lib: introduce log library

Introduce a new `log` library which provides bindings for syslog and,
if available, the OpenWrt libubox ulog functions.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

1 files changed, 1074 insertions, 0 deletions

diff --git a/lib/log.c b/lib/log.c
new file mode 100644
index 0000000..8cd196d
--- /dev/null
+++ b/lib/log.c
@@ -0,0 +1,1074 @@
+/*
+ * Copyright (C) 2023 Jo-Philipp Wich <jo@mein.io>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+/**
+ * # System logging functions
+ *
+ * The `log` module provides bindings to the POSIX syslog functions `openlog()`,
+ * `syslog()` and `closelog()` as well as - when available - the OpenWrt
+ * specific ulog library functions.
+ *
+ * Functions can be individually imported and directly accessed using the
+ * {@link https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import#named_import named import}
+ * syntax:
+ *
+ *   ```
+ *   import { openlog, syslog, LOG_PID, LOG_USER, LOG_ERR } from 'log';
+ *
+ *   openlog("my-log-ident", LOG_PID, LOG_USER);
+ *   syslog(LOG_ERR, "An error occurred!");
+ *
+ *   // OpenWrt specific ulog functions
+ *   import { ulog_open, ulog, ULOG_SYSLOG, LOG_DAEMON, LOG_INFO } from 'log';
+ *
+ *   ulog_open(ULOG_SYSLOG, LOG_DAEMON, "my-log-ident");
+ *   ulog(LOG_INFO, "The current epoch is %d", time());
+ *   ```
+ *
+ * Alternatively, the module namespace can be imported
+ * using a wildcard import statement:
+ *
+ *   ```
+ *   import * as log from 'log';
+ *
+ *   log.openlog("my-log-ident", log.LOG_PID, log.LOG_USER);
+ *   log.syslog(log.LOG_ERR, "An error occurred!");
+ *
+ *   // OpenWrt specific ulog functions
+ *   log.ulog_open(log.ULOG_SYSLOG, log.LOG_DAEMON, "my-log-ident");
+ *   log.ulog(log.LOG_INFO, "The current epoch is %d", time());
+ *   ```
+ *
+ * Additionally, the log module namespace may also be imported by invoking the
+ * `ucode` interpreter with the `-llog` switch.
+ *
+ * ## Constants
+ *
+ * The `log` module declares a number of numeric constants to specify logging
+ * facility, priority and option values, as well as ulog specific channels.
+ *
+ * ### Syslog Options
+ *
+ * | Constant Name | Description                                             |
+ * |---------------|---------------------------------------------------------|
+ * | `LOG_PID`     | Include PID with each message.                          |
+ * | `LOG_CONS`    | Log to console if error occurs while sending to syslog. |
+ * | `LOG_NDELAY`  | Open the connection to the logger immediately.          |
+ * | `LOG_ODELAY`  | Delay open until the first message is logged.           |
+ * | `LOG_NOWAIT`  | Do not wait for child processes created during logging. |
+ *
+ * ### Syslog Facilities
+ *
+ * | Constant Name  | Description                                      |
+ * |----------------|--------------------------------------------------|
+ * | `LOG_AUTH`     | Authentication/authorization messages.           |
+ * | `LOG_AUTHPRIV` | Private authentication messages.                 |
+ * | `LOG_CRON`     | Clock daemon (cron and at commands).             |
+ * | `LOG_DAEMON`   | System daemons without separate facility values. |
+ * | `LOG_FTP`      | FTP server daemon.                               |
+ * | `LOG_KERN`     | Kernel messages.                                 |
+ * | `LOG_LPR`      | Line printer subsystem.                          |
+ * | `LOG_MAIL`     | Mail system.                                     |
+ * | `LOG_NEWS`     | Network news subsystem.                          |
+ * | `LOG_SYSLOG`   | Messages generated internally by syslogd.        |
+ * | `LOG_USER`     | Generic user-level messages.                     |
+ * | `LOG_UUCP`     | UUCP subsystem.                                  |
+ * | `LOG_LOCAL0`   | Local use 0 (custom facility).                   |
+ * | `LOG_LOCAL1`   | Local use 1 (custom facility).                   |
+ * | `LOG_LOCAL2`   | Local use 2 (custom facility).                   |
+ * | `LOG_LOCAL3`   | Local use 3 (custom facility).                   |
+ * | `LOG_LOCAL4`   | Local use 4 (custom facility).                   |
