/// <summary>
/// Returns a RedirectionMap created from the specified datafile. If avaialble, a cached
/// copy of the map is returned; otherwise, the data file is parsed and a new map created.
/// </summary>
/// <param name="datafile">Location of a data file creating comma-separated pairs of
/// old URLs and new URLs for use as redirection targets.</param>
/// <param name="context">The current HTTP Context object.</param>
/// <returns>A (possibly empty) RedirectionMap.</returns>
public static RedirectionMap GetMap(String datafile, HttpContext context)
{
log.Trace("Enter GetMap().");
RedirectionMap map;
Cache cache = context.Cache;
Object lockObj = new Object();
try
{
log.DebugFormat("Load cache for '{0}'.", datafile);
map = (RedirectionMap)cache[datafile];
if (map == null)
{
lock (lockObj)
{
// Check whether the cache was loaded while we waited for the lock.
map = (RedirectionMap)cache[datafile];
if (map == null)
{
// There was no cached redirection map. Load it from the file system.
log.DebugFormat("Cache miss. Loading redirection map from '{0}'.", datafile);
CacheItemRemovedCallback onRemove = new CacheItemRemovedCallback(RemovedItemCallback);
CacheDependency fileDependency = new CacheDependency(datafile);
map = LoadMapFromFile(datafile);
cache.Add(datafile, map, fileDependency, Cache.NoAbsoluteExpiration, Cache.NoSlidingExpiration, CacheItemPriority.AboveNormal, onRemove);
}
else
{
log.Debug("Cached redirection map found on second chance retrieval.");
}
}
}
else
{
// A cached redirection map was found. Return it.
log.Debug("Loading cached redirection map.");
}
}
catch (Exception ex)
{
log.Error("Error while getting the redirection map.", ex);
// Instead of letting the request die,
// swallow the exception and return an empty map.
map = new RedirectionMap();
}
return(map);
}
/// <summary>
/// Private helper method to encapsulate the logic for loading and parsing the datafile.
/// </summary>
/// <param name="datafile">Location of a data file creating comma-separated pairs of
/// old URLs and new URLs for use as redirection targets.</param>
/// <returns></returns>
private static RedirectionMap LoadMapFromFile(String datafile)
{
log.Trace("Enter LoadMapFromFile().");
SimpleRedirectorConfigurationSection config = SimpleRedirectorConfigurationSection.Get();
char[] separators = new char[1];
separators[0] = config.DataSource.Separator;
RedirectionMap map = new RedirectionMap();
try
{
if (!File.Exists(datafile))
{
log.ErrorFormat("Datafile '{0}' not found.", datafile);
throw new FileNotFoundException(datafile);
}
}
catch (Exception ex)
{
log.ErrorFormat("Error while loading urls from {0}.", ex, datafile);
// Swallow the exception. The worst case is we return an empty dictionary
// and nothing gets redirected.
}
String[] listOfUrlPairs = File.ReadAllLines(datafile);
foreach (String urlPair in listOfUrlPairs)
{
String[] urls = urlPair.Trim().Split(separators);
if (urls.Length >= 2)
{
try
{
map.Add(urls[0], urls[1]);
}
catch (Exception ex)
{
log.ErrorFormat("Duplicate URL found in RedirectMap: {0}", ex, urls[0]);
}
}
if (urls.Length != 2)
{
// We can recover from this problem. No exception needed.
log.WarnFormat("Expected only two urls, found {0} in '{1}'.", urls.Length, urlPair);
}
}
return(map);
}