diff --git a/src/blockchain/Block.java b/src/blockchain/Block.java new file mode 100644 index 0000000..dcc4636 --- /dev/null +++ b/src/blockchain/Block.java @@ -0,0 +1,58 @@ +package blockchain; + +import java.io.Serializable; + +public class Block implements Serializable { + + private final Integer id; + private final Long minerId; + private final String hashPreviousBlock; + private final String hash; + private final Long timestamp; + private final Integer magicNumber; + private String data; + + + public Block(Integer id, Long minerId, String hashPreviousBlock, String hash, Long timestamp, + Integer magicNumber, String data) { + this.id = id; + this.minerId = minerId; + this.hashPreviousBlock = hashPreviousBlock; + this.hash = hash; + this.timestamp = timestamp; + this.magicNumber = magicNumber; + this.data = data; + } + + public Integer getId() { + return id; + } + + public String getHashPreviousBlock() { + return hashPreviousBlock; + } + + public String getHash() { + return hash; + } + + public Long getTimestamp() { + return timestamp; + } + + public String getData() { + return data; + } + + public void setData(String data) { + this.data = data; + } + + public Integer getMagicNumber() { + return magicNumber; + } + + public Long getMinerId() { + return minerId; + } +} diff --git a/src/blockchain/BlockBuilder.java b/src/blockchain/BlockBuilder.java new file mode 100644 index 0000000..890f59a --- /dev/null +++ b/src/blockchain/BlockBuilder.java @@ -0,0 +1,51 @@ +package blockchain; + +public class BlockBuilder { + + private Integer id; + private Long minerId; + private String hashPreviousBlock; + private String hash; + private Long timestamp; + private Integer magicNumber; + private String data; + + public BlockBuilder withId(Integer id) { + this.id = id; + return this; + } + + public BlockBuilder withMinerId(Long minerId) { + this.minerId = minerId; + return this; + } + + public BlockBuilder withHashPreviousBlock(String hashPreviousBlock) { + this.hashPreviousBlock = hashPreviousBlock; + return this; + } + + public BlockBuilder withHash(String hash) { + this.hash = hash; + return this; + } + + public BlockBuilder withTimestamp(Long timestamp) { + this.timestamp = timestamp; + return this; + } + + public BlockBuilder withMagicNumber(Integer magicNumber) { + this.magicNumber = magicNumber; + return this; + } + + public BlockBuilder withData(String data) { + this.data = data; + return this; + } + + public Block build() { + return new Block(id, minerId, hashPreviousBlock, hash, timestamp, magicNumber, data); + } +} diff --git a/src/blockchain/Blockchain.java b/src/blockchain/Blockchain.java new file mode 100644 index 0000000..bf83119 --- /dev/null +++ b/src/blockchain/Blockchain.java @@ -0,0 +1,180 @@ +package blockchain; + +import blockchain.data.format.DataFormatter; +import blockchain.io.Persister; +import java.util.Collections; +import java.util.Date; +import java.util.LinkedList; +import java.util.List; +import java.util.Objects; +import java.util.StringJoiner; +import java.util.concurrent.TimeUnit; +import java.util.concurrent.locks.ReentrantReadWriteLock; +import java.util.concurrent.locks.ReentrantReadWriteLock.ReadLock; +import java.util.concurrent.locks.ReentrantReadWriteLock.WriteLock; +import java.util.stream.Stream; + +public class Blockchain { + + private static final Long ACCEPTABLE_TIME = TimeUnit.SECONDS.toMillis(5); + + private final ReentrantReadWriteLock readWritelock; + + private final List blocks; + private final List pendingMessages; + private final Persister persister; + + private int prefixLength; + private DataFormatter dataFormatter; + + public Blockchain(Persister persister, DataFormatter dataFormatter) { + this.readWritelock = new ReentrantReadWriteLock(); + this.persister = persister; + this.dataFormatter = dataFormatter; + this.prefixLength = 0; + List blocks = persister.load(); + if (!blocks.isEmpty() && validateAllChain(blocks)) { + this.blocks = blocks; + } else { + new BlockBuilder().build(); + this.blocks = new LinkedList<>(Collections.singleton( + new BlockBuilder() + .withId(1) + .withMinerId(0L) + .withHashPreviousBlock("") + .withHash("0") + .withMagicNumber(0) + .withTimestamp(new Date().getTime()).build())); + persister.save(blocks); + } + pendingMessages = new LinkedList<>(); + } + + public void accept(Block newBlock) { + WriteLock writeLock = readWritelock.writeLock(); + try { + writeLock.lock(); + if (isValid(newBlock)) { + newBlock.setData(pendingData()); + outputAndAdjust(newBlock); + blocks.add(newBlock); + pendingMessages.clear(); + persister.save(blocks); + } + } finally { + writeLock.unlock(); + } + } + + public void appendData(T data) { + WriteLock writeLock = readWritelock.writeLock(); + try { + writeLock.lock(); + pendingMessages.add(data); + } finally { + writeLock.unlock(); + } + } + + public String getPrefix() { + ReadLock readLock = readWritelock.readLock(); + try { + readLock.lock(); + return Stream.iterate("0", x -> "0") + .limit(prefixLength) + .reduce("", (x, y) -> x + y); + } finally { + readLock.unlock(); + } + } + + public String pendingData() { + ReadLock readLock = readWritelock.readLock(); + try { + readLock.lock(); + StringJoiner stringJoiner = new StringJoiner("\n"); + if (pendingMessages.isEmpty()) { + return "no messages"; + } + pendingMessages.stream() + .map(dataFormatter::format) + .forEach(stringJoiner::add); + return stringJoiner.toString(); + } finally { + readLock.unlock(); + } + } + + public Block tail() { + ReadLock readLock = readWritelock.readLock(); + try { + readLock.lock(); + return blocks.get(blocks.size() - 1); + } finally { + readLock.unlock(); + } + } + + private boolean isValid(Block newBlock) { + Block tailBlock = blocks.get(blocks.size() - 1); + if (!newBlock.getHash().startsWith(getPrefix()) || !Objects + .equals(newBlock.getHashPreviousBlock(), tailBlock.getHash())) { + return false; + } + return true; + } + + private void outputAndAdjust(Block newBlock) { + outputStats(newBlock); + adjustComplexity(newBlock); + } + + private void outputStats(Block newBlock) { + System.out.printf("Block:\n"); + System.out.printf("Id: %s\n", newBlock.getId()); + System.out.printf("Created by miner # %s\n", newBlock.getMinerId()); + System.out.printf("Timestamp: %s\n", newBlock.getTimestamp()); + System.out.printf("Magic number: %s\n", newBlock.getMagicNumber()); + System.out.printf("Hash of the previous block:\n%s\n", newBlock.getHashPreviousBlock()); + System.out.printf("Block data: \n%s\n", newBlock.getData()); + System.out.printf("Magic number: %s\n", newBlock.getMagicNumber()); + System.out + .printf("Block was generating for: %s seconds\n", getGenerationTime(newBlock) / 1000); + } + + private void adjustComplexity(Block newBlock) { + if (!withinAcceptable(newBlock)) { + if (ACCEPTABLE_TIME < getGenerationTime(newBlock)) { + if (prefixLength > 0) { + prefixLength--; + } + System.out.printf("N was decreased to %s\n\n", prefixLength); + } else { + prefixLength++; + System.out.printf("N was increased to %s\n\n", prefixLength); + } + } else { + System.out.printf("N stays the same\n\n"); + } + } + + private Long getGenerationTime(Block newBlock) { + return tail() == null ? 