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Include QUALITY messages in rebroadcast (#597)
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To improve censorship resistance and avoid lack of progress due to
partially disseminated QUALITY messages include them in rebroadcast.

Part of #591
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@masih
masih authored Aug 27, 2024
1 parent 0d6c270 commit 3cd2e35
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Showing 2 changed files with 89 additions and 20 deletions.
39 changes: 32 additions & 7 deletions gpbft/gpbft.go
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Original file line number Diff line number Diff line change
Expand Up @@ -1374,29 +1374,54 @@ func newBroadcastState() *broadcastState {
// record stores messages that are required should rebroadcast becomes necessary.
// The messages stored depend on the current progress of instance. If the
// instance progresses to DECIDE then only the decide message will be recorded.
// Otherwise, all messages except QUALITY from the current and previous rounds
// Otherwise, all messages including QUALITY from the current and previous rounds
// (i.e. the latest two rounds) are recorded.
//
// Note, the messages recorded are more than what FIL-00896 strictly requires at
// the benefit of less reliance on rebroadcast and reduction in the possibility
// of participants getting stuck.
//
// The rationale for including QUALITY messages as part of rebroadcast is to
// improve censorship resistance at the face of unreliable message delivery,
// which can ultimately result in lack of instance progress for extended periods
// of time. See:
// - https://github.com/filecoin-project/FIPs/discussions/809#discussioncomment-10409902
// - https://github.com/filecoin-project/FIPs/discussions/809#discussioncomment-10424988
func (bs *broadcastState) record(mb *MessageBuilder) {
switch mb.Payload.Step {
case DECIDE_PHASE:
// Clear all previous messages, as only DECIDE message need to be rebroadcasted.
// Note that DECIDE message is not associated to any round, and is always
// broadcasted using round zero.
bs.messagesByRound = make(map[uint64][]*MessageBuilder)
clear(bs.messagesByRound)
bs.messagesByRound[0] = []*MessageBuilder{mb}
case COMMIT_PHASE, PREPARE_PHASE, CONVERGE_PHASE:
case QUALITY_PHASE, CONVERGE_PHASE, PREPARE_PHASE, COMMIT_PHASE:
bs.messagesByRound[mb.Payload.Round] = append(bs.messagesByRound[mb.Payload.Round], mb)
// Remove all messages that are older than the latest two rounds.
// Remove all messages that are older than the latest two rounds, except QUALITY
// which only appears in round 0.
for round := int(mb.Payload.Round) - 2; round >= 0; round-- {
redundantRound := uint64(round)
delete(bs.messagesByRound, redundantRound)
switch redundantRound := uint64(round); redundantRound {
case 0:
var found bool
for i, mb := range bs.messagesByRound[0] {
if mb.Payload.Step == QUALITY_PHASE {
bs.messagesByRound[0] = bs.messagesByRound[0][i : i+1 : 1]
found = true
break
}
}
if !found {
log.Warn("No QUALITY message found for round 0 while trimming rebroadcast messages")
delete(bs.messagesByRound, redundantRound)
}
default:
delete(bs.messagesByRound, redundantRound)
}
}
default:
// No need to rebroadcast QUALITY messages.
// There should not be any message recorded with any other payload step. Warn if
// we see any.
log.Warnw("Unexpected payload step while recording broadcasted messages", "step", mb.Payload.Step)
}
}

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70 changes: 57 additions & 13 deletions gpbft/gpbft_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -273,12 +273,14 @@ func TestGPBFT_WithEvenPowerDistribution(t *testing.T) {
driver.RequireNoBroadcast()
// Trigger rebroadcast alarm.
driver.RequireDeliverAlarm()
// Expect rebroadcast of PREPARE only; no QUALITY message should be rebroadcasted.
// Expect rebroadcast of QUALITY and PREPARE messages.
driver.RequireQuality()
driver.RequirePrepare(baseChain)
driver.RequireNoBroadcast()
// Trigger alarm and expect immediate rebroadcast of PREMARE.
driver.RequireDeliverAlarm()
// Expect rebroadcast of PREPARE only; no QUALITY message should be rebroadcasted.
// Expect rebroadcast of QUALITY and PREPARE messages.
driver.RequireQuality()
driver.RequirePrepare(baseChain)
driver.RequireNoBroadcast()

Expand All @@ -302,7 +304,8 @@ func TestGPBFT_WithEvenPowerDistribution(t *testing.T) {
// Trigger rebroadcast alarm.
driver.RequireDeliverAlarm()

// Expect rebroadcast of PREPARE and COMMIT.
// Expect rebroadcast of QUALITY, PREPARE and COMMIT.
driver.RequireQuality()
driver.RequirePrepare(baseChain)
driver.RequireCommit(0, baseChain, evidenceOfPrepare)
driver.RequireNoBroadcast()
Expand Down Expand Up @@ -331,7 +334,8 @@ func TestGPBFT_WithEvenPowerDistribution(t *testing.T) {
// Trigger rebroadcast alarm.
driver.RequireDeliverAlarm()

