/// <summary>
/// Returns the absolute url of a link on a page. If you got the feed links via
/// GetFeedUrlsFromUrl(url) and the url is relative, you can use this method to get the full url.
/// </summary>
/// <param name="pageUrl">the original url to the page</param>
/// <param name="feedLink">a referenced feed (link)</param>
/// <returns>a feed link</returns>
/// <example>GetAbsoluteFeedUrl("codehollow.com", myRelativeFeedLink);</example>
public static HtmlFeedLink GetAbsoluteFeedUrl(string pageUrl, HtmlFeedLink feedLink)
{
string tmpUrl = feedLink.Url.HtmlDecode();
pageUrl = GetAbsoluteUrl(pageUrl);
if (tmpUrl.StartsWith("http://", StringComparison.OrdinalIgnoreCase) ||
tmpUrl.StartsWith("https://", StringComparison.OrdinalIgnoreCase))
{
return(feedLink);
}
if (tmpUrl.StartsWith("//", StringComparison.OrdinalIgnoreCase)) // special case
{
tmpUrl = "http:" + tmpUrl;
}
if (Uri.TryCreate(tmpUrl, UriKind.RelativeOrAbsolute, out Uri finalUri))
{
if (finalUri.IsAbsoluteUri)
{
return(new HtmlFeedLink(feedLink.Title.HtmlDecode(), finalUri.ToString(), feedLink.FeedType));
}
else if (Uri.TryCreate(pageUrl + '/' + tmpUrl.TrimStart('/'), UriKind.Absolute, out finalUri))
{
return(new HtmlFeedLink(feedLink.Title.HtmlDecode(), finalUri.ToString(), feedLink.FeedType));
}
}
throw new UrlNotFoundException($"Could not get the absolute url out of {pageUrl} and {feedLink.Url}");
}
/// <summary>
/// Returns a HtmlFeedLink object from a linktag (link href="" type="")
/// only support application/rss and application/atom as type
/// if type is not supported, null is returned
/// </summary>
/// <param name="input">link tag, e.g. <link rel="alternate" type="application/rss+xml" title="codehollow > Feed" href="https://codehollow.com/feed/" /></param>
/// <returns>Parsed HtmlFeedLink</returns>
public static HtmlFeedLink GetFeedLinkFromLinkTag(string input)
{
string linkTag = input.HtmlDecode();
string type = GetAttributeFromLinkTag("type", linkTag).ToLower();
if (!type.Contains("application/rss") && !type.Contains("application/atom"))
{
return(null);
}
HtmlFeedLink hfl = new HtmlFeedLink();
string title = GetAttributeFromLinkTag("title", linkTag);
string href = GetAttributeFromLinkTag("href", linkTag);
hfl.Title = title;
hfl.Url = href;
hfl.FeedType = type.Contains("rss") ? FeedType.Rss : FeedType.Atom;
return(hfl);
}
