android: Add a Java utility class similar to bio_writer_t

src/frontends/android/src/org/strongswan/android/utils/BufferedByteWriter.java

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+/*
+ * Copyright (C) 2013 Tobias Brunner
+ * Hochschule fuer Technik Rapperswil
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.  See <http://www.fsf.org/copyleft/gpl.txt>.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * for more details.
+ */
+
+package org.strongswan.android.utils;
+
+import java.nio.ByteBuffer;
+
+/**
+ * Very similar to ByteBuffer (although with a stripped interface) but it
+ * automatically resizes the underlying buffer.
+ */
+public class BufferedByteWriter
+{
+	/**
+	 * The underlying byte buffer
+	 */
+	private byte[] mBuffer;
+
+	/**
+	 * ByteBuffer used as wrapper around the buffer to easily convert values
+	 */
+	private ByteBuffer mWriter;
+
+	/**
+	 * Create a writer with a default initial capacity
+	 */
+	public BufferedByteWriter()
+	{
+		this(0);
+	}
+
+	/**
+	 * Create a writer with the given initial capacity (helps avoid expensive
+	 * resizing if known).
+	 * @param capacity initial capacity
+	 */
+	public BufferedByteWriter(int capacity)
+	{
+		capacity = capacity > 4 ? capacity : 32;
+		mBuffer = new byte[capacity];
+		mWriter = ByteBuffer.wrap(mBuffer);
+	}
+
+	/**
+	 * Ensure that there is enough space available to write the requested
+	 * number of bytes. If necessary the internal buffer is resized.
+	 * @param required required number of bytes
+	 */
+	private void ensureCapacity(int required)
+	{
+		if (mWriter.remaining() >= required)
+		{
+			return;
+		}
+		byte[] buffer = new byte[(mBuffer.length + required) * 2];
+		System.arraycopy(mBuffer, 0, buffer, 0, mWriter.position());
+		mBuffer = buffer;
+		ByteBuffer writer = ByteBuffer.wrap(buffer);
+		writer.position(mWriter.position());
+		mWriter = writer;
+	}
+
+	/**
+	 * Write the given byte array to the buffer
+	 * @param value
+	 * @return the writer
+	 */
+	public BufferedByteWriter put(byte[] value)
+	{
+		ensureCapacity(value.length);
+		mWriter.put(value);
+		return this;
+	}
+
+	/**
+	 * Write the given byte to the buffer
+	 * @param value
+	 * @return the writer
+	 */
+	public BufferedByteWriter put(byte value)
+	{
+		ensureCapacity(1);
+		mWriter.put(value);
+		return this;
+	}
+
+	/**
+	 * Write the 8-bit length of the given data followed by the data itself
+	 * @param value
+	 * @return the writer
+	 */
+	public BufferedByteWriter putLen8(byte[] value)
+	{
+		ensureCapacity(1 + value.length);
+		mWriter.put((byte)value.length);
+		mWriter.put(value);
+		return this;
+	}
+
+	/**
+	 * Write the 16-bit length of the given data followed by the data itself
+	 * @param value
+	 * @return the writer
+	 */
+	public BufferedByteWriter putLen16(byte[] value)
+	{
+		ensureCapacity(2 + value.length);
+		mWriter.putShort((short)value.length);
+		mWriter.put(value);
+		return this;
+	}
+
+	/**
+	 * Write the given short value (16-bit) in big-endian order to the buffer
+	 * @param value
+	 * @return the writer
+	 */
+	public BufferedByteWriter put16(short value)
+	{
+		ensureCapacity(2);
+		mWriter.putShort(value);
+		return this;
+	}
+
+	/**
+	 * Write the given int value (32-bit) in big-endian order to the buffer
+	 * @param value
+	 * @return the writer
+	 */
+	public BufferedByteWriter put32(int value)
+	{
+		ensureCapacity(4);
+		mWriter.putInt(value);
+		return this;
+	}
+
+	/**
+	 * Write the given long value (64-bit) in big-endian order to the buffer
+	 * @param value
+	 * @return the writer
+	 */
+	public BufferedByteWriter put64(long value)
+	{
+		ensureCapacity(8);
+		mWriter.putLong(value);
+		return this;
+	}
+
+	/**
+	 * Convert the internal buffer to a new byte array.
+	 * @return byte array
+	 */
+	public byte[] toByteArray()
+	{
+		int length = mWriter.position();
+		byte[] bytes = new byte[length];
+		System.arraycopy(mBuffer, 0, bytes, 0, length);
+		return bytes;
+	}
+}