基于Netty和SpringBoot实现一个轻量级RPC框架-协议篇

前提

最近对网络编程方面比较有兴趣，在微服务实践上也用到了相对主流的RPC框架如Spring Cloud Gateway底层也切换为Reactor-Netty，像Redisson底层也是使用Netty封装通讯协议，最近调研和准备使用的SOFARpc也是基于Netty封装实现了多种协议的兼容。因此，基于Netty造一个轮子，在SpringBoot的加持下，实现一个轻量级的RPC框架。这篇博文介绍的是RPC框架协议的定义以及对应的编码解码处理的实现。

依赖引入

截止本文（2020-01-12）编写完成之时，Netty的最新版本为4.1.44.Final，而SpringBoot的最新版本为2.2.2.RELEASE，因此引入这两个版本的依赖，加上其他工具包和序列化等等的支持，pom文件的核心内容如下：

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-dependencies</artifactId>
            <version>${spring.boot.version}</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>
<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter</artifactId>
    </dependency>
    <dependency>
        <groupId>io.netty</groupId>
        <artifactId>netty-all</artifactId>
        <version>${netty.version}</version>
    </dependency>
    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <version>1.18.10</version>
        <scope>provided</scope>
    </dependency>
    <dependency>
        <groupId>com.alibaba</groupId>
        <artifactId>fastjson</artifactId>
        <version>1.2.61</version>
    </dependency>
    <dependency>
        <groupId>com.google.guava</groupId>
        <artifactId>guava</artifactId>
        <version>28.1-jre</version>
    </dependency>
</dependencies>

部分参数的序列化会依赖到FastJson或者Jackson，具体看偏好而定。

自定义协议的定义

为了提高协议传输的效率，需要定制一套高效的RPC协议，设计协议所需的字段和类型。

基础Packet字段：

字段名	字段类型	字节数(byte)	字段功能	备注
`magicNumber`	`int`	2	魔数，类似于`Java`的字节码文件的魔数是`0xcafebase`
`version`	`int`	2	版本号	预留字段，默认为1
`serialNumber`	`java.lang.String`	4	请求流水号	十分重要，每个请求的唯一标识
`messageType`	`MessageType`	1	消息类型	自定义的枚举类型，见下面的`MessageType`类
`attachments`	`Map<String, String>`	视实际情况而定	附件	`K-V`形式，类似于`HTTP`协议中的`Header`

// 消息枚举类型
@RequiredArgsConstructor
public enum MessageType {

    /**
     * 请求
     */
    REQUEST((byte) 1),

    /**
     * 响应
     */
    RESPONSE((byte) 2),

    /**
     * PING
     */
    PING((byte) 3),

    /**
     * PONG
     */
    PONG((byte) 4),

    /**
     * NULL
     */
    NULL((byte) 5),

    ;

    @Getter
    private final Byte type;

    public static MessageType fromValue(byte value) {
        for (MessageType type : MessageType.values()) {
            if (type.getType() == value) {
                return type;
            }
        }
        throw new IllegalArgumentException(String.format("value = %s", value));
    }
}

// 基础Packet
@Data
public abstract class BaseMessagePacket implements Serializable {

    /**
     * 魔数
     */
    private int magicNumber;

    /**
     * 版本号
     */
    private int version;

    /**
     * 流水号
     */
    private String serialNumber;

    /**
     * 消息类型
     */
    private MessageType messageType;

    /**
     * 附件 - K-V形式
     */
    private Map<String, String> attachments = new HashMap<>();

    /**
     * 添加附件
     */
    public void addAttachment(String key, String value) {
        attachments.put(key, value);
    }
}

请求Packet扩展字段：

字段名	字段类型	字节数(byte)	字段功能	备注
`interfaceName`	`java.lang.String`	视实际情况而定	接口全类名
`methodName`	`java.lang.String`	视实际情况而定	方法名
`methodArgumentSignatures`	`java.lang.String[]`	视实际情况而定	方法参数签名字符串数组	存放方法参数类型全类名字符串数组
`methodArguments`	`java.lang.Object[]`	视实际情况而定	方法参数数组	因为未知方法参数类型，所以用`Object`表示

