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 * DotTerminatedMessageReader is a class used to read messages from a server that are terminated by a single dot followed by a <CR><LF> sequence and
028 * 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
029 * NNTP and POP3 produce messages of this type.
030 * <p>
031 * This class handles stripping of the duplicate period at the beginning of lines starting with a period, and ensures you cannot read past the end of the
032 * message.
033 * <p>
034 * Note: versions since 3.0 extend BufferedReader rather than Reader, and no longer change the CRLF into the local EOL. Also, only DOT CR LF acts as EOF.
035 */
036public final class DotTerminatedMessageReader extends BufferedReader {
037    private static final char LF = '\n';
038    private static final char CR = '\r';
039    private static final int DOT = '.';
040
041    private boolean atBeginning;
042    private boolean eof;
043    private boolean seenCR; // was last character CR?
044
045    /**
046     * Creates a DotTerminatedMessageReader that wraps an existing Reader input source.
047     *
048     * @param reader The Reader input source containing the message.
049     */
050    public DotTerminatedMessageReader(final Reader reader) {
051        super(reader);
052        // Assumes input is at start of message
053        atBeginning = true;
054        eof = false;
055    }
056
057    /**
058     * Closes the message for reading. This doesn't actually close the underlying stream. The underlying stream may still be used for communicating with the
059     * server and therefore is not closed.
060     * <p>
061     * If the end of the message has not yet been reached, this method will read the remainder of the message until it reaches the end, so that the underlying
062     * stream may continue to be used properly for communicating with the server. If you do not fully read a message, you MUST close it, otherwise your program
063     * will likely hang or behave improperly.
064     *
065     * @throws IOException If an error occurs while reading the underlying stream.
066     */
067    @Override
068    public void close() throws IOException {
069        synchronized (lock) {
070            if (!eof) {
071                while (read() != -1) {
072                    // read to EOF
073                }
074            }
075            eof = true;
076            atBeginning = false;
077        }
078    }
079
080    /**
081     * Reads and returns the next character in the message. If the end of the message has been reached, returns -1. Note that a call to this method may result
082     * in multiple reads from the underlying input stream to decode the message properly (removing doubled dots and so on). All of this is transparent to the
083     * programmer and is only mentioned for completeness.
084     *
085     * @return The next character in the message. Returns -1 if the end of the message has been reached.
086     * @throws IOException If an error occurs while reading the underlying stream.
087     */
088    @Override
089    public int read() throws IOException {
090        synchronized (lock) {
091            if (eof) {
092                return NetConstants.EOS; // Don't allow read past EOF
093            }
094            int chint = super.read();
095            if (chint == NetConstants.EOS) { // True EOF
096                eof = true;
097                return NetConstants.EOS;
098            }
099            if (atBeginning) {
100                atBeginning = false;
101                if (chint == DOT) { // Have DOT
102                    mark(2); // need to check for CR LF or DOT
103                    chint = super.read();
104                    switch (chint) {
105                    case NetConstants.EOS:
106                        // new Throwable("Trailing DOT").printStackTrace();
107                        eof = true;
108                        return DOT; // return the trailing DOT
109                    case DOT:
110                        // no need to reset as we want to lose the first DOT
111                        return chint; // i.e. DOT
112                    case CR:
113                        chint = super.read();
114                        if (chint == NetConstants.EOS) { // Still only DOT CR - should not happen
115                            // new Throwable("Trailing DOT CR").printStackTrace();
116                            reset(); // So CR is picked up next time
117                            return DOT; // return the trailing DOT
118                        }
119                        if (chint == LF) { // DOT CR LF
120                            atBeginning = true;
121                            eof = true;
122                            // Do we need to clear the mark somehow?
123                            return NetConstants.EOS;
124                        }
125                        break;
126                    default:
127                        break;
128                    }
129                    // Should not happen - lone DOT at beginning
130                    // new Throwable("Lone DOT followed by "+(char)chint).printStackTrace();
131                    reset();
132                    return DOT;
133                } // have DOT
134            } // atBeginning
135
136            // Handle CRLF in normal flow
137            if (seenCR) {
138                seenCR = false;
139                if (chint == LF) {
140                    atBeginning = true;
141                }
142            }
143            if (chint == CR) {
144                seenCR = true;
145            }
146            return chint;
147        }
148    }
149
150    /**
151     * Reads the next characters from the message into an array and returns the number of characters read. Returns -1 if the end of the message has been
152     * reached.
153     *
154     * @param buffer The character array in which to store the characters.
155     * @return The number of characters read. Returns -1 if the end of the message has been reached.
156     * @throws IOException If an error occurs in reading the underlying stream.
157     */
158    @Override
159    public int read(final char[] buffer) throws IOException {
160        return read(buffer, 0, buffer.length);
161    }
162
163    /**
164     * Reads the next characters from the message into an array and returns the number of characters read. Returns -1 if the end of the message has been
165     * reached. The characters are stored in the array starting from the given offset and up to the length specified.
166     *
167     * @param buffer The character array in which to store the characters.
168     * @param offset The offset into the array at which to start storing characters.
169     * @param length The number of characters to read.
170     * @return The number of characters read. Returns -1 if the end of the message has been reached.
171     * @throws IOException If an error occurs in reading the underlying stream.
172     */
173    @Override
174    public int read(final char[] buffer, int offset, int length) throws IOException {
175        if (length < 1) {
176            return 0;
177        }
178        int ch;
179        synchronized (lock) {
180            if ((ch = read()) == -1) {
181                return NetConstants.EOS;
182            }
183
184            final int off = offset;
185
186            do {
187                buffer[offset++] = (char) ch;
188            } while (--length > 0 && (ch = read()) != -1);
189
190            return offset - off;
191        }
192    }
193
194    /**
195     * Read a line of text. A line is considered to be terminated by carriage return followed immediately by a linefeed. This contrasts with BufferedReader
196     * which also allows other combinations.
197     *
198     * @since 3.0
199     */
200    @Override
201    public String readLine() throws IOException {
202        final StringBuilder sb = new StringBuilder();
203        int intch;
204        synchronized (lock) { // make thread-safe (hopefully!)
205            while ((intch = read()) != NetConstants.EOS) {
206                if (intch == LF && atBeginning) {
207                    return sb.substring(0, sb.length() - 1);
208                }
209                sb.append((char) intch);
210            }
211        }
212        final String string = sb.toString();
213        if (string.isEmpty()) { // immediate EOF
214            return null;
215        }
216        // Should not happen - EOF without CRLF
217        // new Throwable(string).printStackTrace();
218        return string;
219    }
220}