ByteBuffer backed SeekableByteChannel

ByteBufferChannel.java

package io.github.ncruces.utils;

import java.nio.ByteBuffer;
import java.nio.channels.NonWritableChannelException;
import java.nio.channels.SeekableByteChannel;

import static java.lang.Math.min;

public final class ByteBufferChannel implements SeekableByteChannel {
    private final ByteBuffer buf;

    public ByteBufferChannel(ByteBuffer buffer) {
        if (buffer == null) throw new NullPointerException();
        buf = buffer;
    }

    @Override
    public synchronized int read(ByteBuffer dst) {
        if (buf.remaining() == 0) return -1;

        int count = min(dst.remaining(), buf.remaining());
        if (count > 0) {
            ByteBuffer tmp = buf.slice();
            tmp.limit(count);
            dst.put(tmp);
            buf.position(buf.position() + count);
        }
        return count;
    }

    @Override
    public synchronized int write(ByteBuffer src) {
        if (buf.isReadOnly()) throw new NonWritableChannelException();

        int count = min(src.remaining(), buf.remaining());
        if (count > 0) {
            ByteBuffer tmp = src.slice();
            tmp.limit(count);
            buf.put(tmp);
            src.position(src.position() + count);
        }
        return count;
    }

    @Override
    public synchronized long position() {
        return buf.position();
    }

    @Override
    public synchronized ByteBufferChannel position(long newPosition) {
        if ((newPosition | Integer.MAX_VALUE - newPosition) < 0) throw new IllegalArgumentException();
        buf.position((int)newPosition);
        return this;
    }

    @Override
    public synchronized long size() { return buf.limit(); }

    @Override
    public synchronized ByteBufferChannel truncate(long size) {
        if ((size | Integer.MAX_VALUE - size) < 0) throw new IllegalArgumentException();
        int limit = buf.limit();
        if (limit > size) buf.limit((int)size);
        return this;
    }

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

    @Override
    public void close() {}
}