0 : (newBlock.getTimestamp() - tail().getTimestamp()); + } + + private boolean withinAcceptable(Block newBlock) { + return Math.abs(getGenerationTime(newBlock) - ACCEPTABLE_TIME) <= 1000; + } + + private boolean validateAllChain(List blocks) { + for (int i = 1; i < blocks.size(); i++) { + Block prev = blocks.get(i - 1); + Block cur = blocks.get(i); + if (!Objects.equals(prev.getHash(), cur.getHashPreviousBlock())) { + return false; + } + } + return true; + } + +} diff --git a/src/blockchain/Main.java b/src/blockchain/Main.java index adf1d02..a2b2b57 100644 --- a/src/blockchain/Main.java +++ b/src/blockchain/Main.java @@ -1,7 +1,46 @@ package blockchain; +import blockchain.data.Message; +import blockchain.data.format.PlanMessageFormat; +import blockchain.io.FilePersister; +import blockchain.io.Persister; +import blockchain.miners.Miner; +import java.util.List; +import java.util.concurrent.atomic.AtomicLong; +import java.util.stream.Collectors; +import java.util.stream.Stream; + public class Main { - public static void main(String[] args) { - System.out.print("Hello world!"); - } + + private static final String OUTPUT_FILE_NAME = "blockchain.ser"; + private static final int NUMBER_OF_MINERS = 10; + private static AtomicLong ids = new AtomicLong(1); + + public static void main(String[] args) throws InterruptedException { + + Persister persister = new FilePersister(OUTPUT_FILE_NAME); + Blockchain blockchain = new Blockchain<>(persister, + new PlanMessageFormat()); + + List miners = Stream + .generate(() -> new Thread(new Miner(blockchain, ids.getAndIncrement()))) + .limit(NUMBER_OF_MINERS) + .collect(Collectors.toList()); + + miners.forEach(Thread::start); + + Thread.sleep(1000); + blockchain.appendData(new Message("Tom", "Hey, I'm first!")); + blockchain.appendData(new Message("Sarah", "It's not fair!")); + Thread.sleep(2000); + blockchain.appendData( + new Message("Sarah", "You always will be first because it is your blockchain!")); + Thread.sleep(1000); + blockchain.appendData(new Message("Sarah", "Anyway, thank you for this amazing chat.")); + Thread.sleep(2000); + blockchain.appendData(new Message("Tom", "You're welcome :)")); + blockchain.appendData(new Message("Nick", "Hey Tom, nice chat")); + + miners.forEach(Thread::interrupt); + } } \ No newline at end of file diff --git a/src/blockchain/data/Message.java b/src/blockchain/data/Message.java new file mode 100644 index 0000000..d1ecfeb --- /dev/null +++ b/src/blockchain/data/Message.java @@ -0,0 +1,20 @@ +package blockchain.data; + +public class Message { + + private final String author; + private final String text; + + public Message(String author, String text) { + this.author = author; + this.text = text; + } + + public String getAuthor() { + return author; + } + + public String getText() { + return text; + } +} diff --git a/src/blockchain/data/format/DataFormatter.java b/src/blockchain/data/format/DataFormatter.java new file mode 100644 index 0000000..0945a27 --- /dev/null +++ b/src/blockchain/data/format/DataFormatter.java @@ -0,0 +1,6 @@ +package blockchain.data.format; + +public interface DataFormatter { + + String format(T message); +} diff --git a/src/blockchain/data/format/PlanMessageFormat.java b/src/blockchain/data/format/PlanMessageFormat.java new file mode 100644 index 0000000..773b0fb --- /dev/null +++ b/src/blockchain/data/format/PlanMessageFormat.java @@ -0,0 +1,11 @@ +package blockchain.data.format; + +import blockchain.data.Message; + +public class PlanMessageFormat implements DataFormatter { + + @Override + public String format(Message message) { + return String.format("%s: %s", message.getAuthor(), message.getText()); + } +} diff --git a/src/blockchain/io/FilePersister.java b/src/blockchain/io/FilePersister.java new file mode 100644 index 0000000..c996c9a --- /dev/null +++ b/src/blockchain/io/FilePersister.java @@ -0,0 +1,48 @@ +package blockchain.io; + +import blockchain.Block; +import java.io.FileInputStream; +import java.io.FileOutputStream; +import java.io.IOException; +import java.io.ObjectInputStream; +import java.io.ObjectOutputStream; +import