/*
 * $HeadURL: http://svn.apache.org/repos/asf/httpcomponents/httpcore/trunk/module-main/src/main/java/org/apache/http/impl/io/ChunkedOutputStream.java $
 * $Revision: 645081 $
 * $Date: 2008-04-05 04:36:42 -0700 (Sat, 05 Apr 2008) $
 *
 * ====================================================================
 * 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.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 */

package org.apache.http.impl.io;

import java.io.IOException;
import java.io.OutputStream;

import org.apache.http.io.SessionOutputBuffer;

/**
 * Implements chunked transfer coding.
 * See <a href="http://www.w3.org/Protocols/rfc2616/rfc2616.txt">RFC 2616</a>,
 * <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec3.html#sec3.6">section 3.6.1</a>.
 * Writes are buffered to an internal buffer (2048 default size).
 * 
 * @author Mohammad Rezaei (Goldman, Sachs & Co.)
 * @author <a href="mailto:oleg at ural.ru">Oleg Kalnichevski</a>
 * 
 * @since 4.0
 */
public class ChunkedOutputStream extends OutputStream {

    // ----------------------------------------------------- Instance Variables
    private final SessionOutputBuffer out;

    private byte[] cache;

    private int cachePosition = 0;

    private boolean wroteLastChunk = false;

    /** True if the stream is closed. */
    private boolean closed = false;
    
    // ----------------------------------------------------------- Constructors
    /**
     * Wraps a session output buffer and chunks the output.
     * @param out the session output buffer to wrap
     * @param bufferSize minimum chunk size (excluding last chunk)
     * @throws IOException
     */
    public ChunkedOutputStream(final SessionOutputBuffer out, int bufferSize)
            throws IOException {
        super();
        this.cache = new byte[bufferSize];
        this.out = out;
    }

    /**
     * Wraps a session output buffer and chunks the output. The default buffer 
     * size of 2048 was chosen because the chunk overhead is less than 0.5%
     *
     * @param out       the output buffer to wrap
     * @throws IOException
     */
    public ChunkedOutputStream(final SessionOutputBuffer out) 
            throws IOException {
        this(out, 2048);
    }

    // ----------------------------------------------------------- Internal methods
    /**
     * Writes the cache out onto the underlying stream
     * @throws IOException
     */
    protected void flushCache() throws IOException {
        if (this.cachePosition > 0) {
            this.out.writeLine(Integer.toHexString(this.cachePosition));
            this.out.write(this.cache, 0, this.cachePosition);
            this.out.writeLine("");
            this.cachePosition = 0;
        }
    }

    /**
     * Writes the cache and bufferToAppend to the underlying stream
     * as one large chunk
     * @param bufferToAppend
     * @param off
     * @param len
     * @throws IOException
     */
    protected void flushCacheWithAppend(byte bufferToAppend[], int off, int len) throws IOException {
        this.out.writeLine(Integer.toHexString(this.cachePosition + len));
        this.out.write(this.cache, 0, this.cachePosition);
        this.out.write(bufferToAppend, off, len);
        this.out.writeLine("");
        this.cachePosition = 0;
    }

    protected void writeClosingChunk() throws IOException {
        // Write the final chunk.
        this.out.writeLine("0");
        this.out.writeLine("");
    }

    // ----------------------------------------------------------- Public Methods
    /**
     * Must be called to ensure the internal cache is flushed and the closing chunk is written.
     * @throws IOException
     */
    public void finish() throws IOException {
        if (!this.wroteLastChunk) {
            flushCache();
            writeClosingChunk();
            this.wroteLastChunk = true;
        }
    }

    // -------------------------------------------- OutputStream Methods
    public void write(int b) throws IOException {
        if (this.closed) {
            throw new IOException("Attempted write to closed stream.");
        }
        this.cache[this.cachePosition] = (byte) b;
        this.cachePosition++;
        if (this.cachePosition == this.cache.length) flushCache();
    }

    /**
     * Writes the array. If the array does not fit within the buffer, it is
     * not split, but rather written out as one large chunk.
     * @param b
     * @throws IOException
     */
    public void write(byte b[]) throws IOException {
        write(b, 0, b.length);
    }

    public void write(byte src[], int off, int len) throws IOException {
        if (this.closed) {
            throw new IOException("Attempted write to closed stream.");
        }
        if (len >= this.cache.length - this.cachePosition) {
            flushCacheWithAppend(src, off, len);
        } else {
            System.arraycopy(src, off, cache, this.cachePosition, len);
            this.cachePosition += len;
        }
    }

    /**
     * Flushes the content buffer and the underlying stream.
     * @throws IOException
     */
    public void flush() throws IOException {
        flushCache();
        this.out.flush();
    }

    /**
     * Finishes writing to the underlying stream, but does NOT close the underlying stream.
     * @throws IOException
     */
    public void close() throws IOException {
        if (!this.closed) {
            this.closed = true;
            finish();
            this.out.flush();
        }
    }
}