/*
    * Copyright 2009 Red Hat, Inc.
    *
    * Red Hat 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.jboss.netty.buffer;
  
  import java.nio.ByteBuffer;
  import java.nio.ByteOrder;
  import java.nio.CharBuffer;
  import java.nio.charset.CharacterCodingException;
  import java.nio.charset.Charset;
  import java.nio.charset.CharsetDecoder;
  import java.nio.charset.CharsetEncoder;
  import java.nio.charset.CoderResult;
  import java.util.ArrayList;
  import java.util.List;
  
  import org.jboss.netty.util.CharsetUtil;
  
  
  /**
   * Creates a new {@link ChannelBuffer} by allocating new space or by wrapping
   * or copying existing byte arrays, byte buffers and a string.
   *
   * <h3>Use static import</h3>
   * This classes is intended to be used with Java 5 static import statement:
   *
   * <pre>
   * import static org.jboss.netty.buffer.{@link ChannelBuffers}.*;
   *
   * {@link ChannelBuffer} heapBuffer    = buffer(128);
   * {@link ChannelBuffer} directBuffer  = directBuffer(256);
   * {@link ChannelBuffer} dynamicBuffer = dynamicBuffer(512);
   * {@link ChannelBuffer} wrappedBuffer = wrappedBuffer(new byte[128], new byte[256]);
   * {@link ChannelBuffer} copiedBuffe r = copiedBuffer({@link ByteBuffer}.allocate(128));
   * </pre>
   *
   * <h3>Allocating a new buffer</h3>
   *
   * Three buffer types are provided out of the box.
   *
   * <ul>
   * <li>{@link #buffer(int)} allocates a new fixed-capacity heap buffer.</li>
   * <li>{@link #directBuffer(int)} allocates a new fixed-capacity direct buffer.</li>
   * <li>{@link #dynamicBuffer(int)} allocates a new dynamic-capacity heap
   *     buffer, whose capacity increases automatically as needed by a write
   *     operation.</li>
   * </ul>
   *
   * <h3>Creating a wrapped buffer</h3>
   *
   * Wrapped buffer is a buffer which is a view of one or more existing
   * byte arrays and byte buffers.  Any changes in the content of the original
   * array or buffer will be visible in the wrapped buffer.  Various wrapper
   * methods are provided and their name is all {@code wrappedBuffer()}.
   * You might want to take a look at the methods that accept varargs closely if
   * you want to create a buffer which is composed of more than one array to
   * reduce the number of memory copy.
   *
   * <h3>Creating a copied buffer</h3>
   *
   * Copied buffer is a deep copy of one or more existing byte arrays, byte
   * buffers or a string.  Unlike a wrapped buffer, there's no shared data
   * between the original data and the copied buffer.  Various copy methods are
   * provided and their name is all {@code copiedBuffer()}.  It is also convenient
   * to use this operation to merge multiple buffers into one buffer.
   *
   * <h3>Miscellaneous utility methods</h3>
   *
   * This class also provides various utility methods to help implementation
   * of a new buffer type, generation of hex dump and swapping an integer's
   * byte order.
   *
   * @author <a href="http://www.jboss.org/netty/">The Netty Project</a>
   * @author <a href="http://gleamynode.net/">Trustin Lee</a>
   *
   * @version $Rev: 2269 $, $Date: 2010-05-06 16:37:27 +0900 (Thu, 06 May 2010) $
   *
   * @apiviz.landmark
   * @apiviz.has org.jboss.netty.buffer.ChannelBuffer oneway - - creates
   */
  public class ChannelBuffers {
  
      /**
       * Big endian byte order.
       */
      public static final ByteOrder BIG_ENDIAN = ByteOrder.BIG_ENDIAN;
  
     /**
      * Little endian byte order.
      */
     public static final ByteOrder LITTLE_ENDIAN = ByteOrder.LITTLE_ENDIAN;
 
     /**
      * A buffer whose capacity is {@code 0}.
      */
     public static final ChannelBuffer EMPTY_BUFFER = new BigEndianHeapChannelBuffer(0);
 
     private static final char[] HEXDUMP_TABLE = new char[256 * 4];
 
     static {
         final char[] DIGITS = "0123456789abcdef".toCharArray();
         for (int i = 0; i < 256; i ++) {
             HEXDUMP_TABLE[(i << 1) + 0] = DIGITS[i >>> 4 & 0x0F];
             HEXDUMP_TABLE[(i << 1) + 1] = DIGITS[i >>> 0 & 0x0F];
         }
     }
 
     /**
      * Creates a new big-endian Java heap buffer with the specified
      * {@code capacity}.  The new buffer's {@code readerIndex} and
      * {@code writerIndex} are {@code 0}.
      */
     public static ChannelBuffer buffer(int capacity) {
         return buffer(BIG_ENDIAN, capacity);
     }
 
