/*
* Copyright 2011 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.frame;
import static io.netty.buffer.ChannelBuffers.*;
import java.nio.ByteOrder;
import io.netty.buffer.ChannelBuffer;
import io.netty.buffer.ChannelBufferFactory;
import io.netty.channel.Channel;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelHandler.Sharable;
import io.netty.handler.codec.oneone.OneToOneEncoder;
/**
* An encoder that prepends the length of the message. The length value is
* prepended as a binary form. It is encoded in either big endian or little
* endian depending on the default {@link ByteOrder} of the current
* {@link ChannelBufferFactory}.
* <p>
* For example, <tt>{@link LengthFieldPrepender}(2)</tt> will encode the
* following 12-bytes string:
* <pre>
* +----------------+
* | "HELLO, WORLD" |
* +----------------+
* </pre>
* into the following:
* <pre>
* +--------+----------------+
* + 0x000C | "HELLO, WORLD" |
* +--------+----------------+
* </pre>
* If you turned on the {@code lengthIncludesLengthFieldLength} flag in the
* constructor, the encoded data would look like the following
* (12 (original data) + 2 (prepended data) = 14 (0xE)):
* <pre>
* +--------+----------------+
* + 0x000E | "HELLO, WORLD" |
* +--------+----------------+
* </pre>
*/
@Sharable
public class LengthFieldPrepender extends OneToOneEncoder {
private final int lengthFieldLength;
private final boolean lengthIncludesLengthFieldLength;
/**
* Creates a new instance.
*
* @param lengthFieldLength the length of the prepended length field.
* Only 1, 2, 3, 4, and 8 are allowed.
*
* @throws IllegalArgumentException
* if {@code lengthFieldLength} is not 1, 2, 3, 4, or 8
*/
public LengthFieldPrepender(int lengthFieldLength) {
this(lengthFieldLength, false);
}
/**
* Creates a new instance.
*
* @param lengthFieldLength the length of the prepended length field.
* Only 1, 2, 3, 4, and 8 are allowed.
* @param lengthIncludesLengthFieldLength
* if {@code true}, the length of the prepended
* length field is added to the value of the
* prepended length field.
*
* @throws IllegalArgumentException
* if {@code lengthFieldLength} is not 1, 2, 3, 4, or 8
*/
public LengthFieldPrepender(
int lengthFieldLength, boolean lengthIncludesLengthFieldLength) {
if (lengthFieldLength != 1 && lengthFieldLength != 2 &&
lengthFieldLength != 3 && lengthFieldLength != 4 &&
lengthFieldLength != 8) {
throw new IllegalArgumentException(
"lengthFieldLength must be either 1, 2, 3, 4, or 8: " +
lengthFieldLength);
}
this.lengthFieldLength = lengthFieldLength;
this.lengthIncludesLengthFieldLength = lengthIncludesLengthFieldLength;
}
@Override
protected Object encode(
ChannelHandlerContext ctx, Channel channel, Object msg) throws Exception {
if (!(msg instanceof ChannelBuffer)) {
return msg;
}
ChannelBuffer body = (ChannelBuffer) msg;
ChannelBuffer header = channel.getConfig().getBufferFactory().getBuffer(body.order(), lengthFieldLength);
int length = lengthIncludesLengthFieldLength?
body.readableBytes() + lengthFieldLength : body.readableBytes();
switch (lengthFieldLength) {
case 1:
if (length >= 256) {
throw new IllegalArgumentException(
"length does not fit into a byte: " + length);
}
header.writeByte((byte) length);
break;
case 2:
if (length >= 65536) {
throw new IllegalArgumentException(
"length does not fit into a short integer: " + length);
}
header.writeShort((short) length);
break;
case 3:
if (length >= 16777216) {
throw new IllegalArgumentException(
"length does not fit into a medium integer: " + length);
}
header.writeMedium(length);
break;
case 4:
header.writeInt(length);
break;
case 8:
header.writeLong(length);
break;
default:
throw new Error("should not reach here");
}
return wrappedBuffer(header, body);
}
}