Refactor serialization and added message validation

src/Main.java

@@ -1,18 +1,20 @@
 import java.io.File;
+import java.io.IOException;
 import java.util.concurrent.Executors;
 import java.util.concurrent.TimeUnit;
 import java.util.stream.IntStream;
 import model.BlockChain;
-import model.ChatClient;
+import util.ChatClient;
 import model.Miner;
+import util.FileManagement;
 import util.Security;
 
 public final class Main {
 
-    public static void main(final String[] args) throws InterruptedException {
+    public static void main(final String[] args) throws InterruptedException, IOException {
+
         final var nThreads = Runtime.getRuntime().availableProcessors();
-        final var blockChain = new BlockChain();
+        final var blockChain = BlockChain.getInstance();
-        blockChain.load();
 
         // Cryptographic keys management
         final File publicKey = new File(Security.PUBLIC_KEY);
@@ -24,15 +26,13 @@ public final class Main {
 
         final var chatExecutor = Executors.newScheduledThreadPool(nThreads);
 
-        // Mocks 3 chat clients who send messages to the blockchain
+        // Mocks a chat client who send messages to the blockchain
-        IntStream.range(0, 3)
+        chatExecutor.scheduleAtFixedRate(new ChatClient(blockChain), 0, 200, TimeUnit.MILLISECONDS);
-                .mapToObj(chatClientId -> new ChatClient(chatClientId, blockChain))
-                .forEach(e -> chatExecutor.scheduleAtFixedRate(e, 0, 100, TimeUnit.MILLISECONDS));
 
         final var minerExecutor = Executors.newFixedThreadPool(nThreads);
 
-        // Creation of 10 miners
+        // Creation of 5 miners
-        IntStream.range(0, 10)
+        IntStream.range(0, 5)
             .mapToObj(minerId -> new Miner(minerId, blockChain))
             .forEach(minerExecutor::submit);
 
@@ -48,8 +48,8 @@ public final class Main {
             chatExecutor.shutdownNow();
         }
 
-        blockChain.save();
+        FileManagement.saveBlockChain(blockChain);
-    }
 
     }
 
+}

src/model/Block.java

@@ -8,6 +8,7 @@ import java.util.stream.Collectors;
 public class Block implements Serializable {
 
   private static final long serialVersionUID = 1L;
+
   private final String previousBlockHash;
   private final String blockHash;
   private final int minerId;
@@ -24,7 +25,7 @@ public class Block implements Serializable {
       final int id,
       final int magicNumber,
       final float generationSecs,
-          final List<Message> chatMessages
+      final List<Message> blockMessages
   ) {
     this.previousBlockHash = previousBlockHash;
     this.blockHash = blockHash;
@@ -32,7 +33,7 @@ public class Block implements Serializable {
     this.id = id;
     this.magicNumber = magicNumber;
     this.generationSecs = generationSecs;
-    this.chatMessages = chatMessages;
+    this.chatMessages = blockMessages;
     this.timeStamp = new Date().getTime();
   }
 
@@ -58,8 +59,8 @@ public class Block implements Serializable {
   }
 
   public String messagesToString() {
-    return chatMessages.stream()
+    return chatMessages.isEmpty() ? "Empty block\n" : chatMessages.stream()
-            .map(m -> m.getText().concat("\n"))
+        .map(m -> String.valueOf(m.getId()).concat(" - ").concat(m.getText()).concat("\n"))
         .collect(Collectors.joining());
   }
 

src/model/BlockChain.java

@@ -1,5 +1,12 @@
 package model;
 
+import java.io.IOException;
+import java.io.Serializable;
+import java.security.InvalidKeyException;
+import java.security.NoSuchAlgorithmException;
+import java.security.SignatureException;
+import java.security.spec.InvalidKeySpecException;
+import java.util.concurrent.atomic.AtomicInteger;
 import util.FileManagement;
 import util.HashFunction;
 import util.Security;
@@ -9,20 +16,42 @@ import java.util.stream.Collectors;
 
 import static java.lang.String.valueOf;
 
-public class BlockChain {
+public class BlockChain implements Serializable {
+
+  private static final long serialVersionUID = 1L;
+  private static final float LOWER_LIMIT_SECS = 0.1F;
+  private static final float UPPER_LIMIT_SECS = 0.5F;
 
   private final Random random = new Random();
   private final List<Block> blockList = new LinkedList<>();
-  private final List<Message> chatMessages = new ArrayList<>();
+  private final List<Message> incomingChatMessages = new ArrayList<>();
+  private final AtomicInteger lastMessageId = new AtomicInteger(1);
+
   private int hashZeroes;
   private int magicNumber;
   private float generationSecs = 0;
 