     /**
      * Creates a new Java heap buffer with the specified {@code endianness}
      * and {@code capacity}.  The new buffer's {@code readerIndex} and
      * {@code writerIndex} are {@code 0}.
      */
     public static ChannelBuffer buffer(ByteOrder endianness, int capacity) {
         if (endianness == BIG_ENDIAN) {
             if (capacity == 0) {
                 return EMPTY_BUFFER;
             }
             return new BigEndianHeapChannelBuffer(capacity);
         } else if (endianness == LITTLE_ENDIAN) {
             if (capacity == 0) {
                 return EMPTY_BUFFER;
             }
             return new LittleEndianHeapChannelBuffer(capacity);
         } else {
             throw new NullPointerException("endianness");
         }
     }
 
     /**
      * Creates a new big-endian direct buffer with the specified
      * {@code capacity}.  The new buffer's {@code readerIndex} and
      * {@code writerIndex} are {@code 0}.
      */
     public static ChannelBuffer directBuffer(int capacity) {
         return directBuffer(BIG_ENDIAN, capacity);
     }
 
     /**
      * Creates a new direct buffer with the specified {@code endianness} and
      * {@code capacity}.  The new buffer's {@code readerIndex} and
      * {@code writerIndex} are {@code 0}.
      */
     public static ChannelBuffer directBuffer(ByteOrder endianness, int capacity) {
         if (endianness == null) {
             throw new NullPointerException("endianness");
         }
         if (capacity == 0) {
             return EMPTY_BUFFER;
         }
 
         ChannelBuffer buffer = new ByteBufferBackedChannelBuffer(
                 ByteBuffer.allocateDirect(capacity).order(endianness));
         buffer.clear();
         return buffer;
     }
 
     /**
      * Creates a new big-endian dynamic buffer whose estimated data length is
      * {@code 256} bytes.  The new buffer's {@code readerIndex} and
      * {@code writerIndex} are {@code 0}.
      */
     public static ChannelBuffer dynamicBuffer() {
         return dynamicBuffer(BIG_ENDIAN, 256);
     }
 
     public static ChannelBuffer dynamicBuffer(ChannelBufferFactory factory) {
         if (factory == null) {
             throw new NullPointerException("factory");
         }
 
         return new DynamicChannelBuffer(factory.getDefaultOrder(), 256, factory);
     }
 
     /**
      * Creates a new big-endian dynamic buffer with the specified estimated
      * data length.  More accurate estimation yields less unexpected
      * reallocation overhead.  The new buffer's {@code readerIndex} and
      * {@code writerIndex} are {@code 0}.
      */
     public static ChannelBuffer dynamicBuffer(int estimatedLength) {
         return dynamicBuffer(BIG_ENDIAN, estimatedLength);
     }
 
     /**
      * Creates a new dynamic buffer with the specified endianness and
      * the specified estimated data length.  More accurate estimation yields
      * less unexpected reallocation overhead.  The new buffer's
      * {@code readerIndex} and {@code writerIndex} are {@code 0}.
      */
     public static ChannelBuffer dynamicBuffer(ByteOrder endianness, int estimatedLength) {
         return new DynamicChannelBuffer(endianness, estimatedLength);
     }
 
     /**
      * Creates a new big-endian dynamic buffer with the specified estimated
      * data length using the specified factory.  More accurate estimation yields
      * less unexpected reallocation overhead.  The new buffer's {@code readerIndex}
      * and {@code writerIndex} are {@code 0}.
      */
     public static ChannelBuffer dynamicBuffer(int estimatedLength, ChannelBufferFactory factory) {
         if (factory == null) {
             throw new NullPointerException("factory");
         }
 
         return new DynamicChannelBuffer(factory.getDefaultOrder(), estimatedLength, factory);
     }
 
     /**
      * Creates a new dynamic buffer with the specified endianness and
      * the specified estimated data length using the specified factory.
      * More accurate estimation yields less unexpected reallocation overhead.
      * The new buffer's {@code readerIndex} and {@code writerIndex} are {@code 0}.
      */
     public static ChannelBuffer dynamicBuffer(ByteOrder endianness, int estimatedLength, ChannelBufferFactory factory) {
         return new DynamicChannelBuffer(endianness, estimatedLength, factory);
     }
 
     /**
      * Creates a new big-endian buffer which wraps the specified {@code array}.
      * A modification on the specified array's content will be visible to the
      * returned buffer.
      */
     public static ChannelBuffer wrappedBuffer(byte[] array) {
         return wrappedBuffer(BIG_ENDIAN, array);
     }
 
     /**
      * Creates a new buffer which wraps the specified {@code array} with the
      * specified {@code endianness}.  A modification on the specified array's
      * content will be visible to the returned buffer.
      */
     public static ChannelBuffer wrappedBuffer(ByteOrder endianness, byte[] array) {
         if (endianness == BIG_ENDIAN) {
             if (array.length == 0) {
                 return EMPTY_BUFFER;
             }
             return new BigEndianHeapChannelBuffer(array);
         } else if (endianness == LITTLE_ENDIAN) {
             if (array.length == 0) {
                 return EMPTY_BUFFER;
             }
             return new LittleEndianHeapChannelBuffer(array);
         } else {
             throw new NullPointerException("endianness");
         }
     }
 
