discovery: perform initial historical sync for pinned peers

discovery/sync_manager.go

@@ -266,7 +266,9 @@ func (m *SyncManager) syncerHandler() {
 			// For pinned syncers, we will immediately transition
 			// the peer into an active (pinned) sync state.
 			case isPinnedSyncer:
+				attemptHistoricalSync = true
 				s.setSyncType(PinnedSync)
+				s.setSyncState(syncerIdle)
 				m.pinnedActiveSyncers[s.cfg.peerPub] = s
 
 			// Regardless of whether the initial historical sync
@@ -331,7 +333,9 @@ func (m *SyncManager) syncerHandler() {
 			// keep track of the corresponding syncer to properly
 			// handle disconnects. We'll also use a signal to know
 			// when the historical sync completed.
+			if !isPinnedSyncer {
 				setInitialHistoricalSyncer(s)
+			}
 
 		// An existing peer has disconnected, so we'll tear down its
 		// corresponding GossipSyncer.

discovery/sync_manager_test.go

@@ -90,6 +90,8 @@ func TestSyncManagerNumActiveSyncers(t *testing.T) {
 		require.NoError(t, err)
 
 		s := assertSyncerExistence(t, syncMgr, peer)
+		assertTransitionToChansSynced(t, s, peer)
+		assertActiveGossipTimestampRange(t, peer)
 		assertSyncerStatus(t, s, chansSynced, PinnedSync)
 	}
 

discovery/syncer.go

@@ -115,6 +115,12 @@ const (
 	// AuthenticatedGossiper, and decide if we should forward them to our
 	// target peer based on its update horizon.
 	chansSynced
+
+	// syncerIdle is a state in which the gossip syncer can handle external
+	// requests to transition or perform historical syncs. It is used as the
+	// initial state for pinned syncers, as well as a fallthrough case for
+	// chansSynced allowing fully synced peers to facilitate requests.
+	syncerIdle
 )
 
 // String returns a human readable string describing the target syncerState.
@@ -135,6 +141,9 @@ func (s syncerState) String() string {
 	case chansSynced:
 		return "chansSynced"
 
+	case syncerIdle:
+		return "syncerIdle"
+
 	default:
 		return "UNKNOWN STATE"
 	}
@@ -592,10 +601,16 @@ func (g *GossipSyncer) channelGraphSyncer() {
 						g.cfg.peerPub, err)
 				}
 			}
-
 			// With our horizon set, we'll simply reply to any new
 			// messages or process any state transitions and exit if
 			// needed.
+			fallthrough
+
+		// Pinned peers will begin in this state, since they will
+		// immediately receive a request to perform a historical sync.
+		// Otherwise, we fall through after ending in chansSynced to
+		// facilitate new requests.
+		case syncerIdle:
 			select {
 			case req := <-g.syncTransitionReqs:
 				req.errChan <- g.handleSyncTransition(req)