    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 *      https://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 */
    017package org.apache.commons.io.input;
    018
    019import static org.apache.commons.io.IOUtils.EOF;
    020
    021import java.io.IOException;
    022import java.io.Reader;
    023
    024import org.apache.commons.io.IOUtils;
    025
    026/**
    027 * Always returns {@link IOUtils#EOF} to all attempts to read something from it.
    028 * <p>
    029 * Typically uses of this class include testing for corner cases in methods that accept readers and acting as a sentinel
    030 * value instead of a {@code null} reader.
    031 * </p>
    032 *
    033 * @since 2.7
    034 */
    035public class ClosedReader extends Reader {
    036
    037    /**
    038     * The singleton instance.
    039     *
    040     * @since 2.12.0
    041     */
    042    public static final ClosedReader INSTANCE = new ClosedReader();
    043
    044    /**
    045     * The singleton instance.
    046     *
    047     * @deprecated {@link #INSTANCE}.
    048     */
    049    @Deprecated
    050    public static final ClosedReader CLOSED_READER = INSTANCE;
    051
    052    /**
    053     * Construct a new instance.
    054     */
    055    public ClosedReader() {
    056        // empty
    057    }
    058
    059    @Override
    060    public void close() throws IOException {
    061        // noop
    062    }
    063
    064    /**
    065     * A no-op read method that always indicates end-of-stream.
    066     *
    067     * <p>Behavior:</p>
    068     * <ul>
    069     *   <li>If {@code len == 0}, returns {@code 0} immediately (no characters are read).</li>
    070     *   <li>Otherwise, always returns {@value IOUtils#EOF} to signal that the stream is closed or at end-of-stream.</li>
    071     * </ul>
    072     *
    073     * @param cbuf The destination buffer.
    074     * @param off  The offset at which to start storing characters.
    075     * @param len  The maximum number of characters to read.
    076     * @return {@code 0} if {@code len == 0}; otherwise always {@value IOUtils#EOF}.
    077     * @throws IndexOutOfBoundsException If {@code off < 0}, {@code len < 0}, or {@code off + len > cbuf.length}.
    078     */
    079    @Override
    080    public int read(final char[] cbuf, final int off, final int len) {
    081        IOUtils.checkFromIndexSize(cbuf, off, len);
    082        if (len == 0) {
    083            return 0;
    084        }
    085        return EOF;
    086    }
    087
    088}