Back in September, I blogged about the configuration steps required to debug Windows 8 “Metro-style” apps using Fiddler. Since that post was originally written, I’ve made available a new version of Fiddler which runs natively on the .NETv4 Framework, enabling Windows 8 users to run Fiddler without installing older versions of the Framework.
As I mentioned in that post, Metro-style applications run inside isolated processes known as “AppContainers,” and by default, AppContainers are forbidden from sending network traffic to the local computer (loopback). This is, of course, problematic when debugging with Fiddler, as Fiddler is a proxy server which runs on the local computer. The post went on to explain how the CheckNetIsolation tool can be used to permit an AppContainer to send traffic to the local computer. However, using CheckNetIsolation is pretty cumbersome—it requires that you know the AppContainer’s name or security ID, and you must configure each AppContainer individually. To resolve those difficulties, I have built a GUI tool that allows you to very easily reconfigure an AppContainer to enable loopback traffic. This tool requires Windows 8 and runs on the .NET Framework v4. When launched, the utility scans your computer’s AppContainers and displays them in a list view. Each entry has a checkbox to the left of it, indicating whether the AppContainer may send loopback traffic. You can toggle these checkboxes individually, or use the buttons at the top to set all of the checkboxes at once. Click Save Changes to commit the configuration changes you’ve made, or click Refresh to reload the current configuration settings.
After you install the EnableLoopback Utility, a new “Win8 Loopback Exemptions” item is added to Fiddler’s Tools menu; clicking this item launches the utility. To make changes to the exemption list, you must elevate to Administrator.
-Eric
PS: For the technically-inclined, this tool relies on calling the new Network Isolation APIs introduced with Windows 8. Their .NET declarations (as of the BUILD conference) are as follows:
// Call this API to enumerate all of the AppContainers on the system
[DllImport("FirewallAPI.dll")]
internal static extern uint NetworkIsolationEnumAppContainers(out uint pdwCntPublicACs, out IntPtr ppACs);
// Call this API to free the memory returned by the Enumeration API
[DllImport("FirewallAPI.dll")]
internal static extern void NetworkIsolationFreeAppContainers(IntPtr pACs);
// Call this API to load the current list of Loopback-enabled AppContainers
[DllImport("FirewallAPI.dll")]
internal static extern uint NetworkIsolationGetAppContainerConfig(out uint pdwCntACs, out IntPtr appContainerSids);
// Call this API to set the Loopback-exemption list
[DllImport("FirewallAPI.dll")]
internal static extern uint NetworkIsolationSetAppContainerConfig(uint pdwCntACs, SID_AND_ATTRIBUTES[] appContainerSids);
// Use this API to convert a string SID into an actual SID
[DllImport("advapi32.dll", SetLastError=true)]
internal static extern bool ConvertStringSidToSid(string strSid, out IntPtr pSid);
// Use this API to convert a string reference (e.g. "@{blah.pri?ms-resource://whatever}") into a plain string
[DllImport("shlwapi.dll", CharSet=CharSet.Unicode, ExactSpelling=true)]
internal static extern int SHLoadIndirectString(string pszSource, StringBuilder pszOutBuf, int cchOutBuf, IntPtr ppvReserved);