Question

我想使用protobuf并以文本格式创建序列化输出文件以进行测试和替换json。我无法弄清楚如何自己编写它并寻找示例。这是二进制输出的一个：

#include <iostream>
#include <fstream>
#include <string>
#include "addressbook.pb.h"
using namespace std;

// This function fills in a Person message based on user input.
void PromptForAddress(tutorial::Person* person) {
  cout << "Enter person ID number: ";
  int id;
  cin >> id;
  person->set_id(id);
  cin.ignore(256, '\n');

  cout << "Enter name: ";
  getline(cin, *person->mutable_name());

  cout << "Enter email address (blank for none): ";
  string email;
  getline(cin, email);
  if (!email.empty()) {
    person->set_email(email);
  }

  while (true) {
    cout << "Enter a phone number (or leave blank to finish): ";
    string number;
    getline(cin, number);
    if (number.empty()) {
      break;
    }

    tutorial::Person::PhoneNumber* phone_number = person->add_phones();
    phone_number->set_number(number);

    cout << "Is this a mobile, home, or work phone? ";
    string type;
    getline(cin, type);
    if (type == "mobile") {
      phone_number->set_type(tutorial::Person::MOBILE);
    } else if (type == "home") {
      phone_number->set_type(tutorial::Person::HOME);
    } else if (type == "work") {
      phone_number->set_type(tutorial::Person::WORK);
    } else {
      cout << "Unknown phone type.  Using default." << endl;
    }
  }
}

// Main function:  Reads the entire address book from a file,
//   adds one person based on user input, then writes it back out to the same
//   file.
int main(int argc, char* argv[]) {
  // Verify that the version of the library that we linked against is
  // compatible with the version of the headers we compiled against.
  GOOGLE_PROTOBUF_VERIFY_VERSION;

  if (argc != 2) {
    cerr << "Usage:  " << argv[0] << " ADDRESS_BOOK_FILE" << endl;
    return -1;
  }

  tutorial::AddressBook address_book;

  {
    // Read the existing address book.
    fstream input(argv[1], ios::in | ios::binary);
    if (!input) {
      cout << argv[1] << ": File not found.  Creating a new file." << endl;
    } else if (!address_book.ParseFromIstream(&input)) {
      cerr << "Failed to parse address book." << endl;
      return -1;
    }
  }

  // Add an address.
  PromptForAddress(address_book.add_people());

  {
    // Write the new address book back to disk.
    fstream output(argv[1], ios::out | ios::trunc | ios::binary);
    if (!address_book.SerializeToOstream(&output)) {
      cerr << "Failed to write address book." << endl;
      return -1;
    }
  }

  // Optional:  Delete all global objects allocated by libprotobuf.
  google::protobuf::ShutdownProtobufLibrary();

  return 0;
}

我可以在这一个中做一些小的改动，以文本格式输出或者需要做些什么吗？请建议所需的更改或代码存在的任何链接（使用任何语言）。

Answer 1

保证调试字符串输出是有效的文本序列化格式，但不关心协议消息是否实际有效：

std::string s = msg.DebugString();  // or ShortDebugString

如果您想验证，请使用TextFormat::PrintToString：

#include <google/protobuf/text_format.h>

if (std::string s; google::protobuf::TextFormat::PrintToString(msg, &s)) {
  std::cout << "Your message: " << s;
} else {
  std::cerr << "Message not valid (partial content: "
            << msg.ShortDebugString() << ")\n";
}

json_util.h中提供了JSON互操作工具。

Answer 2

此代码将protobuf消息序列化为JSON并将JSON反序列化为protobuf消息。

这是直接从生产代码中提取的（我拥有并在此授予您使用许可，但请相信我）。

这与protobuf 3有关。

标题

struct pretty_json_type {
    void operator()(google::protobuf::util::JsonOptions& opts) const {
        opts.add_whitespace = true;
    }
};
static constexpr pretty_json_type pretty_json{};

struct compact_json_type {
    void operator()(google::protobuf::util::JsonOptions& opts) const {
        opts.add_whitespace = false;
    }
};
static constexpr compact_json_type compact_json{};

struct include_defaults_type {
    void operator()(google::protobuf::util::JsonOptions& opts) const {
        opts.always_print_primitive_fields = true;
    }
};
static constexpr include_defaults_type include_defaults{};

template<class...Options>
auto json_options(Options&&...options)
{
    google::protobuf::util::JsonOptions opts;
    using expand = int [];
    void(expand{
        0,
        ((options(opts)),0)...
    });
    return opts;
}

std::string as_json(const google::protobuf::Message& msg,
                    google::protobuf::util::JsonOptions opts = json_options(pretty_json,
                                                                            include_defaults));

std::string as_json(const google::protobuf::Message* msg,
                    google::protobuf::util::JsonOptions opts = json_options(pretty_json,
                                                                            include_defaults));

google::protobuf::Message& from_json(google::protobuf::Message& msg,
                                     const char* first,
                                     std::size_t size);

inline
decltype(auto) from_json(google::protobuf::Message& msg,
                         const std::string& json)
{
    return from_json(msg, json.data(), json.length());
}

实施

std::string as_json(const google::protobuf::Message& msg,
                    google::protobuf::util::JsonOptions opts)
{
    namespace pb = google::protobuf;
    namespace pbu = google::protobuf::util;

    auto buffer = msg.SerializeAsString();
    std::string result;
    pb::io::ArrayInputStream zistream(buffer.data(), buffer.size());

    auto resolver = std::unique_ptr<pbu::TypeResolver> {
        pbu::NewTypeResolverForDescriptorPool("",
                                              pb::DescriptorPool::generated_pool())
    };

    auto status = google::protobuf::util::BinaryToJsonString(resolver.get(),
                                                             "/" + msg.GetDescriptor()->full_name(),
                                                             buffer,
                                                             std::addressof(result),
                                                             opts);
    if (!status.ok())
    {
        std::ostringstream ss;
        ss << status;
        throw std::runtime_error(ss.str());
    }
    return result;
}

std::string as_json(const google::protobuf::Message* msg,
                    google::protobuf::util::JsonOptions opts)
{
    return as_json(*msg, opts);
}


google::protobuf::Message& from_json(google::protobuf::Message& msg,
                                     const char* first,
                                     std::size_t size)
{
    namespace pb = google::protobuf;
    namespace pbu = google::protobuf::util;

    auto resolver = std::unique_ptr<pbu::TypeResolver> {
        pbu::NewTypeResolverForDescriptorPool("", pb::DescriptorPool::generated_pool())
    };

    auto zistream = std::make_unique<pb::io::ArrayInputStream>(first,
                                                               size);
    auto binary_buffer = std::string {};
    binary_buffer.reserve(size);
    auto zostream = std::make_unique<pb::io::StringOutputStream>(std::addressof(binary_buffer));

    auto status = pbu::JsonToBinaryStream(resolver.get(),
                                          "/" + msg.GetDescriptor()->full_name(),
                                          zistream.get(), zostream.get());
    zistream.reset();
    zostream.reset();
    if (msg.ParseFromString(binary_buffer))
    {
        return msg;
    }

    throw std::runtime_error("invalid message");
}

Answer 3

要将消息通过三行代码转换为JSON，请执行以下操作-

#include <google/protobuf/util/json_util.h>

static std::string ProtoToJson(const google::protobuf::Message& proto)
{
  std::string json;
  google::protobuf::util::MessageToJsonString(proto, &json);
  return json;
}

是否有一个带文本输出的protobuf示例？

3 个答案:

标题

实施