packet_visitor.hpp

#ifndef PACKET_VISITOR_HPP_UYSI8HXZ
#define PACKET_VISITOR_HPP_UYSI8HXZ
 
#include <vanetza/asn1/asn1c_conversion.hpp>
#include <vanetza/common/byte_buffer.hpp>
#include <vanetza/net/chunk_packet.hpp>
#include <vanetza/net/cohesive_packet.hpp>
#include <vanetza/net/osi_layer.hpp>
#include <vanetza/net/packet_variant.hpp>
#include <boost/variant/static_visitor.hpp>
#include <memory>
 
namespace vanetza
{
namespace asn1
{
 
/**
 * PacketVisitor is a helper to extract the ASN.1 wrapper object from a packet's application layer.
 * This is a generalised version of the implementation found in Artery before.
 *
 * ChunkPacket's application layer is simply casted for the sake of speed whenever possible.
 * When casting fails, this helper can fall back to deserialization, see allow_chunk_deserialization.
 * Deserialization is the only option for CohesivePacket's application layer.
 *
 * \param T is the asn1c_wrapper<> type, e.g. Cam or Denm
 */
template<typename T>
class PacketVisitor : public boost::static_visitor<std::shared_ptr<const T>>
{
    public:
        std::shared_ptr<const T> operator()(const ChunkPacket& packet)
        {
            using byte_buffer_impl = convertible::byte_buffer_impl<T>;
            auto impl = dynamic_cast<const byte_buffer_impl*>(packet[OsiLayer::Application].ptr());
            if (impl) {
                m_wrapper = impl->wrapper();
            } else if (m_deserialize_chunk) {
                deserialize(create_byte_view(packet, m_start_layer, OsiLayer::Application));
            } else {
                m_wrapper.reset();
            }
            return m_wrapper;
        }
 
        std::shared_ptr<const T> operator()(const CohesivePacket& packet)
        {
            deserialize(create_byte_view(packet, m_start_layer, OsiLayer::Application));
            return m_wrapper;
        }
 
        std::shared_ptr<const T> get_shared_wrapper() const { return m_wrapper; }
 
        /**
         * Allow deserialization attempt of ChunkPacket when casting failed.
         * \param flag true allows deserialization
         */
        void allow_chunk_deserialization(bool flag)
        {
            m_deserialize_chunk = flag;
        }
 
        /**
         * Set OSI layer where deserialization shall start, it always stops at end of OsiLayer::Application.
         * By default, PacketVisitors starts at OsiLayer::Session for compatibility with BTP parser functions.
         * \param start OSI layer
         */
        void start_deserialization_at(OsiLayer start)
        {
            m_start_layer = start;
        }
 
    private:
        void deserialize(const byte_view_range& range)
        {
            auto tmp = std::make_shared<T>();
            bool decoded = tmp->decode(range.begin().raw(), range.size());
            m_wrapper = decoded ? tmp : nullptr;
        }
 
        std::shared_ptr<const T> m_wrapper;
        bool m_deserialize_chunk = true;
        OsiLayer m_start_layer = OsiLayer::Session;
};
 
} // namespace asn1
} // namespace vanetza
 
#endif /* PACKET_VISITOR_HPP_UYSI8HXZ */