     /**
      * Creates a new big-endian buffer which wraps the sub-region of the
      * specified {@code array}.  A modification on the specified array's
      * content will be visible to the returned buffer.
      */
     public static ChannelBuffer wrappedBuffer(byte[] array, int offset, int length) {
         return wrappedBuffer(BIG_ENDIAN, array, offset, length);
     }
 
     /**
      * Creates a new buffer which wraps the sub-region of the specified
      * {@code array} with the specified {@code endianness}.  A modification on
      * the specified array's content will be visible to the returned buffer.
      */
     public static ChannelBuffer wrappedBuffer(ByteOrder endianness, byte[] array, int offset, int length) {
         if (endianness == null) {
             throw new NullPointerException("endianness");
         }
         if (offset == 0) {
             if (length == array.length) {
                 return wrappedBuffer(endianness, array);
             } else {
                 if (length == 0) {
                     return EMPTY_BUFFER;
                 } else {
                     return new TruncatedChannelBuffer(wrappedBuffer(endianness, array), length);
                 }
             }
         } else {
             if (length == 0) {
                 return EMPTY_BUFFER;
             } else {
                 return new SlicedChannelBuffer(wrappedBuffer(endianness, array), offset, length);
             }
         }
     }
 
     /**
      * Creates a new buffer which wraps the specified NIO buffer's current
      * slice.  A modification on the specified buffer's content will be
      * visible to the returned buffer.
      */
     public static ChannelBuffer wrappedBuffer(ByteBuffer buffer) {
         if (!buffer.hasRemaining()) {
             return EMPTY_BUFFER;
         }
         if (buffer.hasArray()) {
             return wrappedBuffer(buffer.order(), buffer.array(), buffer.arrayOffset() + buffer.position(),buffer.remaining());
         } else {
             return new ByteBufferBackedChannelBuffer(buffer);
         }
     }
 
     /**
      * Creates a new buffer which wraps the specified buffer's readable bytes.
      * A modification on the specified buffer's content will be visible to the
      * returned buffer.
      */
     public static ChannelBuffer wrappedBuffer(ChannelBuffer buffer) {
         if (buffer.readable()) {
             return buffer.slice();
         } else {
             return EMPTY_BUFFER;
         }
     }
 
     /**
      * Creates a new big-endian composite buffer which wraps the specified
      * arrays without copying them.  A modification on the specified arrays'
      * content will be visible to the returned buffer.
      */
     public static ChannelBuffer wrappedBuffer(byte[]... arrays) {
         return wrappedBuffer(BIG_ENDIAN, arrays);
     }
 
     /**
      * Creates a new composite buffer which wraps the specified arrays without
      * copying them.  A modification on the specified arrays' content will be
      * visible to the returned buffer.
      *
      * @param endianness the endianness of the new buffer
      */
     public static ChannelBuffer wrappedBuffer(ByteOrder endianness, byte[]... arrays) {
         switch (arrays.length) {
         case 0:
             break;
         case 1:
             if (arrays[0].length != 0) {
                 return wrappedBuffer(endianness, arrays[0]);
             }
             break;
         default:
             // Get the list of the component, while guessing the byte order.
             final List<ChannelBuffer> components = new ArrayList<ChannelBuffer>(arrays.length);
             for (byte[] a: arrays) {
                 if (a == null) {
                     break;
                 }
                 if (a.length > 0) {
                     components.add(wrappedBuffer(endianness, a));
                 }
             }
             return compositeBuffer(endianness, components);
         }
 
         return EMPTY_BUFFER;
     }
 
     private static ChannelBuffer compositeBuffer(
             ByteOrder endianness, List<ChannelBuffer> components) {
         switch (components.size()) {
         case 0:
             return EMPTY_BUFFER;
         case 1:
             return components.get(0);
         default:
             return new CompositeChannelBuffer(endianness, components);
         }
     }
 
     /**
      * Creates a new composite buffer which wraps the readable bytes of the
      * specified buffers without copying them.  A modification on the content
      * of the specified buffers will be visible to the returned buffer.
      *
      * @throws IllegalArgumentException
      *         if the specified buffers' endianness are different from each
      *         other
      */
     public static ChannelBuffer wrappedBuffer(ChannelBuffer... buffers) {
         switch (buffers.length) {
         case 0:
             break;
         case 1:
             if (buffers[0].readable()) {
                 return wrappedBuffer(buffers[0]);
             }
             break;
         default:
             ByteOrder order = null;
             final List<ChannelBuffer> components = new ArrayList<ChannelBuffer>(buffers.length);
             for (ChannelBuffer c: buffers) {
                 if (c == null) {
                     break;
                 }
                 if (c.readable()) {
                     if (order != null) {
                         if (!order.equals(c.order())) {
                             throw new IllegalArgumentException(
                                     "inconsistent byte order");
                         }
                     } else {
                         order = c.order();
                     }
                     if (c instanceof CompositeChannelBuffer) {
                         // Expand nested composition.
                         components.addAll(
                                 ((CompositeChannelBuffer) c).decompose(
                                         c.readerIndex(), c.readableBytes()));
                     } else {
                         // An ordinary buffer (non-composite)
                         components.add(c.slice());
                     }
                 }
             }
             return compositeBuffer(order, components);
         }
         return EMPTY_BUFFER;
     }
 
