Delete TAP interface before the TAP driver is uninstalled

index 8e9a3832..2ce69444 100644
@@ -454,62 +454,41 @@ msica_op_tap_interface_delete(
 
     DWORD dwResult;
 
-    if (session->rollback_enabled)
-    {
-        int count = 0;
-
-        do {
-            /* Rename the interface to keep it as a backup. */
-            TCHAR szNameBackup[10/*"Interface "*/ + 10/*maximum int*/ + 1/*terminator*/];
-            _stprintf_s(
-                szNameBackup, _countof(szNameBackup),
-                TEXT("Interface %i"),
-                ++count);
-            for (struct tap_interface_node *pInterfaceOther = pInterfaceList; ; pInterfaceOther = pInterfaceOther->pNext)
-            {
-                if (pInterfaceOther == NULL)
-                {
-                    /* No interface with a same name found. All clear to rename the interface. */
-                    dwResult = tap_set_interface_name(&pInterface->guid, szNameBackup);
-                    break;
-                }
-                else if (_tcsicmp(szNameBackup, pInterfaceOther->szName) == 0)
-                {
-                    /* Interface with a same name found. Duplicate interface names are not allowed. */
-                    dwResult = ERROR_ALREADY_EXISTS;
-                    break;
-                }
-            }
-        } while (dwResult == ERROR_ALREADY_EXISTS);
+    /* Delete the interface. */
+    BOOL bRebootRequired = FALSE;
+    dwResult = tap_delete_interface(NULL, &pInterface->guid, &bRebootRequired);
+    if (bRebootRequired)
+        MsiSetMode(session->hInstall, MSIRUNMODE_REBOOTATEND, TRUE);
 
-        if (dwResult == ERROR_SUCCESS) {
-            /* Schedule rollback action to rename the interface back. */
-            msica_op_seq_add_head(
-                &session->seq_cleanup[MSICA_CLEANUP_ACTION_ROLLBACK],
-                msica_op_create_guid_string(
-                    msica_op_tap_interface_set_name,
-                    0,
-                    NULL,
-                    &pInterface->guid,
-                    pInterface->szName));
-
-            /* Schedule commit action to delete the interface. */
-            msica_op_seq_add_tail(
-                &session->seq_cleanup[MSICA_CLEANUP_ACTION_COMMIT],
-                msica_op_create_guid(
-                    msica_op_tap_interface_delete_by_guid,
-                    0,
-                    NULL,
-                    &pInterface->guid));
-        }
-    }
-    else
+    if (session->rollback_enabled)
     {
-        /* Delete the interface. */
-        BOOL bRebootRequired = FALSE;
-        dwResult = tap_delete_interface(NULL, &pInterface->guid, &bRebootRequired);
-        if (bRebootRequired)
-            MsiSetMode(session->hInstall, MSIRUNMODE_REBOOTATEND, TRUE);
+        /*
+        Schedule rollback action to create the interface back. Though it won't be exactly the same interface again.
+
+        The previous version of this function did:
+        - Execution Pass:       rename the interface to some temporary name
+        - Commit/Rollback Pass: delete the interface / rename the interface back to original name
+
+        However, the WiX Toolset's Diffx extension to install and remove drivers removed the TAP driver between the
+        execution and commit passes. TAP driver removal makes all TAP interfaces unavailable and our CA couldn't find
+        the interface to delete any more.
+
+        While the system where OpenVPN was uninstalled didn't have any TAP interfaces any more as expected behaviour,
+        the problem appears after reinstalling the OpenVPN. Some residue TAP interface registry keys remain on the
+        system, causing the TAP interface to reappear as "Ethernet NN" interface next time the TAP driver is
+        installed. This causes TAP interfaces to accumulate over cyclic install-uninstall-install...
+
+        Therefore, it is better to remove the TAP interfaces before the TAP driver is removed, and reinstall the TAP
+        interface back should the rollback be required. I wonder if the WiX Diffx extension supports execute/commit/
+        rollback feature of MSI in the first place.
+        */
+        msica_op_seq_add_head(
+            &session->seq_cleanup[MSICA_CLEANUP_ACTION_ROLLBACK],
+            msica_op_create_string(
+                msica_op_tap_interface_create,
+                0,
+                NULL,
+                pInterface->szName));
     }
 
     return dwResult;

index d1642d6a..99b47bf0 100644
@@ -162,7 +162,7 @@ FindSystemInfo(_In_ MSIHANDLE hInstall)
     struct openvpnmsica_tls_data *s = (struct openvpnmsica_tls_data *)TlsGetValue(openvpnmsica_tlsidx_session);
     s->hInstall = hInstall;
 
