Free SMS service notifications using Google Calendar

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
*
*/

// 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 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(); } }

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

java GCalNotifier ${USERNAME} ${PW} ${CAL} ${TZOFFSET} ${STARTOFFSET} ${ENDOFFSET} "${TITLE}" "${BODY}"