基於Netty和SpringBoot實現一個輕量級RPC框架-協議篇

前提

最近對網絡編程方面比較有興趣，在微服務實踐上也用到了相對主流的RPC框架如Spring Cloud Gateway底層也切換為Reactor-Netty，像Redisson底層也是使用Netty封裝通訊協議，最近調研和准備使用的SOFARpc也是基於Netty封裝實現了多種協議的兼容。因此，基於Netty造一個輪子，在SpringBoot的加持下，實現一個輕量級的RPC框架。這篇博文介紹的是RPC框架協議的定義以及對應的編碼解碼處理的實現。

依賴引入

截止本文（2020-01-12）編寫完成之時，Netty的最新版本為4.1.44.Final，而SpringBoot的最新版本為2.2.2.RELEASE，因此引入這兩個版本的依賴，加上其他工具包和序列化等等的支持，pom文件的核心內容如下：

    <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>

部分參數的序列化會依賴到FastJson或者Jackson，具體看偏好而定。

自定義協議的定義

為了提高協議傳輸的效率，需要定制一套高效的RPC協議，設計協議所需的字段和類型。

基礎Packet字段：

字段名	字段類型	字段功能	備注
magicNumber	int	魔數，類似於Java的字節碼文件的魔數是0xcafebase
version	int	版本號	預留字段，默認為1
serialNumber	java.lang.String	請求流水號	十分重要，每個請求的唯一標識
messageType	MessageType	消息類型	自定義的枚舉類型，見下面的MessageType類
attachments	Map<String, String>	附件	K-V形式，類似於HTTP協議中的Header

// 消息枚舉類型
@RequiredArgsConstructor
public enum MessageType {

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

    /**
     * 響應
     */
    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));
    }
}

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

    /**
     * 魔數
     */
    private int magicNumber;

    /**
     * 版本號
     */
    private int version;

    /**
     * 流水號
     */
    private String serialNumber;

    /**
     * 消息類型
     */
    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);
    }
}

請求Packet擴展字段：

字段名	字段類型	字段功能	備注
interfaceName	java.lang.String	接口全類名
methodName	java.lang.String	方法名
methodArgumentSignatures	java.lang.String[]	方法參數簽名字符串數組	存放方法參數類型全類名字符串數組
methodArguments	java.lang.Object[]	方法參數數組	因為未知方法參數類型，所以用Object表示

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

    /**
     * 接口全類名
     */
    private String interfaceName;

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

    /**
     * 方法參數簽名
     */
    private String[] methodArgumentSignatures;

    /**
     * 方法參數
     */
    private Object[] methodArguments;
}

響應Packet擴展字段：

字段名	字段類型	字段功能	備注
errorCode	java.lang.Long	響應碼
message	java.lang.String	響應消息	如果出現異常，message就是對應的異常信息
payload	java.lang.Object	消息載荷	業務處理返回的消息載荷，定義為Object類型

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

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

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

    /**
     * 消息載荷
     */
    private Object payload;
}

需要注意以下幾點：

• 非基本類型在序列化和反序列化的時候，一定注意要先寫入或者先讀取序列的長度，以java.lang.String類型為例：

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

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

• 特殊編碼的字符串在序列化的時候，要注意字符串編碼的長度，例如UTF-8編碼下一個中文字符占3個字節，這一點可以抽取一個工具類專門處理字符串的序列化：

public enum ByteBufferUtils {

    // 單例
    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);
    }
}

• 方法參數數組的序列化和反序列化方案需要定制，筆者為了簡化自定義協議，定義了方法參數簽名數組，長度和方法參數數組一致，這樣做方便后面編寫服務端代碼的時候，簡化對方法參數數組進行反序列化以及宿主類目標方法的查找。注意一下Object[]的序列化和反序列化相對特殊，因為ByteBuf無法處理自定義類型的寫入和讀取（這個很好理解，網絡編程就是面向0和1的編程）：

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

read Object --> ByteBuf#readInt() && ByteBuf#readBytes() [<== 這個方法返回值是ByteBuf實例]

