syslog_sink.hpp

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// SPDX-FileCopyrightText: 2026 Jarosław Pelczar <jarek@jpelczar.com>
//
// SPDX-License-Identifier: BSD-2-Clause
 
#pragma once
 
#include "../log/sink.hpp"
#include <cstddef>
#include <cstdint>
#include <string_view>
#include <syslog.h>
 
namespace microfmt::log {
 
template <std::size_t Capacity> class syslog_sink;
 
template <std::size_t Capacity> struct syslog_sink_tag {};
 
template <std::size_t Capacity = 256> class syslog_sink {
  static_assert(Capacity > 0, "Capacity must be at least 1 byte");
 
public:
  using write_fn_t = void (*)(int priority, microfmt::string_view message) noexcept;
 
  explicit constexpr syslog_sink(write_fn_t write_fn = write_to_syslog) noexcept : write_fn_(write_fn) {}
 
  [[nodiscard]] log_sink as_sink() & noexcept RELOCO_LIFETIMEBOUND {
    return log_sink(syslog_sink_tag<Capacity>{}, *this);
  }
 
  void log_impl(const log_msg &msg) noexcept {
    if (msg.lvl == level::off) {
      return;
    }
 
    buffer_sink<Capacity> buffer;
    const auto out = buffer.as_sink();
    if (!msg.logger_name.empty()) {
      microfmt::format_to(out, "[{}] ", msg.logger_name);
    }
    microfmt::format_to(out, "{}", msg.payload);
    write_fn_(priority_for(msg.lvl), buffer.view());
  }
 
private:
  // bridges to a C/platform API (FILE*, syslog, android log, raw chunk storage) that takes raw pointers.
  RELOCO_BEGIN_UNSAFE_CODE
  static void write_to_syslog(int priority, microfmt::string_view message) noexcept {
    RELOCO_BEGIN_UNSAFE_BUFFER_USAGE;
 
    ::syslog(priority, "%.*s", static_cast<int>(message.size()), message.data());
 
    RELOCO_END_UNSAFE_BUFFER_USAGE;
  }
  RELOCO_END_UNSAFE_CODE
 
  static int priority_for(level lvl) noexcept {
    switch (lvl) {
    case level::trace:
    case level::debug:
      return LOG_DEBUG;
    case level::info:
      return LOG_INFO;
    case level::warn:
      return LOG_WARNING;
    case level::err:
      return LOG_ERR;
    case level::critical:
      return LOG_CRIT;
    case level::off:
      return LOG_DEBUG;
    }
    return LOG_DEBUG;
  }
 
  write_fn_t write_fn_;
};
 
// Explicit guides: GCC 11 cannot synthesize the implicit CTAD guide because the
// constructor's default argument (write_to_syslog) names a member of the
// still-incomplete class template.
syslog_sink() -> syslog_sink<>;
syslog_sink(void (*)(int, microfmt::string_view) noexcept) -> syslog_sink<>;
 
template <std::size_t Capacity> struct log_sink_traits<syslog_sink_tag<Capacity>> {
  using context_type = syslog_sink<Capacity>;
 
  static void log(value_ref<context_type> ctx, const log_msg &msg) noexcept { ctx->log_impl(msg); }
};
 
} // namespace microfmt::log