+  public static BlockChain getInstance() {
+    try {
+      final BlockChain blockChain = (BlockChain) FileManagement.loadBlockChain();
+      if (!blockChain.validateBlockchain()) {
+        System.out.println("Blockchain not valid! Creating new one");
+        return new BlockChain();
+      } else {
+        return blockChain;
+      }
+    } catch (final ClassNotFoundException | IOException e) {
+      return new BlockChain();
+    }
+  }
+
   public synchronized void addBlock(final int minerId) {
     final int nextId = blockList.size();
     final String previousBlockHash = (nextId > 0) ? blockList.get(nextId - 1).getBlockHash() : "0";
     final String blockHash = calculateBlockHash(minerId);
 
+    incomingChatMessages.sort(Comparator.comparingInt(Message::getId));
+
     final var block = new Block(
         previousBlockHash,
         blockHash,
@@ -30,16 +59,16 @@ public class BlockChain {
         nextId,
         magicNumber,
         generationSecs,
-            chatMessages
+        incomingChatMessages
     );
     blockList.add(block);
     System.out.println(block);
-    this.chatMessages.clear();
+    incomingChatMessages.clear();
 
-    if (generationSecs < 1) {
+    if (generationSecs < LOWER_LIMIT_SECS) {
       hashZeroes += 1;
       System.out.println("N was increased to " + hashZeroes +"\n");
-    } else if (generationSecs > 10) {
+    } else if (generationSecs > UPPER_LIMIT_SECS) {
       hashZeroes -= 1;
       System.out.println("N was decreased by 1\n");
     } else {
@@ -48,42 +77,52 @@ public class BlockChain {
 
   }
 
-  public void acceptMessage(Message message) {
+  public int getNextMessageId() {
-    if (!blockList.isEmpty() || message.getId() > getLastMessageId()) {
+    return lastMessageId.getAndIncrement();
-      chatMessages.add(message);
-    }
   }
 
-  public int getLastMessageId() {
+  public void acceptText(final int nextMessageId, final String name, final String text)
-    return blockList.stream()
+      throws NoSuchAlgorithmException, SignatureException, InvalidKeyException, IOException, InvalidKeySpecException {
-            .map(Block::getMessages)
+    incomingChatMessages.add(new Message(
-            .flatMap(Collection::stream)
+        nextMessageId,
-            .mapToInt(Message::getId)
+        name,
-            .max().orElse(0);
+        text,
+        Security.getPrivate(),
+        Security.getPublic()
+    ));
   }
 
-  public void load() {
+  public boolean validateBlockchain() {
-    FileManagement.loadBlockchain(blockList);
-  }
-
-  public void save() {
-    FileManagement.saveBlockchain(blockList);
-  }
-
-  public String toString() {
-    if (!validateBlockchain()) {
-      System.out.println("Blockchain invalid!");
-    }
-    return blockList.stream().map(Block::toString).collect(Collectors.joining("\n"));
-  }
-
-  private boolean validateBlockchain() {
     if (blockList.isEmpty()) {
       return true;
     }
 
-    //TODO implement message validation
+    // Check message security
+    if (!blockList.stream()
+        .map(Block::getMessages)
+        .flatMap(Collection::stream)
+        .allMatch(Security::messageIsValid)) {
+      return false;
+    }
 
+    // Check messages Id ordering
+    if (!blockList.stream()
+        .map(Block::getMessages)
+        .flatMap(Collection::stream)
+        .map(Message::getId)
+        .sorted()
+        .collect(Collectors.toList())
+        .equals(blockList.stream()
+            .map(Block::getMessages)
+            .flatMap(Collection::stream)
+            .map(Message::getId)
+            .collect(Collectors.toList())
+        )
+    ) {
+      return false;
+    }
+
+    // Check block hashes ordering
     final List<String> previousHashes = blockList.stream()
         .map(Block::getPreviousBlockHash)
         .collect(Collectors.toList());
@@ -100,11 +139,6 @@ public class BlockChain {
     return true;
   }
 
