messageoutputstream.java

java 开发的一个电子邮局,挺实用的

/*
 * MessageOutputStream.java
 * Copyright (C) 1999 dog <[e-mail]>
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 * 
 * This library 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
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 * 
 * You may retrieve the latest version of this library from
 * http://www.dog.net.uk/knife/
 */

package dog.mail.util;

import java.io.*;

/**
 * An output stream that escapes any dots on a line by themself with
 * another dot, for the purposes of sending messages to SMTP and NNTP servers.
 *
 * @author [e-mail]
 * @version 1.0
 */
public class MessageOutputStream extends FilterOutputStream {

	/**
	 * The stream termination octet.
	 */
	public static final int END = 46;
	
	/**
	 * The line termination octet.
	 */
	public static final int LF = 10;

	int last = -1; // the last character written to the stream
	
	/**
	 * Constructs a message output stream connected to the specified output stream.
	 * @param out the target output stream
	 */
	public MessageOutputStream(OutputStream out) {
		super(out);
	}

	/**
	 * Writes a character to the underlying stream.
	 * @exception IOException if an I/O error occurred
	 */
	public void write(int ch) throws IOException {
		if ((last==LF || last==-1) && ch==END)
			out.write(END); // double any lonesome dots
		super.write(ch);
	}

	/**
	 * Writes a portion of a byte array to the underlying stream.
	 * @exception IOException if an I/O error occurred
	 */
	public void write(byte b[], int off, int len) throws IOException {
		int k = last != -1 ? last : LF;
		int l = off;
		len += off;
		for (int i = off; i < len; i++) {
			if (k==LF && b[i]==END) {
				super.write(b, l, i-l);
				out.write(END);
				l = i;
			}
			k = b[i];
		}
		if (len-l > 0)
			super.write(b, l, len-l);
	}
	
}