Linuxc++socket 接收protobuf并解码的demo，每一条消息由消息头、消息体组成。消息采用单字节对齐方式。本接口规范中的所有整数类 型字段都采用低字节序（LITTLE-ENDIAN）编码方式。如用 java 开发客户端接收程序， 需要转整数字段换字节序。

这里是一个 Java 的示例代码，用于接收 protobuf 消息并解码，假设消息头的长度为 4 字节、包含消息体长度和消息类型两个字段，消息体为 protobuf 格式：

import java.io.InputStream;
import java.net.Socket;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;

import com.google.protobuf.Message;

public class MessageReceiver {
    // 消息头长度
    private static final int HEADER_LENGTH = 4;

    // 接收数据
    private static int receiveData(InputStream in, byte[] buffer, int length) throws Exception {
        int recvLen = 0;
        while (recvLen < length) {
            int ret = in.read(buffer, recvLen, length - recvLen);
            if (ret < 0) {
                throw new Exception("Socket receive error");
            }
            recvLen += ret;
        }
        return recvLen;
    }

    // 接收并解析消息
    public static boolean receiveMessage(Socket socket, Message.Builder builder) {
        try {
            InputStream in = socket.getInputStream();

            // 接收消息头
            byte[] header = new byte[HEADER_LENGTH];
            if (receiveData(in, header, HEADER_LENGTH) != HEADER_LENGTH) {
                return false;
            }

            // 解析消息头
            int bodyLength = ByteBuffer.wrap(header).order(ByteOrder.LITTLE_ENDIAN).getInt();
            int messageType = ByteBuffer.wrap(header, 4, 4).order(ByteOrder.LITTLE_ENDIAN).getInt();

            // 接收消息体
            byte[] body = new byte[bodyLength];
            if (receiveData(in, body, bodyLength) != bodyLength) {
                return false;
            }

            // 解码消息体
            builder.clear();
            builder.mergeFrom(body);

            return true;
        } catch (Exception e) {
            e.printStackTrace();
            return false;
        }
    }
}

使用示例：

Socket socket = new Socket("127.0.0.1", 8080);

// 接收并解析消息
MyMessage.Builder builder = MyMessage.newBuilder();
if (MessageReceiver.receiveMessage(socket, builder)) {
    MyMessage msg = builder.build();
    // 处理消息
    ...
}

socket.close();