+ * | `LOG_LOCAL5`   | Local use 5 (custom facility).                   |
+ * | `LOG_LOCAL6`   | Local use 6 (custom facility).                   |
+ * | `LOG_LOCAL7`   | Local use 7 (custom facility).                   |
+ *
+ * ### Syslog Priorities
+ *
+ * | Constant Name | Description                         |
+ * |---------------|-------------------------------------|
+ * | `LOG_EMERG`   | System is unusable.                 |
+ * | `LOG_ALERT`   | Action must be taken immediately.   |
+ * | `LOG_CRIT`    | Critical conditions.                |
+ * | `LOG_ERR`     | Error conditions.                   |
+ * | `LOG_WARNING` | Warning conditions.                 |
+ * | `LOG_NOTICE`  | Normal, but significant, condition. |
+ * | `LOG_INFO`    | Informational message.              |
+ * | `LOG_DEBUG`   | Debug-level message.                |
+ *
+ * ### Ulog channels
+ *
+ * | Constant Name | Description                          |
+ * |---------------|--------------------------------------|
+ * | `ULOG_KMSG`   | Log messages to `/dev/kmsg` (dmesg). |
+ * | `ULOG_STDIO`  | Log messages to stdout.              |
+ * | `ULOG_SYSLOG` | Log messages to syslog.              |
+ *
+ * @module log
+ */
+
+#include <syslog.h>
+#include <errno.h>
+
+#ifdef HAVE_ULOG
+#include <libubox/ulog.h>
+#endif
+
+#include "ucode/module.h"
+
+
+static char log_ident[32];
+
+/**
+ * The following log option strings are recognized:
+ *
+ * | Log Option | Description                                                |
+ * |------------|------------------------------------------------------------|
+ * | `"pid"`    | Include PID with each message.                             |
+ * | `"cons"`   | Log to console if an error occurs while sending to syslog. |
+ * | `"ndelay"` | Open the connection to the logger immediately.             |
+ * | `"odelay"` | Delay open until the first message is logged.              |
+ * | `"nowait"` | Do not wait for child processes created during logging.    |
+ *
+ * @typedef {string} module:log.LogOption
+ * @enum {module:log.LogOption}
+ *
+ */
+static const struct { const char *name; int value; } log_options[] = {
+	{ "pid", LOG_PID },
+	{ "cons", LOG_CONS },
+	{ "ndelay", LOG_NDELAY },
+	{ "odelay", LOG_ODELAY },
+	{ "nowait", LOG_NOWAIT },
+};
+
+/**
+ * The following log facility strings are recognized:
+ *
+ * | Facility     | Description                                      |
+ * |--------------|--------------------------------------------------|
+ * | `"auth"`     | Authentication/authorization messages.           |
+ * | `"authpriv"` | Private authentication messages.                 |
+ * | `"cron"`     | Clock daemon (cron and at commands).             |
+ * | `"daemon"`   | System daemons without separate facility values. |
+ * | `"ftp"`      | FTP server daemon.                               |
+ * | `"kern"`     | Kernel messages.                                 |
+ * | `"lpr"`      | Line printer subsystem.                          |
+ * | `"mail"`     | Mail system.                                     |
+ * | `"news"`     | Network news subsystem.                          |
+ * | `"syslog"`   | Messages generated internally by syslogd.        |
+ * | `"user"`     | Generic user-level messages.                     |
+ * | `"uucp"`     | UUCP subsystem.                                  |
+ * | `"local0"`   | Local use 0 (custom facility).                   |
+ * | `"local1"`   | Local use 1 (custom facility).                   |
+ * | `"local2"`   | Local use 2 (custom facility).                   |
+ * | `"local3"`   | Local use 3 (custom facility).                   |
+ * | `"local4"`   | Local use 4 (custom facility).                   |
+ * | `"local5"`   | Local use 5 (custom facility).                   |
+ * | `"local6"`   | Local use 6 (custom facility).                   |
+ * | `"local7"`   | Local use 7 (custom facility).                   |
+ *
+ * @typedef {string} module:log.LogFacility
+ * @enum {module:log.LogFacility}
+ */
+static const struct { const char *name; int value; } log_facilities[] = {
+	{ "auth", LOG_AUTH },
+#ifdef LOG_AUTHPRIV
