/*
* Copyright 2012 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 io.netty.handler.codec;
import io.netty.buffer.
ByteBuf;
import io.netty.channel.
ChannelHandlerContext;
import java.util.
List;
/**
* A decoder that splits the received {@link ByteBuf}s by the fixed number
* of bytes. For example, if you received the following four fragmented packets:
* <pre>
* +---+----+------+----+
* | A | BC | DEFG | HI |
* +---+----+------+----+
* </pre>
* A {@link FixedLengthFrameDecoder}{@code (3)} will decode them into the
* following three packets with the fixed length:
* <pre>
* +-----+-----+-----+
* | ABC | DEF | GHI |
* +-----+-----+-----+
* </pre>
*/
public class
FixedLengthFrameDecoder extends
ByteToMessageDecoder {
private final int
frameLength;
/**
* Creates a new instance.
*
* @param frameLength the length of the frame
*/
public
FixedLengthFrameDecoder(int
frameLength) {
if (
frameLength <= 0) {
throw new
IllegalArgumentException(
"frameLength must be a positive integer: " +
frameLength);
}
this.
frameLength =
frameLength;
}
@
Override
protected final void
decode(
ChannelHandlerContext ctx,
ByteBuf in,
List<
Object>
out) throws
Exception {
Object decoded =
decode(
ctx,
in);
if (
decoded != null) {
out.
add(
decoded);
}
}
/**
* Create a frame out of the {@link ByteBuf} and return it.
*
* @param ctx the {@link ChannelHandlerContext} which this {@link ByteToMessageDecoder} belongs to
* @param in the {@link ByteBuf} from which to read data
* @return frame the {@link ByteBuf} which represent the frame or {@code null} if no frame could
* be created.
*/
protected
Object decode(
@
SuppressWarnings("UnusedParameters")
ChannelHandlerContext ctx,
ByteBuf in) throws
Exception {
if (
in.
readableBytes() <
frameLength) {
return null;
} else {
return
in.
readRetainedSlice(
frameLength);
}
}
}