traceful_exception.hpp

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#pragma once
 
/// @file userver/utils/traceful_exception.hpp
/// @brief @copybrief utils::TracefulException
 
#include <exception>
#include <string>
#include <type_traits>
 
#include <fmt/format.h>
#include <boost/stacktrace/stacktrace_fwd.hpp>
 
#include <userver/compiler/select.hpp>
#include <userver/utils/fast_pimpl.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace utils {
 
/// @brief Base class implementing backtrace storage and message builder,
/// published only for documentation purposes, please inherit from
/// utils::TracefulException instead.
class TracefulExceptionBase {
public:
    enum class TraceMode {
        kAlways,
        kIfLoggingIsEnabled,
    };
 
    static constexpr size_t kInlineBufferSize = 100;
    using MemoryBuffer = fmt::basic_memory_buffer<char, kInlineBufferSize>;
 
    TracefulExceptionBase();
 
    explicit TracefulExceptionBase(std::string_view what);
 
    explicit TracefulExceptionBase(TraceMode trace_mode);
 
    TracefulExceptionBase(TracefulExceptionBase&&) noexcept;
    virtual ~TracefulExceptionBase() = 0;
 
    const MemoryBuffer& MessageBuffer() const noexcept;
    const boost::stacktrace::basic_stacktrace<>& Trace() const noexcept;
 
    /// Stream-like interface for message extension
    template <typename Exception, typename T>
    friend typename std::enable_if<
        std::is_base_of<TracefulExceptionBase, typename std::remove_reference<Exception>::type>::value,
        Exception&&>::type
    operator<<(Exception&& ex, const T& data) {
        fmt::format_to(std::back_inserter(ex.GetMessageBuffer()), "{}", data);
        ex.EnsureNullTerminated();
        return std::forward<Exception>(ex);
    }
 
private:
    void EnsureNullTerminated();
 
    MemoryBuffer& GetMessageBuffer();
 
    struct Impl;
    static constexpr std::size_t kSize = sizeof(MemoryBuffer) + compiler::SelectSize().For64Bit(24).For32Bit(12);
    utils::FastPimpl<Impl, kSize, alignof(void*)> impl_;
};
 
/// @ingroup userver_universal userver_base_classes
///
/// @brief Exception that remembers the backtrace at the point of its
/// construction
// NOLINTNEXTLINE(fuchsia-multiple-inheritance)
class TracefulException : public std::exception, public TracefulExceptionBase {
public:
    using TracefulExceptionBase::TracefulExceptionBase;
 
    const char* what() const noexcept override;
};
 
namespace impl {
 
template <typename PlainException>
// NOLINTNEXTLINE(fuchsia-multiple-inheritance)
class ExceptionWithAttachedTrace final : public PlainException, public TracefulExceptionBase {
public:
    explicit ExceptionWithAttachedTrace(const PlainException& ex)
        : PlainException(ex), TracefulExceptionBase(ex.what()) {}
};
 
template <typename Exception>
std::enable_if_t<std::is_base_of<std::exception, Exception>::value, ExceptionWithAttachedTrace<Exception>>
AttachTraceToException(const Exception& ex) {
    static_assert(!std::is_base_of<TracefulExceptionBase, Exception>::value, "This exception already contains trace");
    return ExceptionWithAttachedTrace<Exception>(ex);
}
 
}  // namespace impl
}  // namespace utils
 
USERVER_NAMESPACE_END