span.h

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// Copyright 2026 The A11 Authors.
 
#ifndef A11_OBS_SPAN_H_
#define A11_OBS_SPAN_H_
 
#include <cstddef>
#include <cstdint>
#include <new>
#include <string>
#include <string_view>
#include <utility>
#include <vector>
 
#include <absl/status/status.h>
 
#include "a11/data/types.h"
 
namespace a11::obs {
 
enum class SpanKind { kInternal, kServer, kClient, kProducer, kConsumer };
 
enum class SpanStatus { kUnset, kOk, kError };
 
class Span {
 public:
  Span() noexcept = default;
  ~Span();
 
  Span(Span&& other) noexcept;
  Span& operator=(Span&& other) noexcept;
  Span(const Span&) = delete;
  Span& operator=(const Span&) = delete;
 
  [[nodiscard]] bool IsRecording() const noexcept;
 
  // This span's identifiers as lowercase hex (32 chars / 16 chars), or empty
  // strings for an inactive span or an invalid context.
  [[nodiscard]] std::string TraceIdHex() const;
  [[nodiscard]] std::string SpanIdHex() const;
 
  void SetAttribute(std::string_view key, std::string_view value);
  void SetAttribute(std::string_view key, const char* value);
  void SetAttribute(std::string_view key, std::int64_t value);
  void SetAttribute(std::string_view key, bool value);
  void SetAttribute(std::string_view key, double value);
 
  void AddEvent(std::string_view name);
  void AddEvent(
      std::string_view name,
      const std::vector<std::pair<std::string, std::string>>& attributes);
 
  void SetStatus(const absl::Status& status);
 
  void SetStatus(SpanStatus status, std::string_view description = {});
 
  // Renames the span (OTel UpdateName). The exported name is whatever it is at
  // End(). No-op for an inactive span.
  void UpdateName(std::string_view name);
 
  void End() noexcept;
 
  // Serializes this span's context (and any inherited baggage) into the
  // reserved headers so nested or remote actions continue the same trace.
  // A no-op that returns OkStatus for an inactive span.
  absl::Status InjectContext(data::ByteMap& headers) const;
 
 private:
  friend class Tracer;
 
  struct Impl;
  // Sized/aligned to hold Impl (a shared span handle plus a small string).
  // Verified with static_assert in tracer.cc.
  static constexpr std::size_t kStorageSize = 64;
  static constexpr std::size_t kStorageAlign = alignof(std::max_align_t);
 
  // Defined in tracer.cc, where Impl is a complete type (std::launder and
  // Impl's members require completeness).
  [[nodiscard]] Impl* impl() noexcept;
  [[nodiscard]] const Impl* impl() const noexcept;
  // Default-constructs an Impl in the inline storage, marks the span engaged,
  // and returns it for the tracer to populate.
  Impl* Engage() noexcept;
  void Reset() noexcept;
 
  alignas(kStorageAlign) unsigned char storage_[kStorageSize];
  bool engaged_ = false;
};
 
}  // namespace a11::obs
 
#endif  // A11_OBS_SPAN_H_