Protobuf c ++扩展使用 [英] Protobuf c++ extensions use

问题描述

我使用google protobuf库版本2.61并想使用扩展程序

I'm using google protobuf library version 2.61 and want to use extensions,

我有以下proto文件：

I have the following proto files:

package communication;

message BaseMessage {
  required uint64 server_id     = 1;
  required string uuid          = 2;
  required uint64 message_id    = 3;

  extensions 100 to max;
}

message GetIdentify {

  extend BaseMessage {
    optional GetIdentify message = 100;
  }

  required string hostname = 1;
}

我可以使用以下代码构建邮件：

I am able to build the message using the following code:

communication::BaseMessage base_message;
base_message.set_message_id(123456);
base_message.set_server_id(112313123);
base_message.set_uuid("asdaskdjasd213123123asd");
base_message.MutableExtension(communication::GetIdentify::message)->set_hostname("http://test123123123ing");

但是，我想做相反的操作，并获取未知扩展的消息并解析它，扩展它是，并根据它解析。

However I would like to do the opposite action and get message with unknown extension and parse it and find which extension it is and parse according to it.

我使用nanopb为我的c项目和python版本。但我发现很难在c ++中编写protobuf代码，因为我找不到足够好的文档和代码示例。

I've used nanopb for my c project and python version. but I find it really hard to write protobuf code in c++ because I can't find good enough documentation and code examples.

有没有办法做到这一点，变量类型的扩展？

Is there a way to do this without adding additional variable of type of extension?

也是最优雅的方式，在c ++中这样做

Also what is the most elegant way to do so in c++

推荐答案

库解析消息和所有扩展。您可以使用HasExtension方法检查扩展的存在。

The library parse message and all extensions. You can check presence of the extension using HasExtension method.

Java实现需要在解析之前在解析器中注册扩展。但在C ++中，一切都自动完成。请参阅以下代码。 （我用protobuf 2.5.0测试它）

Java implementation needs to register extensions in parser, before parsing. But in C++ everything done automatically. Please see following code. (I tested it with protobuf 2.5.0)

创建并写入消息：

#include <iostream>
#include <fstream>
#include <string>
#include <communication/p.pb.h> 
using namespace std;

int
main(int, char **)
{
    communication::BaseMessage base_message;
    base_message.set_message_id(123456);
    base_message.set_server_id(112313123);
    base_message.set_uuid("asdaskdjasd213123123asd");
    base_message.MutableExtension(communication::GetIdentify::message)->set_hostname("http://test123123123ing");
    base_message.SerializeToOstream(&cout);
    return 0;
}

读取邮件，测试扩充功能并列印：

Read message, test extension and print it:

#include <iostream>
#include <fstream>
#include <string>
#include <communication/p.pb.h>
#include <google/protobuf/text_format.h>
using namespace google::protobuf;
using namespace std;

int
main(int, char **)
{
    communication::BaseMessage base_message;
    base_message.ParseFromIstream(&cin);

    if (base_message.HasExtension(communication::GetIdentify::message)) {
        const communication::GetIdentify &ii = base_message.GetExtension(communication::GetIdentify::message);
        cout << "yes, msg has extension: " << ii.hostname() << endl << endl;
    } else {
        cout << "no, msg has no extension" << endl << endl;
    }

    string res;
    TextFormat::PrintToString(base_message, &res);

    cout << res << endl;
    return 0;
}

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