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java/org/apache/tomcat/util/http/fileupload/ThresholdingOutputStream.java

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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.tomcat.util.http.fileupload;
+
+import java.io.IOException;
+import java.io.OutputStream;
+
+
+/**
+ * An output stream which triggers an event when a specified number of bytes of
+ * data have been written to it. The event can be used, for example, to throw
+ * an exception if a maximum has been reached, or to switch the underlying
+ * stream type when the threshold is exceeded.
+ * <p>
+ * This class overrides all <code>OutputStream</code> methods. However, these
+ * overrides ultimately call the corresponding methods in the underlying output
+ * stream implementation.
+ * <p>
+ * NOTE: This implementation may trigger the event <em>before</em> the threshold
+ * is actually reached, since it triggers when a pending write operation would
+ * cause the threshold to be exceeded.
+ */
+public abstract class ThresholdingOutputStream
+    extends OutputStream
+{
+
+    // ----------------------------------------------------------- Data members
+
+
+    /**
+     * The threshold at which the event will be triggered.
+     */
+    private final int threshold;
+
+
+    /**
+     * The number of bytes written to the output stream.
+     */
+    private long written;
+
+
+    /**
+     * Whether or not the configured threshold has been exceeded.
+     */
+    private boolean thresholdExceeded;
+
+
+    // ----------------------------------------------------------- Constructors
+
+
+    /**
+     * Constructs an instance of this class which will trigger an event at the
+     * specified threshold.
+     *
+     * @param threshold The number of bytes at which to trigger an event.
+     */
+    public ThresholdingOutputStream(final int threshold)
+    {
+        this.threshold = threshold;
+    }
+
+
+    // --------------------------------------------------- OutputStream methods
+
+
+    /**
+     * Writes the specified byte to this output stream.
+     *
+     * @param b The byte to be written.
+     *
+     * @throws IOException if an error occurs.
+     */
+    @Override
+    public void write(final int b) throws IOException
+    {
+        checkThreshold(1);
+        getStream().write(b);
+        written++;
+    }
+
+
+    /**
+     * Writes <code>b.length</code> bytes from the specified byte array to this
+     * output stream.
+     *
+     * @param b The array of bytes to be written.
+     *
+     * @throws IOException if an error occurs.
+     */
+    @Override
+    public void write(final byte b[]) throws IOException
+    {
+        checkThreshold(b.length);
+        getStream().write(b);
+        written += b.length;
+    }
+
+
+    /**
+     * Writes <code>len</code> bytes from the specified byte array starting at
+     * offset <code>off</code> to this output stream.
+     *
+     * @param b   The byte array from which the data will be written.
+     * @param off The start offset in the byte array.
+     * @param len The number of bytes to write.
+     *
+     * @throws IOException if an error occurs.
+     */
+    @Override
+    public void write(final byte b[], final int off, final int len) throws IOException
+    {
+        checkThreshold(len);
+        getStream().write(b, off, len);
+        written += len;
+    }
+
+
+    /**
+     * Flushes this output stream and forces any buffered output bytes to be
+     * written out.
+     *
+     * @throws IOException if an error occurs.
+     */
+    @Override
+    public void flush() throws IOException
+    {
+        getStream().flush();
+    }
+
+
+    /**
+     * Closes this output stream and releases any system resources associated
+     * with this stream.
+     *
+     * @throws IOException if an error occurs.
+     */
+    @Override
+    public void close() throws IOException
+    {
+        try
+        {
+            flush();
+        }
+        catch (final IOException ignored)
+        {
+            // ignore
+        }
+        getStream().close();
+    }
+
+
+    // --------------------------------------------------------- Public methods
+
+
+    /**
+     * Determines whether or not the configured threshold has been exceeded for
+     * this output stream.
+     *
+     * @return {@code true} if the threshold has been reached;
+     *         {@code false} otherwise.
+     */
+    public boolean isThresholdExceeded()
+    {
+        return written > threshold;
+    }
+
+
+    // ------------------------------------------------------ Protected methods
+
+
+    /**
+     * Checks to see if writing the specified number of bytes would cause the
+     * configured threshold to be exceeded. If so, triggers an event to allow
+     * a concrete implementation to take action on this.
+     *
+     * @param count The number of bytes about to be written to the underlying
+     *              output stream.
+     *
+     * @throws IOException if an error occurs.
+     */
+    protected void checkThreshold(final int count) throws IOException
+    {
+        if (!thresholdExceeded && written + count > threshold)
+        {
+            thresholdExceeded = true;
+            thresholdReached();
+        }
+    }
+
+    // ------------------------------------------------------- Abstract methods
+
+
+    /**
+     * Returns the underlying output stream, to which the corresponding
+     * <code>OutputStream</code> methods in this class will ultimately delegate.
+     *
+     * @return The underlying output stream.
+     *
+     * @throws IOException if an error occurs.
+     */
+    protected abstract OutputStream getStream() throws IOException;
+
+
+    /**
+     * Indicates that the configured threshold has been reached, and that a
+     * subclass should take whatever action necessary on this event. This may
+     * include changing the underlying output stream.
+     *
+     * @throws IOException if an error occurs.
+     */
+    protected abstract void thresholdReached() throws IOException;
+}