qpdf/include/qpdf/JSONHandler.hh

// Copyright (c) 2005-2021 Jay Berkenbilt
//
// This file is part of qpdf.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// Versions of qpdf prior to version 7 were released under the terms
// of version 2.0 of the Artistic License. At your option, you may
// continue to consider qpdf to be licensed under those terms. Please
// see the manual for additional information.

#ifndef JSONHANDLER_HH
#define JSONHANDLER_HH

#include <qpdf/DLL.h>
#include <qpdf/PointerHolder.hh>
#include <qpdf/JSON.hh>
#include <string>
#include <map>
#include <functional>
#include <memory>

// This class allows a sax-like walk through a JSON object with
// functionality that mostly mirrors QPDFArgParser. It is primarily
// here to facilitate automatic generation of some of the code to help
// keep QPDFJob json consistent with command-line arguments.

class JSONHandler
{
  public:
    // A QPDFUsage exception is thrown if there are any errors
    // validating the JSON object.
    QPDF_DLL
    JSONHandler();

    QPDF_DLL
    ~JSONHandler() = default;

    // Based on the type of handler, expect the object to be of a
    // certain type. QPDFUsage is thrown otherwise. Multiple handlers
    // may be registered, which allows the object to be of various
    // types. If an anyHandler is added, no other handler will be
    // called. There is no "final" handler -- if the top-level is a
    // dictionary or array, just use its end handler.

    typedef std::function<void(
        std::string const& path, JSON value)> json_handler_t;
    typedef std::function<void(
        std::string const& path)> void_handler_t;
    typedef std::function<void(
        std::string const& path, std::string const& value)> string_handler_t;
    typedef std::function<void(
        std::string const& path, bool value)> bool_handler_t;

    // If an any handler is added, it will be called for any value
    // including null, and no other handler will be called.
    QPDF_DLL
    void addAnyHandler(json_handler_t fn);

    // If any of the remaining handlers are registered, each
    // registered handle will be called.
    QPDF_DLL
    void addNullHandler(void_handler_t fn);
    QPDF_DLL
    void addStringHandler(string_handler_t fn);
    QPDF_DLL
    void addNumberHandler(string_handler_t fn);
    QPDF_DLL
    void addBoolHandler(bool_handler_t fn);

    QPDF_DLL
    void addDictHandlers(void_handler_t start_fn, void_handler_t end_fn);
    QPDF_DLL
    void addDictKeyHandler(
        std::string const& key, std::shared_ptr<JSONHandler>);
    QPDF_DLL
    void addFallbackDictHandler(std::shared_ptr<JSONHandler>);

    QPDF_DLL
    void addArrayHandlers(void_handler_t start_fn,
                          void_handler_t end_fn,
                          std::shared_ptr<JSONHandler> item_handlers);

    // Apply handlers recursively to a JSON object.
    QPDF_DLL
    void handle(std::string const& path, JSON j);

  private:
    JSONHandler(JSONHandler const&) = delete;

    static void usage(std::string const& msg);

    struct Handlers
    {
        Handlers() :
            any_handler(nullptr),
            null_handler(nullptr),
            string_handler(nullptr),
            number_handler(nullptr),
            bool_handler(nullptr),
            dict_start_handler(nullptr),
            dict_end_handler(nullptr),
            array_start_handler(nullptr),
            array_end_handler(nullptr),
            final_handler(nullptr)
        {
        }

        json_handler_t any_handler;
        void_handler_t null_handler;
        string_handler_t string_handler;
        string_handler_t number_handler;
        bool_handler_t bool_handler;
        void_handler_t dict_start_handler;
        void_handler_t dict_end_handler;
        void_handler_t array_start_handler;
        void_handler_t array_end_handler;
        void_handler_t final_handler;
        std::map<std::string, std::shared_ptr<JSONHandler>> dict_handlers;
        std::shared_ptr<JSONHandler> fallback_dict_handler;
        std::shared_ptr<JSONHandler> array_item_handler;
    };

    class Members
    {
        friend class JSONHandler;

      public:
        QPDF_DLL
        ~Members() = default;

      private:
        Members();
        Members(Members const&) = delete;

        Handlers h;
    };
    PointerHolder<Members> m;
};

#endif // JSONHANDLER_HH