streamutils.java

Bluetooth chat Server and Client in j2me

/*
 The Bluetooth Library for client-server communication
 Copyright (C) 2006 Martin Vysny

 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.

 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 net.sf.btw.tools;

import java.io.ByteArrayOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

/**
 * Utilities for working with streams.
 * 
 * @author Martin Vysny
 */
public final class StreamUtils {
	private StreamUtils() {
		// hidden
	}

	/**
	 * Writes the byte array to the output stream.
	 * 
	 * @param bytes
	 *            the bytes to write. Handles <code>null</code> array
	 *            correctly.
	 * @param out
	 *            writes to this stream.
	 * @throws IOException
	 *             if write fails.
	 */
	public static void writeByteArray(final byte[] bytes, final OutputStream out)
			throws IOException {
		writePackedInt(bytes == null ? -1 : bytes.length, out);
		if (bytes != null)
			out.write(bytes);
	}

	/**
	 * Reads the byte array from the input stream. The array must have been
	 * written by {@link #writeByteArray(byte[], OutputStream)}.
	 * 
	 * @param in
	 *            reads from this stream.
	 * @throws IOException
	 *             if read fails.
	 * @return byte array, may be <code>null</code> if a null array was
	 *         written.
	 */
	public static byte[] readByteArray(final InputStream in) throws IOException {
		final int length = readPackedInt(in);
		if (length < 0)
			return null;
		final byte[] result = new byte[length];
		if (length == 0)
			return result;
		if (in.read(result) < length)
			throw new EOFException("Packet.readByteArray()"); //$NON-NLS-1$
		return result;
	}

	/**
	 * Writes the number in a packed format. The number may occupy 1-5 bytes
	 * depending on its value.
	 * 
	 * @param number
	 *            the number to write
	 * @param out
	 *            the output stream.
	 * @throws IOException
	 */
	public static void writePackedInt(final int number, OutputStream out)
			throws IOException {
		int numberToWrite = number;
		final boolean negative = (numberToWrite < 0);
		if (negative)
			numberToWrite = ~numberToWrite;
		byte dataBits = 6;
		int dataMask = 0x3F;
		do {
			int byteToWrite = (numberToWrite & dataMask);
			if ((dataBits == 6) && negative)
				byteToWrite |= 0x40;
			numberToWrite >>= dataBits;
			if (numberToWrite != 0)
				byteToWrite |= 0x80;
			dataBits = 7;
			dataMask = 0x7f;
			out.write(byteToWrite);
		} while (numberToWrite != 0);
	}

	/**
	 * Reads the number in a packed format. The number may occupy 1-5 bytes
	 * depending on its value.
	 * 
	 * @param in
	 *            the input stream.
	 * @return the number.
	 * @throws IOException
	 */
	public static int readPackedInt(InputStream in) throws IOException {
		int result = 0;
		boolean negative = false;
		byte currentBit = 0;
		int byteRead;
		do {
			byteRead = in.read();
			if (byteRead < 0)
				throw new EOFException("StreamUtils.readPackedInt(): EOF"); //$NON-NLS-1$
			if (currentBit == 0) {
				negative = (byteRead & 0x40) != 0;
				byteRead &= ~0x40;
			}
			int value = (byteRead & 0x7f) << currentBit;
			result += value;
			if (currentBit == 0)
				currentBit = 6;
			else
				currentBit += 7;
		} while (byteRead >= 0x80);
		if (negative)
			result = ~result;
		return result;
	}

	/**
	 * Writes given string to data output stream as a string. This method is
	 * incompatible with {@link String#getBytes()}; use
	 * {@link DataInputStream#readUTF()} instead.
	 * 
	 * @param string
	 *            string to convert. Cannot be <code>null</code>.
	 * @return array of bytes.
	 */
	public static byte[] stringToByteArray(final String string) {
		final ByteArrayOutputStream out = new ByteArrayOutputStream(string
				.length());
		final DataOutputStream dataOut = new DataOutputStream(out);
		try {
			dataOut.writeUTF(string);
			dataOut.flush();
		} catch (IOException e) {
			// shouldn't happen...
			Logger.error(null, e);
			throw new Error();
		}
		return out.toByteArray();
	}
}