Imported Upstream version 3.6.0

Former-commit-id: da6be194a6b1221998fc28233f2503bd61dd9d14

mcs/class/System.Web.Mvc3/Mvc/UrlRewriterHelper.cs

@@ -0,0 +1,37 @@
+namespace System.Web.Mvc {
+    using System.Collections.Specialized;
+
+    internal class UrlRewriterHelper {
+        private const string _urlWasRewrittenServerVar = "IIS_WasUrlRewritten";
+        private const string _urlRewriterEnabledServerVar = "IIS_UrlRewriteModule";
+
+        private object _lockObject = new object();
+        private bool _urlRewriterIsTurnedOnValue;
+        private bool _urlRewriterIsTurnedOnCalculated = false;
+
+        private static bool WasThisRequestRewritten(HttpContextBase httpContext) {
+            NameValueCollection serverVars = httpContext.Request.ServerVariables;
+            bool requestWasRewritten = (serverVars != null && serverVars[_urlWasRewrittenServerVar] != null);
+            return requestWasRewritten;
+        }
+
+        private bool IsUrlRewriterTurnedOn(HttpContextBase httpContext) {
+            // Need to do double-check locking because a single instance of this class is shared in the entire app domain (see PathHelpers)
+            if (!_urlRewriterIsTurnedOnCalculated) {
+                lock (_lockObject) {
+                    if (!_urlRewriterIsTurnedOnCalculated) {
+                        NameValueCollection serverVars = httpContext.Request.ServerVariables;
+                        bool urlRewriterIsEnabled = (serverVars != null && serverVars[_urlRewriterEnabledServerVar] != null);
+                        _urlRewriterIsTurnedOnValue = urlRewriterIsEnabled;
+                        _urlRewriterIsTurnedOnCalculated = true;
+                    }
+                }
+            }
+            return _urlRewriterIsTurnedOnValue;
+        }
+
+        public virtual bool WasRequestRewritten(HttpContextBase httpContext) {
+            return IsUrlRewriterTurnedOn(httpContext) && WasThisRequestRewritten(httpContext);
+        }
+    }
+}