logbuf.h

Go to the documentation of this file.

// Copyright (C) 2026 Douglas Quigg (dstroy0) <dquigg123@gmail.com>
// SPDX-License-Identifier: AGPL-3.0-or-later
 
/**
 * @file logbuf.h
 * @brief Fixed-RAM rotating log buffer with severity traps (DETWS_ENABLE_LOGBUF).
 *
 * Keeps the last DETWS_LOG_LINES log lines in a fixed ring (the oldest is pruned
 * on overflow - no heap, bounded latency), each line stored as `<L> message`
 * where L is the severity letter. Dump the ring oldest-first for a `/logs`
 * endpoint, and register a trap callback that fires when a line is logged at or
 * above a severity threshold (forward criticals as an SNMP trap / webhook). Pure
 * and fully host-tested - no ESP32 dependency.
 *
 * @author  Douglas Quigg (dstroy0)
 * @date    2026
 */
 
#ifndef DETERMINISTICESPASYNCWEBSERVER_LOGBUF_H
#define DETERMINISTICESPASYNCWEBSERVER_LOGBUF_H
 
#include "ServerConfig.h"
#include <stddef.h>
#include <stdint.h>
 
#if DETWS_ENABLE_LOGBUF
 
/** @brief Severity levels (ordered low -> high). Compared (level >= threshold) and passed through the
 *  uint8_t trap-callback ABI, so integer constants in a namespacing struct - cast-free. */
struct DetwsLogLevel
{
    static constexpr uint8_t DETWS_LOG_DEBUG = 0;
    static constexpr uint8_t DETWS_LOG_INFO = 1;
    static constexpr uint8_t DETWS_LOG_WARN = 2;
    static constexpr uint8_t DETWS_LOG_ERROR = 3;
};
 
/** @brief Trap callback: fired for a line logged at level >= the threshold. */
typedef void (*detws_log_trap_fn)(uint8_t level, const char *line);
 
/** @brief Empty the ring (and clear the line count). */
void detws_logbuf_reset(void);
 
/** @brief Append @p msg at @p level (stored as `<L> msg`, truncated to fit). */
void detws_log(uint8_t level, const char *msg);
 
/** @brief Number of lines currently held (0 .. DETWS_LOG_LINES). */
uint16_t detws_log_count(void);
 
/** @brief Line @p i (0 = oldest .. count-1 = newest), or nullptr if out of range. */
const char *detws_log_at(uint16_t i);
 
/**
 * @brief Dump all held lines, oldest-first, newline-separated, into @p out.
 * @return characters written, or 0 if @p cap is too small (fail-closed).
 */
int detws_log_dump(char *out, size_t cap);
 
/** @brief Install a trap callback that fires when a line is logged at level >= @p threshold. */
void detws_log_set_trap(uint8_t threshold, detws_log_trap_fn cb);
 
#endif // DETWS_ENABLE_LOGBUF
#endif // DETERMINISTICESPASYNCWEBSERVER_LOGBUF_H