Change sync consensus to favour lower-value block sigs + other changes

API /addresses/{address} now returns lastReference taking unconfirmed into account.

Added DELETE /peers/known to remove all known peers from repository.

Added blockchain locking around Transaction methods like isValidUnconfirmed
as they (temporarily) update account lastReference.

Ditto getInvalidTransactions, etc.

src/main/java/org/qora/account/Account.java

@@ -171,10 +171,28 @@ public class Account {
 	 * @throws DataException
 	 */
 	public byte[] getUnconfirmedLastReference() throws DataException {
+		byte[] reference = getUnconfirmedLastReference(null);
+
+		if (reference == null)
+			// No unconfirmed transactions
+			reference = getLastReference();
+
+		return reference;
+	}
+
+	/**
+	 * Fetch last reference for account, considering unconfirmed transactions only, or return defaultReference.
+	 * <p>
+	 * NOTE: a repository savepoint may be used during execution.
+	 * 
+	 * @return byte[] reference, or defaultReference if no unconfirmed transactions for this account.
+	 * @throws DataException
+	 */
+	public byte[] getUnconfirmedLastReference(byte[] defaultReference) throws DataException {
 		// Newest unconfirmed transaction takes priority
 		List<TransactionData> unconfirmedTransactions = Transaction.getUnconfirmedTransactions(repository);
 
-		byte[] reference = null;
+		byte[] reference = defaultReference;
 
 		for (TransactionData transactionData : unconfirmedTransactions) {
 			String address = PublicKeyAccount.getAddress(transactionData.getCreatorPublicKey());
@@ -183,11 +201,7 @@ public class Account {
 				reference = transactionData.getSignature();
 		}
 
-		if (reference != null)
-			return reference;
-
-		// No unconfirmed transactions
-		return getLastReference();
+		return reference;
 	}
 
 	/**

src/main/java/org/qora/api/resource/AddressesResource.java

@@ -75,6 +75,13 @@ public class AddressesResource {
 			// Not found?
 			if (accountData == null)
 				accountData = new AccountData(address);
+			else {
+				// Unconfirmed transactions could update lastReference
+				Account account = new Account(repository, address);
+				byte[] unconfirmedLastReference = account.getUnconfirmedLastReference(null);
+				if (unconfirmedLastReference != null)
+					accountData.setReference(unconfirmedLastReference);
+			}
 
 			return accountData;
 		} catch (ApiException e) {

src/main/java/org/qora/api/resource/AdminResource.java

@@ -26,6 +26,12 @@ import javax.ws.rs.Produces;
 import javax.ws.rs.core.Context;
 import javax.ws.rs.core.MediaType;
 
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+import org.apache.logging.log4j.core.config.LoggerConfig;
+import org.apache.logging.log4j.core.LoggerContext;
+import org.apache.logging.log4j.core.appender.FileAppender;
+import org.apache.logging.log4j.core.appender.RollingFileAppender;
 import org.qora.account.PrivateKeyAccount;
 import org.qora.api.ApiError;
 import org.qora.api.ApiErrors;

src/main/java/org/qora/api/resource/PeersResource.java

@@ -217,4 +217,37 @@ public class PeersResource {
 		}
 	}
 
+	@DELETE
+	@Path("/known")
+	@Operation(
+		summary = "Remove any known peers from database",
+		responses = {
+			@ApiResponse(
+				description = "true if any peers were removed, false if there were no peers to delete",
+				content = @Content(
+					schema = @Schema(
+						type = "string"
+					)
+				)
+			)
+		}
+	)
+	@ApiErrors({
+		ApiError.INVALID_DATA, ApiError.REPOSITORY_ISSUE
+	})
+	public String removeKnownPeers(String address) {
+		Security.checkApiCallAllowed(request);
+
+		try (final Repository repository = RepositoryManager.getRepository()) {
+			int numDeleted = repository.getNetworkRepository().deleteAllPeers();
+			repository.saveChanges();
+
+			return numDeleted != 0 ? "true" : "false";
+		} catch (ApiException e) {
+			throw e;
+		} catch (DataException e) {
+			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.REPOSITORY_ISSUE, e);
+		}
+	}
+
 }

src/main/java/org/qora/block/BlockGenerator.java

@@ -4,7 +4,7 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
 import java.util.Random;
-import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
 import java.util.stream.Collectors;
 
 import org.apache.logging.log4j.LogManager;
@@ -93,7 +93,7 @@ public class BlockGenerator extends Thread {
 				}
 
