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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at */
#include "mozilla/widget/filedialog/WinFileDialogCommands.h"
#include <type_traits>
#include <shobjidl.h>
#include <shtypes.h>
#include <winerror.h>
#include "WinUtils.h"
#include "mozilla/Logging.h"
#include "mozilla/RefPtr.h"
#include "mozilla/UniquePtrExtensions.h"
#include "mozilla/WinHeaderOnlyUtils.h"
#include "mozilla/ipc/ProtocolUtils.h"
#include "mozilla/ipc/UtilityProcessManager.h"
#include "mozilla/mscom/ApartmentRegion.h"
#include "nsThreadUtils.h"
namespace mozilla::widget::filedialog {
// Visitor to apply commands to the dialog.
struct Applicator {
IFileDialog* dialog = nullptr;
HRESULT Visit(Command const& c) {
switch (c.type()) {
case Command::T__None:
case Command::TSetOptions:
return Apply(c.get_SetOptions());
case Command::TSetTitle:
return Apply(c.get_SetTitle());
case Command::TSetOkButtonLabel:
return Apply(c.get_SetOkButtonLabel());
case Command::TSetFolder:
return Apply(c.get_SetFolder());
case Command::TSetFileName:
return Apply(c.get_SetFileName());
case Command::TSetDefaultExtension:
return Apply(c.get_SetDefaultExtension());
case Command::TSetFileTypes:
return Apply(c.get_SetFileTypes());
case Command::TSetFileTypeIndex:
return Apply(c.get_SetFileTypeIndex());
HRESULT Apply(SetOptions const& c) { return dialog->SetOptions(c.options()); }
HRESULT Apply(SetTitle const& c) { return dialog->SetTitle(c.title().get()); }
HRESULT Apply(SetOkButtonLabel const& c) {
return dialog->SetOkButtonLabel(c.label().get());
HRESULT Apply(SetFolder const& c) {
RefPtr<IShellItem> folder;
if (SUCCEEDED(SHCreateItemFromParsingName(
c.path().get(), nullptr, IID_IShellItem, getter_AddRefs(folder)))) {
return dialog->SetFolder(folder);
// graciously accept that the provided path may have been nonsense
return S_OK;
HRESULT Apply(SetFileName const& c) {
return dialog->SetFileName(c.filename().get());
HRESULT Apply(SetDefaultExtension const& c) {
return dialog->SetDefaultExtension(c.extension().get());
HRESULT Apply(SetFileTypes const& c) {
std::vector<COMDLG_FILTERSPEC> vec;
for (auto const& filter : c.filterList()) {
{.pszName =, .pszSpec = filter.spec().get()});
return dialog->SetFileTypes(vec.size(),;
HRESULT Apply(SetFileTypeIndex const& c) {
return dialog->SetFileTypeIndex(c.index());
namespace {
static HRESULT GetShellItemPath(IShellItem* aItem, nsString& aResultString) {
mozilla::UniquePtr<wchar_t, CoTaskMemFreeDeleter> str;
HRESULT const hr =
aItem->GetDisplayName(SIGDN_FILESYSPATH, getter_Transfers(str));
if (SUCCEEDED(hr)) {
return hr;
} // namespace
#define MOZ_ENSURE_HRESULT_OK(call_) \
do { \
HRESULT const _tmp_hr_ = (call_); \
if (FAILED(_tmp_hr_)) return Err(_tmp_hr_); \
} while (0)
mozilla::Result<RefPtr<IFileDialog>, HRESULT> MakeFileDialog(
FileDialogType type) {
RefPtr<IFileDialog> dialog;
CLSID const clsid = type == FileDialogType::Open ? CLSID_FileOpenDialog
: CLSID_FileSaveDialog;
HRESULT const hr = CoCreateInstance(clsid, nullptr, CLSCTX_INPROC_SERVER,
IID_IFileDialog, getter_AddRefs(dialog));
return std::move(dialog);
HRESULT ApplyCommands(::IFileDialog* dialog,
nsTArray<Command> const& commands) {
Applicator applicator{.dialog = dialog};
for (auto const& cmd : commands) {
HRESULT const hr = applicator.Visit(cmd);
if (FAILED(hr)) {
return hr;
return S_OK;
mozilla::Result<Results, HRESULT> GetFileResults(::IFileDialog* dialog) {
using widget::WinUtils;
// Extract which filter type the user selected
UINT index;
// single selection
if ((fos & FOS_ALLOWMULTISELECT) == 0) {
RefPtr<IShellItem> item;
if (!item) {
return Err(E_FAIL);
nsAutoString path;
MOZ_ENSURE_HRESULT_OK(GetShellItemPath(item, path));
return Results({path}, index);
// multiple selection
RefPtr<IFileOpenDialog> openDlg;
dialog->QueryInterface(IID_IFileOpenDialog, getter_AddRefs(openDlg));
if (!openDlg) {
MOZ_ASSERT(false, "a file-save dialog was given FOS_ALLOWMULTISELECT?");
return Err(E_UNEXPECTED);
RefPtr<IShellItemArray> items;
if (!items) {
return Err(E_FAIL);
nsTArray<nsString> paths;
DWORD count = 0;
for (DWORD idx = 0; idx < count; idx++) {
RefPtr<IShellItem> item;
MOZ_ENSURE_HRESULT_OK(items->GetItemAt(idx, getter_AddRefs(item)));
nsAutoString str;
MOZ_ENSURE_HRESULT_OK(GetShellItemPath(item, str));
return Results(std::move(paths), std::move(index));
mozilla::Result<nsString, HRESULT> GetFolderResults(::IFileDialog* dialog) {
RefPtr<IShellItem> item;
if (!item) {
// shouldn't happen -- probably a precondition failure on our part, but
// might be due to misbehaving shell extensions?
