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authorgdamore <gdamore@users.noreply.github.com>2024-10-27 18:55:51 +0000
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+ <ol class="chapter"><li class="chapter-item expanded affix "><a href="../copyright.html">Copyright</a></li><li class="chapter-item expanded affix "><a href="../dedication.html">Dedication</a></li><li class="chapter-item expanded affix "><a href="../preface.html">Preface</a></li><li class="chapter-item expanded "><a href="../api/index.html"><strong aria-hidden="true">1.</strong> API Reference</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../api/msg.html"><strong aria-hidden="true">1.1.</strong> Messages</a></li><li class="chapter-item expanded "><a href="../api/memory.html"><strong aria-hidden="true">1.2.</strong> Memory</a></li><li class="chapter-item expanded "><a href="../api/time.html"><strong aria-hidden="true">1.3.</strong> Time</a></li><li class="chapter-item expanded "><a href="../api/url.html"><strong aria-hidden="true">1.4.</strong> URLs</a></li><li class="chapter-item expanded "><a href="../api/aio.html"><strong aria-hidden="true">1.5.</strong> Asynchronous I/O</a></li><li class="chapter-item expanded "><a href="../api/synch.html"><strong aria-hidden="true">1.6.</strong> Synchronization</a></li><li class="chapter-item expanded "><a href="../api/thread.html"><strong aria-hidden="true">1.7.</strong> Threads</a></li><li class="chapter-item expanded "><a href="../api/logging.html" class="active"><strong aria-hidden="true">1.8.</strong> Logging</a></li><li class="chapter-item expanded "><a href="../api/stats.html"><strong aria-hidden="true">1.9.</strong> Statistics</a></li><li class="chapter-item expanded "><a href="../api/errors.html"><strong aria-hidden="true">1.10.</strong> Errors</a></li><li class="chapter-item expanded "><a href="../api/misc.html"><strong aria-hidden="true">1.11.</strong> Miscellaneous</a></li><li class="chapter-item expanded "><a href="../api/id_map.html"><strong aria-hidden="true">1.12.</strong> ID Map</a></li><li class="chapter-item expanded "><a href="../api/cmd_opts.html"><strong aria-hidden="true">1.13.</strong> Command Options</a></li></ol></li><li class="chapter-item expanded "><a href="../proto/index.html"><strong aria-hidden="true">2.</strong> Protocols</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../proto/bus.html"><strong aria-hidden="true">2.1.</strong> BUS Protocol</a></li><li class="chapter-item expanded "><a href="../proto/pair.html"><strong aria-hidden="true">2.2.</strong> PAIR Protocol</a></li><li class="chapter-item expanded "><a href="../proto/pub.html"><strong aria-hidden="true">2.3.</strong> PUB Protocol</a></li><li class="chapter-item expanded "><a href="../proto/pull.html"><strong aria-hidden="true">2.4.</strong> PULL Protocol</a></li><li class="chapter-item expanded "><a href="../proto/push.html"><strong aria-hidden="true">2.5.</strong> PUSH Protocol</a></li><li class="chapter-item expanded "><a href="../proto/rep.html"><strong aria-hidden="true">2.6.</strong> REP Protocol</a></li><li class="chapter-item expanded "><a href="../proto/req.html"><strong aria-hidden="true">2.7.</strong> REQ Protocol</a></li><li class="chapter-item expanded "><a href="../proto/respondent.html"><strong aria-hidden="true">2.8.</strong> RESPONDENT Protocol</a></li><li class="chapter-item expanded "><a href="../proto/sub.html"><strong aria-hidden="true">2.9.</strong> SUB Protocol</a></li><li class="chapter-item expanded "><a href="../proto/surveyor.html"><strong aria-hidden="true">2.10.</strong> SURVEYOR Protocol</a></li></ol></li><li class="chapter-item expanded "><a href="../tran/index.html"><strong aria-hidden="true">3.</strong> Transports</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../tran/inproc.html"><strong aria-hidden="true">3.1.</strong> Intra-Process Transport</a></li><li class="chapter-item expanded "><a href="../tran/ipc.html"><strong aria-hidden="true">3.2.</strong> Inter-Process Transport</a></li><li class="chapter-item expanded "><a href="../tran/socket.html"><strong aria-hidden="true">3.3.</strong> BSD Socket (Experimental)</a></li><li class="chapter-item expanded "><a href="../tran/udp.html"><strong aria-hidden="true">3.4.</strong> UDP Transport (Experimental)</a></li></ol></li><li class="chapter-item expanded "><a href="../migrate/index.html"><strong aria-hidden="true">4.</strong> Migration Guides</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../migrate/nng1.html"><strong aria-hidden="true">4.1.</strong> Migrating from NNG 1.x</a></li><li class="chapter-item expanded "><a href="../migrate/nanomsg.html"><strong aria-hidden="true">4.2.</strong> Migrating from libnanomsg</a></li></ol></li><li class="chapter-item expanded "><a href="../indexing.html">Index</a></li></ol>
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+
+</style>
+<h1 id="logging"><a class="header" href="#logging">Logging</a></h1>
+<p>This chapter describes the support for message logs.
