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 * https://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 io.netty5.handler.codec;
17
18 import io.netty5.buffer.api.Buffer;
19 import io.netty5.channel.ChannelHandlerContext;
20
21 import static io.netty5.util.internal.ObjectUtil.checkPositive;
22
23 /**
24 * A decoder that splits the received {@link Buffer}s by the fixed number
25 * of bytes. For example, if you received the following four fragmented packets:
26 * <pre>
27 * +---+----+------+----+
28 * | A | BC | DEFG | HI |
29 * +---+----+------+----+
30 * </pre>
31 * A {@link FixedLengthFrameDecoder}{@code (3)} will decode them into the
32 * following three packets with the fixed length:
33 * <pre>
34 * +-----+-----+-----+
35 * | ABC | DEF | GHI |
36 * +-----+-----+-----+
37 * </pre>
38 */
39 public class FixedLengthFrameDecoder extends ByteToMessageDecoder {
40
41 private final int frameLength;
42
43 /**
44 * Creates a new instance.
45 *
46 * @param frameLength the length of the frame
47 */
48 public FixedLengthFrameDecoder(int frameLength) {
49 checkPositive(frameLength, "frameLength");
50 this.frameLength = frameLength;
51 }
52
53 /**
54 * Creates a new instance.
55 *
56 * @param frameLength the length of the frame
57 */
58 public FixedLengthFrameDecoder(int frameLength, Cumulator cumulator) {
59 super(cumulator);
60 checkPositive(frameLength, "frameLength");
61 this.frameLength = frameLength;
62 }
63
64 @Override
65 protected final void decode(ChannelHandlerContext ctx, Buffer in) throws Exception {
66 Object decoded = decode0(ctx, in);
67 if (decoded != null) {
68 ctx.fireChannelRead(decoded);
69 }
70 }
71
72 /**
73 * Create a frame out of the {@link Buffer} and return it.
74 *
75 * @param ctx the {@link ChannelHandlerContext} which this {@link ByteToMessageDecoder} belongs to
76 * @param in the {@link Buffer} from which to read data
77 * @return frame the {@link Buffer} which represent the frame or {@code null} if no frame could
78 * be created.
79 */
80 protected Object decode0(@SuppressWarnings("UnusedParameters") ChannelHandlerContext ctx, Buffer in)
81 throws Exception {
82 if (in.readableBytes() < frameLength) {
83 return null;
84 } else {
85 return in.readSplit(frameLength);
86 }
87 }
88 }