+	{ "authpriv", LOG_AUTHPRIV },
+#endif
+	{ "cron", LOG_CRON },
+	{ "daemon", LOG_DAEMON },
+#ifdef LOG_FTP
+	{ "ftp", LOG_FTP },
+#endif
+	{ "kern", LOG_KERN },
+	{ "lpr", LOG_LPR },
+	{ "mail", LOG_MAIL },
+	{ "news", LOG_NEWS },
+	{ "syslog", LOG_SYSLOG },
+	{ "user", LOG_USER },
+	{ "uucp", LOG_UUCP },
+	{ "local0", LOG_LOCAL0 },
+	{ "local1", LOG_LOCAL1 },
+	{ "local2", LOG_LOCAL2 },
+	{ "local3", LOG_LOCAL3 },
+	{ "local4", LOG_LOCAL4 },
+	{ "local5", LOG_LOCAL5 },
+	{ "local6", LOG_LOCAL6 },
+	{ "local7", LOG_LOCAL7 },
+};
+
+/**
+ * The following log priority strings are recognized:
+ *
+ * | Priority    | Description                         |
+ * |-------------|-------------------------------------|
+ * | `"emerg"`   | System is unusable.                 |
+ * | `"alert"`   | Action must be taken immediately.   |
+ * | `"crit"`    | Critical conditions.                |
+ * | `"err"`     | Error conditions.                   |
+ * | `"warning"` | Warning conditions.                 |
+ * | `"notice"`  | Normal, but significant, condition. |
+ * | `"info"`    | Informational message.              |
+ * | `"debug"`   | Debug-level message.                |
+ *
+ * @typedef {string} module:log.LogPriority
+ * @enum {module:log.LogPriority}
+ */
+static const struct { const char *name; int value; } log_priorities[] = {
+	{ "emerg", LOG_EMERG },
+	{ "alert", LOG_ALERT },
+	{ "crit", LOG_CRIT },
+	{ "err", LOG_ERR },
+	{ "warning", LOG_WARNING },
+	{ "notice", LOG_NOTICE },
+	{ "info", LOG_INFO },
+	{ "debug", LOG_DEBUG },
+};
+
+
+static int
+parse_facility(uc_value_t *facility)
+{
+	char *s;
+	int rv;
+
+	switch (ucv_type(facility)) {
+	case UC_STRING:
+		s = ucv_string_get(facility);
+
+		for (size_t i = 0; i < ARRAY_SIZE(log_facilities); i++)
+			if (s && !strcasecmp(s, log_facilities[i].name))
+				return log_facilities[i].value;
+
+		return -1;
+
+	case UC_INTEGER:
+		rv = ucv_int64_get(facility);
+
+		if (errno == ERANGE || rv < 0)
+			return -1;
+
+		return rv;
+
+	case UC_NULL:
+		return 0;
+
+	default:
+		return -1;
+	}
+}
+
+static int
+parse_options(uc_value_t *option)
+{
+	char *s;
+	int rv;
+
+	switch (ucv_type(option)) {
+	case UC_ARRAY:
+		rv = 0;
+
+		for (size_t i = 0; i < ucv_array_length(option); i++) {
+			uc_value_t *opt = ucv_array_get(option, i);
+			char *s = ucv_string_get(opt);
+
+			for (size_t j = 0; j < ARRAY_SIZE(log_options); j++) {
+				if (s && !strcasecmp(log_options[j].name, s))
+					rv |= log_options[j].value;
+				else
+					return -1;
+			}
+		}
+
+		return rv;
+
+	case UC_STRING:
+		s = ucv_string_get(option);
+
+		for (size_t i = 0; i < ARRAY_SIZE(log_options); i++)
+			if (s && !strcasecmp(s, log_options[i].name))
+				return log_options[i].value;
+
+		return -1;
+
+	case UC_INTEGER:
+		rv = ucv_int64_get(option);
+
+		if (errno == ERANGE || rv < 0)
+			return -1;
+
+		return rv;
+
+	case UC_NULL:
+		return 0;
+
+	default:
+		return -1;
+	}
+}
+
+static int
+parse_priority(uc_value_t *priority)
+{
+	char *s;
+	int rv;
+
+	switch (ucv_type(priority)) {
+	case UC_STRING:
+		s = ucv_string_get(priority);
+
+		for (size_t i = 0; i < ARRAY_SIZE(log_priorities); i++)
+			if (s && !strcasecmp(s, log_priorities[i].name))
+				return log_priorities[i].value;
+
+		return -1;
+
+	case UC_INTEGER:
+		rv = ucv_int64_get(priority);
+
+		if (errno == ERANGE || rv < 0)
+			return -1;
+
+		return rv;
+
+	case UC_NULL:
+		return LOG_INFO;
+
+	default:
+		return -1;
+	}
+}
+
+static char *
+parse_ident(uc_vm_t *vm, uc_value_t *ident)
+{
+	if (!ident)
+		return NULL;
+
+	char *s = ucv_to_string(vm, ident);
+
+	snprintf(log_ident, sizeof(log_ident), "%s", s ? s : "");
+	free(s);
+
+	return log_ident[0] ? log_ident : NULL;
+}
+
+/**
+ * Open connection to system logger.
+ *
+ * The `openlog()` function instructs the program to establish a connection to
+ * the system log service and configures the default facility and identification
+ * for use in subsequent log operations. It may be omitted, in which case the
+ * first call to `syslog()` will implicitly call `openlog()` with a default
+ * ident value representing the program name and a default `LOG_USER` facility.