• 最后注意釋放ByteBuf的引用，否則有可能導致內存泄漏。

自定義協議編碼解碼實現

自定義協議編碼解碼主要包括四個部分的編碼解碼器：

• 請求Packet編碼器：RequestMessagePacketEncoder，主要用於客戶端把RequestMessagePacket實例序列化為二進制序列。
• 請求Packet解碼器：RequestMessagePacketDecoder，主要用於服務端把二進制序列反序列化為RequestMessagePacket實例。
• 響應Packet編碼器：ResponseMessagePacketEncoder，主要用於服務端把ResponseMessagePacket實例序列化為二進制序列。
• 響應Packet解碼器：ResponseMessagePacketDecoder，主要用於客戶端把二進制序列反序列化為ResponseMessagePacket實例。

畫個圖描述一下幾個組件的交互流程（省略了部分入站和出站處理器）：

序列化器Serializer的代碼如下：

public interface Serializer {

    byte[] encode(Object target);

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

// FastJson實現
public enum FastJsonSerializer implements Serializer {

    // 單例
    X;

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

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

請求Packet編碼器RequestMessagePacketEncoder的代碼如下：

@RequiredArgsConstructor
public class RequestMessagePacketEncoder extends MessageToByteEncoder<RequestMessagePacket> {

    private final Serializer serializer;

    @Override
    protected void encode(ChannelHandlerContext context, RequestMessagePacket packet, ByteBuf out) throws Exception {
        // 魔數
        out.writeInt(packet.getMagicNumber());
        // 版本
        out.writeInt(packet.getVersion());
        // 流水號
        out.writeInt(packet.getSerialNumber().length());
        out.writeCharSequence(packet.getSerialNumber(), ProtocolConstant.UTF_8);
        // 消息類型
        out.writeByte(packet.getMessageType().getType());
        // 附件size
        Map<String, String> attachments = packet.getAttachments();
        out.writeInt(attachments.size());
        // 附件內容
        attachments.forEach((k, v) -> {
            out.writeInt(k.length());
            out.writeCharSequence(k, ProtocolConstant.UTF_8);
            out.writeInt(v.length());
            out.writeCharSequence(v, ProtocolConstant.UTF_8);
        });
        // 接口全類名
        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);
        // 方法參數簽名(String[]類型) - 非必須
        if (null != packet.getMethodArgumentSignatures()) {
            int len = packet.getMethodArgumentSignatures().length;
            // 方法參數簽名數組長度
            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);
        }
        // 方法參數(Object[]類型) - 非必須
        if (null != packet.getMethodArguments()) {
            int len = packet.getMethodArguments().length;
            // 方法參數數組長度
            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);
        }
    }
}

請求Packet解碼器RequestMessagePacketDecoder的代碼如下：

@RequiredArgsConstructor
public class RequestMessagePacketDecoder extends ByteToMessageDecoder {

    @Override
    protected void decode(ChannelHandlerContext context, ByteBuf in, List<Object> list) throws Exception {
        RequestMessagePacket packet = new RequestMessagePacket();
        // 魔數
        packet.setMagicNumber(in.readInt());
        // 版本
        packet.setVersion(in.readInt());
        // 流水號
        int serialNumberLength = in.readInt();
        packet.setSerialNumber(in.readCharSequence(serialNumberLength, ProtocolConstant.UTF_8).toString());
        // 消息類型
        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);
            }
        }
        // 接口全類名
        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());
        // 方法參數簽名
        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);
        }
        // 方法參數
        int methodArgumentArrayLength = in.readInt();
        if (methodArgumentArrayLength > 0) {
            // 這里的Object[]實際上是ByteBuf[] - 后面需要二次加工為對應類型的實例
            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);
    }
}

響應Packet編碼器ResponseMessagePacketEncoder的代碼如下：

@RequiredArgsConstructor
public class ResponseMessagePacketEncoder extends MessageToByteEncoder<ResponseMessagePacket> {

    private final Serializer serializer;

    @Override
    protected void encode(ChannelHandlerContext ctx, ResponseMessagePacket packet, ByteBuf out) throws Exception {
        // 魔數
        out.writeInt(packet.getMagicNumber());
        // 版本
        out.writeInt(packet.getVersion());
        // 流水號
        out.writeInt(packet.getSerialNumber().length());
        out.writeCharSequence(packet.getSerialNumber(), ProtocolConstant.UTF_8);
        // 消息類型
        out.writeByte(packet.getMessageType().getType());
        // 附件size
        Map<String, String> attachments = packet.getAttachments();
        out.writeInt(attachments.size());
        // 附件內容
        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);
    }
}