 				// Make sure we're the only thread modifying the blockchain
-				Lock blockchainLock = Controller.getInstance().getBlockchainLock();
+				ReentrantLock blockchainLock = Controller.getInstance().getBlockchainLock();
 				if (blockchainLock.tryLock())
 					generation: try {
 						List<Block> goodBlocks = new ArrayList<>();
@@ -244,30 +244,30 @@ public class BlockGenerator extends Thread {
 		Block newBlock = new Block(repository, previousBlockData, generator);
 
 		// Make sure we're the only thread modifying the blockchain
-		Lock blockchainLock = Controller.getInstance().getBlockchainLock();
-		if (blockchainLock.tryLock())
-			try {
-				// Delete invalid transactions
-				deleteInvalidTransactions(repository);
+		ReentrantLock blockchainLock = Controller.getInstance().getBlockchainLock();
+		blockchainLock.lock();
+		try {
+			// Delete invalid transactions
+			deleteInvalidTransactions(repository);
 
-				// Add unconfirmed transactions
-				addUnconfirmedTransactions(repository, newBlock);
+			// Add unconfirmed transactions
+			addUnconfirmedTransactions(repository, newBlock);
 
-				// Sign to create block's signature
-				newBlock.sign();
+			// Sign to create block's signature
+			newBlock.sign();
 
-				// Is newBlock still valid?
-				ValidationResult validationResult = newBlock.isValid();
-				if (validationResult != ValidationResult.OK)
-					throw new IllegalStateException(
-							"Valid, generated block now invalid '" + validationResult.name() + "' after adding unconfirmed transactions?");
+			// Is newBlock still valid?
+			ValidationResult validationResult = newBlock.isValid();
+			if (validationResult != ValidationResult.OK)
+				throw new IllegalStateException(
+						"Valid, generated block now invalid '" + validationResult.name() + "' after adding unconfirmed transactions?");
 
-				// Add to blockchain
-				newBlock.process();
-				repository.saveChanges();
-			} finally {
-				blockchainLock.unlock();
-			}
+			// Add to blockchain
+			newBlock.process();
+			repository.saveChanges();
+		} finally {
+			blockchainLock.unlock();
+		}
 	}
 
 }

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

@@ -10,7 +10,6 @@ import java.time.format.DateTimeFormatter;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Properties;
-import java.util.concurrent.locks.Lock;
 import java.util.concurrent.locks.ReentrantLock;
 
 import org.apache.logging.log4j.LogManager;
@@ -66,7 +65,7 @@ public class Controller extends Thread {
 	private final long buildTimestamp;
 
 	/** Lock for only allowing one blockchain-modifying codepath at a time. e.g. synchronization or newly generated block. */
-	private final Lock blockchainLock;
+	private final ReentrantLock blockchainLock;
 
 	private Controller() {
 		Properties properties = new Properties();
@@ -126,7 +125,7 @@ public class Controller extends Thread {
 		}
 	}
 
-	public Lock getBlockchainLock() {
+	public ReentrantLock getBlockchainLock() {
 		return this.blockchainLock;
 	}
 

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

@@ -3,7 +3,7 @@ package org.qora.controller;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
-import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
 
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
@@ -48,7 +48,7 @@ public class Synchronizer {
 	public boolean synchronize(Peer peer) {
 		// Make sure we're the only thread modifying the blockchain
 		// If we're already synchronizing with another peer then this will also return fast
-		Lock blockchainLock = Controller.getInstance().getBlockchainLock();
+		ReentrantLock blockchainLock = Controller.getInstance().getBlockchainLock();
 		if (blockchainLock.tryLock())
 			try {
 				try (final Repository repository = RepositoryManager.getRepository()) {
@@ -67,6 +67,8 @@ public class Synchronizer {
 
 						// First signature is common block
 						BlockData commonBlockData = this.repository.getBlockRepository().fromSignature(signatures.get(0));
+						int commonBlockHeight = commonBlockData.getHeight();
+						LOGGER.info(String.format("Common block with peer %s is at height %d", peer, commonBlockHeight));
 						signatures.remove(0);
 
 						// If common block is too far behind us then we're on massively different forks so give up.
@@ -76,6 +78,42 @@ public class Synchronizer {
 							return false;
 						}
 
