json_schema.h

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// Copyright (c) Microsoft Corporation. All rights reserved.
// Licensed under the Apache 2.0 License.
#pragma once
 
#include "ccf/ds/nonstd.h"
 
#include <optional>
#define FMT_HEADER_ONLY
#include <fmt/format.h>
#include <nlohmann/json.hpp>
#include <set>
#include <unordered_set>
 
namespace ccf::ds::json
{
  struct JsonSchema
  {
    static constexpr auto hyperschema =
      "http://json-schema.org/draft-07/schema#";
 
    nlohmann::json schema;
  };
 
  inline void to_json(nlohmann::json& j, const JsonSchema& s)
  {
    j = s.schema;
  }
 
  inline void from_json(const nlohmann::json& j, JsonSchema& s)
  {
    s.schema = j;
  }
 
  template <typename T>
  inline void fill_number_schema(nlohmann::json& schema)
  {
    schema["type"] = "integer";
    schema["minimum"] = std::numeric_limits<T>::min();
    schema["maximum"] = std::numeric_limits<T>::max();
  }
 
  template <typename T>
  std::string schema_name();
 
  template <typename T>
  void fill_schema(nlohmann::json& schema);
 
  template <typename T>
  void fill_json_schema(nlohmann::json& j, const T* t);
 
  template <typename T>
  nlohmann::json schema_element()
  {
    auto element = nlohmann::json::object();
    fill_schema<T>(element);
    return element;
  }
 
  template <typename T, typename Doc>
  nlohmann::json schema_element()
  {
    auto element = nlohmann::json::object();
    fill_schema<T>(element);
    return element;
  }
 
  namespace adl
  {
#pragma clang diagnostic push
#if defined(__clang__) && __clang_major__ >= 11
#  pragma clang diagnostic ignored "-Wuninitialized-const-reference"
#endif
    template <typename T>
    std::string schema_name()
    {
      T* t = nullptr;
      return schema_name(t);
    }
 
    template <typename T>
    void fill_schema(nlohmann::json& schema)
    {
      T* t = nullptr;
      if constexpr (std::is_enum_v<T>)
      {
        fill_enum_schema(schema, t);
      }
      else
      {
        fill_json_schema(schema, t);
      }
    }
  }
#pragma clang diagnostic pop
 
  template <typename T>
  inline std::string schema_name()
  {
    if constexpr (ccf::nonstd::is_specialization<T, std::optional>::value)
    {
      return schema_name<typename T::value_type>();
    }
    else if constexpr (ccf::nonstd::is_specialization<T, std::vector>::value)
    {
      if constexpr (std::is_same_v<T, std::vector<uint8_t>>)
      {
        // Byte vectors are always base64 encoded
        return "base64string";
      }
      else
      {
        return fmt::format("{}_array", schema_name<typename T::value_type>());
      }
    }
    else if constexpr (
      ccf::nonstd::is_specialization<T, std::set>::value ||
      ccf::nonstd::is_specialization<T, std::unordered_set>::value)
    {
      return fmt::format("{}_set", schema_name<typename T::value_type>());
    }
    else if constexpr (
      ccf::nonstd::is_specialization<T, std::map>::value ||
      ccf::nonstd::is_specialization<T, std::unordered_map>::value)
    {
      return fmt::format(
        "{}_to_{}",
        schema_name<typename T::key_type>(),
        schema_name<typename T::mapped_type>());
    }
    else if constexpr (ccf::nonstd::is_specialization<T, std::pair>::value)
    {
      return fmt::format(
        "{}_and_{}",
        schema_name<typename T::first_type>(),
        schema_name<typename T::second_type>());
    }
    else if constexpr (std::is_same_v<T, std::string>)
    {
      return "string";
    }
    else if constexpr (std::is_same_v<T, bool>)
    {
      return "boolean";
    }
    else if constexpr (std::is_same_v<T, uint8_t>)
    {
      return "uint8";
    }
    else if constexpr (std::is_same_v<T, uint16_t>)
    {
      return "uint16";
    }
    else if constexpr (std::is_same_v<T, uint32_t>)
    {
      return "uint32";
    }
    else if constexpr (std::is_same_v<T, uint64_t>)
    {
      return "uint64";
    }
    else if constexpr (std::is_same_v<T, int8_t>)
    {
      return "int8";
    }
    else if constexpr (std::is_same_v<T, int16_t>)
    {
      return "int16";
    }
    else if constexpr (std::is_same_v<T, int32_t>)
    {
      return "int32";
    }
    else if constexpr (std::is_same_v<T, int64_t>)
    {
      return "int64";
    }
    else if constexpr (std::is_same_v<T, float>)
    {
      return "float";
    }
    else if constexpr (std::is_same_v<T, double>)
    {
      return "double";
    }
    else if constexpr (std::is_same_v<T, nlohmann::json>)
    {
      return "json";
    }
    else if constexpr (std::is_same_v<T, JsonSchema>)
    {
      return "json_schema";
    }
    else
    {
      return adl::schema_name<T>();
    }
  }
 
