View Javadoc

    1   /*
    2    * Copyright 2009 Red Hat, Inc.
    3    *
    4    * Red Hat licenses this file to you under the Apache License, version 2.0
    5    * (the "License"); you may not use this file except in compliance with the
    6    * License.  You may obtain a copy of the License at:
    7    *
    8    *    http://www.apache.org/licenses/LICENSE-2.0
    9    *
    10   * Unless required by applicable law or agreed to in writing, software
    11   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
    12   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
    13   * License for the specific language governing permissions and limitations
    14   * under the License.
    15   */
    16  package org.jboss.netty.example.factorial;
    17
    18  import java.math.BigInteger;
    19
    20  import org.jboss.netty.buffer.ChannelBuffer;
    21  import org.jboss.netty.channel.Channel;
    22  import org.jboss.netty.channel.ChannelHandlerContext;
    23  import org.jboss.netty.handler.codec.frame.CorruptedFrameException;
    24  import org.jboss.netty.handler.codec.frame.FrameDecoder;
    25
    26  /**
    27   * Decodes the binary representation of a {@link BigInteger} prepended
    28   * with a magic number ('F' or 0x46) and a 32-bit integer length prefix into a
    29   * {@link BigInteger} instance.  For example, { 'F', 0, 0, 0, 1, 42 } will be
    30   * decoded into new BigInteger("42").
    31   *
    32   * @author <a href="http://www.jboss.org/netty/">The Netty Project</a>
    33   * @author <a href="http://gleamynode.net/">Trustin Lee</a>
    34   *
    35   * @version $Rev: 2125 $, $Date: 2010-02-02 12:13:15 +0900 (Tue, 02 Feb 2010) $
    36   */
    37  public class BigIntegerDecoder extends FrameDecoder {
    38
    39      @Override
    40      protected Object decode(
    41              ChannelHandlerContext ctx, Channel channel, ChannelBuffer buffer) throws Exception {
    42          // Wait until the length prefix is available.
    43          if (buffer.readableBytes() < 5) {
    44              return null;
    45          }
    46
    47          buffer.markReaderIndex();
    48
    49          // Check the magic number.
    50          int magicNumber = buffer.readUnsignedByte();
    51          if (magicNumber != 'F') {
    52              buffer.resetReaderIndex();
    53              throw new CorruptedFrameException(
    54                      "Invalid magic number: " + magicNumber);
    55          }
    56
    57          // Wait until the whole data is available.
    58          int dataLength = buffer.readInt();
    59          if (buffer.readableBytes() < dataLength) {
    60              buffer.resetReaderIndex();
    61              return null;
    62          }
    63
    64          // Convert the received data into a new BigInteger.
    65          byte[] decoded = new byte[dataLength];
    66          buffer.readBytes(decoded);
    67
    68          return new BigInteger(decoded);
    69      }
    70  }