netty ByteBuf to InputStream adapter

ByteBufInputStream.java

import java.io.IOException;
import java.io.InputStream;

import io.netty.buffer.ByteBuf;

public class ByteBufInputStream extends InputStream {
	
	private ByteBuf buf = null;
	private int len = 0;
	
	public ByteBufInputStream( ByteBuf buf, int len ) {
		this.buf = buf;
		this.len = len;
	}

	@Override
	public int available() throws IOException {
		return this.len;
	}
	
	@Override
	public void close() throws IOException {		
	}
	
	@Override
	public void mark(int readlimit) {
		throw new RuntimeException( "not supported");
	}
	
	@Override
	public boolean markSupported() {
		return false;
	}
	
	@Override
	public int read() throws IOException {
		ensureBytesAvailable( 1 );
		this.len --;
		return this.buf.readByte();
				
	}
	
	@Override
	public int read(byte[] b) throws IOException {
		return read( b, 0, b.length );
	}
	
	@Override
	public int read(byte[] b, int offset, int len) throws IOException {
		ensureBytesAvailable( len );
		this.len -= len;
		this.buf.readBytes(b, offset, len );
		return len;
	}
	
	@Override
	public void reset() throws IOException {
		throw new RuntimeException( "not supported");
	}

	@Override
	public long skip(long n) throws IOException {
		ensureBytesAvailable( (int)n );
		len -= n;
		return n;
	}
	
	private void ensureBytesAvailable( int n ) throws IOException {
		if( n > this.len ) throw new IOException( "available bytes is less than " + n );
	}
}