+ *
+ * The log option argument may be either a single string value containing an
+ * option name, an array of option name strings or a numeric value representing
+ * a bitmask of `LOG_*` option constants.
+ *
+ * The facility argument may be either a single string value containing a
+ * facility name or one of the numeric `LOG_*` facility constants in the module
+ * namespace.
+ *
+ * Returns `true` if the system `openlog()` function was invoked.
+ *
+ * Returns `false` if an invalid argument, such as an unrecognized option or
+ * facility name, was provided.
+ *
+ * @function module:log#openlog
+ *
+ * @param {string} [ident]
+ * A string identifying the program name. If omitted, the name of the calling
+ * process is used by default.
+ *
+ * @param {number|module:log.LogOption|module:log.LogOption[]} [options]
+ * Logging options to use.
+ *
+ * See {@link module:log.LogOption|LogOption} for recognized option names.
+ *
+ * @param {number|module:log.LogFacility} [facility="user"]
+ * The facility to use for log messages generated by subsequent syslog calls.
+ *
+ * See {@link module:log.LogFacility|LogFacility} for recognized facility names.
+ *
+ * @returns {boolean}
+ *
+ * @example
+ * // Example usage of openlog function
+ * openlog("myapp", LOG_PID | LOG_NDELAY, LOG_LOCAL0);
+ *
+ * // Using option names instead of bitmask and LOG_USER facility
+ * openlog("myapp", [ "pid", "ndelay" ], "user");
+ */
+static uc_value_t *
+uc_openlog(uc_vm_t *vm, size_t nargs)
+{
+	char *ident = parse_ident(vm, uc_fn_arg(0));
+	int options = parse_options(uc_fn_arg(1));
+	int facility = parse_facility(uc_fn_arg(2));
+
+	if (options == -1 || facility == -1)
+		return ucv_boolean_new(false);
+
+	openlog(ident, options, facility);
+
+	return ucv_boolean_new(true);
+}
+
+/**
+ * Log a message to the system logger.
+ *
+ * This function logs a message to the system logger. The function behaves in a
+ * sprintf-like manner, allowing the use of format strings and associated
+ * arguments to construct log messages.
+ *
+ * If the `openlog` function has not been called explicitly before, `syslog()`
+ * implicitly calls `openlog()`, using a default ident and `LOG_USER` facility
+ * value before logging the message.
+ *
+ * If the `format` argument is not a string and not `null`, it will be
+ * implicitly converted to a string and logged as-is, without further format
+ * string processing.
+ *
+ * Returns `true` if a message was passed to the system `syslog()` function.
+ *
+ * Returns `false` if an invalid priority value or an empty message was given.
+ *
+ * @function module:log#syslog
+ *
+ * @param {number|module:log.LogPriority} priority
+ * Log message priority. May be either a number value (potentially bitwise OR-ed
+ * with a log facility constant) which is passed as-is to the system `syslog()`
+ * function or a priority name string.
+ *
+ * See {@link module:log.LogPriority|LogPriority} for recognized priority names.
+ *
+ * @param {*} format
+ * The sprintf-like format string for the log message, or any other, non-null,
+ * non-string value type which will be implicitly stringified and logged as-is.
+ *
+ * @param {...*} [args]
+ * In case a format string value was provided in the previous argument, then
+ * all subsequent arguments are used to replace the placeholders in the format
+ * string.
+ *
+ * @returns {boolean}
+ *
+ * @example
+ * // Example usage of syslog function with format string and arguments
+ * const username = "user123";
+ * const errorCode = 404;
+ * syslog(LOG_ERR, "User %s encountered error: %d", username, errorCode);
+ *
+ * // If openlog has not been called explicitly, it is implicitly called with defaults:
+ * syslog(LOG_INFO, "This message will be logged with default settings.");
+ *
+ * // Selectively override used facility by OR-ing numeric constant
+ * const password =" secret";
+ * syslog(LOG_DEBUG|LOG_AUTHPRIV, "The password %s has been wrong", secret);
+ *
+ * // Using priority names for logging
+ * syslog("emerg", "System shutdown imminent!");
+ *
+ * // Implicit stringification
+ * syslog("debug", { foo: 1, bar: true, baz: [1, 2, 3] });
+ */
+static uc_value_t *
+uc_syslog(uc_vm_t *vm, size_t nargs)
+{
+	int priority = parse_priority(uc_fn_arg(0));
+
+	if (priority == -1 || nargs < 2)
+		return ucv_boolean_new(false);
+
+	uc_value_t *fmt = uc_fn_arg(1), *msg;
+	uc_cfn_ptr_t fmtfn;
+	char *s;
+
+	switch (ucv_type(fmt)) {
+	case UC_STRING:
+		fmtfn = uc_stdlib_function("sprintf");
+		msg = fmtfn(vm, nargs - 1);
+
+		if (msg) {
+			syslog(priority, "%s", ucv_string_get(msg));
+			ucv_put(msg);
+
+			return ucv_boolean_new(true);
+		}
+
+		break;
+
+	case UC_NULL:
+		break;
+
+	default:
+		s = ucv_to_string(vm, fmt);
+
+		if (s) {
+			syslog(priority, "%s", s);
+			free(s);
+
+			return ucv_boolean_new(true);
+		}
+
+		break;
+	}
+
+	return ucv_boolean_new(false);
+}
+
+/**
+ * Close connection to system logger.
