Convenient Web Requests

The second part of the alarm pipeline is shown in Listing  2; the REST request sent to the Pushover API server requires two tokens (lines 12 and 13), which users receive when registering with the Pushover service. The trial period lasts for four weeks and allows free access; if you like what you see, you can then buy a license for $5, which covers a single platform: iOS, Android, or the desktop client.

Registered users will find the token assigned to the user key in the Pushover dashboard overview in Figure 4. The token labeled token, on the other hand, identifies the app (Figure 5) to the Pushover service; in this case, it is the Python script in Listing 2, which I registered with Pushover under the name Snapshot.

Figure 4: Registered users can see their user tokens in the dashboard.

Figure 5: Newly registered user apps receive a token.

For a successful REST request with Python's requests library, you also need the message parameter with the message text for the post() method in line 9 to contact Pushover. In typical Python style, the library throws exceptions that abort the program in case of errors if they're not processed and outputs a stack trace that will hopefully help you solve the problem.

The Python requests library keeps its promise of being a self-proclaimed "HTTP for Humans." At least it is more carefully thought out than urllib and urllib2, which you might remember I have complained about before.

Line 6 in Listing 2 retrieves the text sent from the first part of the pipeline from standard input and truncates it with the usual syntax for array slices in Python – [:1024] – to the maximum length of 1,024 characters allowed by Pushover. The if construct in lines 8-15 then uses the regular expression \S to check whether the message contains printable characters and terminates empty runs without further ado.

Friend Cron

All you have to do now is set up a cron job that calls the pipeline about every five minutes and finds the user's home directory and the writable data directory therein for storing the flag file:

*/5 * * * * /path/authwatch | /path/pushover

The Pushover service distributes any messages sent to all devices registered by the user, so it may happen that a failed login attempt triggers a whole explosion of notifications if several mobile devices in the room are actively connected. At least this only counts as one message, though, in the usage constraints, of which users are allowed 7,500 per month on the all-inclusive tier.

Mike Schilli

Mike Schilli works as a software engineer in the San Francisco Bay area of California. In his column, launched back in 1997, he focuses on short projects in Perl and various other languages. You can contact Mike at mailto:mschilli@perlmeister.com.