java.nio.file.Files; +import java.nio.file.Paths; +import java.util.List; + +public class FilePersister implements Persister { + + + private final String filename; + + public FilePersister(String filename) { + this.filename = filename; + } + + @Override + public void save(List blockchain) { + try (FileOutputStream fileOutputStream = new FileOutputStream(filename); + ObjectOutputStream objectOutputStream = new ObjectOutputStream(fileOutputStream)) { + objectOutputStream.writeObject(blockchain); + } catch (IOException e) { + throw new RuntimeException(); + } + } + + @Override + public List load() { + if (fileExists()) { + try (FileInputStream fileInputStream = new FileInputStream(filename); + ObjectInputStream objectInputStream = new ObjectInputStream(fileInputStream)) { + return (List) objectInputStream.readObject(); + } catch (IOException | ClassNotFoundException e) { + return List.of(); + } + } + return List.of(); + } + + private boolean fileExists() { + return Files.exists(Paths.get(filename)); + } +} diff --git a/src/blockchain/io/Persister.java b/src/blockchain/io/Persister.java new file mode 100644 index 0000000..1004ad2 --- /dev/null +++ b/src/blockchain/io/Persister.java @@ -0,0 +1,12 @@ +package blockchain.io; + +import blockchain.Block; +import java.util.List; + +public interface Persister { + + void save(List blockchain); + + List load(); +} + diff --git a/src/blockchain/miners/Miner.java b/src/blockchain/miners/Miner.java new file mode 100644 index 0000000..08bde3c --- /dev/null +++ b/src/blockchain/miners/Miner.java @@ -0,0 +1,48 @@ +package blockchain.miners; + +import blockchain.Block; +import blockchain.BlockBuilder; +import blockchain.Blockchain; +import blockchain.utils.StringUtil; +import java.util.Date; +import java.util.Random; + +public class Miner implements Runnable { + + private final Blockchain blockchain; + private final Long id; + private final Random random; + + public Miner(Blockchain blockchain, Long id) { + this.blockchain = blockchain; + this.id = id; + this.random = new Random(); + } + + @Override + public void run() { + while (!Thread.currentThread().isInterrupted()) { + Block prev = blockchain.tail(); + blockchain.accept(generateNextBlock(prev.getId() + 1, id, prev.getHash())); + } + } + + private Block generateNextBlock(int id, long minerId, String previousHash) { + BlockBuilder blockBuilder = new BlockBuilder() + .withId(id) + .withMinerId(minerId) + .withHashPreviousBlock(previousHash); + Integer magicNumber; + String hash; + String prefix; + do { + prefix = blockchain.getPrefix(); + magicNumber = random.nextInt(); + hash = StringUtil.applySha256(previousHash + magicNumber); + blockBuilder = blockBuilder.withHash(hash) + .withMagicNumber(magicNumber) + .withTimestamp(new Date().getTime()); + } while (!hash.startsWith(prefix)); + return blockBuilder.build(); + } +} diff --git a/src/blockchain/utils/StringUtil.java b/src/blockchain/utils/StringUtil.java new file mode 100644 index 0000000..b883ebd --- /dev/null +++ b/src/blockchain/utils/StringUtil.java @@ -0,0 +1,28 @@ +package blockchain.utils; + +import java.nio.charset.StandardCharsets; +import java.security.MessageDigest; + +public class StringUtil { + + /** + * Applies Sha256 to a string and returns a hash. + */ + public static String applySha256(String input) { + try { + MessageDigest digest = MessageDigest.getInstance("SHA-256"); + byte[] hash = digest.digest(input.getBytes(StandardCharsets.UTF_8)); + StringBuilder hexString = new StringBuilder(); + for (byte elem : hash) { + String hex = Integer.toHexString(0xff & elem); + if (hex.length() == 1) { + hexString.append('0'); + } + hexString.append(hex); + } + return hexString.toString(); + } catch (Exception e) { + throw new RuntimeException(e); + } + } +}