From 31c526443037612a39c69fdfdd7ae63e4c8e17a4 Mon Sep 17 00:00:00 2001
From: Ori Newman <orinewman1@gmail.com>
Date: Tue, 10 Nov 2020 04:43:18 -0800
Subject: [PATCH] [NOD-1527] Allow to process headers while in missing utxo set
 sync state (#1018)

* [NOD-1527] Allow to process headers while in missing utxo set sync state

* [NOD-1527] Add isHeaderOnlyBlock function
---
 .../blockprocessor/validateandinsertblock.go  | 29 ++++++++++++-------
 1 file changed, 19 insertions(+), 10 deletions(-)

diff --git a/domain/consensus/processes/blockprocessor/validateandinsertblock.go b/domain/consensus/processes/blockprocessor/validateandinsertblock.go
index f94353538..89c7ff8f0 100644
--- a/domain/consensus/processes/blockprocessor/validateandinsertblock.go
+++ b/domain/consensus/processes/blockprocessor/validateandinsertblock.go
@@ -15,20 +15,25 @@ func (bp *blockProcessor) validateAndInsertBlock(block *externalapi.DomainBlock)
 
 	hash := consensusserialization.HeaderHash(block.Header)
 	if mode.State == externalapi.SyncStateMissingUTXOSet {
-		headerTipsPruningPoint, err := bp.consensusStateManager.HeaderTipsPruningPoint()
-		if err != nil {
-			return err
-		}
+		if isHeaderOnlyBlock(block) {
+			// Allow processing headers while in state SyncStateMissingUTXOSet
+			mode.State = externalapi.SyncStateHeadersFirst
+		} else {
+			headerTipsPruningPoint, err := bp.consensusStateManager.HeaderTipsPruningPoint()
+			if err != nil {
+				return err
+			}
 
-		if *hash != *headerTipsPruningPoint {
-			return errors.Errorf("cannot insert blocks other than the header pruning point "+
-				"while in %s mode", mode.State)
-		}
+			if *hash != *headerTipsPruningPoint {
+				return errors.Errorf("cannot insert blocks other than the header pruning point "+
+					"while in %s mode", mode.State)
+			}
 
-		mode.State = externalapi.SyncStateMissingBlockBodies
+			mode.State = externalapi.SyncStateMissingBlockBodies
+		}
 	}
 
-	if mode.State == externalapi.SyncStateHeadersFirst && len(block.Transactions) != 0 {
+	if mode.State == externalapi.SyncStateHeadersFirst && !isHeaderOnlyBlock(block) {
 		mode.State = externalapi.SyncStateNormal
 		log.Warnf("block %s contains transactions while validating in header only mode", hash)
 	}
@@ -138,6 +143,10 @@ func (bp *blockProcessor) updateReachabilityReindexRoot(oldHeadersSelectedTip *e
 	return bp.reachabilityManager.UpdateReindexRoot(headersSelectedTip)
 }
 
+func isHeaderOnlyBlock(block *externalapi.DomainBlock) bool {
+	return len(block.Transactions) == 0
+}
+
 func (bp *blockProcessor) checkBlockStatus(hash *externalapi.DomainHash, mode *externalapi.SyncInfo) error {
 	exists, err := bp.blockStatusStore.Exists(bp.databaseContext, hash)
 	if err != nil {