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A set of utilities for Java
There is a newer version: 3.0.0
package org.rx.io;

import io.netty.buffer.ByteBuf;
import lombok.NonNull;
import lombok.Setter;
import org.rx.annotation.ErrorCode;
import org.rx.core.Constants;
import org.rx.exception.InvalidException;
import org.rx.util.Snowflake;

import java.io.*;

public final class MemoryStream extends IOStream implements Serializable {
    private static final long serialVersionUID = 6209361024929311435L;
    @Setter
    private String name;
    private boolean directBuffer;
    private transient ByteBuf buffer;
    private transient InputStream reader;
    private transient OutputStream writer;

    private void writeObject(ObjectOutputStream out) throws IOException {
        out.defaultWriteObject();
        out.writeInt((int) getPosition());
        out.writeInt((int) getLength());
        setPosition(0);
        read(out);
    }

    private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
        in.defaultReadObject();
        int pos = in.readInt();
        int len = in.readInt();
        buffer = directBuffer ? Bytes.directBuffer(len) : Bytes.heapBuffer(len, true);
        setLength(len);
        write(in);
        setPosition(pos);
    }

    @Override
    public String getName() {
        if (name == null) {
            name = String.valueOf(Snowflake.DEFAULT.nextId());
        }
        return name;
    }

    @Override
    public InputStream getReader() {
        if (reader == null) {
            reader = new InputStream() {
                int mark;

                @Override
                public boolean markSupported() {
                    return true;
                }

                @Override
                public synchronized void mark(int readlimit) {
                    mark = buffer.readerIndex();
                }

                @Override
                public synchronized void reset() throws IOException {
                    buffer.readerIndex(mark);
                }

                @Override
                public int available() {
                    return buffer.readableBytes();
                }

                @Override
                public int read(byte[] b, int off, int len) {
                    int readableBytes = buffer.readableBytes();
                    if (readableBytes == 0) {
                        return -1;
                    }
                    int len0 = Math.min(readableBytes, len);
                    buffer.readBytes(b, off, len0);
                    return len0;
                }

                @Override
                public int read() {
                    if (buffer.readableBytes() == 0) {
                        return -1;
                    }
                    // java has no unsigned byte
                    return buffer.readByte() & 0xff;
                }
            };
        }
        return reader;
    }

    @Override
    public OutputStream getWriter() {
        if (writer == null) {
            writer = new OutputStream() {
                @Override
                public void write(byte[] b, int off, int len) {
                    buffer.writerIndex(buffer.readerIndex());
                    buffer.writeBytes(b, off, len);
                    buffer.readerIndex(buffer.writerIndex());
                }

                @Override
                public void write(int b) {
                    buffer.writerIndex(buffer.readerIndex());
                    buffer.writeByte(b);
                    buffer.readerIndex(buffer.writerIndex());
                }
            };
        }
        return writer;
    }

    @Override
    public boolean canSeek() {
        return true;
    }

    @Override
    public long getPosition() {
        return buffer.readerIndex();
    }

    @Override
    public void setPosition(long position) {
        if (position > Integer.MAX_VALUE) {
            throw new InvalidException("Position > Integer.MAX_VALUE");
        }

        buffer.readerIndex((int) position);
    }

    @Override
    public long getLength() {
        return buffer.writerIndex();
    }

    public void setLength(int length) {
        buffer.writerIndex(length);
    }

    @ErrorCode
    public ByteBuf getBuffer() {
        checkNotClosed();

        return buffer;
    }

    public MemoryStream() {
        this(Constants.HEAP_BUF_SIZE, false);
    }

    public MemoryStream(boolean directBuffer) {
        this(Constants.HEAP_BUF_SIZE, directBuffer);
    }

    public MemoryStream(int initialCapacity, boolean directBuffer) {
        buffer = (this.directBuffer = directBuffer) ? Bytes.directBuffer(initialCapacity) : Bytes.heapBuffer(initialCapacity, true);
    }

    public MemoryStream(byte[] buffer, int offset, int length) {
        this(Bytes.wrap(buffer, offset, length), false);
    }

    public MemoryStream(@NonNull ByteBuf buf, boolean forWrite) {
        if (forWrite) {
            buf.readerIndex(buf.writerIndex());
        }
        this.buffer = buf;
    }

    @Override
    protected void freeObjects() {
        if (buffer != null) {
            buffer.release();
        }
    }

    @Override
    public int read(ByteBuf dst, int length) {
        buffer.readBytes(dst, length);
        return length;
    }

    public void read(ByteBuf dst, int dstIndex, int length) {
        buffer.readBytes(dst, dstIndex, length);
    }

    @Override
    public void write(ByteBuf src, int length) {
        buffer.writeBytes(src, length);
    }

    public void write(ByteBuf src, int srcIndex, int length) {
        buffer.writeBytes(src, srcIndex, length);
    }
}