Logging Mechanism

the n3rv framework comes with embedded logging features, which can be quite useful to follow the behaviour of your different nodes. All the logging is handled through the n3rv::logger class. Each service instance or service controller has its own internal n3rv::logger object, which member is n3rv::service::ll

service::ll member

service::ll is a public member, so you can acces it outside of your service class to make settings to your internal service logger:

/* We instanciate a new node */
n3rv::service s1("127.0.0.1",10001);

/* We set the loglevel for our node logger to WARNING */
s1.ll->set_loglevel(n3rv::LOGLV_WARN);

Log() function

Whenever you want to log something, you will have to use the method n3rv::logger::log():

/** Adds str to log buffer and flushes it. */
void logger::log(int log_level, std::string str);

if log_level is lesser than or equal to the calling logger’s log level, the log is made and str is written in destinations, else we discard it.

n3rv::logger* ll = new n3rv::logger(n3rv::LOGLV_CRIT);

/* this log line will not be used since LOGLV_WARN > LOGLV_CRIT */
ll->log(n3rv::LOGLV_WARN,"blabla");

/* On the other hand this one will go to destinations. */
ll->log(n3rv::LOGLV_PANIC,"HAAAAAAAA");

Log Levels

In n3rv the log levels are basically the same as Syslog:

Available log levels
Level Name n3rv Name
0 PANIC LOGLV_PANIC
1 ALERT LOGLV_ALERT
2 CRITICAL LOGLV_CRIT
3 ERROR LOGLV_ERR
4 WARNING LOGLV_WARN
5 NOTICE LOGLV_NOTICE
6 INFO LOGLV_INFO
7 DEBUG LOGLV_DEBUG

Note that when you instanciate a new n3rv::logger object, you must specify as argument the
maximum log level you want your logger to output.

Logging Destinations

In order to add a destination for a logger object, one must use the logger::add_dest() method. the logger class supports 3 different types outputs for logging (which can be combined without any issue)

stdout

Explicitely enough, setting this destination will display the logs on the standard output.

n3rv::logger* ll = new n3rv::logger(LOGLV_DEBUG);
/* tells logger to display its logs on stdout */
ll->add_dest("stdout");

file://<path>

Also quite straightforward, this tells the logger to append its logs in a file.

/* tells logger to append its logs in /opt/logs/n3rv.log */
ll->add_dest("file:///opt/logs/n3rv.log");

syslog:<ident>:<facility>

Probably the most interesting feature of the logger, you can use syslog to log your nodes activity and thus centralize all your logs on a single remote-syslogd (got logstash ? ;-))

/* tells logger to use syslog for logging, with ident "n3rv" and facility "user" */
ll->add_dest("syslog:n3rv:user");

Note: Supported syslog facilities are local0..7, and user.

Sharing a single logger across multiple nodes / service controller

As we saw earlier, when instanciated n3rv::service and n3rv::servicecontroller automatically create an internal logger which is accessible through their ll member. But they can also take an existing logger object in their constructor and use it instead of the default one.

/* We create and setup a new logger */
n3rv::logger* log = new n3rv::logger(n3rv::LOGLV_DEBUG);
log->add_dest("stdout");
log->add_dest("syslog:n3rv:user");

/* We pass this logger as argument for nodes & sc to use it. */

n3rv::service s1("127.0.0.1",10001,log);
n3rv::service s2("127.0.0.1",10001,log);
n3rv::servicecontroller sc("0.0.0.0",10001,log);