From 7005d6ecd0d81157024f7daf581e359b97716306 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Thu, 22 Apr 2021 22:01:26 +0530
Subject: [PATCH] Use RAII for PROPVARIANT

---
 .../mtp/windows/content_enumeration.cpp       | 28 +++++++------------
 .../mtp/windows/device_enumeration.cpp        |  4 +--
 src/calibre/utils/windows/common.h            |  8 ++++++
 3 files changed, 19 insertions(+), 21 deletions(-)

diff --git a/src/calibre/devices/mtp/windows/content_enumeration.cpp b/src/calibre/devices/mtp/windows/content_enumeration.cpp
index db2013925d..60252d8e9c 100644
--- a/src/calibre/devices/mtp/windows/content_enumeration.cpp
+++ b/src/calibre/devices/mtp/windows/content_enumeration.cpp
@@ -326,44 +326,36 @@ find_objects_in(CComPtr<IPortableDeviceContent> &content, CComPtr<IPortableDevic
      * The child ids are put into object_ids. Returns False if any errors
      * occurred (also sets the python exception).
      */
-    IEnumPortableDeviceObjectIDs *children;
+    CComPtr<IEnumPortableDeviceObjectIDs> children;
     HRESULT hr = S_OK, hr2 = S_OK;
     PWSTR child_ids[10];
-    DWORD fetched, i;
-    PROPVARIANT pv;
-    bool ok = true;
-
-    PropVariantInit(&pv);
-    pv.vt      = VT_LPWSTR;
+	prop_variant pv(VT_LPWSTR);
 
     Py_BEGIN_ALLOW_THREADS;
     hr = content->EnumObjects(0, parent_id, NULL, &children);
     Py_END_ALLOW_THREADS;
 
-    if (FAILED(hr)) {hresult_set_exc("Failed to get children from device", hr); ok = false; goto end;}
+    if (FAILED(hr)) {hresult_set_exc("Failed to get children from device", hr); return false;}
 
     hr = S_OK;
 
     while (hr == S_OK) {
+		DWORD fetched;
         Py_BEGIN_ALLOW_THREADS;
-        hr = children->Next(10, child_ids, &fetched);
+        hr = children->Next(arraysz(child_ids), child_ids, &fetched);
         Py_END_ALLOW_THREADS;
         if (SUCCEEDED(hr)) {
-            for(i = 0; i < fetched; i++) {
+			com_wchar_raii cleanup[arraysz(child_ids)];
+            for(DWORD i = 0; i < fetched; i++) { cleanup[i].attach(child_ids[i]); }
+            for(DWORD i = 0; i < fetched; i++) {
                 pv.pwszVal = child_ids[i];
                 hr2 = object_ids->Add(&pv);
                 pv.pwszVal = NULL;
-                if (FAILED(hr2)) { hresult_set_exc("Failed to add child ids to propvariantcollection", hr2); break; }
+                if (FAILED(hr2)) { hresult_set_exc("Failed to add child ids to propvariantcollection", hr2); return false; }
             }
-            for (i = 0; i < fetched; i++) { CoTaskMemFree(child_ids[i]); child_ids[i] = NULL; }
-            if (FAILED(hr2) || !ok) { ok = false; goto end; }
         }
     }
-
-end:
-    if (children != NULL) children->Release();
-    PropVariantClear(&pv);
-    return ok;
+	return true;
 } // }}}
 
 // Single get filesystem {{{
diff --git a/src/calibre/devices/mtp/windows/device_enumeration.cpp b/src/calibre/devices/mtp/windows/device_enumeration.cpp
index e734ab4e25..98319a4fc4 100644
--- a/src/calibre/devices/mtp/windows/device_enumeration.cpp
+++ b/src/calibre/devices/mtp/windows/device_enumeration.cpp
@@ -256,12 +256,10 @@ get_device_information(CComPtr<IPortableDevice> &device, CComPtr<IPortableDevice
 
     bool has_storage = false;
     for (i = 0; i < num_of_categories && !has_storage; i++) {
-        PROPVARIANT pv;
-        PropVariantInit(&pv);
+        prop_variant pv;
         if (SUCCEEDED(categories->GetAt(i, &pv)) && pv.puuid != NULL) {
             if (IsEqualGUID(WPD_FUNCTIONAL_CATEGORY_STORAGE, *pv.puuid)) has_storage = true;
         }
-        PropVariantClear(&pv);
     }
     PyDict_SetItemString(ans, "has_storage", has_storage ? Py_True : Py_False);
 
diff --git a/src/calibre/utils/windows/common.h b/src/calibre/utils/windows/common.h
index 91b90f6fef..eccfd6e255 100644
--- a/src/calibre/utils/windows/common.h
+++ b/src/calibre/utils/windows/common.h
@@ -27,3 +27,11 @@ set_error_from_hresult(PyObject *exc_type, const char *file, const int line, con
 typedef generic_raii<wchar_t*, CoTaskMemFree, NULL> com_wchar_raii;
 static inline void handle_destructor(HANDLE p) { CloseHandle(p); }
 typedef generic_raii<HANDLE, handle_destructor, INVALID_HANDLE_VALUE> handle_raii;
+
+struct prop_variant : PROPVARIANT {
+	prop_variant(VARTYPE vt=VT_EMPTY) noexcept : PROPVARIANT{} { PropVariantInit(this); this->vt = vt;  }
+
+    ~prop_variant() noexcept { clear(); }
+
+    void clear() noexcept { PropVariantClear(this); }
+};