+						// If we have blocks after common block then decide whether we want to sync (lowest block signature wins)
+						for (int height = commonBlockHeight + 1; height <= peerHeight && height <= this.ourHeight; ++height) {
+							int sigIndex = height - commonBlockHeight - 1;
+
+							// Do we need more signatures?
+							if (signatures.size() - 1 < sigIndex) {
+								// Grab more signatures
+								byte[] previousSignature = sigIndex == 0 ? commonBlockData.getSignature() : signatures.get(sigIndex - 1);
+								List<byte[]> moreSignatures = this.getBlockSignatures(peer, previousSignature, MAXIMUM_BLOCK_STEP);
+								if (moreSignatures == null || moreSignatures.isEmpty()) {
+									LOGGER.info(String.format("Peer %s failed to respond with more block signatures after height %d", peer, height - 1));
+									return false;
+								}
+
+								signatures.addAll(moreSignatures);
+							}
+
+							byte[] ourSignature = this.repository.getBlockRepository().fromHeight(height).getSignature();
+							byte[] peerSignature = signatures.get(sigIndex);
+
+							for (int i = 0; i < ourSignature.length; ++i) {
+								/*
+								 * If our byte is lower, we don't synchronize with this peer,
+								 * if their byte is lower, check next height,
+								 * (if bytes are equal, try next byte).
+								 */
+								if (ourSignature[i] < peerSignature[i]) {
+									LOGGER.info(String.format("Not synchronizing with peer %s as we have better block at height %d", peer, height));
+									return false;
+								}
+
+								if (peerSignature[i] < ourSignature[i])
+									break;
+							}
+						}
+
 						if (this.ourHeight > commonBlockData.getHeight()) {
 							// Unwind to common block (unless common block is our latest block)
 							LOGGER.debug(String.format("Orphaning blocks back to height %d", commonBlockData.getHeight()));
@@ -217,6 +255,7 @@ public class Synchronizer {
 			BlockData blockData = this.repository.getBlockRepository().fromSignature(blockSignatures.get(i));
 
 			if (blockData != null) {
+				// Note: index i isn't cleared: List.subList is fromIndex inclusive to toIndex exclusive
 				blockSignatures.subList(0, i).clear();
 				break;
 			}

src/main/java/org/qora/repository/NetworkRepository.java

@@ -12,4 +12,6 @@ public interface NetworkRepository {
 
 	public int delete(PeerData peerData) throws DataException;
 
+	public int deleteAllPeers() throws DataException;
+
 }

src/main/java/org/qora/repository/hsqldb/HSQLDBNetworkRepository.java

@@ -84,4 +84,12 @@ public class HSQLDBNetworkRepository implements NetworkRepository {
 		}
 	}
 
+	@Override
+	public int deleteAllPeers() throws DataException {
+		try {
+			return this.repository.delete("Peers");
+		} catch (SQLException e) {
+			throw new DataException("Unable to delete peers from repository", e);
+		}
+	}
 }

src/main/java/org/qora/repository/hsqldb/HSQLDBRepository.java

@@ -339,6 +339,18 @@ public class HSQLDBRepository implements Repository {
 		}
 	}
 
+	/**
+	 * Delete all rows from database table.
+	 * 
+	 * @param tableName
+	 * @throws SQLException
+	 */
+	public int delete(String tableName) throws SQLException {
+		try (PreparedStatement preparedStatement = this.connection.prepareStatement("DELETE FROM " + tableName)) {
+			return this.checkedExecuteUpdateCount(preparedStatement);
+		}
+	}
+
 	/**
 	 * Returns additional SQL "LIMIT" and "OFFSET" clauses.
 	 * <p>

src/main/java/org/qora/transaction/Transaction.java

@@ -8,6 +8,7 @@ import java.util.Arrays;
 import java.util.Comparator;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.locks.ReentrantLock;
 
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
@@ -15,6 +16,7 @@ import org.qora.account.Account;
 import org.qora.account.PrivateKeyAccount;
 import org.qora.account.PublicKeyAccount;
 import org.qora.block.BlockChain;
+import org.qora.controller.Controller;
 import org.qora.data.block.BlockData;
 import org.qora.data.group.GroupData;
 import org.qora.data.transaction.TransactionData;
@@ -474,6 +476,8 @@ public abstract class Transaction {
 	 * unconfirmed transactions, and hence uses a repository savepoint.
 	 * <p>
 	 * This is not done normally because we don't want unconfirmed transactions affecting validity of transactions already included in a block.
+	 * <p>
+	 * Also temporarily acquires blockchain lock.
 	 * 
 	 * @return true if transaction can be added to unconfirmed transactions, false otherwise
 	 * @throws DataException
@@ -493,6 +497,14 @@ public abstract class Transaction {
 		if (!hasMinimumFee() || !hasMinimumFeePerByte())
 			return ValidationResult.INSUFFICIENT_FEE;
 
