lokinet/llarp/rpc/json_binary_proxy.hpp

#pragma once

#include <nlohmann/json.hpp>

#include <string_view>
#include <unordered_set>

using namespace std::literals;

namespace llarp::rpc
{

  // Binary types that we support for rpc input/output.  For json, these must be specified as hex or
  // base64; for bt-encoded requests these can be accepted as binary, hex, or base64.
  template <typename T>
  inline constexpr bool json_is_binary = false;

  template <typename T>
  inline constexpr bool json_is_binary_container = false;
  template <typename T>
  inline constexpr bool json_is_binary_container<std::vector<T>> = json_is_binary<T>;
  template <typename T>
  inline constexpr bool json_is_binary_container<std::unordered_set<T>> = json_is_binary<T>;

  // De-referencing wrappers around the above:
  template <typename T>
  inline constexpr bool json_is_binary<const T&> = json_is_binary<T>;
  template <typename T>
  inline constexpr bool json_is_binary<T&&> = json_is_binary<T>;
  template <typename T>
  inline constexpr bool json_is_binary_container<const T&> = json_is_binary_container<T>;
  template <typename T>
  inline constexpr bool json_is_binary_container<T&&> = json_is_binary_container<T>;

  void
  load_binary_parameter_impl(
      std::string_view bytes, size_t raw_size, bool allow_raw, uint8_t* val_data);

  // Loads a binary value from a string_view which may contain hex, base64, and (optionally) raw
  // bytes.
  template <typename T, typename = std::enable_if_t<json_is_binary<T>>>
  void
  load_binary_parameter(std::string_view bytes, bool allow_raw, T& val)
  {
    load_binary_parameter_impl(bytes, sizeof(T), allow_raw, reinterpret_cast<uint8_t*>(&val));
  }

  // Wrapper around a nlohmann::json that assigns a binary value either as binary (for bt-encoding);
  // or as hex or base64 (for json-encoding).
  class json_binary_proxy
  {
   public:
    nlohmann::json& e;
    enum class fmt
    {
      bt,
      hex,
      base64
    } format;
    explicit json_binary_proxy(nlohmann::json& elem, fmt format) : e{elem}, format{format}
    {}
    json_binary_proxy() = delete;

    json_binary_proxy(const json_binary_proxy&) = default;
    json_binary_proxy(json_binary_proxy&&) = default;

    /// Dereferencing a proxy element accesses the underlying nlohmann::json
    nlohmann::json&
    operator*()
    {
      return e;
    }
    nlohmann::json*
    operator->()
    {
      return &e;
    }

    /// Descends into the json object, returning a new binary value proxy around the child element.
    template <typename T>
    json_binary_proxy
    operator[](T&& key)
    {
      return json_binary_proxy{e[std::forward<T>(key)], format};
    }

    /// Returns a binary value proxy around the first/last element (requires an underlying list)
    json_binary_proxy
    front()
    {
      return json_binary_proxy{e.front(), format};
    }
    json_binary_proxy
    back()
    {
      return json_binary_proxy{e.back(), format};
    }

    /// Assigns binary data from a string_view/string/etc.
    nlohmann::json&
    operator=(std::string_view binary_data);

    /// Assigns binary data from a string_view over a 1-byte, non-char type (e.g. unsigned char or
    /// uint8_t).
    template <
        typename Char,
        std::enable_if_t<sizeof(Char) == 1 && !std::is_same_v<Char, char>, int> = 0>
    nlohmann::json&
    operator=(std::basic_string_view<Char> binary_data)
    {
      return *this = std::string_view{
                 reinterpret_cast<const char*>(binary_data.data()), binary_data.size()};
    }

    /// Takes a trivial, no-padding data structure (e.g. a crypto::hash) as the value and dumps its
    /// contents as the binary value.
    template <typename T, std::enable_if_t<json_is_binary<T>, int> = 0>
    nlohmann::json&
    operator=(const T& val)
    {
      return *this = std::string_view{reinterpret_cast<const char*>(&val), sizeof(val)};
    }

    /// Takes a vector of some json_binary_proxy-assignable type and builds an array by assigning
    /// each one into a new array of binary values.
    template <typename T, std::enable_if_t<json_is_binary_container<T>, int> = 0>
    nlohmann::json&
    operator=(const T& vals)
    {
      auto a = nlohmann::json::array();
      for (auto& val : vals)
        json_binary_proxy{a.emplace_back(), format} = val;
      return e = std::move(a);
    }
    /// Emplaces a new nlohman::json to the end of an underlying list and returns a
    /// json_binary_proxy wrapping it.
    ///
    /// Example:
    ///
    ///     auto child = wrappedelem.emplace_back({"key1": 1}, {"key2": 2});
    ///     child["binary-key"] = some_binary_thing;
    template <typename... Args>
    json_binary_proxy
    emplace_back(Args&&... args)
    {
      return json_binary_proxy{e.emplace_back(std::forward<Args>(args)...), format};
    }

    /// Adds an element to an underlying list, then copies or moves the given argument onto it via
    /// json_binary_proxy assignment.
    template <typename T>
    void
    push_back(T&& val)
    {
      emplace_back() = std::forward<T>(val);
    }
  };

}  // namespace llarp::rpc