-    // Get Windows version.
+    /* Get Windows version. */
     OSVERSIONINFOEX ver_info = { .dwOSVersionInfoSize = sizeof(OSVERSIONINFOEX) };
     if (!GetVersionEx((LPOSVERSIONINFO)&ver_info)) {
         uiResult = GetLastError();

@@ -170,7 +170,7 @@ FindSystemInfo(_In_ MSIHANDLE hInstall)
         goto cleanup_CoInitialize;
     }
 
-    // The Windows version is usually spoofed, check using RtlGetVersion().
+    /* The Windows version is usually spoofed, check using RtlGetVersion(). */
     TCHAR szDllPath[0x1000];
     ExpandEnvironmentStrings(TEXT("%SystemRoot%\\System32\\ntdll.dll"), szDllPath,
 #ifdef UNICODE

@@ -193,7 +193,7 @@ FindSystemInfo(_In_ MSIHANDLE hInstall)
                     rtl_ver_info.dwMajorVersion == ver_info.dwMajorVersion && rtl_ver_info.dwMinorVersion >  ver_info.dwMinorVersion ||
                     rtl_ver_info.dwMajorVersion == ver_info.dwMajorVersion && rtl_ver_info.dwMinorVersion == ver_info.dwMinorVersion && rtl_ver_info.dwBuildNumber > ver_info.dwBuildNumber)
                 {
-                    // We got RtlGetVersion() and it reported newer version than GetVersionEx().
+                    /* We got RtlGetVersion() and it reported newer version than GetVersionEx(). */
                     ver_info.dwMajorVersion = rtl_ver_info.dwMajorVersion;
                     ver_info.dwMinorVersion = rtl_ver_info.dwMinorVersion;
                     ver_info.dwBuildNumber  = rtl_ver_info.dwBuildNumber;

@@ -204,7 +204,7 @@ FindSystemInfo(_In_ MSIHANDLE hInstall)
         FreeLibrary(hNtDllModule);
     }
 
-    // We don't trust RtlGetVersion() either. Check the version resource of kernel32.dll.
+    /* We don't trust RtlGetVersion() either. Check the version resource of kernel32.dll. */
     ExpandEnvironmentStrings(TEXT("%SystemRoot%\\System32\\kernel32.dll"), szDllPath,
 #ifdef UNICODE
         _countof(szDllPath)

@@ -220,10 +220,10 @@ FindSystemInfo(_In_ MSIHANDLE hInstall)
         LPVOID pVersionInfo = malloc(dwVerInfoSize);
         if (pVersionInfo)
         {
-            // Read version info.
+            /* Read version info. */
             if (GetFileVersionInfo(szDllPath, dwHandle, dwVerInfoSize, pVersionInfo))
             {
-                // Get the value for the root block.
+                /* Get the value for the root block. */
                 UINT uiSize = 0;
                 VS_FIXEDFILEINFO *pVSFixedFileInfo = NULL;
                 if (VerQueryValue(pVersionInfo, TEXT("\\"), &pVSFixedFileInfo, &uiSize) && uiSize && pVSFixedFileInfo)

@@ -231,7 +231,7 @@ FindSystemInfo(_In_ MSIHANDLE hInstall)
                         HIWORD(pVSFixedFileInfo->dwProductVersionMS) == ver_info.dwMajorVersion && LOWORD(pVSFixedFileInfo->dwProductVersionMS) >  ver_info.dwMinorVersion ||
                         HIWORD(pVSFixedFileInfo->dwProductVersionMS) == ver_info.dwMajorVersion && LOWORD(pVSFixedFileInfo->dwProductVersionMS) == ver_info.dwMinorVersion && HIWORD(pVSFixedFileInfo->dwProductVersionLS) > ver_info.dwBuildNumber)
                     {
-                        // We got kernel32.dll version and it is newer.
+                        /* We got kernel32.dll version and it is newer. */
                         ver_info.dwMajorVersion = HIWORD(pVSFixedFileInfo->dwProductVersionMS);
                         ver_info.dwMinorVersion = LOWORD(pVSFixedFileInfo->dwProductVersionMS);
                         ver_info.dwBuildNumber  = HIWORD(pVSFixedFileInfo->dwProductVersionLS);

index 99b47bf0..a2819e62 100644
@@ -144,6 +144,50 @@ openvpnmsica_setup_sequence_filename(
 }
 
