    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
    018    package org.apache.commons.net.io;
    019
    020    import java.io.BufferedReader;
    021    import java.io.IOException;
    022    import java.io.Reader;
    023
    024    /**
    025     * CRLFLineReader implements a readLine() method that requires
    026     * exactly CRLF to terminate an input line.
    027     * This is required for IMAP, which allows bare CR and LF.
    028     *
    029     * @since 3.0
    030     */
    031    public final class CRLFLineReader extends BufferedReader
    032    {
    033        private static final char LF = '\n';
    034        private static final char CR = '\r';
    035
    036        /**
    037         * Creates a CRLFLineReader that wraps an existing Reader
    038         * input source.
    039         * @param reader  The Reader input source.
    040         */
    041        public CRLFLineReader(Reader reader)
    042        {
    043            super(reader);
    044        }
    045
    046        /**
    047         * Read a line of text.
    048         * A line is considered to be terminated by carriage return followed immediately by a linefeed.
    049         * This contrasts with BufferedReader which also allows other combinations.
    050         * @since 3.0
    051         */
    052        @Override
    053        public String readLine() throws IOException {
    054            StringBuilder sb = new StringBuilder();
    055            int intch;
    056            boolean prevWasCR = false;
    057            synchronized(lock) { // make thread-safe (hopefully!)
    058                while((intch = read()) != -1)
    059                {
    060                    if (prevWasCR && intch == LF) {
    061                        return sb.substring(0, sb.length()-1);
    062                    }
    063                    if (intch == CR) {
    064                        prevWasCR = true;
    065                    } else {
    066                        prevWasCR = false;
    067                    }
    068                    sb.append((char) intch);
    069                }
    070            }
    071            String string = sb.toString();
    072            if (string.length() == 0) { // immediate EOF
    073                return null;
    074            }
    075            return string;
    076        }
    077    }