+Both applications and <em>NNG</em> itself can emit logs, which can be useful
+for application field support and debugging. Additionally applications
+can customize the handling of this logging as needed.</p>
+<p>Note that logging is disabled by default unless an application
+configures a suitable logger with <a href="#log-handlers"><code>nng_log_set_logger</code></a>.</p>
+<h2 id="submitting-logs"><a class="header" href="#submitting-logs">Submitting Logs</a></h2>
+<pre><code class="language-c">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, ...);
+</code></pre>
+<p>These <a name="a001"></a> functions inject a a message into the
+logging system, where it will be processed and potentially go to
+system logs, standard output, or procssed further.</p>
+<p>The <em>msgid</em> is a short prefix that should uniquely identify the message,
+possibly also with some kind of category. It is recommended that
+strings between 8 and 16 charactes be used. As this may, but will not necessarily
+be displayed to the user, the content of the message should not appear
+solely in this field. A <code>NULL</code> value is permitted here, but that may
+make filtering the message or other automatic processing more difficult.</p>
+<p>The <em>msg</em> is a <code>printf</code>-style format string, which is used to format the
+message content. The following arguments are consumed in the
+same manner as <code>printf</code>.</p>
+<div class="mdbook-alerts mdbook-alerts-tip">
+<p class="mdbook-alerts-title">
+ <span class="mdbook-alerts-icon"></span>
+ tip
+</p>
+<p>Applications should take care to limit the use of higher severity levels, as message logs
+are potentially expensive, increase stress for end users and administrators, and further may
+mask real problems if incorrectly over used.</p>
+<p>Warnings and error messages should be concise and actionable, and notices should only
+really be those things that are worthy of attention.</p>
+<p>Informational and debug messages used during development should be removed when no longer
+needed, as these messages can overwhelm logging subsystems and can reduce the
+signal-to-noise value for the message logs, impairing the diagnostic value of the logs.</p>
+</div>
+<h2 id="auth-logs"><a class="header" href="#auth-logs">Auth Logs</a></h2>
+<pre><code class="language-c">void nng_log_auth(nng_log_level level, const char *msgid, const char *msg, ...);
+</code></pre>
+<p>The <a name="a002"></a><code>nng_log_auth</code> function formats and injects a security related log message.
+(“Auth” can indicate either “authentication” or “authorization”.)
+The <em>level</em> is a <a href="#log-levels">log level</a>.
+The <em>msgid</em>, <em>msg</em>, and any remaining arguments are processed in a fashion
+similar to the other <a href="#submitting-logs">logging functions</a>, except that the
+logs may be are logged using the <code>NNG_LOG_AUTH</code> <a href="#log-facilities">facility</a>, and thus may be
+redirected or receive other special treatment.</p>
+<h2 id="log-levels"><a class="header" href="#log-levels">Log Levels</a></h2>
+<pre><code class="language-c">typedef enum nng_log_level nng_log_level;
+
+void nng_log_set_level(nng_log_level level);
+nng_log_level nng_log_get_level(void);
+</code></pre>
+<p>The <a name="a003"></a><code>nng_log_level</code> type represents a severity for logged messages.
+These levels correspond to those found in the UNIX syslog subsystem,
+although applications should not depend upon the values being identical.</p>
+<p>The <a name="a004"></a><code>nng_log_set_level</code> function sets the log level.
