FixedConsumer.java

/*
 * FixedConsumer.java February 2007
 *
 * Copyright (C) 2001, Niall Gallagher <niallg@users.sf.net>
 *
 * Licensed 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.simpleframework.http.message;

import java.io.IOException;

import org.simpleframework.util.buffer.Allocator;
import org.simpleframework.util.buffer.Buffer;

/**
 * The <code>FixedConsumer</code> object reads a fixed number of bytes from the
 * cursor. This is typically used when the Content-Length header is used as the
 * body delimiter. In order to determine when the full body has been consumed
 * this counts the bytes read. Once all the bytes have been read any overflow
 * will be reset. All of the bytes read are appended to the internal buffer so
 * they can be read.
 * 
 * @author Niall Gallagher
 */
public class FixedConsumer extends UpdateConsumer {

    /**
     * This is the allocator used to allocate the buffer used.
     */
    private Allocator allocator;

    /**
     * This is the internal buffer used to accumulate the body.
     */
    private Buffer buffer;

    /**
     * This is the number of bytes to be consumed from the cursor.
     */
    private long limit;

    /**
     * Constructor for the <code>FixedConsumer</code> object. This is used to
     * create a consumer that reads a fixed number of bytes from the cursor and
     * accumulates those bytes in an internal buffer so that it can be read at a
     * later stage.
     * 
     * @param allocator
     *            this is used to allocate the internal buffer
     * @param limit
     *            this is the number of bytes that are to be read
     */
    public FixedConsumer(Allocator allocator, long limit) {
        this.allocator = allocator;
        this.limit = limit;
    }

    /**
     * This is used to acquire the body that has been consumed. This will return
     * a body which can be used to read the content of the message, also if the
     * request is multipart upload then all of the parts are provided as
     * <code>Attachment</code> objects. Each part can then be read as an
     * individual message.
     * 
     * @return the body that has been consumed by this instance
     */
    @Override
    public Body getBody() {
        return new BufferBody(this.buffer);
    }

    /**
     * This method is used to append the contents of the array to the internal
     * buffer. The appended bytes can be acquired from the internal buffer using
     * an <code>InputStream</code>, or the text of the appended bytes can be
     * acquired by encoding the bytes.
     * 
     * @param array
     *            this is the array of bytes to be appended
     * @param off
     *            this is the start offset in the array to read from
     * @param len
     *            this is the number of bytes to write to the buffer
     */
    private void append(byte[] array, int off, int len) throws IOException {
        if (this.buffer == null) {
            this.buffer = this.allocator.allocate(this.limit);
        }
        this.buffer.append(array, off, len);
    }

    /**
     * This is used to process the bytes that have been read from the cursor.
     * This will count the number of bytes read, once all of the bytes that form
     * the body have been read this returns the number of bytes that represent
     * the overflow.
     * 
     * @param array
     *            this is a chunk read from the cursor
     * @param off
     *            this is the offset within the array the chunk starts
     * @param count
     *            this is the number of bytes within the array
     * 
     * @return this returns the number of bytes overflow that is read
     */
    @Override
    protected int update(byte[] array, int off, int count) throws IOException {
        int mark = (int) this.limit;

        if (count >= this.limit) {
            this.append(array, off, mark);
            this.finished = true;
            this.limit = 0;
            return count - mark;
        }
        if (count > 0) {
            this.append(array, off, count);
            this.limit -= count;
        }
        return 0;
    }
}