log_helper.hpp

Go to the documentation of this file.

#pragma once
 
/// @file userver/logging/log_helper.hpp
/// @brief @copybrief logging::LogHelper
 
#include <chrono>
#include <exception>
#include <iosfwd>
#include <iterator>
#include <memory>
#include <optional>
#include <string_view>
#include <system_error>
#include <type_traits>
 
#include <fmt/core.h>
 
#include <userver/formats/common/meta.hpp>
#include <userver/logging/fwd.hpp>
#include <userver/logging/level.hpp>
#include <userver/logging/log_extra.hpp>
#include <userver/utils/impl/source_location.hpp>
#include <userver/utils/meta.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace logging {
 
namespace impl {
 
class TagWriter;
 
struct Noop {};
 
struct HexBase {
    std::uint64_t value;
 
    template <typename Unsigned>
        requires std::is_unsigned_v<Unsigned>
    explicit constexpr HexBase(Unsigned value) noexcept : value(value) {
        static_assert(sizeof(Unsigned) <= sizeof(value));
    }
 
    template <typename T>
    explicit HexBase(T* pointer) noexcept : HexBase(reinterpret_cast<std::uintptr_t>(pointer)) {
        static_assert(sizeof(std::uintptr_t) <= sizeof(value));
    }
};
 
}  // namespace impl
 
/// Formats value in a hex mode with the fixed length representation.
struct Hex final : impl::HexBase {
    using impl::HexBase::HexBase;
};
 
/// Formats value in a hex mode with the shortest representation, just like
/// std::to_chars does.
struct HexShort final : impl::HexBase {
    using impl::HexBase::HexBase;
};
 
/// Formats a string as quoted, escaping the '\' and '"' symbols.
struct Quoted final {
    std::string_view string;
};
 
enum class LogClass {
    kLog,
    kTrace,
};
 
/// Stream-like tskv-formatted log message builder.
///
/// Users can add LogHelper& operator<<(LogHelper&, ) overloads to use a faster
/// localeless logging, rather than outputting data through the ostream
/// operator.
class LogHelper final {
public:
    /// @brief Constructs LogHelper with span logging
    /// @param logger to log to
    /// @param level message log level
    /// @param log_class whether this LogHelper will be used to write a log record or a span
    /// @param location source location that will be written to logs
    LogHelper(
        LoggerRef logger,
        Level level,
        LogClass log_class = LogClass::kLog,
        const utils::impl::SourceLocation& location = utils::impl::SourceLocation::Current()
    ) noexcept;
 
    /// @brief Constructs LogHelper with span logging
    /// @param logger to log to (logging to nullptr does not output messages)
    /// @param level message log level
    /// @param log_class whether this LogHelper will be used to write a log record or a span
    /// @param location source location that will be written to logs
    LogHelper(
        const LoggerPtr& logger,
        Level level,
        LogClass log_class = LogClass::kLog,
        const utils::impl::SourceLocation& location = utils::impl::SourceLocation::Current()
    ) noexcept;
 
    ~LogHelper();
 
    LogHelper(LogHelper&&) = delete;
    LogHelper(const LogHelper&) = delete;
    LogHelper& operator=(LogHelper&&) = delete;
    LogHelper& operator=(const LogHelper&) = delete;
 
    // Helper function that could be called on LogHelper&& to get LogHelper&.
    LogHelper& AsLvalue() noexcept { return *this; }
 
