serialization_format.hpp

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// nros-cpp: the serialization format as a compile-time fact (freestanding C++14)
//
// RFC-0088 D5. ROS 2 asks `rmw_get_serialization_format()` at run time because
// it resolves its typesupport through `dlopen`; nano-ros does not `dlopen`, so
// the answer is already known when the image is compiled — one image links one
// backend, and one backend speaks one encoding.
//
// `const char*` throughout, never `std::string` or `std::string_view`: these
// headers must compile against Zephyr's minimal libcpp behind `NROS_CPP_STD`,
// where `<string>` does not exist (issue 0112).
 
#ifndef NROS_CPP_SERIALIZATION_FORMAT_HPP
#define NROS_CPP_SERIALIZATION_FORMAT_HPP
 
#include <cstdint>
 
// `NROS_CPP_SERIALIZATION_FORMAT_ID` — cbindgen output, lowered from
// `nros_cpp`'s own mirror, which a `const _` proves equal to
// `nros_node::session::IMAGE_SERIALIZATION_FORMAT_ID`. Taken from the C++ FFI
// header rather than from `<nros/nros_generated.h>` so that a generated message
// header never pulls a C API header ahead of this one (issue 0160 — the FFI
// struct mirrors make that include order one-way).
#include "nros_cpp_ffi.h"
 
namespace nros {
 
enum class SerializationFormat : uint8_t {
    Cdr = 1,
    Uorb = 2,
};
 
template <typename M> struct format_of {
    static constexpr SerializationFormat value = SerializationFormat::Cdr;
};
 
constexpr SerializationFormat linked_format() {
    return static_cast<SerializationFormat>(NROS_CPP_SERIALIZATION_FORMAT_ID);
}
 
constexpr const char* linked_format_name() {
    return linked_format() == SerializationFormat::Cdr
               ? "cdr"
               : (linked_format() == SerializationFormat::Uorb ? "uorb" : "unknown");
}
 
} // namespace nros
 
#define NROS_CPP_ASSERT_MESSAGE_FORMAT(M)                                                          \
    static_assert(::nros::format_of<M>::value == ::nros::linked_format(),                          \
                  "RFC-0088: this message type is not encoded in the format the linked "           \
                  "backend speaks: one image, one backend, one encoding. A bridge image "          \
                  "is the only place two formats legitimately meet, and it converts "              \
                  "explicitly.")
 
#endif // NROS_CPP_SERIALIZATION_FORMAT_HPP