tagged_log_sink_base.hpp

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// SPDX-FileCopyrightText: 2026 Jarosław Pelczar <jarek@jpelczar.com>
//
// SPDX-License-Identifier: BSD-2-Clause
 
#pragma once
 
#include "../../microfmt.hpp"
#include <cstddef>
#include <string_view>
 
namespace microfmt::log::detail {
 
template <std::size_t TagCapacity> class tagged_log_sink_base {
  static_assert(TagCapacity > 0, "Tag capacity must be at least 1 byte");
 
public:
  void set_tag(microfmt::string_view tag) noexcept {
    RELOCO_BEGIN_UNSAFE_BUFFER_USAGE;
 
    tag_size_ = tag.size() < TagCapacity - 1 ? tag.size() : TagCapacity - 1;
    for (std::size_t i = 0; i < tag_size_; ++i) {
      tag_[i] = tag[i];
    }
    tag_[tag_size_] = '\0';
 
    RELOCO_END_UNSAFE_BUFFER_USAGE;
  }
 
protected:
  constexpr tagged_log_sink_base() noexcept = default;
  explicit tagged_log_sink_base(microfmt::string_view tag) noexcept { set_tag(tag); }
 
  [[nodiscard]] microfmt::string_view resolve_tag(microfmt::string_view logger_name,
                                                  char (&scratch)[TagCapacity]) const & noexcept RELOCO_LIFETIMEBOUND {
    if (logger_name.empty()) {
      return microfmt::string_view(tag_, tag_size_);
    }
 
    RELOCO_BEGIN_UNSAFE_BUFFER_USAGE;
 
    // The index bound is spelled out in the loop condition (not only via a
    // precomputed n) so GCC on riscv64 -O3 can prove i < TagCapacity - 1 and
    // does not emit a false -Wstringop-overflow after unrolling.
    std::size_t n = 0;
    while (n < TagCapacity - 1 && n < logger_name.size()) {
      scratch[n] = logger_name[n];
      ++n;
    }
    scratch[n] = '\0';
 
    RELOCO_END_UNSAFE_BUFFER_USAGE;
    return microfmt::string_view(scratch, n);
  }
 
  [[nodiscard]] microfmt::string_view resolve_tag(microfmt::string_view logger_name,
                                                  char (&scratch)[TagCapacity]) const && = delete;
 
  char tag_[TagCapacity]{};
  std::size_t tag_size_{0};
};
 
} // namespace microfmt::log::detail