# LimitedInputStream.java

    /*
     * 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.commons.fileupload.util;

    import java.io.FilterInputStream;
    import java.io.IOException;
    import java.io.InputStream;

    /**
     * An input stream, which limits its data size. This stream is
     * used, if the content length is unknown.
     */
    public abstract class LimitedInputStream extends FilterInputStream implements Closeable {

        /**
         * The maximum size of an item, in bytes.
         */
        private final long sizeMax;

        /**
         * The current number of bytes.
         */
        private long count;

        /**
         * Whether this stream is already closed.
         */
        private boolean closed;

        /**
         * Creates a new instance.
         *
         * @param inputStream The input stream, which shall be limited.
         * @param sizeMax The limit; no more than this number of bytes
         *   shall be returned by the source stream.
         */
        public LimitedInputStream(final InputStream inputStream, final long sizeMax) {
            super(inputStream);
            this.sizeMax = sizeMax;
        }

        /**
         * Called to check, whether the input streams
         * limit is reached.
         *
         * @throws IOException The given limit is exceeded.
         */
        private void checkLimit() throws IOException {
            if (count > sizeMax) {
                raiseError(sizeMax, count);
            }
        }

        /**
         * Closes this input stream and releases any system resources
         * associated with the stream.
         * This
         * method simply performs {@code in.close()}.
         *
         * @throws  IOException  if an I/O error occurs.
         * @see        java.io.FilterInputStream#in
         */
        @Override
        public void close() throws IOException {
            closed = true;
            super.close();
        }

        /**
         * Returns, whether this stream is already closed.
         *
         * @return True, if the stream is closed, otherwise false.
         * @throws IOException An I/O error occurred.
         */
        @Override
        public boolean isClosed() throws IOException {
            return closed;
        }

        /**
         * Called to indicate, that the input streams limit has
         * been exceeded.
         *
         * @param sizeMax The input streams limit, in bytes.
         * @param count The actual number of bytes.
         * @throws IOException The called method is expected
         *   to raise an IOException.
         */
        protected abstract void raiseError(long sizeMax, long count) throws IOException;

        /**
         * Reads the next byte of data from this input stream. The value
         * byte is returned as an {@code int} in the range
         * {@code 0} to {@code 255}. If no byte is available
         * because the end of the stream has been reached, the value
         * {@code -1} is returned. This method blocks until input data
         * is available, the end of the stream is detected, or an exception
         * is thrown.
         * <p>
         * This method
         * simply performs {@code in.read()} and returns the result.
         * </p>
         *
         * @return     the next byte of data, or {@code -1} if the end of the
         *             stream is reached.
         * @throws  IOException  if an I/O error occurs.
         * @see        java.io.FilterInputStream#in
         */
        @Override
        public int read() throws IOException {
            final int res = super.read();
            if (res != -1) {
                count++;
                checkLimit();
            }
            return res;
        }

        /**
         * Reads up to {@code len} bytes of data from this input stream
         * into an array of bytes. If {@code len} is not zero, the method
         * blocks until some input is available; otherwise, no
         * bytes are read and {@code 0} is returned.
         * <p>
         * This method simply performs {@code in.read(b, off, len)}
         * and returns the result.
         * </p>
         *
         * @param      b     the buffer into which the data is read.
         * @param      off   The start offset in the destination array
         *                   {@code b}.
         * @param      len   the maximum number of bytes read.
         * @return     the total number of bytes read into the buffer, or
         *             {@code -1} if there is no more data because the end of
         *             the stream has been reached.
         * @throws  NullPointerException If {@code b} is {@code null}.
         * @throws  IndexOutOfBoundsException If {@code off} is negative,
         * {@code len} is negative, or {@code len} is greater than
         * {@code b.length - off}
         * @throws  IOException  if an I/O error occurs.
         * @see        java.io.FilterInputStream#in
         */
        @Override
        public int read(final byte[] b, final int off, final int len) throws IOException {
            final int res = super.read(b, off, len);
            if (res > 0) {
                count += res;
                checkLimit();
            }
            return res;
        }

    }