Subscriptions and feeds

Two features sit slightly outside the per-content extractors: importing a user's subscriptions, and a fast channel feed.

Subscriptions

SubscriptionExtractor imports a user's followed channels into a list of SubscriptionItem (serviceId, url, name). It declares where it can import from:

enum ContentSource { CHANNEL_URL, INPUT_STREAM }

and exposes entry points that throw UnsupportedOperationException unless overridden:

abstract String getRelatedUrl();    // where the user finds their export / following list
List<SubscriptionItem> fromChannelUrl(String channelUrl);
List<SubscriptionItem> fromInputStream(InputStream in);
List<SubscriptionItem> fromInputStream(InputStream in, String contentType);

Two services implement it, from different sources:

• YouTube (YoutubeSubscriptionExtractor): INPUT_STREAM. It parses a Google Takeout export, JSON, CSV, or a ZIP containing either.
• SoundCloud (SoundcloudSubscriptionExtractor): CHANNEL_URL. It reads the followings off a user's profile URL.

The app chooses the flow from the declared ContentSource: a file picker for INPUT_STREAM, a URL field for CHANNEL_URL.

Feeds: the channel fast-path

Loading a full channel is heavy: avatar, banner, tabs, counts, first page. For just "what's new", some services expose a lighter feed. FeedExtractor is a ListExtractor<StreamInfoItem> with no extra required methods; FeedInfo.getInfo(service, url) drives it and throws if the service has none.

StreamingService.getFeedExtractor(url) returns null by default. YouTube overrides it (YoutubeFeedExtractor) to read the channel RSS feed, far cheaper than a full channel extraction, which is what the app uses to refresh the subscription feed.

@Override
public FeedExtractor getFeedExtractor(String channelUrl) throws ExtractionException {
    return new YoutubeFeedExtractor(this, getChannelLHFactory().fromUrl(channelUrl));
}

BiliBili's "recommended" lists look similar but are wired as kiosks, not a FeedExtractor. So when you build the app's feed, prefer getFeedExtractor where it exists and fall back to the channel extractor otherwise.