Netty protobuf的编解码使用
Netty为protobuf提供了两个编码器（ProtobufEncoder，ProtobufVarint32LengthFieldPrepender），两个解码器（ProtobufVarint32FrameDecoder，ProtobufDecoder）。
只需要在childHandler()中设置好以上编解码器就可以使用protobuf传输数据。
服务器端：
Netty已经把所有的protobuf的细节给封装过了，包括半包粘包的处理。看一下Netty是如何发送和接受protobuf数据的(基于Netty4.0.33)。
ProtobufVarint32LengthFieldPrepender：
解码的过程无非就是先读出length来，根据length读取出所有的数据来，交给protobuf就能还原消息出来。ProtobufVarint32FrameDecoder：
ProtobufDecoder：
只需要在childHandler()中设置好以上编解码器就可以使用protobuf传输数据。
服务器端：
.childHandler(new ChannelInitializer() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ch.pipeline()
.addLast(new ProtobufVarint32FrameDecoder())
.addLast(new ProtobufDecoder(
ProtoObject.Req.getDefaultInstance()))
.addLast(new ProtobufVarint32LengthFieldPrepender())
.addLast(new ProtobufEncoder())
.addLast(new ServerHandler());
}
}) .childHandler(new ChannelInitializer() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ch.pipeline()
.addLast(new ProtobufVarint32FrameDecoder())
.addLast(new ProtobufDecoder(
ProtoObject.Resp.getDefaultInstance()))
.addLast(new ProtobufVarint32LengthFieldPrepender())
.addLast(new ProtobufEncoder())
.addLast(new ClientHandler());
}
}) Netty已经把所有的protobuf的细节给封装过了，包括半包粘包的处理。看一下Netty是如何发送和接受protobuf数据的(基于Netty4.0.33)。
public class ProtobufEncoder extends MessageToMessageEncoder {
@Override
protected void encode(
ChannelHandlerContext ctx, MessageLiteOrBuilder msg, List ProtobufVarint32LengthFieldPrepender：
public class ProtobufVarint32LengthFieldPrepender extends MessageToByteEncoder {
@Override
protected void encode(
ChannelHandlerContext ctx, ByteBuf msg, ByteBuf out) throws Exception {
int bodyLen = msg.readableBytes();
int headerLen = CodedOutputStream.computeRawVarint32Size(bodyLen);
out.ensureWritable(headerLen + bodyLen);
CodedOutputStream headerOut =
CodedOutputStream.newInstance(new ByteBufOutputStream(out), headerLen);
headerOut.writeRawVarint32(bodyLen);
headerOut.flush();
out.writeBytes(msg, msg.readerIndex(), bodyLen);
}
} * BEFORE DECODE (300 bytes) AFTER DECODE (302 bytes)
* +---------------+ +--------+---------------+
* | Protobuf Data |-------------->| Length | Protobuf Data |
* | (300 bytes) | | 0xAC02 | (300 bytes) |
* +---------------+ +--------+---------------+解码的过程无非就是先读出length来，根据length读取出所有的数据来，交给protobuf就能还原消息出来。ProtobufVarint32FrameDecoder：
public class ProtobufVarint32FrameDecoder extends ByteToMessageDecoder {
// TODO maxFrameLength + safe skip + fail-fast option
// (just like LengthFieldBasedFrameDecoder)
@Override
protected void decode(ChannelHandlerContext ctx, ByteBuf in, ListProtobufDecoder：
public class ProtobufDecoder extends MessageToMessageDecoder {
private static final boolean HAS_PARSER;
static {
boolean hasParser = false;
try {
// MessageLite.getParsetForType() is not available until protobuf 2.5.0.
MessageLite.class.getDeclaredMethod("getParserForType");
hasParser = true;
} catch (Throwable t) {
// Ignore
}
HAS_PARSER = hasParser;
}
private final MessageLite prototype;
private final ExtensionRegistryLite extensionRegistry;
/**
* Creates a new instance.
*/
public ProtobufDecoder(MessageLite prototype) {
this(prototype, null);
}
public ProtobufDecoder(MessageLite prototype, ExtensionRegistry extensionRegistry) {
this(prototype, (ExtensionRegistryLite) extensionRegistry);
}
public ProtobufDecoder(MessageLite prototype, ExtensionRegistryLite extensionRegistry) {
if (prototype == null) {
throw new NullPointerException("prototype");
}
this.prototype = prototype.getDefaultInstanceForType();
this.extensionRegistry = extensionRegistry;
}
@Override
protected void decode(ChannelHandlerContext ctx, ByteBuf msg, List