    /// @cond
    template <typename... Args>
    LogHelper& AsLvalue(fmt::format_string<Args...> fmt, Args&&... args) noexcept {
        VFormat(fmt::string_view(fmt), fmt::make_format_args(args...));
        return *this;
    }
    /// @endcond
 
    bool IsLimitReached() const noexcept;
 
    template <typename T>
    LogHelper& operator<<(const T& value) {
        if constexpr (std::is_constructible_v<std::string_view, T>) {
            // noexcept if the conversion is noexcept
            *this << std::string_view{value};
        } else if constexpr (std::is_signed_v<T>) {
            using LongLong = long long;
            *this << LongLong{value};
        } else if constexpr (std::is_unsigned_v<T>) {
            using UnsignedLongLong = unsigned long long;
            *this << UnsignedLongLong{value};
        } else if constexpr (std::is_base_of_v<std::exception, T>) {
            *this << static_cast<const std::exception&>(value);
        } else if constexpr (meta::IsOstreamWritable<T>) {
            // may throw a non std::exception based exception
            Stream() << value;
            FlushStream();
        } else if constexpr (meta::kIsRange<T> && !formats::common::kIsFormatValue<T>) {
            // may throw a non std::exception based exception
            PutRange(value);
        } else {
            VFormat("{}", fmt::make_format_args(value));
        }
 
        return *this;
    }
 
    LogHelper& operator<<(char value) noexcept;
    LogHelper& operator<<(std::string_view value) noexcept;
    LogHelper& operator<<(float value) noexcept;
    LogHelper& operator<<(double value) noexcept;
    LogHelper& operator<<(long double value) noexcept;
    LogHelper& operator<<(unsigned long long value) noexcept;
    LogHelper& operator<<(long long value) noexcept;
    LogHelper& operator<<(bool value) noexcept;
    LogHelper& operator<<(const std::exception& value) noexcept;
 
    /// Extends internal LogExtra
    LogHelper& operator<<(const LogExtra& extra) noexcept;
 
    /// Extends internal LogExtra
    LogHelper& operator<<(LogExtra&& extra) noexcept;
 
    LogHelper& operator<<(Hex hex) noexcept;
 
    LogHelper& operator<<(HexShort hex) noexcept;
 
    LogHelper& operator<<(Quoted value) noexcept;
 
    LogHelper& PutTag(std::string_view key, const LogExtra::Value& value) noexcept;
    LogHelper& PutSwTag(std::string_view key, std::string_view value) noexcept;
 
    /// @brief Formats a log message using the specified format string and arguments.
    /// @param fmt The format string as per fmtlib.
    /// @param args Arguments to be formatted into the log message.
    /// @return A reference to the LogHelper object for chaining.
    template <typename... Args>
    LogHelper& Format(fmt::format_string<Args...> fmt, Args&&... args) noexcept;
 
    /// @cond
    // For internal use only!
    operator impl::Noop() const noexcept { return {}; }
 
    struct InternalTag;
 
    // For internal use only!
    impl::TagWriter GetTagWriter();
 
    /// @endcond
 
private:
    friend class impl::TagWriter;
 
    void DoLog() noexcept;
 
    void InternalLoggingError(std::string_view message) noexcept;
 
    void PutFloatingPoint(float value);
    void PutFloatingPoint(double value);
    void PutFloatingPoint(long double value);
    void PutUnsigned(unsigned long long value);
    void PutSigned(long long value);
    void PutBoolean(bool value);
    void Put(std::string_view value);
    void Put(char value);
 
    void PutRaw(std::string_view value_needs_no_escaping);
    void PutException(const std::exception& ex);
    void PutQuoted(std::string_view value);
 
    void VFormat(fmt::string_view fmt, fmt::format_args args) noexcept;
 
    template <typename T>
    void PutRangeElement(const T& value);
 
    template <typename T, typename U>
    void PutMapElement(const std::pair<const T, U>& value);
 
    template <typename T>
    void PutRange(const T& range);
 
    std::ostream& Stream();
    void FlushStream();
 
    class Impl;
    std::unique_ptr<Impl> pimpl_;
};
 
inline LogHelper& operator<<(LogHelper& lh, std::error_code ec) {
    lh << ec.category().name() << ':' << ec.value() << " (" << ec.message() << ')';
    return lh;
}
 
template <typename T>
LogHelper& operator<<(LogHelper& lh, const std::atomic<T>& value) {
    return lh << value.load();
}
 
