FFDB-007: Implement a Persistable Filetable

pom.xml

@@ -29,6 +29,11 @@
             <version>${junit.jupiter.version}</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>com.esotericsoftware</groupId>
+            <artifactId>kryo</artifactId>
+            <version>5.5.0</version>
+        </dependency>
     </dependencies>
 
     <build>

src/main/java/com/sahilbondre/firefly/filetable/FilePointer.java

@@ -0,0 +1,45 @@
+package com.sahilbondre.firefly.filetable;
+
+import java.util.Objects;
+
+public class FilePointer {
+    private String fileName;
+    private long offset;
+
+    public FilePointer(String fileName, long offset) {
+        this.fileName = fileName;
+        this.offset = offset;
+    }
+
+    public FilePointer() {
+    }
+
+    public String getFileName() {
+        return fileName;
+    }
+
+    public void setFileName(String fileName) {
+        this.fileName = fileName;
+    }
+
+    public long getOffset() {
+        return offset;
+    }
+
+    public void setOffset(long offset) {
+        this.offset = offset;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        FilePointer that = (FilePointer) o;
+        return offset == that.offset && fileName.equals(that.fileName);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(fileName, offset);
+    }
+}

src/main/java/com/sahilbondre/firefly/filetable/InvalidFileTableException.java

@@ -0,0 +1,7 @@
+package com.sahilbondre.firefly.filetable;
+
+public class InvalidFileTableException extends RuntimeException {
+    public InvalidFileTableException(String message) {
+        super(message);
+    }
+}

src/main/java/com/sahilbondre/firefly/filetable/PersistableFileTable.java

@@ -0,0 +1,11 @@
+package com.sahilbondre.firefly.filetable;
+
+import java.io.FileNotFoundException;
+
+public interface PersistableFileTable {
+    void put(byte[] key, FilePointer value);
+
+    FilePointer get(byte[] key);
+
+    void saveToDisk(String filePath) throws FileNotFoundException;
+}

src/main/java/com/sahilbondre/firefly/filetable/SerializedPersistableFileTable.java

@@ -0,0 +1,58 @@
+package com.sahilbondre.firefly.filetable;
+
+import com.esotericsoftware.kryo.Kryo;
+import com.esotericsoftware.kryo.KryoException;
+import com.esotericsoftware.kryo.io.Input;
+import com.esotericsoftware.kryo.io.Output;
+
+import java.io.*;
+import java.util.HashMap;
+import java.util.Map;
+
+public class SerializedPersistableFileTable implements PersistableFileTable, Serializable {
+
+    private static final Kryo kryo = new Kryo();
+
+    private final Map<String, FilePointer> table;
+
+    public SerializedPersistableFileTable() {
+        kryo.register(SerializedPersistableFileTable.class);
+        kryo.register(HashMap.class);
+        kryo.register(FilePointer.class);
+        this.table = new HashMap<>();
+    }
+
+    public static SerializedPersistableFileTable fromEmpty() {
+        return new SerializedPersistableFileTable();
+    }
+
+    public static SerializedPersistableFileTable fromFile(String filePath) throws FileNotFoundException, KryoException {
+        try (Input input = new Input(new FileInputStream(filePath))) {
+            return kryo.readObject(input, SerializedPersistableFileTable.class);
+        } catch (KryoException e) {
+            throw new InvalidFileTableException("Failed to load FileTable from disk: " + e.getMessage());
+        }
+    }
+
+    @Override
+    public void put(byte[] key, FilePointer value) {
+        if (key != null && value != null) {
+            table.put(new String(key), value);
+        }
+    }
+
+    @Override
+    public FilePointer get(byte[] key) {
+        if (key != null) {
+            return table.get(new String(key));
+        }
+        return null;
+    }
+
+    @Override
+    public void saveToDisk(String filePath) throws FileNotFoundException {
+        Output output = new Output(new FileOutputStream(filePath));
+        kryo.writeObject(output, this);
+        output.close();
+    }
+}

src/main/java/com/sahilbondre/firefly/log/FileChannelRandomAccessLog.java

@@ -1,5 +1,7 @@
 package com.sahilbondre.firefly.log;
 
+import com.sahilbondre.firefly.filetable.FilePointer;
+
 import java.io.IOException;
 import java.io.RandomAccessFile;
 import java.nio.ByteBuffer;
@@ -28,10 +30,11 @@ public String getFilePath() {
     }
 