+ *
+ * The usage of this function is optional, and usually an explicit log
+ * connection tear down is not required.
+ *
+ * @function module:log#closelog
+ */
+static uc_value_t *
+uc_closelog(uc_vm_t *vm, size_t nargs)
+{
+	closelog();
+
+	return NULL;
+}
+
+
+#ifdef HAVE_ULOG
+/**
+ * The following ulog channel strings are recognized:
+ *
+ * | Channel    | Description                                       |
+ * |------------|---------------------------------------------------|
+ * | `"kmsg"`   | Log to `/dev/kmsg`, log messages appear in dmesg. |
+ * | `"syslog"` | Use standard `syslog()` mechanism.                |
+ * | `"stdio"`  | Use stderr for log output.                        |
+ *
+ * @typedef {string} module:log.UlogChannel
+ * @enum {module:log.UlogChannel}
+ */
+static const struct { const char *name; int value; } ulog_channels[] = {
+	{ "kmsg", ULOG_KMSG },
+	{ "syslog", ULOG_SYSLOG },
+	{ "stdio", ULOG_STDIO },
+};
+
+static int
+parse_channels(uc_value_t *channels)
+{
+	char *s;
+	int rv;
+
+	switch (ucv_type(channels)) {
+	case UC_ARRAY:
+		rv = 0;
+
+		for (size_t i = 0; i < ucv_array_length(channels); i++) {
+			uc_value_t *channel = ucv_array_get(channels, i);
+			char *s = ucv_string_get(channel);
+
+			for (size_t j = 0; j < ARRAY_SIZE(ulog_channels); j++) {
+				if (s && !strcasecmp(s, ulog_channels[j].name))
+					rv |= ulog_channels[j].value;
+				else
+					return -1;
+			}
+		}
+
+		return rv;
+
+	case UC_STRING:
+		s = ucv_string_get(channels);
+
+		for (size_t i = 0; i < ARRAY_SIZE(ulog_channels); i++)
+			if (s && !strcasecmp(s, ulog_channels[i].name))
+				return ulog_channels[i].value;
+
+		return -1;
+
+	case UC_INTEGER:
+		rv = ucv_uint64_get(channels);
+
+		if (errno == ERANGE)
+			return -1;
+
+		return rv & (ULOG_KMSG|ULOG_STDIO|ULOG_SYSLOG);
+
+	case UC_NULL:
+		return 0;
+
+	default:
+		return -1;
+	}
+}
+
+/**
+ * Configure ulog logger.
+ *
+ * This functions configures the ulog mechanism and is analogeous to using the
+ * `openlog()` function in conjuncton with `syslog()`.
+ *
+ * The `ulog_open()` function is OpenWrt specific and may not be present on
+ * other systems. Use `openlog()` and `syslog()` instead for portability to
+ * non-OpenWrt environments.
+ *
+ * A program may use multiple channels to simultaneously output messages using
+ * different means. The channel argument may either be a single string value
+ * containing a channel name, an array of channel names or a numeric value
+ * representing a bitmask of `ULOG_*` channel constants.
+ *
+ * The facility argument may be either a single string value containing a
+ * facility name or one of the numeric `LOG_*` facility constants in the module
+ * namespace.
+ *
+ * The default facility value varies, depending on the execution context of the
+ * program. In OpenWrt's preinit boot phase, or when stdout is not connected to
+ * an interactive terminal, the facility defaults to `"daemon"` (`LOG_DAEMON`),
+ * otherwise to `"user"` (`LOG_USER`).
+ *
+ * Likewise, the default channel is selected depending on the context. During
+ * OpenWrt's preinit boot phase, the `"kmsg"` channel is used, for interactive
+ * terminals the `"stdio"` one and for all other cases the `"syslog"` channel
+ * is selected.
+ *
+ * Returns `true` if ulog was configured.
+ *
+ * Returns `false` if an invalid argument, such as an unrecognized channel or
+ * facility name, was provided.
+ *
+ * @function module:log#ulog_open
+ *
+ * @param {number|module:log.UlogChannel|module:log.UlogChannel[]} [channel]
+ * Specifies the log channels to use.
+ *
+ * See {@link module:log.UlogChannel|UlogChannel} for recognized channel names.