template <typename T>
LogHelper& operator<<(LogHelper& lh, const T* value) noexcept {
    if (value == nullptr) {
        lh << std::string_view{"(null)"};
    } else if constexpr (std::is_same_v<T, char>) {
        lh << std::string_view{value};
    } else {
        lh << Hex{value};
    }
    return lh;
}
 
template <typename T>
LogHelper& operator<<(LogHelper& lh, T* value) {
    static_assert(
        !std::is_function_v<T>,
        "An attempt to log the function address is denied. If you really know what you're doing, cast it to void*."
    );
    return lh << static_cast<const T*>(value);
}
 
template <typename T>
LogHelper& operator<<(LogHelper& lh, const std::optional<T>& value) {
    if (value) {
        lh << *value;
    } else {
        lh << "(none)";
    }
    return lh;
}
 
template <typename Fun>
requires std::is_invocable_r_v<void, Fun, LogHelper&>
LogHelper& operator<<(LogHelper& lh, Fun&& value) {
    std::forward<Fun>(value)(lh);
    return lh;
}
 
template <class Result, class... Args>
LogHelper& operator<<(LogHelper& lh, Result (*)(Args...)) {
    static_assert(!sizeof(Result), "Outputting functions or std::ostream formatters is forbidden");
    return lh;
}
 
LogHelper& operator<<(LogHelper& lh, std::chrono::system_clock::time_point tp);
LogHelper& operator<<(LogHelper& lh, std::chrono::seconds value);
LogHelper& operator<<(LogHelper& lh, std::chrono::milliseconds value);
LogHelper& operator<<(LogHelper& lh, std::chrono::microseconds value);
LogHelper& operator<<(LogHelper& lh, std::chrono::nanoseconds value);
LogHelper& operator<<(LogHelper& lh, std::chrono::minutes value);
LogHelper& operator<<(LogHelper& lh, std::chrono::nanoseconds value);
LogHelper& operator<<(LogHelper& lh, std::chrono::hours value);
 
template <typename T>
void LogHelper::PutRangeElement(const T& value) {
    if constexpr (std::is_constructible_v<std::string_view, T>) {
        *this << Quoted{value};
    } else {
        *this << value;
    }
}
 
template <typename T, typename U>
void LogHelper::PutMapElement(const std::pair<const T, U>& value) {
    PutRangeElement(value.first);
    *this << ": ";
    PutRangeElement(value.second);
}
 
template <typename T>
void LogHelper::PutRange(const T& range) {
    static_assert(meta::kIsRange<T>);
    using std::begin;
    using std::end;
 
    static_assert(
        !std::is_same_v<meta::RangeValueType<T>, char>,
        "You should either manually convert type to 'std::string_view' or provide 'operator<<' specialization for your "
        "type: 'logging::LogHelper& operator<<(logging::LogHelper& lh, const T& value)' or make your type convertible "
        "to 'std::string_view'"
    );
 
    constexpr std::string_view kSeparator = ", ";
    *this << '[';
 
    bool is_first = true;
    auto curr = begin(range);
    const auto end_iter = end(range);
 
    while (curr != end_iter) {
        if (IsLimitReached()) {
            break;
        }
        if (is_first) {
            is_first = false;
        } else {
            *this << kSeparator;
        }
 
        if constexpr (meta::kIsMap<T>) {
            PutMapElement(*curr);
        } else {
            PutRangeElement(*curr);
        }
        ++curr;
    }
 
    const auto extra_elements = std::distance(curr, end_iter);
 
    if (extra_elements != 0) {
        if (!is_first) {
            *this << kSeparator;
        }
        *this << "..." << extra_elements << " more";
    }
 
    *this << ']';
}
 
template <typename... Args>
LogHelper& LogHelper::Format(fmt::format_string<Args...> fmt, Args&&... args) noexcept {
    VFormat(fmt::string_view(fmt), fmt::make_format_args(args...));
    return *this;
}
 
}  // namespace logging
 
USERVER_NAMESPACE_END