didWork)
{
mSlot.getSCPDriver().acceptedBallotPrepared(mSlot.getSlotIndex(),
ballot);
emitCurrentStateStatement();
}
return didWork;
}
bool
BallotProtocol::attemptPreparedConfirmed(SCPStatement const& hint)
{
if (mPhase != SCP_PHASE_PREPARE)
{
return false;
}
// check if we could accept this ballot as prepared
if (!mPrepared)
{
return false;
}
auto candidates = getPrepareCandidates(hint);
// see if we can accept any of the candidates, starting with the highest
SCPBallot newH;
bool newHfound = false;
auto cur = candidates.rbegin();
for (; cur != candidates.rend(); cur++)
{
SCPBallot ballot = *cur;
// only consider it if we can potentially raise h
if (mHighBallot && compareBallots(*mHighBallot, ballot) >= 0)
{
break;
}
bool ratified = federatedRatify(
std::bind(&BallotProtocol::hasPreparedBallot, ballot, _1));
if (ratified)
{
newH = ballot;
newHfound = true;
break;
}
}
bool res = false;
if (newHfound)
{
SCPBallot newC;
// now, look for newC (left as 0 if no update)
// step (3) from the paper
SCPBallot b = mCurrentBallot ? *mCurrentBallot : SCPBallot();
if (!mCommit &&
(!mPrepared || !areBallotsLessAndIncompatible(newH, *mPrepared)) &&
(!mPreparedPrime ||
!areBallotsLessAndIncompatible(newH, *mPreparedPrime)))
{
// continue where we left off (cur is at newH at this point)
for (; cur != candidates.rend(); cur++)
{
SCPBallot ballot = *cur;
if (compareBallots(ballot, b) < 0)
{
break;
}
// c and h must be compatible
if (!areBallotsLessAndCompatible(*cur, newH))
{
continue;
}
bool ratified = federatedRatify(
std::bind(&BallotProtocol::hasPreparedBallot, ballot, _1));
if (ratified)
{
newC = ballot;
}
else
{
break;
}
}
}