     /**
      * Creates a new composite buffer which wraps the slices of the specified
      * NIO buffers without copying them.  A modification on the content of the
      * specified buffers will be visible to the returned buffer.
      *
      * @throws IllegalArgumentException
      *         if the specified buffers' endianness are different from each
      *         other
      */
     public static ChannelBuffer wrappedBuffer(ByteBuffer... buffers) {
         switch (buffers.length) {
         case 0:
             break;
         case 1:
             if (buffers[0].hasRemaining()) {
                 return wrappedBuffer(buffers[0]);
             }
             break;
         default:
             ByteOrder order = null;
             final List<ChannelBuffer> components = new ArrayList<ChannelBuffer>(buffers.length);
             for (ByteBuffer b: buffers) {
                 if (b == null) {
                     break;
                 }
                 if (b.hasRemaining()) {
                     if (order != null) {
                         if (!order.equals(b.order())) {
                             throw new IllegalArgumentException(
                                     "inconsistent byte order");
                         }
                     } else {
                         order = b.order();
                     }
                     components.add(wrappedBuffer(b));
                 }
             }
             return compositeBuffer(order, components);
         }
 
         return EMPTY_BUFFER;
     }
 
     /**
      * Creates a new big-endian buffer whose content is a copy of the
      * specified {@code array}.  The new buffer's {@code readerIndex} and
      * {@code writerIndex} are {@code 0} and {@code array.length} respectively.
      */
     public static ChannelBuffer copiedBuffer(byte[] array) {
         return copiedBuffer(BIG_ENDIAN, array);
     }
 
     /**
      * Creates a new buffer with the specified {@code endianness} whose
      * content is a copy of the specified {@code array}.  The new buffer's
      * {@code readerIndex} and {@code writerIndex} are {@code 0} and
      * {@code array.length} respectively.
      */
     public static ChannelBuffer copiedBuffer(ByteOrder endianness, byte[] array) {
         if (endianness == BIG_ENDIAN) {
             if (array.length == 0) {
                 return EMPTY_BUFFER;
             }
             return new BigEndianHeapChannelBuffer(array.clone());
         } else if (endianness == LITTLE_ENDIAN) {
             if (array.length == 0) {
                 return EMPTY_BUFFER;
             }
             return new LittleEndianHeapChannelBuffer(array.clone());
         } else {
             throw new NullPointerException("endianness");
         }
     }
 
     /**
      * Creates a new big-endian buffer whose content is a copy of the
      * specified {@code array}'s sub-region.  The new buffer's
      * {@code readerIndex} and {@code writerIndex} are {@code 0} and
      * the specified {@code length} respectively.
      */
     public static ChannelBuffer copiedBuffer(byte[] array, int offset, int length) {
         return copiedBuffer(BIG_ENDIAN, array, offset, length);
     }
 
     /**
      * Creates a new buffer with the specified {@code endianness} whose
      * content is a copy of the specified {@code array}'s sub-region.  The new
      * buffer's {@code readerIndex} and {@code writerIndex} are {@code 0} and
      * the specified {@code length} respectively.
      */
     public static ChannelBuffer copiedBuffer(ByteOrder endianness, byte[] array, int offset, int length) {
         if (endianness == null) {
             throw new NullPointerException("endianness");
         }
         if (length == 0) {
             return EMPTY_BUFFER;
         }
         byte[] copy = new byte[length];
         System.arraycopy(array, offset, copy, 0, length);
         return wrappedBuffer(endianness, copy);
     }
 
     /**
      * Creates a new buffer whose content is a copy of the specified
      * {@code buffer}'s current slice.  The new buffer's {@code readerIndex}
      * and {@code writerIndex} are {@code 0} and {@code buffer.remaining}
      * respectively.
      */
     public static ChannelBuffer copiedBuffer(ByteBuffer buffer) {
         int length = buffer.remaining();
         if (length == 0) {
             return EMPTY_BUFFER;
         }
         byte[] copy = new byte[length];
         int position = buffer.position();
         try {
             buffer.get(copy);
         } finally {
             buffer.position(position);
         }
         return wrappedBuffer(buffer.order(), copy);
     }
 
     /**
      * Creates a new buffer whose content is a copy of the specified
      * {@code buffer}'s readable bytes.  The new buffer's {@code readerIndex}
      * and {@code writerIndex} are {@code 0} and {@code buffer.readableBytes}
      * respectively.
      */
     public static ChannelBuffer copiedBuffer(ChannelBuffer buffer) {
         if (buffer.readable()) {
             return buffer.copy();
         } else {
             return EMPTY_BUFFER;
         }
     }
 
