Subscribe and Feed Update procedure

[holgerkrupp]

A basic podcast client needs to subscribe to feeds (xml files), read the updates performed in these feeds and react if there are changes. This discussion is to share the strategy I'm planning to implement. Feel free to comment or add your thoughts.

Subscribing to a new feed

• User adds a new URL for a Feed (either manually, selected from a search or by importing OPML file)
• The Downloadmanager checks if the URL is valid and responding with HTTPcode 200 and the content-type is matching to rss/xml feeds
• • if the file behind the URL is a valid feed, it's downloaded and parsed by the XMLParser
• • if the file is invalid, a Error message is shown to the user why the feed will not be added (file not existing or not a podcast feed or already in the database)
• • • FUTURE Improvement: If the content type is HTML the HTML head could be checked if there is a valid podcast feed inside
• The XMLParser checks the feed. Extracts the Head/Podcast information as well as the information for each tag containing episodes as a swift dictionary
• The XMLPatser delegate takes the extracted dictionary and creates a new Podcast in the database.

Updating a feed

In Foreground:

• The user refreshes the Podcast (manually by pulling down or by pressing a button)

In Background

• The App is starting a background refresh timer (current: minimum waiting time 1hour).
• • The BackgroundtaskManager is sorting the podcast by last update attempt.
• • The oldest Podcasts are checked first. The date of this update attempt is saved (for next time).
• • FUTURE ADDION: Previous Episode could be checked for update frequency. This analyzes could be used to make a smarter priorization of the update queue.

General Update procedure

• The App checks the HTTP Header if the feed has had an update since last processing
• The Downloadmanager downloads the feed and shows the progress in the user interface.
• The Downloadmanager parses the feed data.
• If there are new episodes in the feed, these episodes are added to the Podcast database
• If an episode is existing, but contains changes, these changes are applied to the existing database entry.
• • To determine if the episode is the same, the episode number, season are taking into account.
• • Fields that can change: Title, Description, link,...
• The downloadmanager checks the Settings what should happen next. (There will be default settings, and the possibility to override settings per podcast.)
• • Settings can indicate if
• • • the file should be downloaded directly
• • • the the episode should be added to the "play next" queue. The episode can be added at the top or the bottom of the queue. (May be podcasts can be priorized on a scale of 1-10 to make this more granual)
• • The file itself is checked for chapters (or podcast simple chapters if existing). If the settings indicate "skip words", chapters containing these words will be marked to be skipped during playback.
• If a new episode has been added, a local notification is created. If the app is in foreground, the notification is ignored. otherwise it's shown on the lock screen (respecting the users notification settings)

Showing new episodes

• There shall be different ways of showing new episodes:
• • on the detail page of a podcast
• • in the play next page (if added automatically)
• • in the list of unplayed and not in play next list episode
• • in a list of all episodes
• • FURURE ADDION could be automatic playlists/filters that are generated on the fly