C++实用技术 – protobuf动态解析proto

利用protobuf的反射功能，我们可以解析任意message的任意字段信息。
有时候我们可能需要动态加载proto文件，利用新加载进来的proto文件的信息去解析数据。并把数据输出或者转格式
这时候我们就需要利用到protobuf的google::protobuf::compiler::DiskSourceTree类去加载proto文件。
利用google::protobuf::compiler::Importer类去导入proto文件

实现代码

测试用的proto文件

//sylar.proto
package sylar;

message AA {
    optional string name = 1;
    optional int32 age = 2;
}

message Test {
    optional string name = 1;
    optional int32 age = 2;
    repeated string phones = 3;
    repeated AA aa = 4;
}

message XX {
    optional string name = 1;
    repeated AA aa = 4;
}

动态解析proto文件代码

int DynamicParseFromPBFile(const std::string& filename
    , const std::string& classname
    , std::function<void(::google::protobuf::Message* msg)> cb) {
    //TODO 检查文件名是否合法
    auto pos = filename.find_last_of('/');
    std::string path;
    std::string file;
    if(pos == std::string::npos) {
        file = filename;
    } else {
        path = filename.substr(0, pos);
        file = filename.substr(pos + 1);
    }

    ::google::protobuf::compiler::DiskSourceTree sourceTree;
    sourceTree.MapPath("", path);
    ::google::protobuf::compiler::Importer importer(&sourceTree, NULL);
    importer.Import(file);
    const ::google::protobuf::Descriptor *descriptor
        = importer.pool()->FindMessageTypeByName(classname);
    if(!descriptor) {
        return 1;
    }
    ::google::protobuf::DynamicMessageFactory factory;
    const ::google::protobuf::Message *message
        = factory.GetPrototype(descriptor);
    if(!message) {
        return 2;
    }
    ::google::protobuf::Message* msg = message->New();
    if(!msg) {
        return 3;
    }
    cb(msg);
    delete msg;
    return 0;
}

动态解析proto string

int DynamicParseFromPBString(const std::string& proto_string
    , const std::string& classname
    , std::function<void(::google::protobuf::Message* msg)> cb) {
    std::stringstream ss;
    ss << "/tmp/dps_" << rand() << "_" << rand() << ".proto";
    std::ofstream ofs(ss.str());
    ofs << proto_string;
    ofs.close();
    return DynamicParseFromPBFile(ss.str(), classname, cb);
}

测试代码

#include <google/protobuf/message.h>
#include <google/protobuf/descriptor.h>
#include <google/protobuf/descriptor.pb.h>
#include <google/protobuf/dynamic_message.h>
#include <google/protobuf/compiler/importer.h>

#include "sylar.pb.h"

#include <functional>
#include <iostream>
#include <fstream>
#include <string>
#include <sstream>

//filename proto文件名
//classname proto文件里面的class， 格式package.Classname
//cb, 创建好proto文件里面的classname类之后执行的回调，可以在该回调里面操作数据
int DynamicParseFromPBFile(const std::string& filename
    , const std::string& classname
    , std::function<void(::google::protobuf::Message* msg)> cb);

//proto_string proto文件的内容
//classname proto文件里面的class， 格式package.Classname
//cb, 创建好proto文件里面的classname类之后执行的回调，可以在该回调里面操作数据
int DynamicParseFromPBString(const std::string& proto_string
    , const std::string& classname
    , std::function<void(::google::protobuf::Message* msg)> cb);

int main(int argc, char** argv) {
    //创建一个测试类，并进行初始化
    sylar::Test test;
    test.set_name("test_name");
    test.set_age(100);
    test.add_phones("138xxxxxx");
    test.add_phones("139xxxxxx");

    for(int i = 0; i < 3; ++i) {
        auto* a = test.add_aa();
        a->set_name("a_name_" + std::to_string(i));
        a->set_age(100 + i);
    }
    std::string pb_str;
    //把测试类，序列化到string中，以供后续解析
    test.SerializeToString(&pb_str);
    //打印测试类的数据信息
    std::cout << test.DebugString() << std::endl;
    std::cout << "===============================" << std::endl;
    //从文件中sylar.proto中的sylar.XX类，解析上面测试类的序列化二进制
    //并输出序列化后的sylar.XX的信息
    DynamicParseFromPBFile("sylar.proto", "sylar.XX"
        , [pb_str](::google::protobuf::Message* msg) {
        if(msg->ParseFromString(pb_str)) {
            std::cout << msg->DebugString() << std::endl;
        }
    });
    std::cout << "===============================" << std::endl;
    //从文件中sylar.proto中的sylar.Test，解析上面测试类的序列化二进制
    //并输出序列化后的sylar.Test的信息
    DynamicParseFromPBFile("sylar.proto", "sylar.Test"
        , [pb_str](::google::protobuf::Message* msg) {
        if(msg->ParseFromString(pb_str)) {
            std::cout << msg->DebugString() << std::endl;
        }
    });

    //字符串pb文件内容
    std::string pbstr = "package xx;\n"
        "message BB { \n"
        "    optional string name = 1; \n"
        "    optional int32 age = 2; \n"
        "} \n"
        "message TT { \n"
        "    optional string name = 1; \n"
        "    optional int32 age = 2; \n"
        "    repeated string phones = 3; \n"
        "    repeated BB aa = 4; \n"
        "}";

    std::cout << "===============================" << std::endl;
    //pbstr的proto信息中的xx.TT，解析上面测试类的序列化二进制
    //并输出序列化后的xx.TT的信息
    DynamicParseFromPBString(pbstr, "xx.TT"
        , [pb_str](::google::protobuf::Message* msg) {
        if(msg->ParseFromString(pb_str)) {
            std::cout << msg->DebugString() << std::endl;
        }
    });

    return 0;
}

测试结果输出

name: "test_name"
age: 100
phones: "138xxxxxx"
phones: "139xxxxxx"
aa {
  name: "a_name_0"
  age: 100
}
aa {
  name: "a_name_1"
  age: 101
}
aa {
  name: "a_name_2"
  age: 102
}

===============================
name: "test_name"
aa {
  name: "a_name_0"
  age: 100
}
aa {
  name: "a_name_1"
  age: 101
}
aa {
  name: "a_name_2"
  age: 102
}
2: 100
3 {
  6: 0x7878787878783833
}
3 {
  6: 0x7878787878783933
}

===============================
name: "test_name"
age: 100
phones: "138xxxxxx"
phones: "139xxxxxx"
aa {
  name: "a_name_0"
  age: 100
}
aa {
  name: "a_name_1"
  age: 101
}
aa {
  name: "a_name_2"
  age: 102
}

===============================
name: "test_name"
age: 100
phones: "138xxxxxx"
phones: "139xxxxxx"
aa {
  name: "a_name_0"
  age: 100
}
aa {
  name: "a_name_1"
  age: 101
}
aa {
  name: "a_name_2"
  age: 102
}

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