XML output formatter

Rather than re-invent the wheel, the java.util.logging.XMLFormatter format was used. It has an official DTD. See Appendix A of Oracle’s [java-logging-overview] (https://docs.oracle.com/javase/10/core/java-logging-overview.htm).

Or, here

The millis element is the number of milliseconds since the epoch. The nanos element is number of nanoseconds to add to that.

So, to create them from a timespec:

	struct timespec *ts;
	long int time_millis;
	long int time_nanos;

	time_millis = ts->tv_sec * 1000 + ts->tv_nsec / 1000000;
	time_nanos = ts->tv_nsec % 1000000;

To create the values for the millis and nanos element

Tinylogger to XMLFormatter xml element mapping

The date element is in the same ISO 8601 format, except the millisecond fraction is added

  <date>2020-06-14T10:48:35.634</date>

The millis element is the same.

  <millis>1592146115634</millis>

The nanos element (added in JDK 9) is the same.

  <nanos>587985</nanos>

The sequence element is the same.

  <sequence>0</sequence>

The logger element, which is normally the name of the logger class, is filled with tinylogger.

  <logger>tinylogger</logger>

The level element is filled with the standard Java labels when a log level from Java is used. When there is no corresponding Java pre-defined level, an integer representing its interpolated level is used.

  <level>INFO</level>

The class element is filled with the source code file name instead of the class;

  <class>formats.c</class>

The method element is filled with the function name.

  <method>main</method>

The thread element is filled with the thread id returned by gettid(). This is different than the pthread_t thread id.

  <thread>407953</thread>

And finally, the message element is filled with the actual message.

  <message>this message uses the &quot;&lg;xml&gt;&quot; format &amp; it&apos;s easy!</message>

Special Character “escaping”

The following characters are replace with the corresponding xml entities:

character | entity | description ———-|———-|———— ‘<’ | “<” | less than ‘>’ | “>” | greater than ‘&’ | “&” | ampersand ‘'’ | “'” | apostrophe ‘"’ | “"” | quote (using c style notation for “char” and “string” - probably not appropriate)

example

The following program:

#include "tinylogger.h"

#define LOG_FILE "tinylogger.xml"
#define N_MSGS 3

int main(void) {
	/*
	 * Print a series of xml formatted messages
	 * Use the xml formatter
	 * Use line buffered output
	 */
	LOG_CHANNEL *ch1 = log_open_channel_f(LOG_FILE, LL_INFO, log_fmt_xml, true);
	(void) ch1;	// quiet the "unused variable" warning

	for (int n = 0; n < N_MSGS; n++) {
		log_info("this message uses the \"<xml>\" format it's #%d", n);
	}

	log_done();

	return 0;
}

produces:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE log SYSTEM "logger.dtd">
<log>
<record>
  <date>2020-06-15T12:59:55.288</date>
  <millis>1592240395288</millis>
  <nanos>895371</nanos>
  <sequence>0</sequence>
  <logger>tinylogger</logger>
  <level>INFO</level>
  <class>xml.c</class>
  <method>main</method>
  <thread>488739</thread>
  <message>this message uses the &quot;&lt;xml&gt;&quot; format it&apos;s #0</message>
</record>
<record>
  <date>2020-06-15T12:59:55.289</date>
  <millis>1592240395289</millis>
  <nanos>103486</nanos>
  <sequence>1</sequence>
  <logger>tinylogger</logger>
  <level>INFO</level>
  <class>xml.c</class>
  <method>main</method>
  <thread>488739</thread>
  <message>this message uses the &quot;&lt;xml&gt;&quot; format it&apos;s #1</message>
</record>
<record>
  <date>2020-06-15T12:59:55.289</date>
  <millis>1592240395289</millis>
  <nanos>143152</nanos>
  <sequence>2</sequence>
  <logger>tinylogger</logger>
  <level>INFO</level>
  <class>xml.c</class>
  <method>main</method>
  <thread>488739</thread>
  <message>this message uses the &quot;&lt;xml&gt;&quot; format it&apos;s #2</message>
</record>
</log>

When read by a java program that reads files produced with the java.util.logging.XMLForatter formatter:

Jun 15, 2020 12:59:55 PM xml.c main
INFO: this message uses the "<xml>" format it's #0
Jun 15, 2020 12:59:55 PM xml.c main
INFO: this message uses the "<xml>" format it's #1
Jun 15, 2020 12:59:55 PM xml.c main
INFO: this message uses the "<xml>" format it's #2