+		/*
+		 * We have to grab the blockchain lock because we're updating
+		 * when we fake the creator's last reference,
+		 * even though we throw away the update when we rollback the
+		 * savepoint.
+		 */
+		ReentrantLock blockchainLock = Controller.getInstance().getBlockchainLock();
+		blockchainLock.lock();
 		repository.setSavepoint();
 		try {
 			PublicKeyAccount creator = this.getCreator();
@@ -513,6 +525,7 @@ public abstract class Transaction {
 			return result;
 		} finally {
 			repository.rollbackToSavepoint();
+			blockchainLock.unlock();
 		}
 	}
 
@@ -558,10 +571,12 @@ public abstract class Transaction {
 	}
 
 	/**
-	 * Returns sorted, unconfirmed transactions, deleting invalid.
+	 * Returns sorted, unconfirmed transactions, excluding invalid.
 	 * <p>
 	 * NOTE: temporarily updates accounts' lastReference to that from
 	 * unconfirmed transactions, hence uses a repository savepoint.
+	 * <p>
+	 * Also temporarily acquires blockchain lock.
 	 * 
 	 * @return sorted unconfirmed transactions
 	 * @throws DataException
@@ -573,6 +588,14 @@ public abstract class Transaction {
 
 		unconfirmedTransactions.sort(getDataComparator());
 
+		/*
+		 * We have to grab the blockchain lock because we're updating
+		 * when we fake the creator's last reference,
+		 * even though we throw away the update when we rollback the
+		 * savepoint.
+		 */
+		ReentrantLock blockchainLock = Controller.getInstance().getBlockchainLock();
+		blockchainLock.lock();
 		repository.setSavepoint();
 		try {
 			for (int i = 0; i < unconfirmedTransactions.size(); ++i) {
@@ -587,11 +610,23 @@ public abstract class Transaction {
 		} finally {
 			// Throw away temporary updates to account lastReference
 			repository.rollbackToSavepoint();
+			blockchainLock.unlock();
 		}
 
 		return unconfirmedTransactions;
 	}
 
+	/**
+	 * Returns invalid, unconfirmed transactions.
+	 * <p>
+	 * NOTE: temporarily updates accounts' lastReference to that from
+	 * unconfirmed transactions, hence uses a repository savepoint.
+	 * <p>
+	 * Also temporarily acquires blockchain lock.
+	 * 
+	 * @return sorted unconfirmed transactions
+	 * @throws DataException
+	 */
 	public static List<TransactionData> getInvalidTransactions(Repository repository) throws DataException {
 		BlockData latestBlockData = repository.getBlockRepository().getLastBlock();
 
@@ -600,6 +635,14 @@ public abstract class Transaction {
 
 		unconfirmedTransactions.sort(getDataComparator());
 
+		/*
+		 * We have to grab the blockchain lock because we're updating
+		 * when we fake the creator's last reference,
+		 * even though we throw away the update when we rollback the
+		 * savepoint.
+		 */
+		ReentrantLock blockchainLock = Controller.getInstance().getBlockchainLock();
+		blockchainLock.lock();
 		repository.setSavepoint();
 		try {
 			for (int i = 0; i < unconfirmedTransactions.size(); ++i) {
@@ -616,6 +659,7 @@ public abstract class Transaction {
 		} finally {
 			// Throw away temporary updates to account lastReference
 			repository.rollbackToSavepoint();
+			blockchainLock.unlock();
 		}
 
 		return invalidTransactions;
@@ -627,6 +671,10 @@ public abstract class Transaction {
 	 * NOTE: temporarily updates creator's lastReference to that from
 	 * unconfirmed transactions, and hence caller should use a repository
 	 * savepoint or invoke <tt>repository.discardChanges()</tt>.
+	 * <p>
+	 * Caller should also hold the blockchain lock as we're 'updating'
+	 * when we fake the transaction creator's last reference, even if
+	 * it discarded at rollback.
 	 * 
 	 * @return true if transaction can be added to unconfirmed transactions, false otherwise
 	 * @throws DataException