+ *
+ * @param {number|module:log.LogFacility} [facility]
+ * The facility to use for log messages generated by subsequent `ulog()` calls.
+ *
+ * See {@link module:log.LogFacility|LogFacility} for recognized facility names.
+ *
+ * @param {string} [ident]
+ * A string identifying the program name. If omitted, the name of the calling
+ * process is used by default.
+ *
+ * @returns {boolean}
+ *
+ * @example
+ * // Log to dmesg and stderr
+ * ulog_open(["stdio", "kmsg"], "daemon", "my-program");
+ *
+ * // Use numeric constants and use implicit default ident
+ * ulog_open(ULOG_SYSLOG, LOG_LOCAL0);
+ */
+static uc_value_t *
+uc_ulog_open(uc_vm_t *vm, size_t nargs)
+{
+	int channels = parse_channels(uc_fn_arg(0));
+	int facility = parse_facility(uc_fn_arg(1));
+	char *ident = parse_ident(vm, uc_fn_arg(2));
+
+	if (channels == -1 || facility == -1)
+		return ucv_boolean_new(false);
+
+	ulog_open(channels, facility, ident);
+
+	return ucv_boolean_new(true);
+}
+
+static uc_value_t *
+uc_ulog_log_common(uc_vm_t *vm, size_t nargs, int priority)
+{
+	uc_value_t *fmt = uc_fn_arg(0), *msg;
+	uc_cfn_ptr_t fmtfn;
+	char *s;
+
+	switch (ucv_type(fmt)) {
+	case UC_STRING:
+		fmtfn = uc_stdlib_function("sprintf");
+		msg = fmtfn(vm, nargs);
+
+		if (msg) {
+			ulog(priority, "%s", ucv_string_get(msg));
+			ucv_put(msg);
+
+			return ucv_boolean_new(true);
+		}
+
+		break;
+
+	case UC_NULL:
+		break;
+
+	default:
+		s = ucv_to_string(vm, fmt);
+
+		if (s) {
+			ulog(priority, "%s", s);
+			free(s);
+
+			return ucv_boolean_new(true);
+		}
+
+		break;
+	}
+
+	return ucv_boolean_new(false);
+}
+
+/**
+ * Log a message via the ulog mechanism.
+ *
+ * The `ulog()` function outputs the given log message to all configured ulog
+ * channels unless the given priority level exceeds the globally configured ulog
+ * priority threshold. See {@link module:log#ulog_threshold|ulog_threshold()}
+ * for details.
+ *
+ * The `ulog()` function is OpenWrt specific and may not be present on other
+ * systems. Use `syslog()` instead for portability to non-OpenWrt environments.
+ *
+ * Like `syslog()`, the function behaves in a sprintf-like manner, allowing the
+ * use of format strings and associated arguments to construct log messages.
+ *
+ * If the `ulog_open()` function has not been called explicitly before, `ulog()`
+ * implicitly configures certain defaults, see
+ * {@link module:log#ulog_open|ulog_open()} for a detailled description.
+ *
+ * If the `format` argument is not a string and not `null`, it will be
+ * implicitly converted to a string and logged as-is, without further format
+ * string processing.
+ *
+ * Returns `true` if a message was passed to the underlying `ulog()` function.
+ *
+ * Returns `false` if an invalid priority value or an empty message was given.
+ *
+ * @function module:log#ulog
+ *
+ * @param {number|module:log.LogPriority} priority
+ * Log message priority. May be either a number value or a priority name string.
+ *
+ * See {@link module:log.LogPriority|LogPriority} for recognized priority names.
+ *
+ * @param {*} format
+ * The sprintf-like format string for the log message, or any other, non-null,
+ * non-string value type which will be implicitly stringified and logged as-is.
+ *
+ * @param {...*} [args]
+ * In case a format string value was provided in the previous argument, then
+ * all subsequent arguments are used to replace the placeholders in the format
+ * string.
+ *
+ * @returns {boolean}
+ *
+ * @example
+ * // Example usage of ulog function with format string and arguments
+ * const username = "user123";
+ * const errorCode = 404;
+ * ulog(LOG_ERR, "User %s encountered error: %d", username, errorCode);
+ *
+ * // Using priority names for logging
+ * ulog("err", "General error encountered");
+ *
+ * // Implicit stringification
+ * ulog("debug", { foo: 1, bar: true, baz: [1, 2, 3] });
+ *
+ * @see module:log#ulog_open
+ * @see module:log#ulog_threshold
+ * @see module:log#syslog
+ */
+static uc_value_t *
+uc_ulog_log(uc_vm_t *vm, size_t nargs)
+{
+	int priority = parse_priority(uc_fn_arg(0));
+
+	if (priority == -1 || nargs < 2)
+		return ucv_boolean_new(false);
+
+	return uc_ulog_log_common(vm, nargs - 1, priority);
+}
+
+/**
+ * Close ulog logger.