@EqualsAndHashCode(callSuper = true)
@Data
public class RequestMessagePacket extends BaseMessagePacket {

    /**
     * 接口全类名
     */
    private String interfaceName;

    /**
     * 方法名
     */
    private String methodName;

    /**
     * 方法参数签名
     */
    private String[] methodArgumentSignatures;

    /**
     * 方法参数
     */
    private Object[] methodArguments;
}

响应Packet扩展字段：

字段名	字段类型	字节数(byte)	字段功能	备注
`errorCode`	`java.lang.Long`	4	响应码
`message`	`java.lang.String`	视实际情况而定	响应消息	如果出现异常，`message`就是对应的异常信息
`payload`	`java.lang.Object`	视实际情况而定	消息载荷	业务处理返回的消息载荷，定义为`Object`类型

@EqualsAndHashCode(callSuper = true)
@Data
public class ResponseMessagePacket extends BaseMessagePacket {

    /**
     * error code
     */
    private Long errorCode;

    /**
     * 消息描述
     */
    private String message;

    /**
     * 消息载荷
     */
    private Object payload;
}

需要注意以下几点：

非基本类型在序列化和反序列化的时候，一定注意要先写入或者先读取序列的长度，以java.lang.String类型为例：

// 序列化 - 流水号
out.writeInt(packet.getSerialNumber().length());
out.writeCharSequence(packet.getSerialNumber(), ProtocolConstant.UTF_8);

// 反序列化 - 流水号
int serialNumberLength = in.readInt();
packet.setSerialNumber(in.readCharSequence(serialNumberLength, ProtocolConstant.UTF_8).toString());

特殊编码的字符串在序列化的时候，要注意字符串编码的长度，例如UTF-8编码下一个中文字符占3个字节，这一点可以抽取一个工具类专门处理字符串的序列化：

public enum ByteBufferUtils {

    // 单例
    X;

    public void encodeUtf8CharSequence(ByteBuf byteBuf, CharSequence charSequence) {
        int writerIndex = byteBuf.writerIndex();
        byteBuf.writeInt(0);
        int length = ByteBufUtil.writeUtf8(byteBuf, charSequence);
        byteBuf.setInt(writerIndex, length);
    }
}

方法参数数组的序列化和反序列化方案需要定制，笔者为了简化自定义协议，定义了方法参数签名数组，长度和方法参数数组一致，这样做方便后面编写服务端代码的时候，简化对方法参数数组进行反序列化以及宿主类目标方法的查找。注意一下Object[]的序列化和反序列化相对特殊，因为ByteBuf无法处理自定义类型的写入和读取（这个很好理解，网络编程就是面向0和1的编程）：

write Object --> ByteBuf#writeInt() && ByteBuf#writeBytes()

read Object --> ByteBuf#readInt() && ByteBuf#readBytes() [<== 这个方法返回值是ByteBuf实例]

最后注意释放ByteBuf的引用，否则有可能导致内存泄漏。

自定义协议编码解码实现

自定义协议编码解码主要包括四个部分的编码解码器：

请求Packet编码器：RequestMessagePacketEncoder，主要用于客户端把RequestMessagePacket实例序列化为二进制序列。
请求Packet解码器：RequestMessagePacketDecoder，主要用于服务端把二进制序列反序列化为RequestMessagePacket实例。
响应Packet编码器：ResponseMessagePacketEncoder，主要用于服务端把ResponseMessagePacket实例序列化为二进制序列。
响应Packet解码器：ResponseMessagePacketDecoder，主要用于客户端把二进制序列反序列化为ResponseMessagePacket实例。

画个图描述一下几个组件的交互流程（省略了部分入站和出站处理器）：

序列化器Serializer的代码如下：

public interface Serializer {

    byte[] encode(Object target);

    Object decode(byte[] bytes, Class<?> targetClass);
}

// FastJson实现
public enum FastJsonSerializer implements Serializer {

    // 单例
    X;

