Feature: Status “badges” for Web pages

Completed implementation of ``Web badges'', which allow users to display their most recent weight log entry and the energy balance and rate of gain/loss for a specified trend interval. A new badge configuration page, accessible from the main utility menu, allows enabling the badge and selecting the trend interval, which is kept in a new \verb+badge_trend+ field in the {\tt user} object. When this field is nonzero, any operation which modifies a log entry calls {\tt history::drawBadgeImage} to update the {\tt BadgeImage.png} file in the user's directory. (This file is swapped into place with a {\tt mv} command to avoid race conditions if it is being retrieved at the time an update is in progress.)

The badge configuration page takes the user to a confirmation page which, if badge generation is enabled, shows XHTML code the user can copy and paste into a Web page to display the badge. This code invokes a new stand-alone lightweight CGI program named {\tt HackDietBadge}, which is called with an opaque argument which is the user file name of the owner of the badge salted and encrypted with the application's master key using AES in CBC mode. The {\tt HackDietBadge} program is separate so as to avoid having to load the full application and all of the modules it requires just to display a badge image on a Web page which may be hit far more frequently than full-fledged application transactions. The {\tt HackDietBadge} program decrypts and validates the argument and, if all is well, copies the badge image for the specified user to standard output hacing specified a {\tt Content-type} of {\tt image/png}. If the argument is in error, or the specified user has disabled badge generation, a canned ``Invalid request'' image is returned instead.