+ *
+ * Resets the ulog channels, the default facility and the log ident value to
+ * defaults.
+ *
+ * In case the `"syslog"` channel has been configured, the underlying
+ * `closelog()` function will be invoked.
+ *
+ * The usage of this function is optional, and usually an explicit ulog teardown
+ * is not required.
+ *
+ * The `ulog_close()` function is OpenWrt specific and may not be present on
+ * other systems. Use `closelog()` in conjunction with `syslog()` instead for
+ * portability to non-OpenWrt environments.
+ *
+ * @function module:log#ulog_close
+ *
+ * @see module:log#closelog
+ */
+static uc_value_t *
+uc_ulog_close(uc_vm_t *vm, size_t nargs)
+{
+	ulog_close();
+
+	return NULL;
+}
+
+/**
+ * Set ulog priority threshold.
+ *
+ * This function configures the application wide log message threshold for log
+ * messages emitted with `ulog()`. Any message with a priority higher (= less
+ * severe) than the threshold priority will be discarded. This is useful to
+ * implement application wide verbosity settings without having to wrap `ulog()`
+ * invocations into a helper function or guarding code.
+ *
+ * When no explicit threshold has been set, `LOG_DEBUG` is used by default,
+ * allowing log messages with all known priorities.
+ *
+ * The `ulog_threshold()` function is OpenWrt specific and may not be present on
+ * other systems. There is no syslog equivalent to this ulog specific threshold
+ * mechanism.
+ *
+ * The priority argument may be either a string value containing a priority name
+ * or one of the numeric `LOG_*` priority constants in the module namespace.
+ *
+ * Returns `true` if a threshold was set.
+ *
+ * Returns `false` if an invalid priority value was given.
+ *
+ * @function module:log#ulog_threshold
+ *
+ * @param {number|module:log.LogPriority} [priority]
+ * The priority threshold to configure.
+ *
+ * See {@link module:log.LogPriority|LogPriority} for recognized priority names.
+ *
+ * @returns {boolean}
+ *
+ * @example
+ * // Set threshold to "warning" or more severe
+ * ulog_threshold(LOG_WARNING);
+ *
+ * // This message will be supressed
+ * ulog(LOG_DEBUG, "Testing thresholds");
+ *
+ * // Using priority name
+ * ulog_threshold("debug");
+ */
+static uc_value_t *
+uc_ulog_threshold(uc_vm_t *vm, size_t nargs)
+{
+	int priority = parse_priority(uc_fn_arg(0));
+
+	if (priority == -1)
+		return ucv_boolean_new(false);
+
+	ulog_threshold(priority);
+
+	return ucv_boolean_new(true);
+}
+
+/**
+ * Invoke ulog with LOG_INFO.
+ *
+ * This function is convenience wrapper for `ulog(LOG_INFO, ...)`.
+ *
+ * See {@link module:log#ulog|ulog()} for details.
+ *
+ * @function module:log#INFO
+ *
+ * @param {*} format
+ * The sprintf-like format string for the log message, or any other, non-null,
+ * non-string value type which will be implicitly stringified and logged as-is.
+ *
+ * @param {...*} [args]
+ * In case a format string value was provided in the previous argument, then
+ * all subsequent arguments are used to replace the placeholders in the format
+ * string.
+ *
+ * @returns {boolean}
+ *
+ * @example
+ * INFO("This is an info log message");
+ */
+static uc_value_t *
+uc_ulog_INFO(uc_vm_t *vm, size_t nargs)
+{
+	return uc_ulog_log_common(vm, nargs, LOG_INFO);
+}
+
+/**
+ * Invoke ulog with LOG_NOTICE.
+ *
+ * This function is convenience wrapper for `ulog(LOG_NOTICE, ...)`.
+ *
+ * See {@link module:log#ulog|ulog()} for details.
+ *
+ * @function module:log#NOTE
+ *
+ * @param {*} format
+ * The sprintf-like format string for the log message, or any other, non-null,
+ * non-string value type which will be implicitly stringified and logged as-is.
+ *
+ * @param {...*} [args]
+ * In case a format string value was provided in the previous argument, then
+ * all subsequent arguments are used to replace the placeholders in the format
+ * string.
+ *
+ * @returns {boolean}
+ *
+ * @example
+ * NOTE("This is a notification log message");
+ */
+static uc_value_t *
+uc_ulog_NOTE(uc_vm_t *vm, size_t nargs)
+{
+	return uc_ulog_log_common(vm, nargs, LOG_NOTICE);
+}
+
+/**
+ * Invoke ulog with LOG_WARNING.