// Expect rebroadcast of all messages from previous and current round (except QUALITY)
// Expect rebroadcast of all messages from previous and current round, including QUALITY.
driver.RequireQuality()
driver.RequirePrepare(baseChain)
driver.RequireCommit(0, baseChain, evidenceOfPrepare)
driver.RequireConverge(1, baseChain, evidenceOfPrepareForBase)
Expand All @@ -357,39 +361,79 @@ func TestGPBFT_WithEvenPowerDistribution(t *testing.T) {
// Trigger rebroadcast alarm.
driver.RequireDeliverAlarm()

// Expect rebroadcast of all messages from previous and current round, except
// Expect rebroadcast of all messages from previous and current round, including
// QUALITY.
driver.RequireQuality()
driver.RequirePrepare(baseChain)
driver.RequireCommit(0, baseChain, evidenceOfPrepare)
driver.RequireConverge(1, baseChain, evidenceOfPrepareForBase)
driver.RequirePrepareAtRound(1, baseChain, evidenceOfPrepareForBase)
driver.RequireCommit(1, baseChain, evidenceOfPrepareAtRound1)

// Deliver COMMIT at round 1 to facilitate progress to DECIDE.
// Facilitate skip to future round to assert rebroadcast only contains messages
// from the latest 2 rounds, plus QUALITY from round 0.

futureRoundProposal := instance.Proposal().Extend(tipSet4.Key)
evidenceOfPrepareAtRound76 := instance.NewJustification(76, gpbft.PREPARE_PHASE, futureRoundProposal, 0, 1)

// Send Prepare messages to facilitate weak quorum of prepare at future round.
driver.RequireDeliverMessage(&gpbft.GMessage{
Sender: 1,
Vote: instance.NewCommit(1, baseChain),
Justification: evidenceOfPrepareAtRound1,
Vote: instance.NewPrepare(77, futureRoundProposal),
Justification: evidenceOfPrepareAtRound76,
})
// Send Converge at future round to facilitate proposal with highest ticket.
driver.RequireDeliverMessage(&gpbft.GMessage{
Sender: 1,
Vote: instance.NewConverge(77, futureRoundProposal),
Justification: evidenceOfPrepareAtRound76,
Ticket: emulator.ValidTicket,
})
// Expect skip to round.
driver.RequireConverge(77, futureRoundProposal, evidenceOfPrepareAtRound76)
driver.RequirePrepareAtRound(77, futureRoundProposal, evidenceOfPrepareAtRound76)
driver.RequireCommit(77, futureRoundProposal, evidenceOfPrepareAtRound76)
// Expect no messages until the rebroadcast timeout has expired.
driver.RequireNoBroadcast()
// Trigger rebroadcast alarm.
driver.RequireDeliverAlarm()

// Assert that rebroadcast includes QUALITY and messages from round 77, but none
// from round 1 since the node should only retain messages from the latest two
// rounds, plus quality since it skiped round and has never seen round 76.
//
// See: https://github.com/filecoin-project/go-f3/issues/595
driver.RequireQuality()
driver.RequireConverge(77, futureRoundProposal, evidenceOfPrepareAtRound76)
driver.RequirePrepareAtRound(77, futureRoundProposal, evidenceOfPrepareAtRound76)
driver.RequireCommit(77, futureRoundProposal, evidenceOfPrepareAtRound76)
driver.RequireNoBroadcast()

// Deliver COMMIT at round 77 to facilitate progress to DECIDE.
driver.RequireDeliverMessage(&gpbft.GMessage{
Sender: 1,
Vote: instance.NewCommit(77, futureRoundProposal),
Justification: evidenceOfPrepareAtRound76,
})

// Expect DECIDE with strong evidence of COMMIT.
evidenceOfCommit := instance.NewJustification(1, gpbft.COMMIT_PHASE, baseChain, 0, 1)
driver.RequireDecide(baseChain, evidenceOfCommit)
evidenceOfCommit := instance.NewJustification(77, gpbft.COMMIT_PHASE, futureRoundProposal, 0, 1)
driver.RequireDecide(futureRoundProposal, evidenceOfCommit)

// Trigger alarm and expect immediate rebroadcast, because DECIDE phase has no
// phase timeout.
driver.RequireDeliverAlarm()

// Expect rebroadcast of only the DECIDE message.
driver.RequireDecide(baseChain, evidenceOfCommit)
driver.RequireDecide(futureRoundProposal, evidenceOfCommit)

// Deliver DECIDE to facilitate progress to decision.
driver.RequireDeliverMessage(&gpbft.GMessage{
Sender: 1,
Vote: instance.NewDecide(0, baseChain),
Vote: instance.NewDecide(0, futureRoundProposal),
Justification: evidenceOfCommit,
})
driver.RequireDecision(instance.ID(), baseChain)
driver.RequireDecision(instance.ID(), futureRoundProposal)
})
}

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