json_syntax_check.h

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   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */

/*
  This file defines various function for checking if a string is a valid JSON.
  The checking is done by the rapidjson library, but we extend the checks a bit
  further by rejecting JSON objects/array that are nested deeper than
  JSON_DOCUMENT_MAX_DEPTH levels.
*/

#include <cstddef>
#include <string>
#include <utility>

#include "my_rapidjson_size_t.h"  // IWYU pragma: keep

#include <rapidjson/encodings.h>
#include <rapidjson/reader.h>

#include "sql-common/json_error_handler.h"

/**
  Check if the depth of a JSON document exceeds the maximum supported
  depth (JSON_DOCUMENT_MAX_DEPTH). Raise an error if the maximum depth
  has been exceeded.

  @param[in] depth   the current depth of the document
  @param[in] handler callback function that gets called when maximum depth is
                     exceeded
  @return true if the maximum depth is exceeded, false otherwise
*/
bool check_json_depth(size_t depth, const JsonErrorHandler &handler);
bool check_json_depth(size_t depth,
                      const JsonSerializationErrorHandler &handler);

/**
  This class implements a handler for use with rapidjson::Reader when
  we want to check if a string is a valid JSON text. The handler does
  not build a DOM structure, so it is quicker than Json_dom::parse()
  in the cases where we don't care about the DOM, such as in the
  JSON_VALID() function.

  The handler keeps track of how deeply nested the document is, and it
  raises an error and stops parsing when the depth exceeds
  JSON_DOCUMENT_MAX_DEPTH.

  All the member functions follow the rapidjson convention of
  returning true on success and false on failure.
*/
class Syntax_check_handler : public rapidjson::BaseReaderHandler<> {
 public:
  bool StartObject();
  bool EndObject(rapidjson::SizeType);
  bool StartArray();
  bool EndArray(rapidjson::SizeType);

  bool too_deep_error_raised() const { return m_too_deep_error_raised; }
  explicit Syntax_check_handler(JsonErrorHandler m_depth_handler);

 private:
  size_t m_depth{0};  ///< The current depth of the document

  bool m_too_deep_error_raised{false};
  /// Pointer to a function that should handle error occurred when depth is
  /// exceeded.
  JsonErrorHandler m_depth_handler{nullptr};
};

/**
  Check if a string is a valid JSON.

  @param[in] text A pointer to the start of the text
  @param[in] length The length of the text
  @param[out] error_offset If the text is not a valid JSON, this variable will
                           be set to the position in the input string where
                           the error occurred. Can be nullptr.
  @param[out] error_message If the text is not a valid JSON, this variable
                            will contain a readable error message. Can be
                            nullptr.
  @param[in] depth_handler Pointer to a function that should handle error
                           occurred when depth is exceeded.

  @retval true if the input text is a valid JSON.
  @retval false if the input text is not a valid JSON.
*/
bool is_valid_json_syntax(const char *text, size_t length, size_t *error_offset,
                          std::string *error_message,
                          const JsonErrorHandler &depth_handler);

/**
  Extract a readable error from a rapidjson reader and return it to the
  caller.

  @param[in] reader The rapidjson reader to extract the error from.
  @return A pair where the first element is a readable error and the second
          element is the position in the input string where the error was
          found.
*/
std::pair<std::string, size_t> get_error_from_reader(
    const rapidjson::Reader &reader);