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    1   /*
    2    * Copyright 2012 The Netty Project
    3    *
    4    * The Netty Project licenses this file to you under the Apache License,
    5    * version 2.0 (the "License"); you may not use this file except in compliance
    6    * with the 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.handler.codec.protobuf;
    17
    18  import org.jboss.netty.buffer.ChannelBuffer;
    19  import org.jboss.netty.channel.Channel;
    20  import org.jboss.netty.channel.ChannelHandlerContext;
    21  import org.jboss.netty.handler.codec.frame.CorruptedFrameException;
    22  import org.jboss.netty.handler.codec.frame.FrameDecoder;
    23
    24  import com.google.protobuf.CodedInputStream;
    25
    26  /**
    27   * A decoder that splits the received {@link ChannelBuffer}s dynamically by the
    28   * value of the Google Protocol Buffers
    29   * <a href="http://code.google.com/apis/protocolbuffers/docs/encoding.html#varints">Base
    30   * 128 Varints</a> integer length field in the message.  For example:
    31   * <pre>
    32   * BEFORE DECODE (302 bytes)       AFTER DECODE (300 bytes)
    33   * +--------+---------------+      +---------------+
    34   * | Length | Protobuf Data |----->| Protobuf Data |
    35   * | 0xAC02 |  (300 bytes)  |      |  (300 bytes)  |
    36   * +--------+---------------+      +---------------+
    37   * </pre>
    38   *
    39   * @see com.google.protobuf.CodedInputStream
    40   */
    41  public class ProtobufVarint32FrameDecoder extends FrameDecoder {
    42
    43      // TODO maxFrameLength + safe skip + fail-fast option
    44      //      (just like LengthFieldBasedFrameDecoder)
    45
    46      /**
    47       * Creates a new instance.
    48       */
    49      public ProtobufVarint32FrameDecoder() {
    50          super();
    51      }
    52
    53      @Override
    54      protected Object decode(ChannelHandlerContext ctx, Channel channel, ChannelBuffer buffer) throws Exception {
    55          buffer.markReaderIndex();
    56          final byte[] buf = new byte[5];
    57          for (int i = 0; i < buf.length; i ++) {
    58              if (!buffer.readable()) {
    59                  buffer.resetReaderIndex();
    60                  return null;
    61              }
    62
    63              buf[i] = buffer.readByte();
    64              if (buf[i] >= 0) {
    65                  int length = CodedInputStream.newInstance(buf, 0, i + 1).readRawVarint32();
    66                  if (length < 0) {
    67                      throw new CorruptedFrameException("negative length: " + length);
    68                  }
    69
    70                  if (buffer.readableBytes() < length) {
    71                      buffer.resetReaderIndex();
    72                      return null;
    73                  } else {
    74                      return buffer.readBytes(length);
    75                  }
    76              }
    77          }
    78
    79          // Couldn't find the byte whose MSB is off.
    80          throw new CorruptedFrameException("length wider than 32-bit");
    81      }
    82  }