     /**
      * Creates a new big-endian buffer whose content is a merged copy of
      * the specified {@code arrays}.  The new buffer's {@code readerIndex}
      * and {@code writerIndex} are {@code 0} and the sum of all arrays'
      * {@code length} respectively.
      */
     public static ChannelBuffer copiedBuffer(byte[]... arrays) {
         return copiedBuffer(BIG_ENDIAN, arrays);
     }
 
     /**
      * Creates a new buffer with the specified {@code endianness} whose
      * content is a merged copy of the specified {@code arrays}.  The new
      * buffer's {@code readerIndex} and {@code writerIndex} are {@code 0}
      * and the sum of all arrays' {@code length} respectively.
      */
     public static ChannelBuffer copiedBuffer(ByteOrder endianness, byte[]... arrays) {
         switch (arrays.length) {
         case 0:
             return EMPTY_BUFFER;
         case 1:
             if (arrays[0].length == 0) {
                 return EMPTY_BUFFER;
             } else {
                 return copiedBuffer(endianness, arrays[0]);
             }
         }
 
         // Merge the specified arrays into one array.
         int length = 0;
         for (byte[] a: arrays) {
             if (Integer.MAX_VALUE - length < a.length) {
                 throw new IllegalArgumentException(
                         "The total length of the specified arrays is too big.");
             }
             length += a.length;
         }
 
         if (length == 0) {
             return EMPTY_BUFFER;
         }
 
         byte[] mergedArray = new byte[length];
         for (int i = 0, j = 0; i < arrays.length; i ++) {
             byte[] a = arrays[i];
             System.arraycopy(a, 0, mergedArray, j, a.length);
             j += a.length;
         }
 
         return wrappedBuffer(endianness, mergedArray);
     }
 
     /**
      * Creates a new buffer whose content is a merged copy of the specified
      * {@code buffers}' readable bytes.  The new buffer's {@code readerIndex}
      * and {@code writerIndex} are {@code 0} and the sum of all buffers'
      * {@code readableBytes} respectively.
      *
      * @throws IllegalArgumentException
      *         if the specified buffers' endianness are different from each
      *         other
      */
     public static ChannelBuffer copiedBuffer(ChannelBuffer... buffers) {
         switch (buffers.length) {
         case 0:
             return EMPTY_BUFFER;
         case 1:
             return copiedBuffer(buffers[0]);
         }
 
         ChannelBuffer[] copiedBuffers = new ChannelBuffer[buffers.length];
         for (int i = 0; i < buffers.length; i ++) {
             copiedBuffers[i] = copiedBuffer(buffers[i]);
         }
         return wrappedBuffer(copiedBuffers);
     }
 
     /**
      * Creates a new buffer whose content is a merged copy of the specified
      * {@code buffers}' slices.  The new buffer's {@code readerIndex} and
      * {@code writerIndex} are {@code 0} and the sum of all buffers'
      * {@code remaining} respectively.
      *
      * @throws IllegalArgumentException
      *         if the specified buffers' endianness are different from each
      *         other
      */
     public static ChannelBuffer copiedBuffer(ByteBuffer... buffers) {
         switch (buffers.length) {
         case 0:
             return EMPTY_BUFFER;
         case 1:
             return copiedBuffer(buffers[0]);
         }
 
         ChannelBuffer[] copiedBuffers = new ChannelBuffer[buffers.length];
         for (int i = 0; i < buffers.length; i ++) {
             copiedBuffers[i] = copiedBuffer(buffers[i]);
         }
         return wrappedBuffer(copiedBuffers);
     }
 
     /**
      * Creates a new big-endian buffer whose content is the specified
      * {@code string} encoded in the specified {@code charset}.
      * The new buffer's {@code readerIndex} and {@code writerIndex} are
      * {@code 0} and the length of the encoded string respectively.
      */
     public static ChannelBuffer copiedBuffer(CharSequence string, Charset charset) {
         return copiedBuffer(BIG_ENDIAN, string, charset);
     }
 
     /**
      * Creates a new big-endian buffer whose content is a subregion of
      * the specified {@code string} encoded in the specified {@code charset}.
      * The new buffer's {@code readerIndex} and {@code writerIndex} are
      * {@code 0} and the length of the encoded string respectively.
      */
     public static ChannelBuffer copiedBuffer(
             CharSequence string, int offset, int length, Charset charset) {
         return copiedBuffer(BIG_ENDIAN, string, offset, length, charset);
     }
 
     /**
      * Creates a new buffer with the specified {@code endianness} whose
      * content is the specified {@code string} encoded in the specified
      * {@code charset}.  The new buffer's {@code readerIndex} and
      * {@code writerIndex} are {@code 0} and the length of the encoded string
      * respectively.
      */
     public static ChannelBuffer copiedBuffer(ByteOrder endianness, CharSequence string, Charset charset) {
         if (string == null) {
             throw new NullPointerException("string");
         }
 
         if (string instanceof CharBuffer) {
             return copiedBuffer(endianness, (CharBuffer) string, charset);
         }
 
