private CacheInfo TryLoadFromDisk(string url)
{
if (_directoryOnDisk == null)
{
return(null); // no place to cache
}
CacheInfo found = null;
// look for all files matching the prefix
// looking for the one matching url that is not expired
// removing expired (or invalid) ones
string pattern = GetTempFileNamePrefixFromUrl(url) + "_*.feed";
string[] files = Directory.GetFiles(_directoryOnDisk, pattern, SearchOption.TopDirectoryOnly);
foreach (string feedFilename in files)
{
XmlDocument feedDoc = null;
bool isFeedFileValid = false;
DateTime utcExpiryFromFeedFile = DateTime.MinValue;
string urlFromFeedFile = null;
try
{
feedDoc = new XmlDocument();
feedDoc.Load(feedFilename);
// look for special XML comment (before the root tag)'
// containing expiration and url
XmlComment comment = feedDoc.DocumentElement.PreviousSibling as XmlComment;
if (comment != null)
{
string c = comment.Value ?? string.Empty;
int i = c.IndexOf('@');
long expiry;
if (i >= 0 && long.TryParse(c.Substring(0, i), out expiry))
{
utcExpiryFromFeedFile = DateTime.FromBinary(expiry);
urlFromFeedFile = c.Substring(i + 1);
isFeedFileValid = true;
}
}
}
catch (XmlException)
{
// error processing one file shouldn't stop processing other files
}
// remove invalid or expired file
if (!isFeedFileValid || utcExpiryFromFeedFile < DateTime.UtcNow)
{
TryDeleteFile(feedFilename);
// try next file
continue;
}
// match url
if (urlFromFeedFile == url)
{
// keep the one that expires last
if (found == null || found.Expiry < utcExpiryFromFeedFile)
{
// if we have a previously found older expiration, kill it...
if (found != null)
{
found.Dispose();
TryDeleteFile(found.FeedFilename);
}
// create DOM and set expiry (as found on disk)
found = new CacheInfo(feedDoc, utcExpiryFromFeedFile, feedFilename);
}
}
}
// return best fit
return(found);
}
