Google Protobuf自动反射-初步分析

看了下Google Protobuf的源码，对于反射机制，无论c++实现还是java实现都是采用map查找，这个应很高效率。实际我们在项目中无形中也用 到了这种思路，仅仅没系统化。通过一个类的原型对象做辅助，然后配合map结构，就可很简单的根据符号名字来反射对象。从而实现一种抽象接口的稳定，把变 化隔离到了通讯协议 的数据内。

可参考http://blog.chinaunix.net/uid-52437-id-3142718.html文章。

原型 prototype pattern参考http://blog.chinaunix.net/uid-52437-id-2108601.html

wiki: 

看一下从网络反射过程：

inline google::protobuf::Message* createMessage(const std::string& type_name)
{
  google::protobuf::Message* message = NULL;
  const google::protobuf::Descriptor* descriptor =
    google::protobuf::DescriptorPool::generated_pool()->FindMessageTypeByName(type_name);
  if (descriptor)
  {
    const google::protobuf::Message* prototype =
      google::protobuf::MessageFactory::generated_factory()->GetPrototype(descriptor);
    if (prototype)
    {
      message = prototype->New();
    }
  }
  return message;
}

//////////////以下是使用

buf[numbytes] = '\0'; //buf为从网络收到的数据
String data = buf;

//"gamesrv.RepLuaMsg"为 类名字
google::protobuf::Message* reply = createMessage("gamesrv.RepLuaMsg");

//gamesrv::RepLuaMsg p2;
reply->ParseFromString(data); //直接反序列化

下面是一个采用反射实现的简单客户端

// g++ -g `pkg-config --cflags protobuf`  luaclient.cpp LuaCmd.pb.cc -o luacli  `pkg-config --libs protobuf`
#include <stdio.h>
#include <unistd.h>
#include <strings.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <string>
#include <iostream>
#include "LuaCmd.pb.h"
#include <google/protobuf/descriptor.h>

#include <google/protobuf/dynamic_message.h>

#define HOST "localhost"
#define PORT 8889
#define MAXDATASIZE 100

using namespace std;


inline google::protobuf::Message* createMessage(const std::string& type_name)
{
  google::protobuf::Message* message = NULL;
  const google::protobuf::Descriptor* descriptor =
    google::protobuf::DescriptorPool::generated_pool()->FindMessageTypeByName(type_name);
  if (descriptor)
  {
    const google::protobuf::Message* prototype =
      google::protobuf::MessageFactory::generated_factory()->GetPrototype(descriptor);
    if (prototype)
    {
      message = prototype->New();
    }
  }
  return message;
}


int main(int argc, char ** argv)
{
  int fd, numbytes;
  char buf[MAXDATASIZE];
  struct hostent *he;
  struct sockaddr_in server;



  if (argc != 2) {
    printf("Usage: %s \"COMMAND\"\n",argv[0]);
    exit(0);
  }

  he = gethostbyname("10.57.220.70");
  fd = socket(AF_INET, SOCK_STREAM, 0);
  bzero(&server, sizeof(server));
  server.sin_family = AF_INET;
  server.sin_port = htons(PORT);
  server.sin_addr = *((struct in_addr *)he->h_addr);

  int ret = connect(fd, (struct sockaddr *)&server, sizeof(struct sockaddr));

  //for send
  string data;
  int cmdid = 1000;
  char szTemp[1024]={'\0'};
  gamesrv::LuaMsg p;
  p.set_account("123");
  p.set_msg("[e-mail]");
  p.SerializeToString(&data);


  *(int*)(szTemp+4) = htonl(cmdid);

  int len = 4+4;
  memmove(szTemp+8,data.c_str(),data.length());
  len +=data.length();
  *(int*)(szTemp) = htonl(len);
  ret =send(fd, szTemp, len, 0);

  memset(buf,0,sizeof(buf));
  numbytes = recv(fd, buf, 8, 0);
  numbytes = ntohl(*(int*)(buf))-8;
  ret = recv(fd, buf, numbytes, 0);

  buf[numbytes] = '\0';
  data = buf;

  google::protobuf::Message* reply = createMessage("gamesrv.RepLuaMsg");

  reply->ParseFromString(data);
  gamesrv::RepLuaMsg* rep = (gamesrv::RepLuaMsg*)reply;
  cout << "People: " << endl;
  cout << "ID: " << rep->account() << endl;
  cout << "Email: " << rep->msg() << endl;
  string mm =  rep->msg();
  close(fd);



  return 0;
}

对应的proto文件LuaCmd.proto

package gamesrv;


option java_package = "gamesrv.Request.protocol";
option java_outer_classname = "LuaCmdProtos";

message LuaMsg {
    required  string account = 1;        // Unique ID number for this person.
  optional string msg = 2;
}

message RepLuaMsg {
  required  string account = 1;        // Unique ID number for this person.
  optional string msg = 2;
  }