Added new settings "maxBlocksPerRequest" and "maxBlocksPerResponse", to control the number of blocks requested and returned by nodes when using GetBlocksMessage and BlocksMessage.

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

@@ -1245,6 +1245,10 @@ public class Controller extends Thread {
 				return;
 			}
 
+			// Ensure that we don't serve more blocks than the amount specified in the settings
+			// Serializing multiple blocks is very slow, so by default we are using a low limit
+			int blockLimitPerRequest = Settings.getInstance().getMaxBlocksPerResponse();
+
 			List<BlockData> blockDataList = new ArrayList<>();
 
 			// Attempt to serve from our cache of latest blocks
@@ -1256,7 +1260,7 @@ public class Controller extends Thread {
 			}
 
 			if (blockDataList.isEmpty()) {
-				int numberRequested = Math.min(Network.MAX_BLOCKS_PER_REPLY, getBlocksMessage.getNumberRequested());
+				int numberRequested = Math.min(blockLimitPerRequest, getBlocksMessage.getNumberRequested());
 
 				BlockData blockData = repository.getBlockRepository().fromReference(parentSignature);
 
@@ -1274,9 +1278,11 @@ public class Controller extends Thread {
 
 			List<Block> blocks = new ArrayList<>();
 			for (BlockData blockData : blockDataList) {
+				if (blocks.size() < blockLimitPerRequest) {
 					Block block = new Block(repository, blockData);
 					blocks.add(block);
 				}
+			}
 
 			Message blocksMessage = new BlocksMessage(blocks);
 			blocksMessage.setId(message.getId());

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

@@ -56,9 +56,6 @@ public class Synchronizer {
 	/** Maximum number of block signatures we ask from peer in one go */
 	private static final int MAXIMUM_REQUEST_SIZE = 200; // XXX move to Settings?
 
-	/** Maximum number of blocks we ask from peer in one go */
-	private static final int MAXIMUM_BLOCKS_REQUEST_SIZE = 1; // XXX move to Settings?
-
 	/** Number of retry attempts if a peer fails to respond with the requested data */
 	private static final int MAXIMUM_RETRIES = 1; // XXX move to Settings?
 
@@ -380,13 +377,17 @@ public class Synchronizer {
 		if (Settings.getInstance().isFastSyncEnabledWhenResolvingFork() && peer.getPeersVersion() >= PEER_VERSION_150) {
 			// This peer supports syncing multiple blocks at once via GetBlocksMessage, and it is enabled in the settings
 			int numberBlocksRequired = additionalPeerBlocksAfterCommonBlock - peerBlocks.size();
+
+			// Ensure that we don't request more blocks than specified in the settings
+			int maxBlocksPerRequest = Settings.getInstance().getMaxBlocksPerRequest();
+
 			while (numberBlocksRequired > 0) {
 				if (Controller.isStopping())
 					return SynchronizationResult.SHUTTING_DOWN;
 
 				byte[] latestPeerSignature = peerBlocks.isEmpty() ? commonBlockSig : peerBlocks.get(peerBlocks.size() - 1).getSignature();
 				int lastPeerHeight = commonBlockHeight + peerBlocks.size();
-				int numberOfBlocksToRequest = Math.min(numberBlocksRequired, MAXIMUM_BLOCKS_REQUEST_SIZE);
+				int numberOfBlocksToRequest = Math.min(numberBlocksRequired, maxBlocksPerRequest);
 
 				LOGGER.trace(String.format("Requesting %d block%s after height %d, sig %.8s",
 						numberOfBlocksToRequest, (numberOfBlocksToRequest != 1 ? "s" : ""), lastPeerHeight, Base58.encode(latestPeerSignature)));
@@ -600,11 +601,14 @@ public class Synchronizer {
 		// Fetch, and apply, blocks from peer
 		int maxBatchHeight = commonBlockHeight + SYNC_BATCH_SIZE;
 
+		// Ensure that we don't request more blocks than specified in the settings
+		int maxBlocksPerRequest = Settings.getInstance().getMaxBlocksPerRequest();
+
 		while (ourHeight < peerHeight && ourHeight < maxBatchHeight) {
 			if (Controller.isStopping())
 				return SynchronizationResult.SHUTTING_DOWN;
 
-			int numberRequested = Math.min(maxBatchHeight - ourHeight, MAXIMUM_BLOCKS_REQUEST_SIZE);
+			int numberRequested = Math.min(maxBatchHeight - ourHeight, maxBlocksPerRequest);
 
 			LOGGER.trace(String.format("Fetching %d blocks after height %d, sig %.8s from %s", numberRequested, ourHeight, Base58.encode(latestPeerSignature), peer));
 			List<Block> blocks = this.fetchBlocks(repository, peer, latestPeerSignature, numberRequested);

src/main/java/org/qortal/network/Network.java

@@ -89,7 +89,6 @@ public class Network {
 
 	public static final int MAX_SIGNATURES_PER_REPLY = 500;
 	public static final int MAX_BLOCK_SUMMARIES_PER_REPLY = 500;
-	public static final int MAX_BLOCKS_PER_REPLY = 500;
 
 	// Generate our node keys / ID
 	private final Ed25519PrivateKeyParameters edPrivateKeyParams = new Ed25519PrivateKeyParameters(new SecureRandom());

src/main/java/org/qortal/network/message/BlocksMessage.java

@@ -78,6 +78,7 @@ public class BlocksMessage extends Message {
 				bytes.write(Ints.toByteArray(block.getBlockData().getHeight()));
 				bytes.write(BlockTransformer.toBytes(block));
 			}
+			LOGGER.trace(String.format("Total length of %d blocks is %d bytes", this.blocks.size(), bytes.size()));
 
 			return bytes.toByteArray();
 		} catch (IOException e) {

src/main/java/org/qortal/settings/Settings.java

@@ -127,6 +127,10 @@ public class Settings {
 	private boolean fastSyncEnabled = false;
 	/** Whether to sync multiple blocks at once when the peer has a different chain */
 	private boolean fastSyncEnabledWhenResolvingFork = true;
+	/** Maximum number of blocks to request at once */
+	private int maxBlocksPerRequest = 1;
+	/** Maximum number of blocks this node will serve in a single response */
+	private int maxBlocksPerResponse = 5;
 
 	// Which blockchains this node is running
 	private String blockchainConfig = null; // use default from resources
@@ -449,6 +453,10 @@ public class Settings {
 		return this.fastSyncEnabledWhenResolvingFork;
 	}
 
+	public int getMaxBlocksPerRequest() { return this.maxBlocksPerRequest; }
+
+	public int getMaxBlocksPerResponse() { return this.maxBlocksPerResponse; }
+
 	public boolean isAutoUpdateEnabled() {
 		return this.autoUpdateEnabled;
 	}