-  private boolean messageIsValid(Message msg) {
-    //TODO correct signature issues
-    return Security.verifySignature(msg.getId() + msg.getText(), msg.getSignature(), msg.getPublicKey());
-  }
-
   private String calculateBlockHash(final int minerId) {
     final long start = System.currentTimeMillis();
     var hash = "";
@@ -113,7 +147,7 @@ public class BlockChain {
           + valueOf(new Date().getTime())
           + calculateMagicNumber()
       );
-    } while (!hash.matches("(?s)0{" + hashZeroes + "}([^0].*)?"));
+    } while (!hash.startsWith("0".repeat(hashZeroes)));
     final long end = System.currentTimeMillis();
     generationSecs = (end - start) / 1000F;
     return hash;

src/model/ChatClient.java

@@ -1,54 +0,0 @@
-package model;
-
-import util.Security;
-
-import java.io.IOException;
-import java.security.InvalidKeyException;
-import java.security.NoSuchAlgorithmException;
-import java.security.SignatureException;
-import java.security.spec.InvalidKeySpecException;
-import java.util.Random;
-
-public class ChatClient implements Runnable {
-
-    private final int clientId;
-    private final BlockChain blockChain;
-    private static final Random random = new Random();
-
-    public ChatClient(final int chatClientId, final BlockChain blockChain) {
-        this.clientId = chatClientId;
-        this.blockChain = blockChain;
-    }
-
-    @Override
-    public void run() {
-        try {
-            blockChain.acceptMessage(createMessage());
-        } catch (NoSuchAlgorithmException | SignatureException | InvalidKeyException | IOException | InvalidKeySpecException e) {
-            e.printStackTrace();
-        }
-    }
-
-    private Message createMessage()
-            throws NoSuchAlgorithmException, SignatureException, InvalidKeyException, IOException, InvalidKeySpecException {
-        return new Message(
-                blockChain.getLastMessageId() + 1,
-                clientId,
-                generateRandomAlphabeticString(),
-                Security.getPrivate(),
-                Security.getPublic()
-        );
-    }
-
-    private String generateRandomAlphabeticString() {
-        final int leftLimit = 97; // letter 'a'
-        final int rightLimit = 122; // letter 'z'
-        final int targetStringLength = 10;
-
-        return random.ints(leftLimit, rightLimit + 1)
-                .limit(targetStringLength)
-                .collect(StringBuilder::new, StringBuilder::appendCodePoint, StringBuilder::append)
-                .toString();
-    }
-
-}

src/model/Message.java

@@ -8,15 +8,16 @@ import java.security.*;
 public class Message implements Serializable  {
 
     private static final long serialVersionUID = 1L;
+
     private final int id;
     private final String text;
     private final byte[] signature;
     private final PublicKey publicKey;
 
-    public Message(final int id, final int clientId, final String text, final PrivateKey privateKey, final PublicKey publicKey)
+    public Message(final int id, final String name, final String text, final PrivateKey privateKey, final PublicKey publicKey)
         throws NoSuchAlgorithmException, InvalidKeyException, SignatureException {
         this.id = id;
-        this.text = "Client " + clientId + " says: " + text;
+        this.text = "Chatter " + name + " says: " + text;
         this.signature = Security.sign(text, privateKey);
         this.publicKey = publicKey;
     }

src/util/ChatClient.java

@@ -0,0 +1,53 @@
+package util;
+
+import model.BlockChain;
+
+import java.io.IOException;
+import java.security.InvalidKeyException;
+import java.security.NoSuchAlgorithmException;
+import java.security.SignatureException;
+import java.security.spec.InvalidKeySpecException;
+import java.util.Random;
+
+public class ChatClient implements Runnable {
+
+    private static final Random random = new Random();
+
+    private final BlockChain blockChain;
+
+    public ChatClient(final BlockChain blockChain) {
+        this.blockChain = blockChain;
+    }
+
+    @Override
+    public void run() {
+        try {
+            blockChain.acceptText(blockChain.getNextMessageId(), generateRandomName(), generateRandomText());
+        } catch (final NoSuchAlgorithmException | SignatureException | InvalidKeyException | IOException | InvalidKeySpecException e) {
+            e.printStackTrace();
+        }
+    }
+
+    private String generateRandomName() {
+        final int leftLimit = 97; // letter 'a'
+        final int rightLimit = 122; // letter 'z'
+        final int targetStringLength = 5;
+
+        return random.ints(leftLimit, rightLimit + 1)
+            .limit(targetStringLength)
+            .collect(StringBuilder::new, StringBuilder::appendCodePoint, StringBuilder::append)
+            .toString();
+    }
+
+    private String generateRandomText() {
+        final int leftLimit = 97; // letter 'a'
+        final int rightLimit = 122; // letter 'z'
+        final int targetStringLength = 20;
+
+        return random.ints(leftLimit, rightLimit + 1)
+            .limit(targetStringLength)
+            .collect(StringBuilder::new, StringBuilder::appendCodePoint, StringBuilder::append)
+            .toString();
+    }
+
+}

src/util/FileManagement.java

@@ -1,43 +1,37 @@
 package util;
 