    @Override
    public byte[] encode(Object target) {
        return JSON.toJSONBytes(target);
    }

    @Override
    public Object decode(byte[] bytes, Class<?> targetClass) {
        return JSON.parseObject(bytes, targetClass);
    }
}

请求Packet编码器RequestMessagePacketEncoder的代码如下：

@RequiredArgsConstructor
public class RequestMessagePacketEncoder extends MessageToByteEncoder<RequestMessagePacket> {

    private final Serializer serializer;

    @Override
    protected void encode(ChannelHandlerContext context, RequestMessagePacket packet, ByteBuf out) throws Exception {
        // 魔数
        out.writeInt(packet.getMagicNumber());
        // 版本
        out.writeInt(packet.getVersion());
        // 流水号
        out.writeInt(packet.getSerialNumber().length());
        out.writeCharSequence(packet.getSerialNumber(), ProtocolConstant.UTF_8);
        // 消息类型
        out.writeByte(packet.getMessageType().getType());
        // 附件size
        Map<String, String> attachments = packet.getAttachments();
        out.writeInt(attachments.size());
        // 附件内容
        attachments.forEach((k, v) -> {
            out.writeInt(k.length());
            out.writeCharSequence(k, ProtocolConstant.UTF_8);
            out.writeInt(v.length());
            out.writeCharSequence(v, ProtocolConstant.UTF_8);
        });
        // 接口全类名
        out.writeInt(packet.getInterfaceName().length());
        out.writeCharSequence(packet.getInterfaceName(), ProtocolConstant.UTF_8);
        // 方法名
        out.writeInt(packet.getMethodName().length());
        out.writeCharSequence(packet.getMethodName(), ProtocolConstant.UTF_8);
        // 方法参数签名(String[]类型) - 非必须
        if (null != packet.getMethodArgumentSignatures()) {
            int len = packet.getMethodArgumentSignatures().length;
            // 方法参数签名数组长度
            out.writeInt(len);
            for (int i = 0; i < len; i++) {
                String methodArgumentSignature = packet.getMethodArgumentSignatures()[i];
                out.writeInt(methodArgumentSignature.length());
                out.writeCharSequence(methodArgumentSignature, ProtocolConstant.UTF_8);
            }
        } else {
            out.writeInt(0);
        }
        // 方法参数(Object[]类型) - 非必须
        if (null != packet.getMethodArguments()) {
            int len = packet.getMethodArguments().length;
            // 方法参数数组长度
            out.writeInt(len);
            for (int i = 0; i < len; i++) {
                byte[] bytes = serializer.encode(packet.getMethodArguments()[i]);
                out.writeInt(bytes.length);
                out.writeBytes(bytes);
            }
        } else {
            out.writeInt(0);
        }
    }
}

请求Packet解码器RequestMessagePacketDecoder的代码如下：

@RequiredArgsConstructor
public class RequestMessagePacketDecoder extends ByteToMessageDecoder {