         return copiedBuffer(endianness, CharBuffer.wrap(string), charset);
     }
 
     /**
      * Creates a new buffer with the specified {@code endianness} whose
      * content is a subregion of the specified {@code string} encoded in the
      * specified {@code charset}.  The new buffer's {@code readerIndex} and
      * {@code writerIndex} are {@code 0} and the length of the encoded string
      * respectively.
      */
     public static ChannelBuffer copiedBuffer(
             ByteOrder endianness, CharSequence string, int offset, int length, Charset charset) {
         if (string == null) {
             throw new NullPointerException("string");
         }
         if (length == 0) {
             return EMPTY_BUFFER;
         }
 
         if (string instanceof CharBuffer) {
             CharBuffer buf = (CharBuffer) string;
             if (buf.hasArray()) {
                 return copiedBuffer(
                         endianness,
                         buf.array(),
                         buf.arrayOffset() + buf.position() + offset,
                         length, charset);
             }
 
             buf = buf.slice();
             buf.limit(length);
             buf.position(offset);
             return copiedBuffer(endianness, buf, charset);
         }
 
         return copiedBuffer(
                 endianness, CharBuffer.wrap(string, offset, offset + length),
                 charset);
     }
 
     /**
      * Creates a new big-endian buffer whose content is the specified
      * {@code array} encoded in the specified {@code charset}.
      * The new buffer's {@code readerIndex} and {@code writerIndex} are
      * {@code 0} and the length of the encoded string respectively.
      */
     public static ChannelBuffer copiedBuffer(char[] array, Charset charset) {
         return copiedBuffer(BIG_ENDIAN, array, 0, array.length, charset);
     }
 
     /**
      * Creates a new big-endian buffer whose content is a subregion of
      * the specified {@code array} encoded in the specified {@code charset}.
      * The new buffer's {@code readerIndex} and {@code writerIndex} are
      * {@code 0} and the length of the encoded string respectively.
      */
     public static ChannelBuffer copiedBuffer(
             char[] array, int offset, int length, Charset charset) {
         return copiedBuffer(BIG_ENDIAN, array, offset, length, charset);
     }
 
     /**
      * Creates a new buffer with the specified {@code endianness} whose
      * content is the specified {@code array} encoded in the specified
      * {@code charset}.  The new buffer's {@code readerIndex} and
      * {@code writerIndex} are {@code 0} and the length of the encoded string
      * respectively.
      */
     public static ChannelBuffer copiedBuffer(ByteOrder endianness, char[] array, Charset charset) {
         return copiedBuffer(endianness, array, 0, array.length, charset);
     }
 
     /**
      * Creates a new buffer with the specified {@code endianness} whose
      * content is a subregion of the specified {@code array} encoded in the
      * specified {@code charset}.  The new buffer's {@code readerIndex} and
      * {@code writerIndex} are {@code 0} and the length of the encoded string
      * respectively.
      */
     public static ChannelBuffer copiedBuffer(
             ByteOrder endianness, char[] array, int offset, int length, Charset charset) {
         if (array == null) {
             throw new NullPointerException("array");
         }
         if (length == 0) {
             return EMPTY_BUFFER;
         }
         return copiedBuffer(
                 endianness, CharBuffer.wrap(array, offset, length), charset);
     }
 
     private static ChannelBuffer copiedBuffer(ByteOrder endianness, CharBuffer buffer, Charset charset) {
         CharBuffer src = buffer;
         ByteBuffer dst = ChannelBuffers.encodeString(src, charset);
         ChannelBuffer result = wrappedBuffer(endianness, dst.array());
         result.writerIndex(dst.remaining());
         return result;
     }
 
     /**
      * @deprecated Use {@link #copiedBuffer(CharSequence, Charset)} instead.
      */
     @Deprecated
     public static ChannelBuffer copiedBuffer(String string, String charsetName) {
         return copiedBuffer(string, Charset.forName(charsetName));
     }
 
     /**
      * @deprecated Use {@link #copiedBuffer(ByteOrder, CharSequence, Charset)} instead.
      */
     @Deprecated
     public static ChannelBuffer copiedBuffer(ByteOrder endianness, String string, String charsetName) {
         return copiedBuffer(endianness, string, Charset.forName(charsetName));
     }
 
     /**
      * Creates a read-only buffer which disallows any modification operations
      * on the specified {@code buffer}.  The new buffer has the same
      * {@code readerIndex} and {@code writerIndex} with the specified
      * {@code buffer}.
      */
     public static ChannelBuffer unmodifiableBuffer(ChannelBuffer buffer) {
         if (buffer instanceof ReadOnlyChannelBuffer) {
             buffer = ((ReadOnlyChannelBuffer) buffer).unwrap();
         }
         return new ReadOnlyChannelBuffer(buffer);
     }
 
     /**
      * Returns a <a href="http://en.wikipedia.org/wiki/Hex_dump">hex dump</a>
      * of the specified buffer's readable bytes.
      */
     public static String hexDump(ChannelBuffer buffer) {
         return hexDump(buffer, buffer.readerIndex(), buffer.readableBytes());
     }
 
