Buffer Management

/**
 * Immutable view for data in bytes with different backing implementations
 * Provides unified interface for file, memory, and Netty-backed data
 */
public abstract class ManagedBuffer {
    /**
     * Number of bytes of data in this buffer
     * @return Size in bytes
     */
    public abstract long size();
    
    /**
     * Expose this buffer's data as a NIO ByteBuffer
     * Multiple calls may return the same ByteBuffer or different ByteBuffers
     * @return ByteBuffer view of the data
     * @throws IOException if buffer cannot be converted
     */
    public abstract ByteBuffer nioByteBuffer() throws IOException;
    
    /**
     * Expose this buffer's data as an InputStream for streaming reads
     * @return InputStream for reading the data
     * @throws IOException if stream cannot be created
     */
    public abstract InputStream createInputStream() throws IOException;
    
    /**
     * Increment the reference count of this buffer if applicable
     * @return This buffer for method chaining
     */
    public abstract ManagedBuffer retain();
    
    /**
     * Decrement the reference count and deallocate if zero
     * @return This buffer for method chaining
     */
    public abstract ManagedBuffer release();
    
    /**
     * Convert this buffer to a Netty ByteBuf or FileRegion for efficient transfer
     * @return Netty object (ByteBuf for memory, FileRegion for files)
     * @throws IOException if conversion fails
     */
    public abstract Object convertToNetty() throws IOException;
}

// Working with a managed buffer
ManagedBuffer buffer = // ... obtained from somewhere
try {
    long size = buffer.size();
    System.out.println("Buffer size: " + size + " bytes");
    
    // Read as ByteBuffer
    ByteBuffer bb = buffer.nioByteBuffer();
    byte[] data = new byte[bb.remaining()];
    bb.get(data);
    
    // Or read as stream
    try (InputStream is = buffer.createInputStream()) {
        byte[] streamData = new byte[(int) size];
        is.read(streamData);
    }
    
} finally {
    // Always release when done
    buffer.release();
}

/**
 * ManagedBuffer backed by a segment in a file
 * Enables efficient access to portions of large files without loading entire file
 */
public final class FileSegmentManagedBuffer extends ManagedBuffer {
    /**
     * Create a buffer backed by a file segment
     * @param conf Transport configuration for memory mapping settings
     * @param file File to read from
     * @param offset Starting offset in the file
     * @param length Number of bytes to include from the offset
     */
    public FileSegmentManagedBuffer(TransportConf conf, File file, long offset, long length);
    
    /**
     * Get the underlying file
     * @return File instance
     */
    public File getFile();
    
    /**
     * Get the starting offset in the file
     * @return Offset in bytes
     */
    public long getOffset();
    
    /**
     * Get the length of the segment
     * @return Length in bytes
     */
    public long getLength();
}

import java.io.File;

// Create a buffer for part of a large file
File dataFile = new File("/path/to/large/data.bin");
long offset = 1024 * 1024; // Start at 1MB
long length = 512 * 1024;  // Read 512KB

FileSegmentManagedBuffer fileBuffer = new FileSegmentManagedBuffer(
    conf, dataFile, offset, length
);

try {
    System.out.println("Reading " + fileBuffer.getLength() + " bytes from " + 
                      fileBuffer.getFile().getName() + " at offset " + fileBuffer.getOffset());
    
    // Efficient zero-copy transfer to Netty
    Object nettyObject = fileBuffer.convertToNetty();
    
    // Or read as stream
    try (InputStream stream = fileBuffer.createInputStream()) {
        // Process stream data
    }
    
} finally {
    fileBuffer.release();
}

/**
 * ManagedBuffer backed by a Netty ByteBuf
 * Integrates with Netty's reference counting and memory management
 */
public class NettyManagedBuffer extends ManagedBuffer {
    /**
     * Create a buffer backed by a Netty ByteBuf
     * @param buf Netty ByteBuf to wrap
     */
    public NettyManagedBuffer(ByteBuf buf);
}

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;

// Create from Netty ByteBuf
ByteBuf nettyBuf = Unpooled.copiedBuffer("Hello, World!".getBytes());
NettyManagedBuffer buffer = new NettyManagedBuffer(nettyBuf);

try {
    // Use as managed buffer
    ByteBuffer nio = buffer.nioByteBuffer();
    System.out.println("Data: " + new String(nio.array()));
    
    // Convert back to Netty (efficient, no copy)
    Object nettyObject = buffer.convertToNetty();
    
} finally {
    buffer.release(); // This will release the underlying ByteBuf
}

/**
 * ManagedBuffer backed by a NIO ByteBuffer
 * Provides ManagedBuffer interface for standard Java ByteBuffers
 */
public class NioManagedBuffer extends ManagedBuffer {
    /**
     * Create a buffer backed by a NIO ByteBuffer
     * @param buf NIO ByteBuffer to wrap
     */
    public NioManagedBuffer(ByteBuffer buf);
}

import java.nio.ByteBuffer;

// Create from NIO ByteBuffer
ByteBuffer nioBuf = ByteBuffer.wrap("Hello, NIO!".getBytes());
NioManagedBuffer buffer = new NioManagedBuffer(nioBuf);

try {
    // Access data
    System.out.println("Buffer size: " + buffer.size());
    
    // Get as ByteBuffer (may return same instance)
    ByteBuffer bb = buffer.nioByteBuffer();
    
    // Read as stream
    try (InputStream stream = buffer.createInputStream()) {
        byte[] data = new byte[(int) buffer.size()];
        stream.read(data);
        System.out.println("Stream data: " + new String(data));
    }
    
} finally {
    buffer.release();
}

// For file-based data (large files, zero-copy I/O)
FileSegmentManagedBuffer fileBuffer = new FileSegmentManagedBuffer(
    conf, file, 0, file.length()
);

// For in-memory data with Netty integration
ByteBuf nettyBuf = ctx.alloc().buffer(1024);
NettyManagedBuffer nettyBuffer = new NettyManagedBuffer(nettyBuf);

// For existing NIO ByteBuffer integration
ByteBuffer existing = // ... from somewhere
NioManagedBuffer nioBuffer = new NioManagedBuffer(existing);

ManagedBuffer buffer = createBuffer();
try {
    // Use buffer
    processBuffer(buffer);
} finally {
    buffer.release(); // Essential for preventing memory leaks
}

ManagedBuffer buffer = new FileSegmentManagedBuffer(conf, file, 0, file.length());
try {
    // Efficient zero-copy transfer
    Object nettyObject = buffer.convertToNetty();
    
    if (nettyObject instanceof FileRegion) {
        // File-based zero-copy
        channel.writeAndFlush(nettyObject);
    } else if (nettyObject instanceof ByteBuf) {
        // Memory-based transfer
        channel.writeAndFlush(nettyObject);
    }
} finally {
    buffer.release();
}

public ManagedBuffer processData(ManagedBuffer input) {
    try (InputStream stream = input.createInputStream()) {
        // Process data
        byte[] processed = transformData(stream);
        
        // Return new buffer with processed data
        return new NioManagedBuffer(ByteBuffer.wrap(processed));
    } catch (IOException e) {
        throw new RuntimeException("Processing failed", e);
    }
}