    @Override
    protected void decode(ChannelHandlerContext context, ByteBuf in, List<Object> list) throws Exception {
        RequestMessagePacket packet = new RequestMessagePacket();
        // 魔数
        packet.setMagicNumber(in.readInt());
        // 版本
        packet.setVersion(in.readInt());
        // 流水号
        int serialNumberLength = in.readInt();
        packet.setSerialNumber(in.readCharSequence(serialNumberLength, ProtocolConstant.UTF_8).toString());
        // 消息类型
        byte messageTypeByte = in.readByte();
        packet.setMessageType(MessageType.fromValue(messageTypeByte));
        // 附件
        Map<String, String> attachments = Maps.newHashMap();
        packet.setAttachments(attachments);
        int attachmentSize = in.readInt();
        if (attachmentSize > 0) {
            for (int i = 0; i < attachmentSize; i++) {
                int keyLength = in.readInt();
                String key = in.readCharSequence(keyLength, ProtocolConstant.UTF_8).toString();
                int valueLength = in.readInt();
                String value = in.readCharSequence(valueLength, ProtocolConstant.UTF_8).toString();
                attachments.put(key, value);
            }
        }
        // 接口全类名
        int interfaceNameLength = in.readInt();
        packet.setInterfaceName(in.readCharSequence(interfaceNameLength, ProtocolConstant.UTF_8).toString());
        // 方法名
        int methodNameLength = in.readInt();
        packet.setMethodName(in.readCharSequence(methodNameLength, ProtocolConstant.UTF_8).toString());
        // 方法参数签名
        int methodArgumentSignatureArrayLength = in.readInt();
        if (methodArgumentSignatureArrayLength > 0) {
            String[] methodArgumentSignatures = new String[methodArgumentSignatureArrayLength];
            for (int i = 0; i < methodArgumentSignatureArrayLength; i++) {
                int methodArgumentSignatureLength = in.readInt();
                methodArgumentSignatures[i] = in.readCharSequence(methodArgumentSignatureLength, ProtocolConstant.UTF_8).toString();
            }
            packet.setMethodArgumentSignatures(methodArgumentSignatures);
        }
        // 方法参数
        int methodArgumentArrayLength = in.readInt();
        if (methodArgumentArrayLength > 0) {
            // 这里的Object[]实际上是ByteBuf[] - 后面需要二次加工为对应类型的实例
            Object[] methodArguments = new Object[methodArgumentArrayLength];
            for (int i = 0; i < methodArgumentArrayLength; i++) {
                int byteLength = in.readInt();
                methodArguments[i] = in.readBytes(byteLength);
            }
            packet.setMethodArguments(methodArguments);
        }
        list.add(packet);
    }
}

响应Packet编码器ResponseMessagePacketEncoder的代码如下：

@RequiredArgsConstructor
public class ResponseMessagePacketEncoder extends MessageToByteEncoder<ResponseMessagePacket> {

    private final Serializer serializer;

    @Override
    protected void encode(ChannelHandlerContext ctx, ResponseMessagePacket packet, ByteBuf out) throws Exception {
        // 魔数
        out.writeInt(packet.getMagicNumber());
        // 版本
        out.writeInt(packet.getVersion());
        // 流水号
        out.writeInt(packet.getSerialNumber().length());
        out.writeCharSequence(packet.getSerialNumber(), ProtocolConstant.UTF_8);
        // 消息类型
        out.writeByte(packet.getMessageType().getType());
        // 附件size
        Map<String, String> attachments = packet.getAttachments();
        out.writeInt(attachments.size());
        // 附件内容
        attachments.forEach((k, v) -> {
            out.writeInt(k.length());
            out.writeCharSequence(k, ProtocolConstant.UTF_8);
            out.writeInt(v.length());
            out.writeCharSequence(v, ProtocolConstant.UTF_8);
        });
        // error code
        out.writeLong(packet.getErrorCode());
        // message
        String message = packet.getMessage();
        ByteBufferUtils.X.encodeUtf8CharSequence(out, message);
        // payload
        byte[] bytes = serializer.encode(packet.getPayload());
        out.writeInt(bytes.length);
        out.writeBytes(bytes);
    }
}

响应Packet解码器ResponseMessagePacketDecoder的代码如下：

public class ResponseMessagePacketDecoder extends ByteToMessageDecoder {

    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
        ResponseMessagePacket packet = new ResponseMessagePacket();
        // 魔数
        packet.setMagicNumber(in.readInt());
        // 版本
        packet.setVersion(in.readInt());
        // 流水号
        int serialNumberLength = in.readInt();
        packet.setSerialNumber(in.readCharSequence(serialNumberLength, ProtocolConstant.UTF_8).toString());
        // 消息类型
        byte messageTypeByte = in.readByte();
        packet.setMessageType(MessageType.fromValue(messageTypeByte));
        // 附件
        Map<String, String> attachments = Maps.newHashMap();
        packet.setAttachments(attachments);
        int attachmentSize = in.readInt();
        if (attachmentSize > 0) {
            for (int i = 0; i < attachmentSize; i++) {
                int keyLength = in.readInt();
                String key = in.readCharSequence(keyLength, ProtocolConstant.UTF_8).toString();
                int valueLength = in.readInt();
                String value = in.readCharSequence(valueLength, ProtocolConstant.UTF_8).toString();
                attachments.put(key, value);
            }
        }
        // error code
        packet.setErrorCode(in.readLong());
        // message
        int messageLength = in.readInt();
        packet.setMessage(in.readCharSequence(messageLength, ProtocolConstant.UTF_8).toString());
        // payload - ByteBuf实例
        int payloadLength = in.readInt();
        packet.setPayload(in.readBytes(payloadLength));
        out.add(packet);
    }
}

