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 *      http://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.BufferedReader;
021import java.io.IOException;
022import java.io.Reader;
023
024import org.apache.commons.net.util.NetConstants;
025
026/**
027 * CRLFLineReader implements a readLine() method that requires exactly CRLF to terminate an input line. This is required for IMAP, which allows bare CR and LF.
028 *
029 * @since 3.0
030 */
031public final class CRLFLineReader extends BufferedReader {
032    private static final char LF = '\n';
033    private static final char CR = '\r';
034
035    /**
036     * Creates a CRLFLineReader that wraps an existing Reader input source.
037     *
038     * @param reader The Reader input source.
039     */
040    public CRLFLineReader(final Reader reader) {
041        super(reader);
042    }
043
044    /**
045     * Read a line of text. A line is considered to be terminated by carriage return followed immediately by a linefeed. This contrasts with BufferedReader
046     * which also allows other combinations.
047     *
048     * @since 3.0
049     */
050    @Override
051    public String readLine() throws IOException {
052        final StringBuilder sb = new StringBuilder();
053        int intch;
054        boolean prevWasCR = false;
055        synchronized (lock) { // make thread-safe (hopefully!)
056            while ((intch = read()) != NetConstants.EOS) {
057                if (prevWasCR && intch == LF) {
058                    return sb.substring(0, sb.length() - 1);
059                }
060                prevWasCR = intch == CR;
061                sb.append((char) intch);
062            }
063        }
064        final String string = sb.toString();
065        if (string.isEmpty()) { // immediate EOF
066            return null;
067        }
068        return string;
069    }
070}