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   /*
    * Copyright 2013 The Netty Project
    *
    * The Netty Project 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.io.IOException;
  import java.io.InputStream;
  import java.io.OutputStream;
  import java.nio.ByteBuffer;
  import java.nio.channels.GatheringByteChannel;
  import java.nio.channels.ScatteringByteChannel;
  
  /**
   * An immutable empty buffer implementation. Typically used as a singleton via
   * {@link ChannelBuffers#EMPTY_BUFFER} and returned by {@link ChannelBuffers#buffer(int)} etc when
   * an empty buffer is requested.
   *
   * <p>Note: For backwards compatibility, this class extends {@link BigEndianHeapChannelBuffer}.
   * However, it never makes any writes to the reader and writer indices, which avoids contention
   * when the singleton instance is used concurrently.
   */
  public class EmptyChannelBuffer extends BigEndianHeapChannelBuffer {
  
      private static final byte[] BUFFER = {};
  
      EmptyChannelBuffer() {
          super(BUFFER);
      }
  
      @Override
      public void clear() {
      }
  
      @Override
      public void readerIndex(int readerIndex) {
          if (readerIndex != 0) {
              throw new IndexOutOfBoundsException("Invalid readerIndex: "
                      + readerIndex + " - Maximum is 0");
          }
      }
  
      @Override
      public void writerIndex(int writerIndex) {
          if (writerIndex != 0) {
              throw new IndexOutOfBoundsException("Invalid writerIndex: "
                      + writerIndex + " - Maximum is 0");
          }
      }
  
      @Override
      public void setIndex(int readerIndex, int writerIndex) {
          if (writerIndex != 0 || readerIndex != 0) {
              throw new IndexOutOfBoundsException("Invalid writerIndex: "
                      + writerIndex + " - Maximum is " + readerIndex + " or "
                      + capacity());
          }
      }
  
      @Override
      public void markReaderIndex() {
      }
  
      @Override
      public void resetReaderIndex() {
      }
  
      @Override
      public void markWriterIndex() {
      }
  
      @Override
      public void resetWriterIndex() {
      }
  
      @Override
      public void discardReadBytes() {
      }
  
      @Override
      public ChannelBuffer readBytes(int length) {
          checkReadableBytes(length);
          return this;
      }
  
      @Override
      public ChannelBuffer readSlice(int length) {
         checkReadableBytes(length);
         return this;
     }
 
     @Override
     public void readBytes(byte[] dst, int dstIndex, int length) {
         checkReadableBytes(length);
     }
 
     @Override
     public void readBytes(byte[] dst) {
         checkReadableBytes(dst.length);
     }
 
     @Override
     public void readBytes(ChannelBuffer dst) {
         checkReadableBytes(dst.writableBytes());
     }
 
     @Override
     public void readBytes(ChannelBuffer dst, int length) {
         checkReadableBytes(length);
     }
 
     @Override
     public void readBytes(ChannelBuffer dst, int dstIndex, int length) {
         checkReadableBytes(length);
     }
 
     @Override
     public void readBytes(ByteBuffer dst) {
         checkReadableBytes(dst.remaining());
     }
 
     @Override
     public int readBytes(GatheringByteChannel out, int length) throws IOException {
         checkReadableBytes(length);
         return 0;
     }
 
     @Override
     public void readBytes(OutputStream out, int length) throws IOException {
         checkReadableBytes(length);
     }
 
     @Override
     public void skipBytes(int length) {
         checkReadableBytes(length);
     }
 
     @Override
     public void writeBytes(byte[] src, int srcIndex, int length) {
         checkWritableBytes(length);
     }
 
     @Override
     public void writeBytes(ChannelBuffer src, int length) {
         checkWritableBytes(length);
     }
 
     @Override
     public void writeBytes(ChannelBuffer src, int srcIndex, int length) {
         checkWritableBytes(length);
     }
 
     @Override
     public void writeBytes(ByteBuffer src) {
         checkWritableBytes(src.remaining());
     }
 
     @Override
     public int writeBytes(InputStream in, int length) throws IOException {
         checkWritableBytes(length);
         return 0;
     }
 
     @Override
     public int writeBytes(ScatteringByteChannel in, int length) throws IOException {
         checkWritableBytes(length);
         return 0;
     }
 
     @Override
     public void writeZero(int length) {
         checkWritableBytes(length);
     }
 
     /**
      * Throws an {@link IndexOutOfBoundsException} the length is not 0.
      */
     private void checkWritableBytes(int length) {
         if (length == 0) {
             return;
         }
         if (length > 0) {
             throw new IndexOutOfBoundsException("Writable bytes exceeded - Need "
                     + length + ", maximum is " + 0);
         } else {
             throw new IndexOutOfBoundsException("length < 0");
         }
     }
 
     /**
      * Throws an {@link IndexOutOfBoundsException} the length is not 0.
      */
     protected void checkReadableBytes(int length) {
         if (length == 0) {
             return;
         }
         if (length > 0) {
             throw new IndexOutOfBoundsException("Not enough readable bytes - Need "
                     + length + ", maximum is " + readableBytes());
         } else {
             throw new IndexOutOfBoundsException("length < 0");
         }
     }
 }