核心的编码解码器已经编写完，接着要注意一下TCP协议二进制包发送的时候只保证了包的发送顺序、确认发送以及重传，无法保证二进制包是否完整（有些博客也称此类场景为粘包、半包等等，其实网络协议里面并没有定义这些术语，估计是有人杜撰出来），因此这里采取了定长帧编码和解码器LengthFieldPrepender和LengthFieldBasedFrameDecoder，简单来说就是在消息帧的开头几位定义了整个帧的长度，读取到整个长度的消息帧才认为是一个完整的二进制报文。举个几个例子：

|<--------packet frame--------->|
| Length Field | Actual Content |

序号	Length Field	Actual Content
0	4	abcd
1	9	throwable
2	14	{“name”:”doge”}

编写测试客户端和服务端

客户端代码如下：

@Slf4j
public class TestProtocolClient {

    public static void main(String[] args) throws Exception {
        int port = 9092;
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        Bootstrap bootstrap = new Bootstrap();
        try {
            bootstrap.group(workerGroup);
            bootstrap.channel(NioSocketChannel.class);
            bootstrap.option(ChannelOption.SO_KEEPALIVE, Boolean.TRUE);
            bootstrap.option(ChannelOption.TCP_NODELAY, Boolean.TRUE);
            bootstrap.handler(new ChannelInitializer<SocketChannel>() {

                @Override
                protected void initChannel(SocketChannel ch) throws Exception {
                    ch.pipeline().addLast(new LengthFieldBasedFrameDecoder(1024, 0, 4, 0, 4));
                    ch.pipeline().addLast(new LengthFieldPrepender(4));
                    ch.pipeline().addLast(new RequestMessagePacketEncoder(FastJsonSerializer.X));
                    ch.pipeline().addLast(new ResponseMessagePacketDecoder());
                    ch.pipeline().addLast(new SimpleChannelInboundHandler<ResponseMessagePacket>() {
                        @Override
                        protected void channelRead0(ChannelHandlerContext ctx, ResponseMessagePacket packet) throws Exception {
                            Object targetPayload = packet.getPayload();
                            if (targetPayload instanceof ByteBuf) {
                                ByteBuf byteBuf = (ByteBuf) targetPayload;
                                int readableByteLength = byteBuf.readableBytes();
                                byte[] bytes = new byte[readableByteLength];
                                byteBuf.readBytes(bytes);
                                targetPayload = FastJsonSerializer.X.decode(bytes, String.class);
                                byteBuf.release();
                            }
                            packet.setPayload(targetPayload);
                            log.info("接收到来自服务端的响应消息,消息内容:{}", JSON.toJSONString(packet));
                        }
                    });
                }
            });
            ChannelFuture future = bootstrap.connect("localhost", port).sync();
            log.info("启动NettyClient[{}]成功...", port);
            Channel channel = future.channel();
            RequestMessagePacket packet = new RequestMessagePacket();
            packet.setMagicNumber(ProtocolConstant.MAGIC_NUMBER);
            packet.setVersion(ProtocolConstant.VERSION);
            packet.setSerialNumber(SerialNumberUtils.X.generateSerialNumber());
            packet.setMessageType(MessageType.REQUEST);
            packet.setInterfaceName("club.throwable.contract.HelloService");
            packet.setMethodName("sayHello");
            packet.setMethodArgumentSignatures(new String[]{"java.lang.String"});
            packet.setMethodArguments(new Object[]{"doge"});
            channel.writeAndFlush(packet);
            future.channel().closeFuture().sync();
        } finally {
            workerGroup.shutdownGracefully();
        }
    }
}

