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 */
017package org.apache.commons.io.output;
018
019import java.io.IOException;
020import java.io.OutputStream;
021
022import org.apache.commons.io.function.IOConsumer;
023import org.apache.commons.io.function.IOFunction;
024
025/**
026 * An output stream which triggers an event when a specified number of bytes of data have been written to it. The event
027 * can be used, for example, to throw an exception if a maximum has been reached, or to switch the underlying stream
028 * type when the threshold is exceeded.
029 * <p>
030 * This class overrides all {@code OutputStream} methods. However, these overrides ultimately call the corresponding
031 * methods in the underlying output stream implementation.
032 * </p>
033 * <p>
034 * NOTE: This implementation may trigger the event <em>before</em> the threshold is actually reached, since it triggers
035 * when a pending write operation would cause the threshold to be exceeded.
036 * </p>
037 */
038public class ThresholdingOutputStream extends OutputStream {
039
040    /**
041     * Noop output stream getter function.
042     */
043    private static IOFunction<ThresholdingOutputStream, OutputStream> NOOP_OS_GETTER = os -> NullOutputStream.NULL_OUTPUT_STREAM;
044
045    /**
046     * The threshold at which the event will be triggered.
047     */
048    private final int threshold;
049
050    /**
051     * Accepts reaching the threshold.
052     */
053    private final IOConsumer<ThresholdingOutputStream> thresholdConsumer;
054
055    /**
056     * Gets the output stream.
057     */
058    private final IOFunction<ThresholdingOutputStream, OutputStream> outputStreamGetter;
059
060    /**
061     * The number of bytes written to the output stream.
062     */
063    private long written;
064
065    /**
066     * Whether or not the configured threshold has been exceeded.
067     */
068    private boolean thresholdExceeded;
069
070    /**
071     * Constructs an instance of this class which will trigger an event at the specified threshold.
072     *
073     * @param threshold The number of bytes at which to trigger an event.
074     */
075    public ThresholdingOutputStream(final int threshold) {
076        this(threshold, IOConsumer.noop(), NOOP_OS_GETTER);
077    }
078
079    /**
080     * Constructs an instance of this class which will trigger an event at the specified threshold.
081     *
082     * @param threshold The number of bytes at which to trigger an event.
083     * @param thresholdConsumer Accepts reaching the threshold.
084     * @param outputStreamGetter Gets the output stream.
085     * @since 2.9.0
086     */
087    public ThresholdingOutputStream(final int threshold, final IOConsumer<ThresholdingOutputStream> thresholdConsumer,
088        final IOFunction<ThresholdingOutputStream, OutputStream> outputStreamGetter) {
089        this.threshold = threshold;
090        this.thresholdConsumer = thresholdConsumer == null ? IOConsumer.noop() : thresholdConsumer;
091        this.outputStreamGetter = outputStreamGetter == null ? NOOP_OS_GETTER : outputStreamGetter;
092    }
093
094    /**
095     * Checks to see if writing the specified number of bytes would cause the configured threshold to be exceeded. If
096     * so, triggers an event to allow a concrete implementation to take action on this.
097     *
098     * @param count The number of bytes about to be written to the underlying output stream.
099     *
100     * @throws IOException if an error occurs.
101     */
102    protected void checkThreshold(final int count) throws IOException {
103        if (!thresholdExceeded && written + count > threshold) {
104            thresholdExceeded = true;
105            thresholdReached();
106        }
107    }
108
109    /**
110     * Closes this output stream and releases any system resources associated with this stream.
111     *
112     * @throws IOException if an error occurs.
113     */
114    @Override
115    public void close() throws IOException {
116        try {
117            flush();
118        } catch (final IOException ignored) {
119            // ignore
120        }
121        getStream().close();
122    }
123
124    /**
125     * Flushes this output stream and forces any buffered output bytes to be written out.
126     *
127     * @throws IOException if an error occurs.
128     */
129    @SuppressWarnings("resource") // the underlying stream is managed by a subclass.
130    @Override
131    public void flush() throws IOException {
132        getStream().flush();
133    }
134
135    /**
136     * Returns the number of bytes that have been written to this output stream.
137     *
138     * @return The number of bytes written.
139     */
140    public long getByteCount() {
141        return written;
142    }
143
144    /**
145     * Returns the underlying output stream, to which the corresponding {@code OutputStream} methods in this class will
146     * ultimately delegate.
147     *
148     * @return The underlying output stream.
149     *
150     * @throws IOException if an error occurs.
151     */
152    protected OutputStream getStream() throws IOException {
153        return outputStreamGetter.apply(this);
154    }
155
156    /**
157     * Returns the threshold, in bytes, at which an event will be triggered.
158     *
159     * @return The threshold point, in bytes.
160     */
161    public int getThreshold() {
162        return threshold;
163    }
164
165    /**
166     * Determines whether or not the configured threshold has been exceeded for this output stream.
167     *
168     * @return {@code true} if the threshold has been reached; {@code false} otherwise.
169     */
170    public boolean isThresholdExceeded() {
171        return written > threshold;
172    }
173
174    /**
175     * Resets the byteCount to zero. You can call this from {@link #thresholdReached()} if you want the event to be
176     * triggered again.
177     */
178    protected void resetByteCount() {
179        this.thresholdExceeded = false;
180        this.written = 0;
181    }
182
183    /**
184     * Sets the byteCount to count. Useful for re-opening an output stream that has previously been written to.
185     *
186     * @param count The number of bytes that have already been written to the output stream
187     *
188     * @since 2.5
189     */
190    protected void setByteCount(final long count) {
191        this.written = count;
192    }
193
194    /**
195     * Indicates that the configured threshold has been reached, and that a subclass should take whatever action
196     * necessary on this event. This may include changing the underlying output stream.
197     *
198     * @throws IOException if an error occurs.
199     */
200    protected void thresholdReached() throws IOException {
201        thresholdConsumer.accept(this);
202    }
203
204    /**
205     * Writes {@code b.length} bytes from the specified byte array to this output stream.
206     *
207     * @param b The array of bytes to be written.
208     *
209     * @throws IOException if an error occurs.
210     */
211    @SuppressWarnings("resource") // the underlying stream is managed by a subclass.
212    @Override
213    public void write(final byte[] b) throws IOException {
214        checkThreshold(b.length);
215        getStream().write(b);
216        written += b.length;
217    }
218
219    /**
220     * Writes {@code len} bytes from the specified byte array starting at offset {@code off} to this output stream.
221     *
222     * @param b The byte array from which the data will be written.
223     * @param off The start offset in the byte array.
224     * @param len The number of bytes to write.
225     *
226     * @throws IOException if an error occurs.
227     */
228    @SuppressWarnings("resource") // the underlying stream is managed by a subclass.
229    @Override
230    public void write(final byte[] b, final int off, final int len) throws IOException {
231        checkThreshold(len);
232        getStream().write(b, off, len);
233        written += len;
234    }
235
236    /**
237     * Writes the specified byte to this output stream.
238     *
239     * @param b The byte to be written.
240     *
241     * @throws IOException if an error occurs.
242     */
243    @SuppressWarnings("resource") // the underlying stream is managed by a subclass.
244    @Override
245    public void write(final int b) throws IOException {
246        checkThreshold(1);
247        getStream().write(b);
248        written++;
249    }
250}