protobuf 格式分析

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package com;

message helloworld{
    required int32 id = 1;
    required string str = 3;
    optional int32 age = 2;
}

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protoc -I=. --cpp_out=. helloworld.proto
protoc -I=. --java_out=./java helloworld.proto

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/**
 * C++ Udp server
 */ 
void udpServer()
{
        int s;
        struct sockaddr_in addr_serv;
        struct sockaddr_in client;

        s = socket(AF_INET, SOCK_DGRAM, 0);

        memset(&addr_serv, 0, sizeof(addr_serv));
        addr_serv.sin_family = AF_INET;
        addr_serv.sin_addr.s_addr = htonl(INADDR_ANY);
        addr_serv.sin_port = htons(PORT_SERV);

        bind(s, (struct sockaddr*)&addr_serv, sizeof(addr_serv));

        int n;
        char buff[BUFF_LEN];
        socklen_t len;

        while(1)
        {
                len = sizeof(client);
                n = recvfrom(s, buff, BUFF_LEN, 0, (struct sockaddr*)&client, &len);

                // unserialize
                helloworld rmsg;
                rmsg.ParseFromArray( buff, BUFF_LEN );
                printf( "Recv: %sn", rmsg.DebugString().c_str() );
        }
}

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/**
 * UDP 发送pb数据包
 */
public static void sendPbPacket() {
	// Builder 
	Helloworld.helloworld.Builder builder = Helloworld.helloworld.newBuilder();
	builder.setId(505100).setStr("hello world");
	builder.setAge(18);
	
	// Make object
	Helloworld.helloworld hw = builder.build();
	System.out.println( hw.toString() );

	// 序列化
	byte[] buf = hw.toByteArray();
	try {
		// 反序列化
		Helloworld.helloworld hw1 = Helloworld.helloworld.parseFrom(buf);
		System.out.println( hw1.toString() );
	} catch (InvalidProtocolBufferException e) {
		e.printStackTrace();
	}

	// UDP发送
	DatagramSocket client = null;
		
	try {
		client = new DatagramSocket();

		InetAddress addr = InetAddress.getByName(host);
		DatagramPacket sendPacket = new DatagramPacket(buf, buf.length, addr, port);
		client.send(sendPacket);
	} catch (Exception e) {
		e.printStackTrace();
	}finally{
		client.close();
	}
}

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Recv: id: 505100
str: "hello world"
age: 18