json_schema.h

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#ifndef SQL_JSON_SCHEMA_H_INCLUDED
#define SQL_JSON_SCHEMA_H_INCLUDED

/**
  @file json_schema.h

  Functions for validating a string against a JSON Schema

  A JSON Schema is a way to describe the structure of a JSON document. The JSON
  Schema is a JSON document in itself, and allows you to define required
  names/attributes, data types etc. As an example, here is a minimal example of
  a JSON Schema describing that the JSON document MUST be an object:

    {
      "type": "object"
    }

  If the JSON document to be validated is anything else than an object (array,
  scalar), the validation will fail.

  This file contains one class for validation JSON documents against a cached
  JSON Schema, and free functions for validation any string input against a
  (unparsed) JSON Schema. We use the rapidjson library to do the actual
  validation with the following notable behaviors:

  1) Remote references are not supported. If the user provides a JSON Schema
     with a remote reference, an error will be raised.
  2) JSON Schema supports regex patterns, and we use std::regex as the regex
     engine. If an invalid regex pattern is provided in the JSON Schema, the
     regex pattern will be silently ignored.
  3) rapidjson currently supports JSON Schema draft-v4, while there are newer
     versions available (as of writing, draft-v7 is the latest version).
 */

#include <cstddef>
#include <string>

#include "my_alloc.h"
#include "sql-common/json_error_handler.h"

class Json_schema_validator_impl;
struct MEM_ROOT;

/**
  Json_schema_validation_report contains a more detailed report about a failed
  JSON Schema validation. It's mainly used by the function
  JSON_SCHEMA_VALIDATION_REPORT to print out a more detailed report to the user.
*/
class Json_schema_validation_report {
 public:
  /// @returns a human readable reason why the validation failed
  std::string human_readable_reason() const;

  /**
    @returns a JSON pointer in URI format, pointing to where in the JSON
             Schema the validation failed
  */
  const std::string &schema_location() const { return m_schema_location; }

  /**
    @returns a string describing the name of the JSON Schema keyword that
             failed validation
  */
  const std::string &schema_failed_keyword() const {
    return m_schema_failed_keyword;
  }

  /**
    @returns a JSON pointer in URI format, pointing to where in the JSON
             document the validation failed
  */
  const std::string &document_location() const { return m_document_location; }

  /**
    Populates the object with validation information.

    @param schema_location a JSON pointer in URI format, pointing to where in
           the JSON Schema the validation failed
    @param schema_failed_keyword a string describing the name of the JSON Schema
           keyword that failed validation
    @param document_location a JSON pointer in URI format, pointing to where in
           the JSON document the validation failed
  */
  void set_error_report(std::string &&schema_location,
                        const char *schema_failed_keyword,
                        std::string &&document_location) {
    m_schema_location = std::move(schema_location);
    m_schema_failed_keyword = schema_failed_keyword;
    m_document_location = std::move(document_location);
  }

 private:
  std::string m_schema_location;
  std::string m_schema_failed_keyword;
  std::string m_document_location;
};

/**
  This function will validate a JSON document against a JSON Schema using the
  validation provided by rapidjson.

  @param document_str A pointer to the JSON document to be validated.
  @param document_length The length of the JSON document to be validated.
  @param json_schema_str A pointer to the JSON Schema.
  @param json_schema_length The length of the JSON Schema.
  @param error_handler Error handlers to be called when parsing errors occur.
  @param depth_handler Pointer to a function that should handle error
                       occurred when depth is exceeded.
  @param[out] is_valid A variable containing the result of the validation. If
                       true, the JSON document is valid according to the given
                       JSON Schema.
  @param[out] report A structure containing a detailed report from the
                     validation. Is only populated if is_valid is set to
                     "false". Can be nullptr if a detailed report isn't needed.

  @retval true if anything went wrong (like parsing the JSON inputs). my_error
               has been called with an appropriate error message.
  @retval false if the validation succeeded. The result of the validation can be
                found in the output variable "is_valid".
*/
bool is_valid_json_schema(const char *document_str, size_t document_length,
                          const char *json_schema_str,
                          size_t json_schema_length,
                          const JsonSchemaErrorHandler &error_handler,
                          const JsonErrorHandler &depth_handler, bool *is_valid,
                          Json_schema_validation_report *report);

/**
  This is just a facade to the Json_schema_validator and it is used to
  hide the dependency on the rapidjson lib.
*/
class Json_schema_validator {
 private:
  Json_schema_validator_impl *m_json_schema_validator{nullptr};

 public:
  /**
    Initialize a Json_schema_validator_impl, allocated on a given MEM_ROOT

    @param mem_root The MEM_ROOT to allocate the validator on
    @param json_schema_str A pointer to the JSON Schema
    @param json_schema_length The length of the JSON Schema input
    @param error_handler Error handlers to be called when parsing errors occur.
    @param depth_handler Pointer to a function that should handle error
        occurred when depth is exceeded.

    @retval true on error (my_error has been called)
  */
  bool initialize(MEM_ROOT *mem_root, const char *json_schema_str,
                  size_t json_schema_length,
                  const JsonSchemaErrorHandler &error_handler,
                  const JsonErrorHandler &depth_handler);

  bool is_valid(const char *document_str, size_t document_length,
                const JsonSchemaErrorHandler &error_handler,
                const JsonErrorHandler &depth_handler, bool *is_valid,
                Json_schema_validation_report *report) const;
  bool is_initialized() const { return m_json_schema_validator != nullptr; }
  ~Json_schema_validator();
};

#endif