服务端代码如下：

@Slf4j
public class TestProtocolServer {

    public static void main(String[] args) throws Exception {
        int port = 9092;
        ServerBootstrap bootstrap = new ServerBootstrap();
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            bootstrap.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .childHandler(new ChannelInitializer<SocketChannel>() {

                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ch.pipeline().addLast(new LengthFieldBasedFrameDecoder(1024, 0, 4, 0, 4));
                            ch.pipeline().addLast(new LengthFieldPrepender(4));
                            ch.pipeline().addLast(new RequestMessagePacketDecoder());
                            ch.pipeline().addLast(new ResponseMessagePacketEncoder(FastJsonSerializer.X));
                            ch.pipeline().addLast(new SimpleChannelInboundHandler<RequestMessagePacket>() {

                                @Override
                                protected void channelRead0(ChannelHandlerContext ctx, RequestMessagePacket packet) throws Exception {
                                    log.info("接收到来自客户端的请求消息,消息内容:{}", JSON.toJSONString(packet));
                                    ResponseMessagePacket response = new ResponseMessagePacket();
                                    response.setMagicNumber(packet.getMagicNumber());
                                    response.setVersion(packet.getVersion());
                                    response.setSerialNumber(packet.getSerialNumber());
                                    response.setAttachments(packet.getAttachments());
                                    response.setMessageType(MessageType.RESPONSE);
                                    response.setErrorCode(200L);
                                    response.setMessage("Success");
                                    response.setPayload("{\"name\":\"throwable\"}");
                                    ctx.writeAndFlush(response);
                                }
                            });
                        }
                    });
            ChannelFuture future = bootstrap.bind(port).sync();
            log.info("启动NettyServer[{}]成功...", port);
            future.channel().closeFuture().sync();
        } finally {
            workerGroup.shutdownGracefully();
            bossGroup.shutdownGracefully();
        }
    }
}

这里在测试的环境中，最大的消息帧长度暂时定义为1024。先启动服务端，再启动客户端，见控制台输出如下：

// 服务端
22:29:32.596 [main] INFO club.throwable.protocol.TestProtocolServer - 启动NettyServer[9092]成功...
...省略其他日志...
22:29:53.538 [nioEventLoopGroup-3-1] INFO club.throwable.protocol.TestProtocolServer - 接收到来自客户端的请求消息,消息内容:{"attachments":{},"interfaceName":"club.throwable.contract.HelloService","magicNumber":10086,"messageType":"REQUEST","methodArgumentSignatures":["java.lang.String"],"methodArguments":[{"contiguous":true,"direct":true,"readOnly":false,"readable":true,"writable":false}],"methodName":"sayHello","serialNumber":"7f992c7cf9f445258601def1cac9bec0","version":1}

// 客户端
22:31:28.360 [main] INFO club.throwable.protocol.TestProtocolClient - 启动NettyClient[9092]成功...
...省略其他日志...
22:31:39.320 [nioEventLoopGroup-2-1] INFO club.throwable.protocol.TestProtocolClient - 接收到来自服务端的响应消息,消息内容:{"attachments":{},"errorCode":200,"magicNumber":10086,"message":"Success","messageType":"RESPONSE","payload":"{\"name\":\"throwable\"}","serialNumber":"320808e709b34edbb91ba557780b58ad","version":1}

小结

一个基于Netty实现的简单的自定义协议基本完成，但是要编写一个优秀的RPC框架，还需要做服务端的宿主类和目标方法查询、调用，客户端的动态代理，Netty的NIO模式下的同步调用改造，心跳处理，异常处理等等。后面会使用多篇文章逐个问题解决，网络编程其实挺好玩了，就是编码量会比较大(゜-゜)つロ。

Demo项目：