"unexpected lack of item: was `Show`'s return value checked?");
return Err(E_FAIL);
// If the user chose a Win7 Library, resolve to the library's
// default save folder.
RefPtr<IShellLibrary> shellLib;
RefPtr<IShellItem> folderPath;
CoCreateInstance(CLSID_ShellLibrary, nullptr, CLSCTX_INPROC_SERVER,
IID_IShellLibrary, getter_AddRefs(shellLib)));
if (shellLib && SUCCEEDED(shellLib->LoadLibraryFromItem(item, STGM_READ)) &&
SUCCEEDED(shellLib->GetDefaultSaveFolder(DSFT_DETECT, IID_IShellItem,
getter_AddRefs(folderPath)))) {
// get the folder's file system path
nsAutoString str;
MOZ_ENSURE_HRESULT_OK(GetShellItemPath(item, str));
return str;
namespace detail {
void LogProcessingError(LogModule* aModule, ipc::IProtocol* aCaller,
ipc::HasResultCodes::Result aCode,
const char* aReason) {
LogLevel const level = [&]() {
switch (aCode) {
case ipc::HasResultCodes::MsgProcessed:
// Normal operation. (We probably never actually get this code.)
return LogLevel::Verbose;
case ipc::HasResultCodes::MsgDropped:
return LogLevel::Verbose;
return LogLevel::Error;
// Processing errors are sometimes unhelpfully formatted. We can't fix that
// directly because the unhelpful formatting has made its way to telemetry
// (table `telemetry.socorro_crash`, column `ipc_channel_error`) and is being
// aggregated on. :(
nsCString reason(aReason);
if (reason.Last() == '\n') {
reason.Truncate(reason.Length() - 1);
if (MOZ_LOG_TEST(aModule, level)) {
const char* const side = [&]() {
switch (aCaller->GetSide()) {
case ipc::ParentSide:
return "parent";
case ipc::ChildSide:
return "child";
case ipc::UnknownSide:
return "unknown side";
return "<illegal value>";
const char* const errorStr = [&]() {
switch (aCode) {
case ipc::HasResultCodes::MsgProcessed:
return "Processed";
case ipc::HasResultCodes::MsgDropped:
return "Dropped";
case ipc::HasResultCodes::MsgNotKnown:
return "NotKnown";
case ipc::HasResultCodes::MsgNotAllowed:
return "NotAllowed";
case ipc::HasResultCodes::MsgPayloadError:
return "PayloadError";
case ipc::HasResultCodes::MsgProcessingError:
return "ProcessingError";
case ipc::HasResultCodes::MsgRouteError:
return "RouteError";
case ipc::HasResultCodes::MsgValueError:
return "ValueError";
return "<illegal error type>";
MOZ_LOG(aModule, level,
("%s [%s]: IPC error (%s): %s", aCaller->GetProtocolName(), side,
errorStr, reason.get()));
if (level == LogLevel::Error) {
// kill the child process...
if (aCaller->GetSide() == ipc::ParentSide) {
// ... which isn't us
} else {
// ... which (presumably) is us
CrashReporter::Annotation::ipc_channel_error, reason);
MOZ_CRASH("IPC error");
// Given a (synchronous) Action returning a Result<T, HRESULT>, perform that
// action on a new single-purpose "File Dialog" thread, with COM initialized as
// STA. (The thread will be destroyed afterwards.)
