/// <summary>
/// Detects a loop in the redirects list given the new redirect.
/// Uses Floyd's cycle-finding algorithm.
/// </summary>
/// <param name="oldUrl">Old URL for new redirect</param>
/// <param name="newUrl">New URL for new redirect</param>
/// <returns>True if loop detected, false if no loop detected</returns>
private static bool DetectLoop(string oldUrl, string newUrl)
{
// quick check for any links to this new redirect
if (!_redirects.ContainsKey(newUrl) && !_redirects.Any(x => x.Value.NewUrl.Equals(oldUrl))) return false;
// clone redirect list
var linkedList = _redirects.ToDictionary(entry => entry.Key, entry => entry.Value);
var redirect = new Redirect() { OldUrl = oldUrl, NewUrl = newUrl };
// add new redirect to cloned list for traversing
if (!linkedList.ContainsKey(oldUrl))
linkedList.Add(oldUrl, redirect);
// Use Floyd's cycle finding algorithm to detect loops in a linked list
var slowP = redirect;
var fastP = redirect;
while (slowP != null && fastP != null && linkedList.ContainsKey(fastP.NewUrl))
{
slowP = linkedList[slowP.NewUrl];
fastP = linkedList[linkedList[fastP.NewUrl].NewUrl];
if (slowP == fastP)
{
return true;
}
}
return false;
}
/// <summary>
/// Update a given redirect
/// </summary>
/// <param name="redirect">Redirect to update</param>
/// <returns>Updated redirect if successful</returns>
public static Redirect UpdateRedirect(Redirect redirect)
{
if (redirect == null) throw new ArgumentNullException("redirect");
if (!redirect.OldUrl.IsSet()) throw new ArgumentNullException("redirect.OldUrl");
if (!redirect.NewUrl.IsSet()) throw new ArgumentNullException("redirect.NewUrl");
//Ensure starting slash
redirect.OldUrl = redirect.OldUrl.EnsurePrefix("/").ToLower();
redirect.NewUrl = redirect.NewUrl.EnsurePrefix("/").ToLower();
var existingRedirect = _redirects.ContainsKey(redirect.OldUrl) ? _redirects[redirect.OldUrl] : null;
if (existingRedirect != null && existingRedirect.Id != redirect.Id) throw new ArgumentException("A redirect for " + redirect.OldUrl + " already exists");
//get DB Context, set update time, and persist
var db = ApplicationContext.Current.DatabaseContext.Database;
redirect.LastUpdated = DateTime.Now.ToUniversalTime();
db.Update(redirect);
//Update in-memory list
_redirects[redirect.OldUrl] = redirect;
//return updated redirect
return redirect;
}
/// <summary>
/// Update a given redirect
/// </summary>
/// <param name="redirect">Redirect to update</param>
/// <returns>Updated redirect if successful</returns>
public static Redirect UpdateRedirect(Redirect redirect)
{
if (redirect == null) throw new ArgumentNullException("redirect");
if (!redirect.OldUrl.IsSet()) throw new ArgumentNullException("redirect.OldUrl");
if (!redirect.NewUrl.IsSet()) throw new ArgumentNullException("redirect.NewUrl");
//Ensure starting slash
if(!redirect.IsRegex)
redirect.OldUrl = redirect.OldUrl.EnsurePrefix("/").ToLower();
// Allow external redirects and ensure slash if not absolute
redirect.NewUrl = Uri.IsWellFormedUriString(redirect.NewUrl, UriKind.Absolute) ?
redirect.NewUrl.ToLower() :
redirect.NewUrl.EnsurePrefix("/").ToLower();
var existingRedirect = _redirects.ContainsKey(redirect.OldUrl) ? _redirects[redirect.OldUrl] : null;
if (existingRedirect != null && existingRedirect.Id != redirect.Id) throw new ArgumentException("A redirect for " + redirect.OldUrl + " already exists");
if (!redirect.IsRegex && DetectLoop(redirect.OldUrl, redirect.NewUrl)) throw new ApplicationException("Adding this redirect would cause a redirect loop");
//get DB Context, set update time, and persist
var db = ApplicationContext.Current.DatabaseContext.Database;
redirect.LastUpdated = DateTime.Now.ToUniversalTime();
db.Update(redirect);
//if we are changing the oldUrl property, let's move things around
var oldRedirect = _redirects.FirstOrDefault(x => x.Value.Id.Equals(redirect.Id));
if (oldRedirect.Value != null && redirect.OldUrl != oldRedirect.Value.OldUrl)
_redirects.Remove(oldRedirect.Value.OldUrl);
//Update in-memory list
_redirects[redirect.OldUrl] = redirect;
//return updated redirect
return redirect;
}