src/main/java/org/apache/commons/net/io/DotTerminatedMessageWriter.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.commons.net.io;

import java.io.IOException;
import java.io.Writer;

/***
 * DotTerminatedMessageWriter is a class used to write messages to a
 * server that are terminated by a single dot followed by a
 * <CR><LF>
 * sequence and with double dots appearing at the begining of lines which
 * do not signal end of message yet start with a dot.  Various Internet
 * protocols such as NNTP and POP3 produce messages of this type.
 * <p>
 * This class handles the doubling of line-starting periods,
 * converts single linefeeds to NETASCII newlines, and on closing
 * will send the final message terminator dot and NETASCII newline
 * sequence.
 *
 *
 ***/

public final class DotTerminatedMessageWriter extends Writer
{
    private static final int NOTHING_SPECIAL_STATE = 0;
    private static final int LAST_WAS_CR_STATE = 1;
    private static final int LAST_WAS_NL_STATE = 2;

    private int state;
    private Writer output;


    /***
     * Creates a DotTerminatedMessageWriter that wraps an existing Writer
     * output destination.
     *
     * @param output  The Writer output destination to write the message.
     ***/
    public DotTerminatedMessageWriter(final Writer output)
    {
        super(output);
        this.output = output;
        this.state = NOTHING_SPECIAL_STATE;
    }


    /***
     * Writes a character to the output.  Note that a call to this method
     * may result in multiple writes to the underling Writer in order to
     * convert naked linefeeds to NETASCII line separators and to double
     * line-leading periods.  This is transparent to the programmer and
     * is only mentioned for completeness.
     *
     * @param ch  The character to write.
     * @throws IOException  If an error occurs while writing to the
     *            underlying output.
     ***/
    @Override
    public void write(final int ch) throws IOException
    {
        synchronized (lock)
        {
            switch (ch)
            {
            case '\r':
                state = LAST_WAS_CR_STATE;
                output.write('\r');
                return ;
            case '\n':
                if (state != LAST_WAS_CR_STATE) {
                    output.write('\r');
                }
                output.write('\n');
                state = LAST_WAS_NL_STATE;
                return ;
            case '.':
                // Double the dot at the beginning of a line
                if (state == LAST_WAS_NL_STATE) {
                    output.write('.');
                }
                //$FALL-THROUGH$
            default:
                state = NOTHING_SPECIAL_STATE;
                output.write(ch);
            }
        }
    }


    /***
     * Writes a number of characters from a character array to the output
     * starting from a given offset.
     *
     * @param buffer  The character array to write.
     * @param offset  The offset into the array at which to start copying data.
     * @param length  The number of characters to write.
     * @throws IOException If an error occurs while writing to the underlying
     *            output.
     ***/
    @Override
    public void write(final char[] buffer, int offset, int length) throws IOException
    {
        synchronized (lock)
        {
            while (length-- > 0) {
                write(buffer[offset++]);
            }
        }
    }


    /***
     * Writes a character array to the output.
     *
     * @param buffer  The character array to write.
     * @throws IOException If an error occurs while writing to the underlying
     *            output.
     ***/
    @Override
    public void write(final char[] buffer) throws IOException
    {
        write(buffer, 0, buffer.length);
    }


    /***
     * Writes a String to the output.
     *
     * @param string  The String to write.
     * @throws IOException If an error occurs while writing to the underlying
     *            output.
     ***/
    @Override
    public void write(final String string) throws IOException
    {
        write(string.toCharArray());
    }


    /***
     * Writes part of a String to the output starting from a given offset.
     *
     * @param string  The String to write.
     * @param offset  The offset into the String at which to start copying data.
     * @param length  The number of characters to write.
     * @throws IOException If an error occurs while writing to the underlying
     *            output.
     ***/
    @Override
    public void write(final String string, final int offset, final int length) throws IOException
    {
        write(string.toCharArray(), offset, length);
    }


    /***
     * Flushes the underlying output, writing all buffered output.
     *
     * @throws IOException If an error occurs while writing to the underlying
     *            output.
     ***/
    @Override
    public void flush() throws IOException
    {
        synchronized (lock)
        {
            output.flush();
        }
    }


    /***
     * Flushes the underlying output, writing all buffered output, but doesn't
     * actually close the underlying stream.  The underlying stream may still
     * be used for communicating with the server and therefore is not closed.
     *
     * @throws IOException If an error occurs while writing to the underlying
     *            output or closing the Writer.
     ***/
    @Override
    public void close() throws IOException
    {
        synchronized (lock)
        {
            if (output == null) {
                return ;
            }

            if (state == LAST_WAS_CR_STATE) {
                output.write('\n');
            } else if (state != LAST_WAS_NL_STATE) {
                output.write("\r\n");
            }

            output.write(".\r\n");

            output.flush();
            output = null;
        }
    }

}