= nng_log(3)
//
// Copyright 2024 Staysail Systems, Inc. <info@staysail.tech>
//
// This document is supplied under the terms of the MIT License, a
// copy of which should be located in the distribution where this
// file was obtained (LICENSE.txt).  A copy of the license may also be
// found online at https://opensource.org/licenses/MIT.
//

== NAME

nng_log - log messages

== SYNOPSIS

[source, c]
----
#include <nng/nng.h>

void nng_log_err(const char *msgid, const char *msg, ...);
void nng_log_warn(const char *msgid, const char *msg, ...);
void nng_log_notice(const char *msgid, const char *msg, ...);
void nng_log_info(const char *msgid, const char *msg, ...);
void nng_log_debug(const char *msgid, const char *msg, ...);

void nng_log_auth(nng_log_level level, const char *msgid, const char *msg, ...);
----

== DESCRIPTION

These functions are used to post a message to system or application logs.

The first five forms all post a message at the severity indicated by the function name.
The _msgid_ should be a short message identifier that should indicate the message in question.
A `NULL` value for _msgid_ canbe used as well.

Message identifiers can be used to assist in filtering logs.
These should uniquely identify the nature of the problem, whe possible, to assist in trouble-shooting.
They should also be short.
Eight characters or less is ideal, and more than sixteen is strongly discouraged.

The message is formatting as if by `sprintf`, using `msg` as the format, and remaining arguments as arguments to the format.

The final function, `nng_log_auth`, is used for posting authentication related messages which might be treated specially, such as be storing them in a separate secured log file.
It takes the severity as a level in _level_.
The severity can be one of the following values:

* `NNG_LOG_ERR`
* `NNG_LOG_WARN`
* `NNG_LOG_NOTICE`
* `NNG_LOG_INFO`
* `NNG_LOG_DEBUG`

The message itself is handled according to the logging facility set up with xref:nng_mg_set_logger.3.adoc[`nng_log_set_logger`].
Message delivery is best effort, and messages may be suppressed based on the priority set with xref:nng_log_set_level.3.adoc[`nng_log_set_level`].

Note that in order to get log messages, a suitable logger must be set using `nng_log_set_logger`.
The default logger, `nng_null_logger` simply discards logged content.

== SEE ALSO

xref:nng_log_set_facility.3.adoc[nng_log_set_facility(3)],
xref:nng_log_set_level.3.adoc[nng_log_set_level(3)],
xref:nng_log_set_logger.3.adoc[nng_log_set_logger(3)]