響應Packet解碼器ResponseMessagePacketDecoder的代碼如下：

public class ResponseMessagePacketDecoder extends ByteToMessageDecoder {

    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
        ResponseMessagePacket packet = new ResponseMessagePacket();
        // 魔數
        packet.setMagicNumber(in.readInt());
        // 版本
        packet.setVersion(in.readInt());
        // 流水號
        int serialNumberLength = in.readInt();
        packet.setSerialNumber(in.readCharSequence(serialNumberLength, ProtocolConstant.UTF_8).toString());
        // 消息類型
        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實例
        int payloadLength = in.readInt();
        packet.setPayload(in.readBytes(payloadLength));
        out.add(packet);
    }
}

核心的編碼解碼器已經編寫完，接着要注意一下TCP協議二進制包發送的時候只保證了包的發送順序、確認發送以及重傳，無法保證二進制包是否完整（有些博客也稱此類場景為粘包、半包等等，其實網絡協議里面並沒有定義這些術語，估計是有人杜撰出來），因此這里采取了定長幀編碼和解碼器LengthFieldPrepender和LengthFieldBasedFrameDecoder，簡單來說就是在消息幀的開頭幾位定義了整個幀的長度，讀取到整個長度的消息幀才認為是一個完整的二進制報文。舉個幾個例子：

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

序號	Length Field	Actual Content
0	4	abcd
1	9	throwable
2	14	{"name":"doge"}

編寫測試客戶端和服務端

客戶端代碼如下：

@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("接收到來自服務端的響應消息,消息內容:{}", JSON.toJSONString(packet));
                        }
                    });
                }
            });
            ChannelFuture future = bootstrap.connect("localhost", port).sync();
            log.info("啟動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();
        }
    }
}

服務端代碼如下：

@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("接收到來自客戶端的請求消息,消息內容:{}", 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("啟動NettyServer[{}]成功...", port);
            future.channel().closeFuture().sync();
        } finally {
            workerGroup.shutdownGracefully();
            bossGroup.shutdownGracefully();
        }
    }
}

這里在測試的環境中，最大的消息幀長度暫時定義為1024。先啟動服務端，再啟動客戶端，見控制台輸出如下：

// 服務端
22:29:32.596 [main] INFO club.throwable.protocol.TestProtocolServer - 啟動NettyServer[9092]成功...
...省略其他日志...
22:29:53.538 [nioEventLoopGroup-3-1] INFO club.throwable.protocol.TestProtocolServer - 接收到來自客戶端的請求消息,消息內容:{"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}

// 客戶端
22:31:28.360 [main] INFO club.throwable.protocol.TestProtocolClient - 啟動NettyClient[9092]成功...
...省略其他日志...
22:31:39.320 [nioEventLoopGroup-2-1] INFO club.throwable.protocol.TestProtocolClient - 接收到來自服務端的響應消息,消息內容:{"attachments":{},"errorCode":200,"magicNumber":10086,"message":"Success","messageType":"RESPONSE","payload":"{\"name\":\"throwable\"}","serialNumber":"320808e709b34edbb91ba557780b58ad","version":1}

小結

一個基於Netty實現的簡單的自定義協議基本完成，但是要編寫一個優秀的RPC框架，還需要做服務端的宿主類和目標方法查詢、調用，客戶端的動態代理，Netty的NIO模式下的同步調用改造，心跳處理，異常處理等等。后面會使用多篇文章逐個問題解決，網絡編程其實挺好玩了，就是編碼量會比較大(゜-゜)つロ。

Demo項目：

• ch0-custom-rpc-protocol

（e-a-20200112 c-1-d）

技術公眾號（《Throwable文摘》），不定期推送筆者原創技術文章（絕不抄襲或者轉載）：

娛樂公眾號（《天天沙雕》），甄選奇趣沙雕圖文和視頻不定期推送，緩解生活工作壓力：