attribute_handler.hpp

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#pragma once
 
#include <cassert>
#include <cstdint>
#include <type_traits>
#include <utility>  // forward, move
#include <vector>
 
#include "open62541pp/bitmask.hpp"
#include "open62541pp/common.hpp"  // AttributeId, WriteMask, EventNotifier, AccessLevel
#include "open62541pp/detail/open62541/common.h"
#include "open62541pp/types.hpp"
 
namespace opcua::services::detail {
 
inline Result<Variant> getVariant(DataValue&& dv) noexcept {
    if (dv.status().isBad()) {
        return BadResult(dv.status());
    }
    if (!dv.hasValue()) {
        return BadResult(UA_STATUSCODE_BADUNEXPECTEDERROR);
    }
    return std::move(dv).value();
}
 
/**
 * Attribute handler to convert DataValue objects to/from the attribute specific types.
 * Template specializations must be provided for all AttributeIds.
 */
template <AttributeId Attribute>
struct AttributeHandler;
 
struct AttributeHandlerVariant {
    using Type = Variant;
 
    static Result<Variant> fromDataValue(DataValue&& dv) noexcept {
        return getVariant(std::move(dv));
    }
 
    static DataValue toDataValue(const Variant& value) noexcept {
        DataValue dv;
        dv->value = value;  // shallow copy
        dv->value.storageType = UA_VARIANT_DATA_NODELETE;  // prevent double delete
        dv->hasValue = true;
        return dv;
    }
};
 
template <typename T, typename Enable = void>
struct AttributeHandlerScalar {
    using Type = T;
 
    static Result<Type> fromDataValue(DataValue&& dv) noexcept {
        return getVariant(std::move(dv)).transform([](Variant&& var) {
            assert(var.isType<T>());
            assert(var.isScalar());
            return std::move(var).scalar<T>();
        });
    }
 
    template <typename U>
    static DataValue toDataValue(U&& value) {
        return DataValue(Variant(std::forward<U>(value)));
    }
};
 
template <typename T>
struct AttributeHandlerScalar<T, std::enable_if_t<std::is_enum_v<T>>> {
    using Type = T;
    using UnderlyingType = std::underlying_type_t<Type>;
    using UnderlyingHandler = AttributeHandlerScalar<UnderlyingType>;
 
    static Result<Type> fromDataValue(DataValue&& dv) noexcept {
        return UnderlyingHandler::fromDataValue(std::move(dv)).transform([](auto value) {
            return static_cast<Type>(value);
        });
    }
 
    static DataValue toDataValue(Type value) {
        return UnderlyingHandler::toDataValue(static_cast<UnderlyingType>(value));
    }
};
 
template <typename T>
struct AttributeHandlerScalar<Bitmask<T>> {
    using Type = Bitmask<T>;
    using UnderlyingType = typename Bitmask<T>::Underlying;
    using UnderlyingHandler = AttributeHandlerScalar<UnderlyingType>;
 
    static Result<Type> fromDataValue(DataValue&& dv) noexcept {
        return UnderlyingHandler::fromDataValue(std::move(dv)).transform([](auto value) {
            return Bitmask<T>(value);
        });
    }
 
    static DataValue toDataValue(Type value) {
        return UnderlyingHandler::toDataValue(value.get());
    }
};
 
template <>
struct AttributeHandler<AttributeId::NodeId> : AttributeHandlerScalar<NodeId> {};
 
template <>
struct AttributeHandler<AttributeId::NodeClass> {
    using Type = NodeClass;
 
    static Result<Type> fromDataValue(DataValue&& dv) noexcept {
        return getVariant(std::move(dv)).transform([](const Variant& var) {
            // workaround to read enum from variant...
            return *static_cast<const NodeClass*>(var.data());
        });
    }
};
 
template <>
struct AttributeHandler<AttributeId::BrowseName> : AttributeHandlerScalar<QualifiedName> {};
 
template <>
struct AttributeHandler<AttributeId::DisplayName> : AttributeHandlerScalar<LocalizedText> {};
 
template <>
struct AttributeHandler<AttributeId::Description> : AttributeHandlerScalar<LocalizedText> {};
 
template <>
struct AttributeHandler<AttributeId::WriteMask> : AttributeHandlerScalar<Bitmask<WriteMask>> {};
 
template <>
struct AttributeHandler<AttributeId::UserWriteMask> : AttributeHandlerScalar<Bitmask<WriteMask>> {};
 
template <>
struct AttributeHandler<AttributeId::IsAbstract> : AttributeHandlerScalar<bool> {};
 
template <>
struct AttributeHandler<AttributeId::Symmetric> : AttributeHandlerScalar<bool> {};
 
template <>
struct AttributeHandler<AttributeId::InverseName> : AttributeHandlerScalar<LocalizedText> {};
 
template <>
struct AttributeHandler<AttributeId::ContainsNoLoops> : AttributeHandlerScalar<bool> {};
 
template <>
struct AttributeHandler<AttributeId::EventNotifier>
    : AttributeHandlerScalar<Bitmask<EventNotifier>> {};
 
template <>
struct AttributeHandler<AttributeId::Value> : AttributeHandlerVariant {};
 
template <>
struct AttributeHandler<AttributeId::DataType> : AttributeHandlerScalar<NodeId> {};
 
template <>
struct AttributeHandler<AttributeId::ValueRank> : AttributeHandlerScalar<ValueRank> {};
 
template <>
struct AttributeHandler<AttributeId::ArrayDimensions> {
    using Type = std::vector<uint32_t>;
 
    static Result<Type> fromDataValue(DataValue&& dv) noexcept {
        return getVariant(std::move(dv)).transform([](Variant&& var) {
            assert(var.isType<uint32_t>());
            assert(var.isArray());
            return std::move(var).to<Type>();
        });
    }
 
    static DataValue toDataValue(Span<const uint32_t> dimensions) {
        return DataValue(Variant(dimensions));
    }
};
 
template <>
struct AttributeHandler<AttributeId::AccessLevel> : AttributeHandlerScalar<Bitmask<AccessLevel>> {};
 
template <>
struct AttributeHandler<AttributeId::UserAccessLevel>
    : AttributeHandlerScalar<Bitmask<AccessLevel>> {};
 
template <>
struct AttributeHandler<AttributeId::MinimumSamplingInterval> : AttributeHandlerScalar<double> {};
 
template <>
struct AttributeHandler<AttributeId::Historizing> : AttributeHandlerScalar<bool> {};
 
template <>
struct AttributeHandler<AttributeId::Executable> : AttributeHandlerScalar<bool> {};
 
template <>
struct AttributeHandler<AttributeId::UserExecutable> : AttributeHandlerScalar<bool> {};
 
template <>
struct AttributeHandler<AttributeId::DataTypeDefinition> : AttributeHandlerVariant {};
 
}  // namespace opcua::services::detail