     /**
      * Returns a <a href="http://en.wikipedia.org/wiki/Hex_dump">hex dump</a>
      * of the specified buffer's sub-region.
      */
     public static String hexDump(ChannelBuffer buffer, int fromIndex, int length) {
         if (length < 0) {
             throw new IllegalArgumentException("length: " + length);
         }
         if (length == 0) {
             return "";
         }
 
         int endIndex = fromIndex + length;
         char[] buf = new char[length << 1];
 
         int srcIdx = fromIndex;
         int dstIdx = 0;
         for (; srcIdx < endIndex; srcIdx ++, dstIdx += 2) {
             System.arraycopy(
                     HEXDUMP_TABLE, buffer.getUnsignedByte(srcIdx) << 1,
                     buf, dstIdx, 2);
         }
 
         return new String(buf);
     }
 
     /**
      * Calculates the hash code of the specified buffer.  This method is
      * useful when implementing a new buffer type.
      */
     public static int hashCode(ChannelBuffer buffer) {
         final int aLen = buffer.readableBytes();
         final int intCount = aLen >>> 2;
         final int byteCount = aLen & 3;
 
         int hashCode = 1;
         int arrayIndex = buffer.readerIndex();
         if (buffer.order() == BIG_ENDIAN) {
             for (int i = intCount; i > 0; i --) {
                 hashCode = 31 * hashCode + buffer.getInt(arrayIndex);
                 arrayIndex += 4;
             }
         } else {
             for (int i = intCount; i > 0; i --) {
                 hashCode = 31 * hashCode + swapInt(buffer.getInt(arrayIndex));
                 arrayIndex += 4;
             }
         }
 
         for (int i = byteCount; i > 0; i --) {
             hashCode = 31 * hashCode + buffer.getByte(arrayIndex ++);
         }
 
         if (hashCode == 0) {
             hashCode = 1;
         }
 
         return hashCode;
     }
 
     /**
      * Returns {@code true} if and only if the two specified buffers are
      * identical to each other as described in {@code ChannelBuffer#equals(Object)}.
      * This method is useful when implementing a new buffer type.
      */
     public static boolean equals(ChannelBuffer bufferA, ChannelBuffer bufferB) {
         final int aLen = bufferA.readableBytes();
         if (aLen != bufferB.readableBytes()) {
             return false;
         }
 
         final int longCount = aLen >>> 3;
         final int byteCount = aLen & 7;
 
         int aIndex = bufferA.readerIndex();
         int bIndex = bufferB.readerIndex();
 
         if (bufferA.order() == bufferB.order()) {
             for (int i = longCount; i > 0; i --) {
                 if (bufferA.getLong(aIndex) != bufferB.getLong(bIndex)) {
                     return false;
                 }
                 aIndex += 8;
                 bIndex += 8;
             }
         } else {
             for (int i = longCount; i > 0; i --) {
                 if (bufferA.getLong(aIndex) != swapLong(bufferB.getLong(bIndex))) {
                     return false;
                 }
                 aIndex += 8;
                 bIndex += 8;
             }
         }
 
         for (int i = byteCount; i > 0; i --) {
             if (bufferA.getByte(aIndex) != bufferB.getByte(bIndex)) {
                 return false;
             }
             aIndex ++;
             bIndex ++;
         }
 
         return true;
     }
 
     /**
      * Compares the two specified buffers as described in {@link ChannelBuffer#compareTo(ChannelBuffer)}.
      * This method is useful when implementing a new buffer type.
      */
     public static int compare(ChannelBuffer bufferA, ChannelBuffer bufferB) {
         final int aLen = bufferA.readableBytes();
         final int bLen = bufferB.readableBytes();
         final int minLength = Math.min(aLen, bLen);
         final int uintCount = minLength >>> 2;
         final int byteCount = minLength & 3;
 
         int aIndex = bufferA.readerIndex();
         int bIndex = bufferB.readerIndex();
 
         if (bufferA.order() == bufferB.order()) {
             for (int i = uintCount; i > 0; i --) {
                 long va = bufferA.getUnsignedInt(aIndex);
                 long vb = bufferB.getUnsignedInt(bIndex);
                 if (va > vb) {
                     return 1;
                 } else if (va < vb) {
                     return -1;
                 }
                 aIndex += 4;
                 bIndex += 4;
             }
         } else {
             for (int i = uintCount; i > 0; i --) {
                 long va = bufferA.getUnsignedInt(aIndex);
                 long vb = swapInt(bufferB.getInt(bIndex)) & 0xFFFFFFFFL;
                 if (va > vb) {
                     return 1;
                 } else if (va < vb) {
                     return -1;
                 }
                 aIndex += 4;
                 bIndex += 4;
             }
         }
 
         for (int i = byteCount; i > 0; i --) {
             short va = bufferA.getUnsignedByte(aIndex);
             short vb = bufferB.getUnsignedByte(bIndex);
             if (va > vb) {
                 return 1;
             } else if (va < vb) {
                 return -1;
             }
             aIndex ++;
             bIndex ++;
         }
 
         return aLen - bLen;
     }
 
     /**
      * The default implementation of {@link ChannelBuffer#indexOf(int, int, byte)}.
      * This method is useful when implementing a new buffer type.
      */
     public static int indexOf(ChannelBuffer buffer, int fromIndex, int toIndex, byte value) {
         if (fromIndex <= toIndex) {
             return firstIndexOf(buffer, fromIndex, toIndex, value);
         } else {
             return lastIndexOf(buffer, fromIndex, toIndex, value);
         }
     }
 