+ *
+ * This function is convenience wrapper for `ulog(LOG_WARNING, ...)`.
+ *
+ * See {@link module:log#ulog|ulog()} for details.
+ *
+ * @function module:log#WARN
+ *
+ * @param {*} format
+ * The sprintf-like format string for the log message, or any other, non-null,
+ * non-string value type which will be implicitly stringified and logged as-is.
+ *
+ * @param {...*} [args]
+ * In case a format string value was provided in the previous argument, then
+ * all subsequent arguments are used to replace the placeholders in the format
+ * string.
+ *
+ * @returns {boolean}
+ *
+ * @example
+ * WARN("This is a warning");
+ */
+static uc_value_t *
+uc_ulog_WARN(uc_vm_t *vm, size_t nargs)
+{
+	return uc_ulog_log_common(vm, nargs, LOG_WARNING);
+}
+
+/**
+ * Invoke ulog with LOG_ERR.
+ *
+ * This function is convenience wrapper for `ulog(LOG_ERR, ...)`.
+ *
+ * See {@link module:log#ulog|ulog()} for details.
+ *
+ * @function module:log#ERR
+ *
+ * @param {*} format
+ * The sprintf-like format string for the log message, or any other, non-null,
+ * non-string value type which will be implicitly stringified and logged as-is.
+ *
+ * @param {...*} [args]
+ * In case a format string value was provided in the previous argument, then
+ * all subsequent arguments are used to replace the placeholders in the format
+ * string.
+ *
+ * @returns {boolean}
+ *
+ * @example
+ * ERR("This is an error!");
+ */
+static uc_value_t *
+uc_ulog_ERR(uc_vm_t *vm, size_t nargs)
+{
+	return uc_ulog_log_common(vm, nargs, LOG_ERR);
+}
+#endif
+
+
+static const uc_function_list_t global_fns[] = {
+	{ "openlog",		uc_openlog },
+	{ "syslog",			uc_syslog },
+	{ "closelog",		uc_closelog },
+
+#ifdef HAVE_ULOG
+	{ "ulog_open",		uc_ulog_open },
+	{ "ulog",			uc_ulog_log },
+	{ "ulog_close",		uc_ulog_close },
+	{ "ulog_threshold",	uc_ulog_threshold },
+	{ "INFO",			uc_ulog_INFO },
+	{ "NOTE",			uc_ulog_NOTE },
+	{ "WARN",			uc_ulog_WARN },
+	{ "ERR",			uc_ulog_ERR },
+#endif
+};
+
+
+void uc_module_init(uc_vm_t *vm, uc_value_t *scope)
+{
+	uc_function_list_register(scope, global_fns);
+
+#define ADD_CONST(x) ucv_object_add(scope, #x, ucv_int64_new(x))
+
+	ADD_CONST(LOG_PID);
+	ADD_CONST(LOG_CONS);
+	ADD_CONST(LOG_NDELAY);
+	ADD_CONST(LOG_ODELAY);
+	ADD_CONST(LOG_NOWAIT);
+
+	ADD_CONST(LOG_AUTH);
+#ifdef LOG_AUTHPRIV
+	ADD_CONST(LOG_AUTHPRIV);
+#endif
+	ADD_CONST(LOG_CRON);
+	ADD_CONST(LOG_DAEMON);
+#ifdef LOG_FTP
+	ADD_CONST(LOG_FTP);
+#endif
+	ADD_CONST(LOG_KERN);
+	ADD_CONST(LOG_LPR);
+	ADD_CONST(LOG_MAIL);
+	ADD_CONST(LOG_NEWS);
+	ADD_CONST(LOG_SYSLOG);
+	ADD_CONST(LOG_USER);
+	ADD_CONST(LOG_UUCP);
+	ADD_CONST(LOG_LOCAL0);
+	ADD_CONST(LOG_LOCAL1);
+	ADD_CONST(LOG_LOCAL2);
+	ADD_CONST(LOG_LOCAL3);
+	ADD_CONST(LOG_LOCAL4);
+	ADD_CONST(LOG_LOCAL5);
+	ADD_CONST(LOG_LOCAL6);
+	ADD_CONST(LOG_LOCAL7);
+
+	ADD_CONST(LOG_EMERG);
+	ADD_CONST(LOG_ALERT);
+	ADD_CONST(LOG_CRIT);
+	ADD_CONST(LOG_ERR);
+	ADD_CONST(LOG_WARNING);
+	ADD_CONST(LOG_NOTICE);
+	ADD_CONST(LOG_INFO);
+	ADD_CONST(LOG_DEBUG);
+
+#ifdef HAVE_ULOG
+	ADD_CONST(ULOG_KMSG);
+	ADD_CONST(ULOG_SYSLOG);
+	ADD_CONST(ULOG_STDIO);
+#endif
+}