 
+#ifdef _DEBUG
+
+/**
+ * Pops up a message box creating a time window to attach a debugger to the installer process in
+ * order to debug custom actions.
+ *
+ * @param szFunctionName  Function name that triggered the pop-up. Displayed in message box's
+ *                        title.
+ */
+static void
+_openvpnmsica_debug_popup(_In_z_ LPCTSTR szFunctionName)
+{
+    TCHAR szTitle[0x100], szMessage[0x100+MAX_PATH], szProcessPath[MAX_PATH];
+
+    /* Compose pop-up title. The dialog title will contain function name to ease the process
+       locating. Mind that Visual Studio displays window titles on the process list. */
+    _stprintf_s(szTitle, _countof(szTitle), TEXT("%s v%s"), szFunctionName, TEXT(PACKAGE_VERSION));
+
+    /* Get process name. */
+    GetModuleFileName(NULL, szProcessPath, _countof(szProcessPath));
+    LPCTSTR szProcessName = _tcsrchr(szProcessPath, TEXT('\\'));
+    szProcessName = szProcessName ? szProcessName + 1 : szProcessPath;
+
+    /* Compose the pop-up message. */
+    _stprintf_s(
+        szMessage, _countof(szMessage),
+        TEXT("The %s process (PID: %u) has started to execute the %s custom action.\r\n")
+        TEXT("\r\n")
+        TEXT("If you would like to debug the custom action, attach a debugger to this process and set breakpoints before dismissing this dialog.\r\n")
+        TEXT("\r\n")
+        TEXT("If you are not debugging this custom action, you can safely ignore this message."),
+        szProcessName,
+        GetCurrentProcessId(),
+        szFunctionName);
+
+    MessageBox(NULL, szMessage, szTitle, MB_OK);
+}
+
+#define openvpnmsica_debug_popup(f) _openvpnmsica_debug_popup(f)
+#else
+#define openvpnmsica_debug_popup(f)
+#endif
+
+
 UINT __stdcall
 FindSystemInfo(_In_ MSIHANDLE hInstall)
 {

@@ -151,9 +195,7 @@ FindSystemInfo(_In_ MSIHANDLE hInstall)
 #pragma comment(linker, DLLEXP_EXPORT)
 #endif
 
-#ifdef _DEBUG
-    MessageBox(NULL, TEXT("Attach debugger!"), TEXT(__FUNCTION__) TEXT(" v")  TEXT(PACKAGE_VERSION), MB_OK);
-#endif
+    openvpnmsica_debug_popup(TEXT(__FUNCTION__));
 
     UINT uiResult;
     BOOL bIsCoInitialized = SUCCEEDED(CoInitialize(NULL));

@@ -265,9 +307,7 @@ FindTAPInterfaces(_In_ MSIHANDLE hInstall)
 #pragma comment(linker, DLLEXP_EXPORT)
 #endif
 
-#ifdef _DEBUG
-    MessageBox(NULL, TEXT("Attach debugger!"), TEXT(__FUNCTION__) TEXT(" v")  TEXT(PACKAGE_VERSION), MB_OK);
-#endif
+    openvpnmsica_debug_popup(TEXT(__FUNCTION__));
 
     UINT uiResult;
     BOOL bIsCoInitialized = SUCCEEDED(CoInitialize(NULL));

@@ -371,9 +411,7 @@ EvaluateTAPInterfaces(_In_ MSIHANDLE hInstall)
 #pragma comment(linker, DLLEXP_EXPORT)
 #endif
 
-#ifdef _DEBUG
-    MessageBox(NULL, TEXT("Attach debugger!"), TEXT(__FUNCTION__) TEXT(" v")  TEXT(PACKAGE_VERSION), MB_OK);
-#endif
+    openvpnmsica_debug_popup(TEXT(__FUNCTION__));
 
     UINT uiResult;
     BOOL bIsCoInitialized = SUCCEEDED(CoInitialize(NULL));

@@ -633,9 +671,7 @@ ProcessDeferredAction(_In_ MSIHANDLE hInstall)
 #pragma comment(linker, DLLEXP_EXPORT)
 #endif
 
-#ifdef _DEBUG
-    MessageBox(NULL, TEXT("Attach debugger!"), TEXT(__FUNCTION__) TEXT(" v")  TEXT(PACKAGE_VERSION), MB_OK);
-#endif
+    openvpnmsica_debug_popup(TEXT(__FUNCTION__));
 
     UINT uiResult;
     BOOL bIsCoInitialized = SUCCEEDED(CoInitialize(NULL));