    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      https://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017
    018package org.apache.commons.net.io;
    019
    020import java.io.IOException;
    021import java.io.Writer;
    022
    023/**
    024 * DotTerminatedMessageWriter is a class used to write messages to a server that are terminated by a single dot followed by a &lt;CR&gt;&lt;LF&gt; sequence and
    025 * with double dots appearing at the beginning of lines which do not signal end of message yet start with a dot. Various Internet protocols such as
    026 * NNTP and POP3 produce messages of this type.
    027 * <p>
    028 * This class handles the doubling of line-starting periods, converts single linefeeds to NETASCII newlines, and on closing will send the final message
    029 * terminator dot and NETASCII newline sequence.
    030 * </p>
    031 */
    032public final class DotTerminatedMessageWriter extends Writer {
    033    private static final int NOTHING_SPECIAL_STATE = 0;
    034    private static final int LAST_WAS_CR_STATE = 1;
    035    private static final int LAST_WAS_NL_STATE = 2;
    036
    037    private int state;
    038    private Writer output;
    039
    040    /**
    041     * Creates a DotTerminatedMessageWriter that wraps an existing Writer output destination.
    042     *
    043     * @param output The Writer output destination to write the message.
    044     */
    045    public DotTerminatedMessageWriter(final Writer output) {
    046        super(output);
    047        this.output = output;
    048        this.state = NOTHING_SPECIAL_STATE;
    049    }
    050
    051    /**
    052     * Flushes the underlying output, writing all buffered output, but doesn't actually close the underlying stream. The underlying stream may still be used for
    053     * communicating with the server and therefore is not closed.
    054     *
    055     * @throws IOException If an error occurs while writing to the underlying output or closing the Writer.
    056     */
    057    @Override
    058    public void close() throws IOException {
    059        synchronized (lock) {
    060            if (output == null) {
    061                return;
    062            }
    063
    064            if (state == LAST_WAS_CR_STATE) {
    065                output.write('\n');
    066            } else if (state != LAST_WAS_NL_STATE) {
    067                output.write("\r\n");
    068            }
    069
    070            output.write(".\r\n");
    071
    072            output.flush();
    073            output = null;
    074        }
    075    }
    076
    077    /**
    078     * Flushes the underlying output, writing all buffered output.
    079     *
    080     * @throws IOException If an error occurs while writing to the underlying output.
    081     */
    082    @Override
    083    public void flush() throws IOException {
    084        synchronized (lock) {
    085            output.flush();
    086        }
    087    }
    088
    089    /**
    090     * Writes a character array to the output.
    091     *
    092     * @param buffer The character array to write.
    093     * @throws IOException If an error occurs while writing to the underlying output.
    094     */
    095    @Override
    096    public void write(final char[] buffer) throws IOException {
    097        write(buffer, 0, buffer.length);
    098    }
    099
    100    /**
    101     * Writes a number of characters from a character array to the output starting from a given offset.
    102     *
    103     * @param buffer The character array to write.
    104     * @param offset The offset into the array at which to start copying data.
    105     * @param length The number of characters to write.
    106     * @throws IOException If an error occurs while writing to the underlying output.
    107     */
    108    @Override
    109    public void write(final char[] buffer, int offset, int length) throws IOException {
    110        synchronized (lock) {
    111            while (length-- > 0) {
    112                write(buffer[offset++]);
    113            }
    114        }
    115    }
    116
    117    /**
    118     * 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
    119     * linefeeds to NETASCII line separators and to double line-leading periods. This is transparent to the programmer and is only mentioned for completeness.
    120     *
    121     * @param ch The character to write.
    122     * @throws IOException If an error occurs while writing to the underlying output.
    123     */
    124    @Override
    125    public void write(final int ch) throws IOException {
    126        synchronized (lock) {
    127            switch (ch) {
    128            case '\r':
    129                state = LAST_WAS_CR_STATE;
    130                output.write('\r');
    131                return;
    132            case '\n':
    133                if (state != LAST_WAS_CR_STATE) {
    134                    output.write('\r');
    135                }
    136                output.write('\n');
    137                state = LAST_WAS_NL_STATE;
    138                return;
    139            case '.':
    140                // Double the dot at the beginning of a line
    141                if (state == LAST_WAS_NL_STATE) {
    142                    output.write('.');
    143                }
    144                // falls through$
    145            default:
    146                state = NOTHING_SPECIAL_STATE;
    147                output.write(ch);
    148            }
    149        }
    150    }
    151
    152    /**
    153     * Writes a String to the output.
    154     *
    155     * @param string The String to write.
    156     * @throws IOException If an error occurs while writing to the underlying output.
    157     */
    158    @Override
    159    public void write(final String string) throws IOException {
    160        write(string.toCharArray());
    161    }
    162
    163    /**
    164     * Writes part of a String to the output starting from a given offset.
    165     *
    166     * @param string The String to write.
    167     * @param offset The offset into the String at which to start copying data.
    168     * @param length The number of characters to write.
    169     * @throws IOException If an error occurs while writing to the underlying output.
    170     */
    171    @Override
    172    public void write(final String string, final int offset, final int length) throws IOException {
    173        write(string.toCharArray(), offset, length);
    174    }
    175
    176}