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package com.sun.ukit.jaxp;

import java.io.Reader;
import java.io.InputStream;
import java.io.IOException;
import java.io.UnsupportedEncodingException;

/**
 * UTF-8 transformed UCS-2 character stream reader.
 *
 * This reader converts UTF-8 transformed UCS-2 characters to Java characters.
 * The UCS-2 subset of UTF-8 transformation is described in RFC-2279 #2 
 * "UTF-8 definition":
 *  0000 0000-0000 007F   0xxxxxxx
 *  0000 0080-0000 07FF   110xxxxx 10xxxxxx
 *  0000 0800-0000 FFFF   1110xxxx 10xxxxxx 10xxxxxx
 *
 * This reader will return incorrect last character on broken UTF-8 stream. 
 */
public class ReaderUTF8
	extends Reader
{
	private InputStream is;

	/**
	 * Constructor.
	 *
     * @param is A byte input stream.
	 */
	public ReaderUTF8(InputStream is)
	{
		this.is = is;
	}

	/**
	 * Reads characters into a portion of an array.
	 *
	 * @param cbuf Destination buffer.
	 * @param off Offset at which to start storing characters.
	 * @param len Maximum number of characters to read.
     * @exception IOException If any IO errors occur.
     * @exception UnsupportedEncodingException If UCS-4 character occur in the stream.
	 */
	public int read(char[] cbuf, int off, int len)
		throws IOException
	{
		int  num = 0;
		int  val;
		while (num < len) {
			if ((val = is.read()) < 0)
				return (num != 0)? num: -1;
			switch (val & 0xf0) {
			case 0xc0:
			case 0xd0:
				cbuf[off++] = (char)(((val & 0x1f) << 6) | (is.read() & 0x3f));
				break;

			case 0xe0:
				cbuf[off++] = (char)(((val & 0x0f) << 12) | 
					((is.read() & 0x3f) << 6) | (is.read() & 0x3f));
				break;

			case 0xf0:	// UCS-4 character
				throw new UnsupportedEncodingException();

			default:
				cbuf[off++] = (char)val;
				break;
			}
			num++;
		}
		return num;
	}

	/**
	 * Reads a single character.
	 *
	 * @return The character read, as an integer in the range 0 to 65535 
	 *	(0x00-0xffff), or -1 if the end of the stream has been reached.
     * @exception IOException If any IO errors occur.
     * @exception UnsupportedEncodingException If UCS-4 character occur in the stream.
	 */
	public int read()
		throws IOException
	{
		int  val;
		if ((val = is.read()) < 0)
			return -1;
		switch (val & 0xf0) {
		case 0xc0:
		case 0xd0:
			val = ((val & 0x1f) << 6) | (is.read() & 0x3f);
			break;

		case 0xe0:
			val = ((val & 0x0f) << 12) | 
				((is.read() & 0x3f) << 6) | (is.read() & 0x3f);
			break;

		case 0xf0:	// UCS-4 character
			throw new UnsupportedEncodingException();

		default:
			break;
		}
		return val;
	}

	/**
	 * Closes the stream.
	 *
     * @exception IOException If any IO errors occur.
	 */
	public void close()
		throws IOException
	{
		is.close();
	}
}