+Messages with a severity that is numerically greater than this (less-severe)
+will be discarded.</p>
+<p>The <a name="a005"></a><code>nng_log_get_level</code> function returns the log level most recently
+set by <code>nng_log_set_level</code> or the default
+if that function has not been called.</p>
+<p>The log levels are defined as follows:</p>
+<pre><code class="language-c">typedef enum nng_log_level {
+ NNG_LOG_NONE = 0, // used for filters only, NNG suppresses these
+ NNG_LOG_ERR = 3,
+ NNG_LOG_WARN = 4,
+ NNG_LOG_NOTICE = 5,
+ NNG_LOG_INFO = 6,
+ NNG_LOG_DEBUG = 7
+} nng_log_level;
+</code></pre>
+<p>The value <code>NNG_LOG_NONE</code> may be useful to suppress message logs altogether.</p>
+<p>The default level is typically <code>NNG_LOG_NOTICE</code>, but applications should
+select a value rather than relying upon the default.</p>
+<h2 id="log-facilities"><a class="header" href="#log-facilities">Log Facilities</a></h2>
+<pre><code class="language-c">typedef enum nng_log_facility
+
+void nng_log_set_facility(nng_log_facility facility);
+</code></pre>
+<p>Logging facilities are used to indicate the source of a log message,
+and may be useful in routing and processing these logs.
+Traditionally these are used with the UNIX <code>syslog</code> system, and
+the values here represent some (but not all) of the values found there.</p>
+<p>The following values are defined:</p>
+<pre><code class="language-c">typedef enum nng_log_facility {
+ NNG_LOG_USER = 1,
+ NNG_LOG_DAEMON = 3,
+ NNG_LOG_AUTH = 10,
+ NNG_LOG_LOCAL0 = 16,
+ NNG_LOG_LOCAL1 = 17,
+ NNG_LOG_LOCAL2 = 18,
+ NNG_LOG_LOCAL3 = 19,
+ NNG_LOG_LOCAL4 = 20,
+ NNG_LOG_LOCAL5 = 21,
+ NNG_LOG_LOCAL6 = 22,
+ NNG_LOG_LOCAL7 = 23,
+} nng_log_facility;
+</code></pre>
+<p>The <a name="a006"></a><code>nng_log_set_facility</code> function can be used to
+set the facility that the application will use when emitting log
+messages. This should be called as part of initialization of the
+application, if logging is to be used.</p>
+<p>The default facility is typically <code>NNG_LOG_USER</code>, but applications should
+select a value rather than relying upon the default.</p>
+<h2 id="log-handlers"><a class="header" href="#log-handlers">Log Handlers</a></h2>
+<pre><code class="language-c">typedef void (*nng_logger)(nng_log_level level, nng_log_facility facility,
+ const char *msgid, const char *msg);
+
+void nng_null_logger(nng_log_level, nng_log_facility, const char *, const char *);
+void nng_stderr_logger(nng_log_level, nng_log_facility, const char *, const char *);
+void nng_system_logger(nng_log_level, nng_log_facility, const char *, const char *);
+
+void nng_log_set_logger(nng_logger logger);
+</code></pre>
+<p><a name="a007"></a>Log handlers are responsible for actually processing the logged messages.</p>
+<p>The <a name="a008"></a><code>nng_log_set_logger</code> function installs the named <em>logger</em>, of type <a name="a009"></a><code>nng_logger</code>,
+as the log handler. The function <em>logger</em> will be called when any message is meant to
+be processed. (Messages are first filtered by <a href="#log-levels">severity</a>, then formatted,
+before calling the logger.)</p>
+<p>Any previously installed logger is replaced by <em>logger</em>.</p>
+<p>The <a name="a010"></a><code>nng_null_logger</code> function is an implementation of <code>nng_logger</code> that simply discards the content.
+This is the default logger, so logging is disabled by default.</p>
+<p>The <a name="a011"></a><code>nng_stderr_logger</code> function is an implementation that logs messages to the standard error stream.
+It will attempt to colorize messages by the severity, if the standard error is a terminal device.
+This can be suppressed by setting either the <code>NO_COLOR</code> or <code>NNG_LOG_NO_COLOR</code> environment variables.</p>
+<p>The <a name="a012"></a><code>nng_system_logger</code> attempts to use an appropriate system facility to log messages.
+For POSIX systems, this means using <code>syslog</code> to process the messages.
+For other systems the defauilt behavior may be the same as <code>nng_stderr_logger</code>.</p>
+<h2 id="see-also"><a class="header" href="#see-also">See Also</a></h2>
+<p>The Syslog Protocol upon which this is based is documented in the following two IETF
+RFCS,</p>
+<ul>
+<li>R. Gerhards, <a href="https://datatracker.ietf.org/doc/html/rfc5424">RFC 5424</a>, <em>The Syslog Protocol</em>,
+March 2009</li>
+<li>C. Lonvick, <a href="https://datatracker.ietf.org/doc/html/rfc3164">RFC 3164</a>, <em>The BSD syslog Protocol</em>,
+August 2001</li>
+</ul>
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