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    }