     /**
      * The default implementation of {@link ChannelBuffer#indexOf(int, int, ChannelBufferIndexFinder)}.
      * This method is useful when implementing a new buffer type.
      */
     public static int indexOf(ChannelBuffer buffer, int fromIndex, int toIndex, ChannelBufferIndexFinder indexFinder) {
         if (fromIndex <= toIndex) {
             return firstIndexOf(buffer, fromIndex, toIndex, indexFinder);
         } else {
             return lastIndexOf(buffer, fromIndex, toIndex, indexFinder);
         }
     }
 
     /**
      * Toggles the endianness of the specified 16-bit short integer.
      */
     public static short swapShort(short value) {
         return (short) (value << 8 | value >>> 8 & 0xff);
     }
 
     /**
      * Toggles the endianness of the specified 24-bit medium integer.
      */
     public static int swapMedium(int value) {
         return value << 16 & 0xff0000 | value & 0xff00 | value >>> 16 & 0xff;
     }
 
     /**
      * Toggles the endianness of the specified 32-bit integer.
      */
     public static int swapInt(int value) {
         return swapShort((short) value) <<  16 |
                swapShort((short) (value >>> 16)) & 0xffff;
     }
 
     /**
      * Toggles the endianness of the specified 64-bit long integer.
      */
     public static long swapLong(long value) {
         return (long) swapInt((int) value) <<  32 |
                       swapInt((int) (value >>> 32)) & 0xffffffffL;
     }
 
     private static int firstIndexOf(ChannelBuffer buffer, int fromIndex, int toIndex, byte value) {
         fromIndex = Math.max(fromIndex, 0);
         if (fromIndex >= toIndex || buffer.capacity() == 0) {
             return -1;
         }
 
         for (int i = fromIndex; i < toIndex; i ++) {
             if (buffer.getByte(i) == value) {
                 return i;
             }
         }
 
         return -1;
     }
 
     private static int lastIndexOf(ChannelBuffer buffer, int fromIndex, int toIndex, byte value) {
         fromIndex = Math.min(fromIndex, buffer.capacity());
         if (fromIndex < 0 || buffer.capacity() == 0) {
             return -1;
         }
 
         for (int i = fromIndex - 1; i >= toIndex; i --) {
             if (buffer.getByte(i) == value) {
                 return i;
             }
         }
 
         return -1;
     }
 
     private static int firstIndexOf(ChannelBuffer buffer, int fromIndex, int toIndex, ChannelBufferIndexFinder indexFinder) {
         fromIndex = Math.max(fromIndex, 0);
         if (fromIndex >= toIndex || buffer.capacity() == 0) {
             return -1;
         }
 
         for (int i = fromIndex; i < toIndex; i ++) {
             if (indexFinder.find(buffer, i)) {
                 return i;
             }
         }
 
         return -1;
     }
 
     private static int lastIndexOf(ChannelBuffer buffer, int fromIndex, int toIndex, ChannelBufferIndexFinder indexFinder) {
         fromIndex = Math.min(fromIndex, buffer.capacity());
         if (fromIndex < 0 || buffer.capacity() == 0) {
             return -1;
         }
 
         for (int i = fromIndex - 1; i >= toIndex; i --) {
             if (indexFinder.find(buffer, i)) {
                 return i;
             }
         }
 
         return -1;
     }
 
     static ByteBuffer encodeString(CharBuffer src, Charset charset) {
         final CharsetEncoder encoder = CharsetUtil.getEncoder(charset);
         final ByteBuffer dst = ByteBuffer.allocate(
                 (int) ((double) src.remaining() * encoder.maxBytesPerChar()));
         try {
             CoderResult cr = encoder.encode(src, dst, true);
             if (!cr.isUnderflow()) {
                 cr.throwException();
             }
             cr = encoder.flush(dst);
             if (!cr.isUnderflow()) {
                 cr.throwException();
             }
         } catch (CharacterCodingException x) {
             throw new IllegalStateException(x);
         }
         dst.flip();
         return dst;
     }
 
     static String decodeString(ByteBuffer src, Charset charset) {
         final CharsetDecoder decoder = CharsetUtil.getDecoder(charset);
         final CharBuffer dst = CharBuffer.allocate(
                 (int) ((double) src.remaining() * decoder.maxCharsPerByte()));
         try {
             CoderResult cr = decoder.decode(src, dst, true);
             if (!cr.isUnderflow()) {
                 cr.throwException();
             }
             cr = decoder.flush(dst);
             if (!cr.isUnderflow()) {
                 cr.throwException();
             }
         } catch (CharacterCodingException x) {
             throw new IllegalStateException(x);
         }
         return dst.flip().toString();
     }
 
     private ChannelBuffers() {
         // Unused
     }
 }