-import model.Block;
+import java.io.BufferedInputStream;
+import java.io.BufferedOutputStream;
 import java.io.File;
 import java.io.FileInputStream;
 import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.ObjectInputStream;
 import java.io.ObjectOutputStream;
-import java.util.List;
 
 public final class FileManagement {
 
   private static final String BLOCKCHAIN = "blockChain.txt";
 
-  public static void saveBlockchain(final List<Block> blockList) {
+  private FileManagement() {
-    final var blockChainFile = new File(BLOCKCHAIN);
+    throw new IllegalStateException("FileManagement class");
-    try (final var fileOut = new FileOutputStream(blockChainFile);
-         final var objectOut = new ObjectOutputStream(fileOut)) {
-      for (final var block : blockList) {
-        objectOut.writeObject(block);
-      }
-    } catch (final IOException e) {
-      e.printStackTrace();
-    }
   }
 
-  public static void loadBlockchain(final List<Block> blockList) {
+  public static void saveBlockChain(final Object obj) throws IOException {
-    final var blockChainFile = new File(BLOCKCHAIN);
+    final FileOutputStream fos = new FileOutputStream(BLOCKCHAIN);
-    if (blockChainFile.exists()) {
+    final BufferedOutputStream bos = new BufferedOutputStream(fos);
-      try (final var fileIn = new FileInputStream(blockChainFile);
+    final ObjectOutputStream oos = new ObjectOutputStream(bos);
-           final var objectIn = new ObjectInputStream(fileIn)) {
+    oos.writeObject(obj);
-        while (fileIn.available() > 0) {
+    oos.close();
-          final var object = objectIn.readObject();
-          blockList.add((Block) object);
-        }
-      } catch (final IOException | ClassNotFoundException e) {
-        e.printStackTrace();
-      }
   }
+
+  public static Object loadBlockChain() throws IOException, ClassNotFoundException {
+    final FileInputStream fis = new FileInputStream(BLOCKCHAIN);
+    final BufferedInputStream bis = new BufferedInputStream(fis);
+    final ObjectInputStream ois = new ObjectInputStream(bis);
+    final Object obj = ois.readObject();
+    ois.close();
+    return obj;
   }
 
   public static void saveKey(final String path, final byte[] key) throws IOException {

src/util/HashFunction.java

@@ -4,6 +4,11 @@ import java.nio.charset.StandardCharsets;
 import java.security.MessageDigest;
 
 public final class HashFunction {
+
+  private HashFunction() {
+    throw new IllegalStateException("HashFunction class");
+  }
+
   /* Applies Sha256 to a string and returns a hash. */
   public static String applySha256(final String input) throws RuntimeException {
     try {
@@ -22,4 +27,5 @@ public final class HashFunction {
       throw new RuntimeException(e);
     }
   }
+
 }

src/util/Security.java

@@ -7,12 +7,17 @@ import java.security.*;
 import java.security.spec.InvalidKeySpecException;
 import java.security.spec.PKCS8EncodedKeySpec;
 import java.security.spec.X509EncodedKeySpec;
+import model.Message;
 
 public final class Security {
 
     public static final String PRIVATE_KEY = "KeyPair/privateKey";
     public static final String PUBLIC_KEY = "KeyPair/publicKey";
 
+    private Security() {
+        throw new IllegalStateException("Security class");
+    }
+
     public static PublicKey getPublic()
         throws NoSuchAlgorithmException, IOException, InvalidKeySpecException {
         final byte[] keyBytes = Files.readAllBytes(new File(PUBLIC_KEY).toPath());
@@ -37,6 +42,10 @@ public final class Security {
         return rsa.sign();
     }
 
+    public static boolean messageIsValid(final Message msg) {
+        return Security.verifySignature(msg.getId() + msg.getText(), msg.getSignature(), msg.getPublicKey());
+    }
+
     public static boolean verifySignature(final String data, final byte[] signature, final PublicKey publicKey) {
         try {
             final Signature verifier = Signature.getInstance("SHA1withRSA");