Fixed bug which would cause other peers to not be compared against each other, if we had no blocks ourselves.

Again, this wouldn't have affected anything in 1.5.0 or before, but it will become more significant if we switch to same-length chain weight comparisons.

src/main/java/org/qortal/controller/Synchronizer.java

@@ -267,7 +267,7 @@ public class Synchronizer {
 
 					// Calculate the length of the shortest peer chain sharing this common block, including our chain
 					final int ourAdditionalBlocksAfterCommonBlock = ourHeight - commonBlockSummary.getHeight();
-					int minChainLength = this.calculateMinChainLength(commonBlockSummary, ourAdditionalBlocksAfterCommonBlock, peersSharingCommonBlock);
+					int minChainLength = this.calculateMinChainLengthOfPeers(peersSharingCommonBlock, commonBlockSummary);
 
 					// Fetch block summaries from each peer
 					for (Peer peer : peersSharingCommonBlock) {
@@ -325,10 +325,15 @@ public class Synchronizer {
 					final int ourSummariesRequired = Math.min(ourAdditionalBlocksAfterCommonBlock, MAXIMUM_REQUEST_SIZE);
 					LOGGER.trace(String.format("About to fetch our block summaries from %d to %d. Our height: %d", commonBlockSummary.getHeight() + 1, commonBlockSummary.getHeight() + ourSummariesRequired, ourHeight));
 					List<BlockSummaryData> ourBlockSummaries = repository.getBlockRepository().getBlockSummaries(commonBlockSummary.getHeight() + 1, commonBlockSummary.getHeight() + ourSummariesRequired);
-					if (ourBlockSummaries.isEmpty())
+					if (ourBlockSummaries.isEmpty()) {
 						LOGGER.debug(String.format("We don't have any block summaries so can't compare our chain against peers with this common block. We can still compare them against each other."));
-					else
+					}
+					else {
 						populateBlockSummariesMinterLevels(repository, ourBlockSummaries);
+						// Reduce minChainLength if we have less summaries
+						if (ourBlockSummaries.size() < minChainLength)
+							minChainLength = ourBlockSummaries.size();
+					}
 
 					// Create array to hold peers for comparison
 					List<Peer> superiorPeersForComparison = new ArrayList<>();
@@ -426,14 +431,14 @@ public class Synchronizer {
 		return commonBlocks;
 	}
 
-	private int calculateMinChainLength(BlockSummaryData commonBlockSummary, int ourAdditionalBlocksAfterCommonBlock, List<Peer> peersSharingCommonBlock) {
+	private int calculateMinChainLengthOfPeers(List<Peer> peersSharingCommonBlock, BlockSummaryData commonBlockSummary) {
 		// Calculate the length of the shortest peer chain sharing this common block, including our chain
-		int minChainLength = ourAdditionalBlocksAfterCommonBlock;
+		int minChainLength = 0;
 		for (Peer peer : peersSharingCommonBlock) {
 			final int peerHeight = peer.getChainTipData().getLastHeight();
 			final int peerAdditionalBlocksAfterCommonBlock = peerHeight - commonBlockSummary.getHeight();
 
-			if (peerAdditionalBlocksAfterCommonBlock < minChainLength)
+			if (peerAdditionalBlocksAfterCommonBlock < minChainLength || minChainLength == 0)
 				minChainLength = peerAdditionalBlocksAfterCommonBlock;
 		}
 		return minChainLength;