Fixes #13732 - IsBackOfficeRequest is extremely inefficient (#13743)

* Update UmbracoRequestPaths.cs

* Update UmbracoRequestPaths.cs

* remove redundant check

---------

Co-authored-by: Michael <michael@crossingpaths.be>
(cherry picked from commit de27eb697e)

# Conflicts:
#	src/Umbraco.Core/Routing/UmbracoRequestPaths.cs

src/Umbraco.Core/Routing/UmbracoRequestPaths.cs

@@ -14,9 +14,9 @@ public class UmbracoRequestPaths
     private readonly string _appPath;
     private readonly string _backOfficeMvcPath;
     private readonly string _backOfficePath;
-    private readonly List<string> _defaultUmbPaths;
+    private readonly string _defaultUmbPath;
+    private readonly string _defaultUmbPathWithSlash;
     private readonly string _installPath;
-    private readonly string _mvcArea;
     private readonly string _previewMvcPath;
     private readonly string _surfaceMvcPath;
 
@@ -25,18 +25,19 @@ public class UmbracoRequestPaths
     /// </summary>
     public UmbracoRequestPaths(IOptions<GlobalSettings> globalSettings, IHostingEnvironment hostingEnvironment)
     {
-        var applicationPath = hostingEnvironment.ApplicationVirtualPath;
-        _appPath = applicationPath.TrimStart(Constants.CharArrays.ForwardSlash);
+        _appPath = hostingEnvironment.ApplicationVirtualPath;
 
         _backOfficePath = globalSettings.Value.GetBackOfficePath(hostingEnvironment)
-            .EnsureStartsWith('/').TrimStart(_appPath.EnsureStartsWith('/')).EnsureStartsWith('/');
+            .EnsureStartsWith('/').TrimStart(_appPath).EnsureStartsWith('/');
 
-        _mvcArea = globalSettings.Value.GetUmbracoMvcArea(hostingEnvironment);
-        _defaultUmbPaths = new List<string> { "/" + _mvcArea, "/" + _mvcArea + "/" };
-        _backOfficeMvcPath = "/" + _mvcArea + "/BackOffice/";
-        _previewMvcPath = "/" + _mvcArea + "/Preview/";
-        _surfaceMvcPath = "/" + _mvcArea + "/Surface/";
-        _apiMvcPath = "/" + _mvcArea + "/Api/";
+        string mvcArea = globalSettings.Value.GetUmbracoMvcArea(hostingEnvironment);
+
+        _defaultUmbPath = "/" + mvcArea;
+        _defaultUmbPathWithSlash = "/" + mvcArea + "/";
+        _backOfficeMvcPath = "/" + mvcArea + "/BackOffice/";
+        _previewMvcPath = "/" + mvcArea + "/Preview/";
+        _surfaceMvcPath = "/" + mvcArea + "/Surface/";
+        _apiMvcPath = "/" + mvcArea + "/Api/";
         _installPath = hostingEnvironment.ToAbsolute(Constants.SystemDirectories.Install);
     }
 
@@ -67,50 +68,65 @@ public class UmbracoRequestPaths
     /// </remarks>
     public bool IsBackOfficeRequest(string absPath)
     {
-        var fullUrlPath = absPath.TrimStart(Constants.CharArrays.ForwardSlash);
-        var urlPath = fullUrlPath.TrimStart(_appPath).EnsureStartsWith('/');
+        string urlPath = absPath.TrimStart(_appPath).EnsureStartsWith('/');
 
         // check if this is in the umbraco back office
-        var isUmbracoPath = urlPath.InvariantStartsWith(_backOfficePath);
-
-        // if not, then def not back office
-        if (isUmbracoPath == false)
+        if (!urlPath.InvariantStartsWith(_backOfficePath))
         {
             return false;
         }
 
         // if its the normal /umbraco path
-        if (_defaultUmbPaths.Any(x => urlPath.InvariantEquals(x)))
+        if (urlPath.InvariantEquals(_defaultUmbPath) || urlPath.InvariantEquals(_defaultUmbPathWithSlash))
         {
             return true;
         }
 
         // check for special back office paths
-        if (urlPath.InvariantStartsWith(_backOfficeMvcPath)
-            || urlPath.InvariantStartsWith(_previewMvcPath))
+        if (urlPath.InvariantStartsWith(_backOfficeMvcPath) || urlPath.InvariantStartsWith(_previewMvcPath))
         {
             return true;
         }
 
         // check for special front-end paths
-        if (urlPath.InvariantStartsWith(_surfaceMvcPath)
-            || urlPath.InvariantStartsWith(_apiMvcPath))
+        if (urlPath.InvariantStartsWith(_surfaceMvcPath) || urlPath.InvariantStartsWith(_apiMvcPath))
         {
             return false;
         }
 
-        // if its none of the above, we will have to try to detect if it's a PluginController route, we can detect this by
-        // checking how many parts the route has, for example, all PluginController routes will be routed like
+        // if its none of the above, we will have to try to detect if it's a PluginController route
+        return !IsPluginControllerRoute(urlPath);
+    }
+
+    /// <summary>
+    /// Checks if the path is from a PluginController route.
+    /// </summary>
+    private static bool IsPluginControllerRoute(string path)
+    {
+        // Detect this by checking how many parts the route has, for example, all PluginController routes will be routed like
         // Umbraco/MYPLUGINAREA/MYCONTROLLERNAME/{action}/{id}
-        // so if the path contains at a minimum 3 parts: Umbraco + MYPLUGINAREA + MYCONTROLLERNAME then we will have to assume it is a
-        // plugin controller for the front-end.
-        if (urlPath.Split(Constants.CharArrays.ForwardSlash, StringSplitOptions.RemoveEmptyEntries).Length >= 3)
+        // so if the path contains at a minimum 3 parts: Umbraco + MYPLUGINAREA + MYCONTROLLERNAME then we will have to assume it is a plugin controller for the front-end.
+
+        int count = 0;
+
+        for (int i = 0; i < path.Length; i++)
         {
-            return false;
+            char chr = path[i];
+
+            if (chr == '/')
+            {
+                count++;
+                continue;
+            }
+
+            // Check last char so we can properly determine the number of parts, e.g. /url/path/ has two parts, /url/path/test has three.
+            if (count == 3)
+            {
+                return true;
+            }
         }
 
-        // if its anything else we can assume it's back office
-        return true;
+        return false;
     }
 
     /// <summary>