Today I had a small revelation.

I was wracking my brains trying to figure out the SMS messaging provider to use to send myself service outage notifications for my clients’ web sites. Given that I have just a handful of clients so far, it makes no sense to use a provider that requires a minimum monthly or yearly spend.

Ideally of course, I’d like to spend nothing at all, and in exasperation I finally threw my hands in the air (they’re detachable) and whined: “Google sends SMS’s for free - why is it so hard for everyone else?”

(answer: not everyone has billions of dollars)

And then came the revelation: Why not create a command-line tool that uses Google’s Calendar API to create events 6 minutes in the future that have an SMS notification set for 5 minutes prior to launch? That way, within a minute you get a notification sent to your phone for free within 1 minute. Sweet!

So, here’s the code (it’s in Java… sorry) /** * Simple command-line notification command that uses Google Calendar ATOM API to create * a single event 6 minutes in the future with a 5 minute SMS reminder * * @author Daniel Walmsley * */

import java.io.IOException; import java.net.MalformedURLException; import java.net.URL; import java.util.Date; import java.util.List;

import com.google.gdata.client.calendar.CalendarService; import com.google.gdata.data.DateTime; import com.google.gdata.data.PlainTextConstruct; import com.google.gdata.data.calendar.CalendarEntry; import com.google.gdata.data.calendar.CalendarEventEntry; import com.google.gdata.data.calendar.CalendarFeed; import com.google.gdata.data.extensions.Reminder; import com.google.gdata.data.extensions.When; import com.google.gdata.data.extensions.Reminder.Method; import com.google.gdata.util.AuthenticationException; import com.google.gdata.util.ServiceException;

/** * This is a test template */

public class GCalNotifier {

public static void main(String[] args) {

	/**
	 * Command line args:
	 *
	 * username
	 * password
	 * calendar name (e.g. "Notifications")
	 * TimeZone offset (in hours)
	 * event start offset (in minutes)
	 * event end offset (in minutes)
	 * title
	 * description
	 */

	try {

		// Create a new Calendar service
		CalendarService myService = new CalendarService("GCal Event Notifier");
		myService.setUserCredentials(args[0], args[1]);

		String calendarName = args[2];
		Long tzOffset = new Double(Double.parseDouble(args[3])).longValue() * 60 * 60 * 1000;
		Long startOffset = new Integer(Integer.parseInt(args[4])).longValue() * 60 * 1000;
		Long endOffset = new Integer(Integer.parseInt(args[5])).longValue() * 60 * 1000;
		String title = args[6];
		String description = args[7];

		// Get a list of all entries
		URL metafeedUrl = new URL(
				"http://www.google.com/calendar/feeds/default/allcalendars/full");
		System.out.println("Getting Calendar entries...\n");
		CalendarFeed resultFeed = myService.getFeed(metafeedUrl,
				CalendarFeed.class);
		List<CalendarEntry> entries = resultFeed.getEntries();
		for (int i = 0; i < entries.size(); i++) {
			CalendarEntry entry = entries.get(i);
			String currCalendarName = entry.getTitle().getPlainText();
			System.out.println("\t" + currCalendarName);

			if (currCalendarName.equals(calendarName)) {
				sendDowntimeAlert(myService, entry,
						title, description, startOffset, endOffset, tzOffset);
			}
		}
		System.out.println("\nTotal Entries: " + entries.size());

	} catch (AuthenticationException e) {
		e.printStackTrace();
	} catch (MalformedURLException e) {
		e.printStackTrace();
	} catch (ServiceException e) {
		e.printStackTrace();
	} catch (IOException e) {
		e.printStackTrace();
	}
}

private static void sendDowntimeAlert(CalendarService myService,
		CalendarEntry entry, String title, String description, Long startOffset, Long endOffset, Long tzOffset) throws IOException,
		ServiceException {

	String postUrlString = entry.getLink("alternate", "application/atom+xml").getHref();

	URL postUrl = new URL(postUrlString);//was: "http://www.google.com/calendar/feeds/jo@gmail.com/private/full"

	CalendarEventEntry myEntry = new CalendarEventEntry();

	myEntry.setTitle(new PlainTextConstruct(title));
	myEntry.setContent(new PlainTextConstruct(description));

	Date now = new Date();

	Date startDate = new Date(now.getTime()+startOffset);
	Date endDate = new Date(now.getTime()+endOffset);

	DateTime startTime = new DateTime(startDate.getTime()+tzOffset);

	DateTime endTime = new DateTime(endDate.getTime()+tzOffset);

	When eventTimes = new When();
	eventTimes.setStartTime(startTime);
	eventTimes.setEndTime(endTime);
	myEntry.addTime(eventTimes);

	// Send the request and receive the response:
	CalendarEventEntry insertedEntry = myService.insert(postUrl, myEntry);
	System.err.println("Got response for: "+insertedEntry.getTitle().getPlainText());
	for(When when : insertedEntry.getTimes()) {
		System.err.println("When: "+when.getStartTime()+" to "+when.getEndTime());
	}

	//5 minute reminder
	Reminder reminder = new Reminder();
	reminder.setMinutes(5);
	reminder.setMethod(Method.SMS);
	insertedEntry.getReminder().add(reminder);
	insertedEntry.update();
} }</code>

Don’t forget, you’ll need to download the Google Data APIs and put their JARs in your classpath before this will work!

Personally I use this with Nagios. I always use the same args for the calendar offsets, so I’ve encapsulated most of my settings (except title and body) in a script. #!/bin/sh

export SCRIPTDIR=/opt/calAlert export USERNAME=username@gmail.com export PW=mySecurePassword export CAL=Notifications export TZOFFSET=10 export STARTOFFSET=7 export ENDOFFSET=12 export TITLE=$1 export BODY=$2

export CURRDIR=pwd

export CLASSPATH=”${SCRIPTDIR}/calAlert.jar” #assumes GData libs are in “libs” subdirectory of SCRIPTDIR

for jarfile in $(ls “${SCRIPTDIR}/lib”) do CLASSPATH=”${CLASSPATH}:${SCRIPTDIR}/lib/${jarfile}” echo lib/${jarfile} done

echo “CLASSPATH=${CLASSPATH}”

export CLASSPATH

java GCalNotifier ${USERNAME} ${PW} ${CAL} ${TZOFFSET} ${STARTOFFSET} ${ENDOFFSET} “${TITLE}” “${BODY}” </code>