    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
    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 */
    031public 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(final 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        final 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        final String string = sb.toString();
    072        if (string.length() == 0) { // immediate EOF
    073            return null;
    074        }
    075        return string;
    076    }
    077}