// Returns a Promise which will resolve to T (if the action returns Ok) or
// reject with an HRESULT (if the action either returns Err or couldn't be
// performed).
template <typename Res, typename Action, size_t N>
RefPtr<Promise<Res>> SpawnFileDialogThread(const char (&where)[N],
Action action) {
RefPtr<nsIThread> thread;
nsresult rv = NS_NewNamedThread("File Dialog", getter_AddRefs(thread),
nullptr, {.isUiThread = true});
if (NS_FAILED(rv)) {
return Promise<Res>::CreateAndReject((HRESULT)rv, where);
// `thread` is single-purpose, and should not perform any additional work
// after `action`. Shut it down after we've dispatched that.
auto close_thread_ = MakeScopeExit([&]() {
auto const res = thread->AsyncShutdown();
std::is_same_v<uint32_t, std::underlying_type_t<decltype(res)>>);
if (NS_FAILED(res)) {
MOZ_LOG(sLogFileDialog, LogLevel::Warning,
("thread->AsyncShutdown() failed: res=0x%08" PRIX32,
// our eventual return value
RefPtr promise = MakeRefPtr<typename Promise<Res>::Private>(where);
// alias to reduce indentation depth
auto const dispatch = [&](auto closure) {
return thread->DispatchToQueue(
NS_NewRunnableFunction(where, std::move(closure)),
dispatch([thread, promise, where, action = std::move(action)]() {
// Like essentially all COM UI components, the file dialog is STA: it must
// be associated with a specific thread to create its HWNDs and receive
// messages for them. If it's launched from a thread in the multithreaded
// apartment (including via implicit MTA), COM will proxy out to the
// process's main STA thread, and the file-dialog's modal loop will run
// there.
// This of course would completely negate any point in using a separate
// thread, since behind the scenes the dialog would still be running on the
// process's main thread. In particular, under that arrangement, file
// dialogs (and other nested modal loops, like those performed by
// `SpinEventLoopUntil`) will resolve in strictly LIFO order, effectively
// remaining suspended until all later modal loops resolve.
// To avoid this, we initialize COM as STA, so that it (rather than the main
// STA thread) is the file dialog's "home" thread and the IFileDialog's home
// apartment.
mozilla::mscom::STARegion staRegion;
if (!staRegion) {
MOZ_LOG(sLogFileDialog, LogLevel::Error,
("COM init failed on file dialog thread: hr = %08lx",
HRESULT const hr = ::CoGetApartmentType(&at, &atq);
MOZ_LOG(sLogFileDialog, LogLevel::Error,
(" current COM apartment state: hr = %08lX, APTTYPE = "
hr, at, atq));
// If this happens in the utility process, crash so we learn about it.
// (TODO: replace this with a telemetry ping.)
if (!XRE_IsParentProcess()) {
// Preserve relevant data on the stack for later analysis.
std::tuple volatile info{staRegion.GetHResult(), hr, at, atq};
MOZ_CRASH("Could not initialize COM STA in utility process");
// If this happens in the parent process, don't crash; just fall back to a
// nested modal loop. This isn't ideal, but it will probably still work
// well enough for the common case, wherein no other modal loops are
// active.
// (TODO: replace this with a telemetry ping, too.)
// Actually invoke the action and report the result.
Result<Res, HRESULT> val = action();
if (val.isErr()) {
promise->Reject(val.unwrapErr(), where);
} else {
promise->Resolve(val.unwrap(), where);
return promise;
// For F returning `Result<T, E>`, yields the type `T`.
template <typename F, typename... Args>
using inner_result_of =
typename std::remove_reference_t<decltype(std::declval<F>()(
template <typename ExtractorF,
typename RetT = inner_result_of<ExtractorF, IFileDialog*>>
auto SpawnPickerT(HWND parent, FileDialogType type, ExtractorF&& extractor,
nsTArray<Command> commands) -> RefPtr<Promise<Maybe<RetT>>> {
return detail::SpawnFileDialogThread<Maybe<RetT>>(
[=, commands = std::move(commands)]() -> Result<Maybe<RetT>, HRESULT> {
// On Win10, the picker doesn't support per-monitor DPI, so we create it
// with our context set temporarily to system-dpi-aware.
WinUtils::AutoSystemDpiAware dpiAwareness;
RefPtr<IFileDialog> dialog;
MOZ_TRY_VAR(dialog, MakeFileDialog(type));
if (HRESULT const rv = ApplyCommands(dialog, commands); FAILED(rv)) {
return mozilla::Err(rv);
if (HRESULT const rv = dialog->Show(parent); FAILED(rv)) {
return Result<Maybe<RetT>, HRESULT>(Nothing());
return mozilla::Err(rv);
RetT res;
MOZ_TRY_VAR(res, extractor(dialog.get()));
return Some(res);
} // namespace detail
RefPtr<Promise<Maybe<Results>>> SpawnFilePicker(HWND parent,
FileDialogType type,
nsTArray<Command> commands) {
return detail::SpawnPickerT(parent, type, GetFileResults,
RefPtr<Promise<Maybe<nsString>>> SpawnFolderPicker(HWND parent,
nsTArray<Command> commands) {
return detail::SpawnPickerT(parent, FileDialogType::Open, GetFolderResults,
} // namespace mozilla::widget::filedialog