blockchain/v2: respect fast_sync option (#4772)

Not thoroughly tested, but seems to work. Will do further testing as this is integrated with state sync.

Fixes #4688.

CHANGELOG_PENDING.md

@@ -45,4 +45,5 @@ Friendly reminder, we have a [bug bounty program](https://hackerone.com/tendermi
 ### BUG FIXES:
 
 - [blockchain/v2] [\#4761](https://github.com/tendermint/tendermint/pull/4761) Fix excessive CPU usage caused by spinning on closed channels (@erikgrinaker)
+- [blockchain/v2] Respect `fast_sync` option (@erikgrinaker)
 - [light] [\#4741](https://github.com/tendermint/tendermint/pull/4741) Correctly return  `ErrSignedHeaderNotFound` and `ErrValidatorSetNotFound` on corresponding RPC errors (@erikgrinaker)

blockchain/v2/reactor.go

@@ -129,6 +129,7 @@ type blockStore interface {
 type BlockchainReactor struct {
 	p2p.BaseReactor
 
+	fastSync  bool       // if true, enable fast sync on start
 	events    chan Event // XXX: Rename eventsFromPeers
 	scheduler *Routine
 	processor *Routine
@@ -156,7 +157,7 @@ type blockApplier interface {
 // XXX: unify naming in this package around tmState
 // XXX: V1 stores a copy of state as initialState, which is never mutated. Is that nessesary?
 func newReactor(state state.State, store blockStore, reporter behaviour.Reporter,
-	blockApplier blockApplier, bufferSize int) *BlockchainReactor {
+	blockApplier blockApplier, bufferSize int, fastSync bool) *BlockchainReactor {
 	scheduler := newScheduler(state.LastBlockHeight, time.Now())
 	pContext := newProcessorContext(store, blockApplier, state)
 	// TODO: Fix naming to just newProcesssor
@@ -170,6 +171,7 @@ func newReactor(state state.State, store blockStore, reporter behaviour.Reporter
 		store:     store,
 		reporter:  reporter,
 		logger:    log.NewNopLogger(),
+		fastSync:  fastSync,
 	}
 }
 
@@ -180,7 +182,7 @@ func NewBlockchainReactor(
 	store blockStore,
 	fastSync bool) *BlockchainReactor {
 	reporter := behaviour.NewMockReporter()
-	return newReactor(state, store, reporter, blockApplier, 1000)
+	return newReactor(state, store, reporter, blockApplier, 1000, fastSync)
 }
 
 // SetSwitch implements Reactor interface.
@@ -224,9 +226,11 @@ func (r *BlockchainReactor) SetLogger(logger log.Logger) {
 // Start implements cmn.Service interface
 func (r *BlockchainReactor) Start() error {
 	r.reporter = behaviour.NewSwitchReporter(r.BaseReactor.Switch)
-	go r.scheduler.start()
-	go r.processor.start()
-	go r.demux()
+	if r.fastSync {
+		go r.scheduler.start()
+		go r.processor.start()
+		go r.demux()
+	}
 	return nil
 }
 

blockchain/v2/reactor_test.go

@@ -156,7 +156,7 @@ func newTestReactor(p testReactorParams) *BlockchainReactor {
 		sm.SaveState(db, state)
 	}
 
-	r := newReactor(state, store, reporter, appl, p.bufferSize)
+	r := newReactor(state, store, reporter, appl, p.bufferSize, true)
 	logger := log.TestingLogger()
 	r.SetLogger(logger.With("module", "blockchain"))