  template <typename T>
  inline void fill_schema(nlohmann::json& schema)
  {
    if constexpr (ccf::nonstd::is_specialization<T, std::optional>::value)
    {
      fill_schema<typename T::value_type>(schema);
    }
    else if constexpr (
      ccf::nonstd::is_specialization<T, std::vector>::value ||
      ccf::nonstd::is_specialization<T, std::set>::value ||
      ccf::nonstd::is_specialization<T, std::unordered_set>::value)
    {
      if constexpr (std::is_same_v<T, std::vector<uint8_t>>)
      {
        // Byte vectors are always base64 encoded
        schema["type"] = "string";
        schema["format"] = "base64";
      }
      else
      {
        schema["type"] = "array";
        schema["items"] = schema_element<typename T::value_type>();
      }
    }
    else if constexpr (
      ccf::nonstd::is_specialization<T, std::map>::value ||
      ccf::nonstd::is_specialization<T, std::unordered_map>::value)
    {
      // Nlohmann JSON serialises some maps as objects, if the keys can be
      // converted to strings. This should detect those cases. The others are
      // serialised as list-of-pairs
      if constexpr (nlohmann::detail::
                      is_compatible_object_type<nlohmann::json, T>::value)
      {
        schema["type"] = "object";
        schema["additionalProperties"] =
          schema_element<typename T::mapped_type>();
      }
      else
      {
        schema["type"] = "array";
        auto items = nlohmann::json::object();
        {
          items["type"] = "array";
 
          auto sub_items = nlohmann::json::array();
          sub_items.push_back(schema_element<typename T::key_type>());
          sub_items.push_back(schema_element<typename T::mapped_type>());
          items["items"] = sub_items;
        }
        schema["items"] = items;
      }
    }
    else if constexpr (ccf::nonstd::is_specialization<T, std::pair>::value)
    {
      schema["type"] = "array";
      auto items = nlohmann::json::array();
      items.push_back(schema_element<typename T::first_type>());
      items.push_back(schema_element<typename T::second_type>());
      schema["items"] = items;
    }
    else if constexpr (std::is_same_v<T, std::string>)
    {
      schema["type"] = "string";
    }
    else if constexpr (std::is_same_v<T, bool>)
    {
      schema["type"] = "boolean";
    }
    else if constexpr (std::is_same_v<T, nlohmann::json>)
    {
      // Any field that contains more json is completely unconstrained, so we
      // do not add a type or any other fields
      schema = nlohmann::json::object();
    }
    else if constexpr (std::is_integral_v<T>)
    {
      fill_number_schema<T>(schema);
    }
    else if constexpr (std::is_floating_point_v<T>)
    {
      schema["type"] = "number";
    }
    else if constexpr (std::is_same_v<T, JsonSchema>)
    {
      schema["type"] = "object";
    }
    else
    {
      adl::fill_schema<T>(schema);
    }
  }
 
  template <typename T>
  inline nlohmann::json build_schema(const std::string& title = "")
  {
    auto schema = nlohmann::json::object();
 
    if (!title.empty())
    {
      schema["title"] = title;
    }
 
    fill_schema<T>(schema);
 
    return schema;
  }
}