Adds a new app setting (enableFileSystemMonitoring:bool) (#19)

* Adds a new app setting (enableFileSystemMonitoring:bool) to specify whether file system monitoring should be enabled for the nuget server

* Explanatory note about consequences of disabling file system monitoring

Author: niklaskallander

src/NuGet.Server/Infrastructure/ServerPackageRepository.cs

@@ -569,7 +569,7 @@ public void ClearCache()
 
         private void MonitorFileSystem(bool monitor)
         {
-            if (!_runBackgroundTasks)
+            if (!EnableFileSystemMonitoring || !_runBackgroundTasks)
             {
                 return;
             }
@@ -599,7 +599,7 @@ private void MonitorFileSystem(bool monitor)
         private void RegisterFileSystemWatcher()
         {
             // When files are moved around, recreate the package cache
-            if (_runBackgroundTasks && _fileSystemWatcher == null && !string.IsNullOrEmpty(Source) && Directory.Exists(Source))
+            if (EnableFileSystemMonitoring && _runBackgroundTasks && _fileSystemWatcher == null && !string.IsNullOrEmpty(Source) && Directory.Exists(Source))
             {
                 // ReSharper disable once UseObjectOrCollectionInitializer
                 _fileSystemWatcher = new FileSystemWatcher(Source);
@@ -694,7 +694,16 @@ private bool EnableFrameworkFiltering
                 return _getSetting("enableFrameworkFiltering", false);
             }
         }
-        
+
+        private bool EnableFileSystemMonitoring
+        {
+            get
+            {
+                // If the setting is misconfigured, treat it as on (backwards compatibility).
+                return _getSetting("enableFileSystemMonitoring", true);
+            }
+        }
+
         private static bool GetBooleanAppSetting(string key, bool defaultValue)
         {
             var appSettings = WebConfigurationManager.AppSettings;

src/NuGet.Server/Web.config

@@ -49,6 +49,13 @@
     Uncomment the following configuration entry to enable NAT support.
     -->
     <!-- <add key="aspnet:UseHostHeaderForRequestUrl" value="true" /> -->
+    <!--
+    Set enableFileSystemMonitoring to true (default) to enable file system monitoring (which will update the package cache appropriately on file system changes).
+    Set it to false to disable file system monitoring.
+    NOTE: Disabling file system monitoring may result in increased storage capacity requirements as package cache may only be purged by a background job running 
+    on a fixed 1-hour interval.
+    -->
+    <add key="enableFileSystemMonitoring" value="true" />
   </appSettings>
   <!--
     For a description of web.config changes see http://go.microsoft.com/fwlink/?LinkId=235367.