NetNewsWire/Safari Extension/netnewswire-subscribe-to-feed.js

var thisPageLinkObjects = null;

// I convert the native "link" node into an object that I can pass out to the global page
function objectFromLink(theLink) {
	var linkObject = new Object();

	linkObject.href = theLink.href;
	linkObject.type = theLink.type;
	linkObject.title = theLink.title;

	return linkObject;
}

// Some sites will list feeds with inappropriate or at least less-than-ideal information
// in the MIME type attribute. We cover some edge cases here that allow to be passed through,
// where they will successfully open as "feed://" URLs in the browser.
function isValidFeedLink(theLink) {
	var isValid = false;

	switch (theLink.type)
	{
		case "application/atom+xml":
		case "application/x.atom+xml":
		case "application/rss+xml":
			// These types do not require other criteria.
			isValid = (theLink.href != null);

		case "text/xml":
		case "application/rdf+xml":
			// These types require a title that has "RSS" in it.
			if (theLink.title && theLink.title.search(/RSS/i) != -1)
			{
				isValid = (theLink.href != null);
			}
	}

	return isValid;
}

function scanForSyndicationFeeds() {
	// In case we don't find any, we establish that we have at least tried by setting the
	// variables to empty instead of null.
	thisPageLinkObjects = []

	thisPageLinks = document.querySelectorAll("link[href][rel~='alternate'][type]");

	for (thisLinkIndex = 0; thisLinkIndex < thisPageLinks.length; thisLinkIndex++)
	{
		var thisLink = thisPageLinks[thisLinkIndex];
		if (isValidFeedLink(thisLink))
		{
			thisPageLinkObjects.push(objectFromLink(thisLink));
		}
	}
}

function subscribeToFeed(theFeed) {
	// Convert the URL to a feed:// scheme because Safari
	// will refuse to load e.g. a feed that is listed merely
	// as "text/xml". We do some preflighting of the link rel
	// in the PageLoadEnd.js so we can be more confident it's a
	// good feed: URL.
	var feedURL = theFeed.href;
	if (!feedURL.startsWith('feed:'))
	{
		feedURL = 'feed:' + feedURL;
	}

	safari.extension.dispatchMessage("subscribeToFeed", { "url": feedURL });
}

function messageHandler(event) {
	if (event.name === "toolbarButtonClicked")
	{
		// Workaround Radar #31182842, in which residual copies of our
		// app extension may remain loaded in context of pages in Safari,
		// causing multiple responses to broadcast message about toolbar
		// button being clicked. In the case of the "extra" injections,
		// the document location is null, so we can avoid doing on anything.
		if ((document.location != null) && (thisPageLinkObjects.length > 0))
		{
			feedToOpen = thisPageLinkObjects[0];
			subscribeToFeed(feedToOpen);
		}
	}
	else if (event.name === "ping")
	{
		// Just a hack to get the toolbar icon validation to work as expected.
		// If we don't pong back, the extension knows we are not loaded in a page.

		// There is a bug in Safari where the messageHandler is apparently held on to by Safari
		// even after an extension is disabled. So an effort to "ping" an extension's scripts will
		// succeed even if its been disabled and the page reloaded. Checking for the existance of
		// document.location seems to ensure we have enough of a handle still on the document that
		// we can do something useful with it.
		var shouldValidate = (document.location != null) && (thisPageLinkObjects.length > 0);

		// Pass back the same validationID we were handed so they can look up the correlated validationHandler
		safari.extension.dispatchMessage("pong", { "validationID": event.message.validationID, "shouldValidate": shouldValidate });
	}
}

document.addEventListener("DOMContentLoaded", function(event) {
	// Prevent injecting the JavaScript in IFRAMES, and from acting before Safari is ready...
	if ((window.top === window) && 	(typeof safari != 'undefined') && (document.location != null))
	{
		safari.self.addEventListener("message", messageHandler, false)
		scanForSyndicationFeeds();
	}
});