     @Override
-    public void append(byte[] message) throws IOException {
+    public FilePointer append(byte[] message) throws IOException {
         fileChannel.position(fileChannel.size());
         ByteBuffer buffer = ByteBuffer.wrap(message);
         fileChannel.write(buffer);
+        return new FilePointer(filePath, fileChannel.size() - message.length);
     }
 
     @Override

src/main/java/com/sahilbondre/firefly/log/RandomAccessLog.java

@@ -1,13 +1,15 @@
 package com.sahilbondre.firefly.log;
 
+import com.sahilbondre.firefly.filetable.FilePointer;
+
 import java.io.IOException;
 
 public interface RandomAccessLog {
     long size() throws IOException;
 
     String getFilePath();
 
-    void append(byte[] message) throws IOException;
+    FilePointer append(byte[] message) throws IOException;
 
     byte[] read(long offset, long length) throws IOException, InvalidRangeException;
 

src/test/java/com/sahilbondre/firefly/filetable/SerializedPersistableFileTableTest.java

@@ -0,0 +1,107 @@
+package com.sahilbondre.firefly.filetable;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class SerializedPersistableFileTableTest {
+
+    private static final String TEST_FILE_PATH = "src/test/resources/map";
+    private SerializedPersistableFileTable fileTable;
+
+    @BeforeEach
+    void setUp() throws IOException {
+        Files.deleteIfExists(Paths.get(TEST_FILE_PATH));
+        fileTable = SerializedPersistableFileTable.fromEmpty();
+    }
+
+    @AfterEach
+    void tearDown() throws IOException {
+        Files.deleteIfExists(Paths.get(TEST_FILE_PATH));
+    }
+
+    @Test
+    void given_KeyValue_When_PuttingAndGet_Then_RetrievedValueMatches() {
+        // Given
+        byte[] key = "testKey".getBytes();
+        FilePointer expectedValue = new FilePointer("test.txt", 42);
+
+        // When
+        fileTable.put(key, new FilePointer("test.txt", 42));
+        FilePointer retrievedValue = fileTable.get(key);
+
+        // Then
+        assertEquals(expectedValue, retrievedValue);
+    }
+
+    @Test
+    void given_NullKey_When_PuttingAndGet_Then_RetrievedValueIsNull() {
+        // Given
+        FilePointer value = new FilePointer("test.txt", 42);
+
+        // When
+        fileTable.put(null, value);
+        FilePointer retrievedValue = fileTable.get(null);
+
+        // Then
+        assertNull(retrievedValue);
+    }
+
+    @Test
+    void given_NullValue_When_PuttingAndGet_Then_RetrievedValueIsNull() {
+        // Given
+        byte[] key = "testKey".getBytes();
+
+        // When
+        fileTable.put(key, null);
+        FilePointer retrievedValue = fileTable.get(key);
+
+        // Then
+        assertNull(retrievedValue);
+    }
+
+    @Test
+    void given_KeyValue_When_SavingToDiskAndLoadingFromFile_Then_RetrievedValueMatches() throws FileNotFoundException {
+        // Given
+        byte[] key = "testKey".getBytes();
+        FilePointer value = new FilePointer("test.txt", 42);
+
+        // When
+        fileTable.put(key, value);
+        fileTable.saveToDisk(TEST_FILE_PATH);
+        SerializedPersistableFileTable loadedFileTable = SerializedPersistableFileTable.fromFile(TEST_FILE_PATH);
+        FilePointer retrievedValue = loadedFileTable.get(key);
+
+        // Then
+        assertEquals(value, retrievedValue);
+    }
+
+    @Test
+    void given_NonexistentFile_When_LoadingFromFile_Then_FileNotFoundExceptionIsThrown() {
+        // When
+        // Then
+        assertThrows(FileNotFoundException.class,
+            () -> SerializedPersistableFileTable.fromFile(TEST_FILE_PATH));
+    }
+
+    @Test
+    void given_CorruptedFile_When_LoadingFromFile_Then_InvalidFileTableExceptionIsThrown() throws IOException {
+        // Given
+        // Create a corrupted file by writing invalid data
+        Path filePath = Paths.get(TEST_FILE_PATH);
+        Files.write(filePath, List.of("Invalid Data"));
+
+        // Then
+        assertThrows(InvalidFileTableException.class,
+            () -> SerializedPersistableFileTable.fromFile(TEST_FILE_PATH));
+    }
+}