Re: emscripten and qt5 for wasm reading files from the local file system

Balázs Varga Mon, 17 Oct 2022 02:29:15 -0700

Hi!

I would have a question about the FS.writeFile function.


I tried to use is in c++ similar like this:
https://github.com/emscripten-core/emscripten/issues/17230

But didn't worked for me with this:

void Test::read()
{
    auto onFileReady = [=](const QString &fileName, const QByteArray
&fileContents) {
        if (fileName.isEmpty()) {
            // Report error1
        } else {
            emscripten::val fileContentView =
emscripten::val(emscripten::typed_memory_view(fileContents.size(),
fileContents.constData()));
            emscripten::val fileContentCopy =
emscripten::val::global("ArrayBuffer").new_(fileContents.size());
            emscripten::val fileContentCopyView =
emscripten::val::global("Uint8Array").new_(fileContentCopy);
            fileContentCopyView.call<void>("set", fileContentView);
            //emscripten::val contentArray = emscripten::val::array();
            //contentArray.call<void>("push", fileContentCopyView);
            std::string path = fileName.toStdString();
            EM_ASM({
                FS.writeFile(path, new Uint8Array([ 1, 2, 3, 4 ]));
            });
        }
    };

    QFileDialog::getOpenFileContent("*.*", onFileReady);
}

If I tried to use a variable like 'path' in the example, it didn't work.
EM_ASM({
          FS.writeFile(path, new Uint8Array([ 1, 2, 3, 4 ]));
});

But If I used like this, it works:
EM_ASM({
          FS.writeFile("/write_file.txt", new Uint8Array([ 1, 2, 3, 4 ]));
});

So my question is, how can I use a variable inside the EM_ASM({ }) ?
Furthermore, how can I convert a char* to Uint8Array for the FS.writeFile()
function? I tried a lot of ways (like in the example with emscripten::val)
but it didn't work.

Thanks for the help in advance.

All the best,
Balázs

Balázs Varga <balazs.varga...@gmail.com> ezt írta (időpont: 2022. okt. 14.,
P, 12:23):

> Thanks for getting back to me. :) Yes, the code is a c++ and not a JS
> library, so MAIN_THREAD_EM_ASM can be useful. But I have no idea yet how to
> make it work with that.
>
> Best,
> Balázs
>
> 'Sam Clegg' via emscripten-discuss <emscripten-discuss@googlegroups.com>
> ezt írta (időpont: 2022. okt. 13., Cs, 18:35):
>
>> It looks like that API only works on the main thread (since it uses the
>> DOM).
>>
>> If you really need to call such APIs on a background thread there are
>> various ways to proxy the work back to the main thread.  See
>> https://emscripten.org/docs/porting/pthreads.html#proxying.   If the
>> code in question is not a JS library (e.g. if its written in EM_JS or
>> EM_ASM) you can use `MAIN_THREAD_EM_ASM` and/or
>> `emscripten_sync_run_in_main_thread` helpers.
>>
>> cheers,
>> sam
>>
>>
>> On Thu, Oct 13, 2022 at 8:31 AM Balázs Varga <balazs.varga...@gmail.com>
>> wrote:
>>
>>> Hi!
>>>
>>> I run into a problem with
>>> QFileDialog::getOpenFileContent function, which are use to access to the
>>> local filesystem with emscripten:
>>> https://doc.qt.io/qt-5/qfiledialog.html#getOpenFileContent
>>>
>>> I tried to call it on a different thread then what on the wasm
>>> application is running:
>>> std::thread th1 (QFileDialog::getOpenFileContent, "*.*", onFileReady);
>>> th1.join();
>>>
>>> But in that case, it froze at the emscripten part in the openFileDialog
>>> function and no file dialogue was opened.
>>> emscripten::val document = emscripten::val::global("document");
>>> emscripten::val input = document.call<emscripten::val>("createElement",
>>> std::string("input"));
>>>
>>>
>>> *I got the error message at creating the input value.*
>>>
>>> *https://codereview.qt-project.org/c/qt/qtbase/+/250461/7/src/gui/platform/wasm/qwasmlocalfileaccess.cpp#129*
>>> <https://codereview.qt-project.org/c/qt/qtbase/+/250461/7/src/gui/platform/wasm/qwasmlocalfileaccess.cpp#129>
>>>
>>> Running on the main thread there is no error and works fine.
>>> Any idea what could be the problem/solution here?
>>> I got this error message:
>>>
>>> worker.js onmessage() captured an uncaught exception: TypeError: Cannot
>>> read properties of undefined (reading 'createElement')
>>> self.onmessage @ soffice.worker.js:207
>>> soffice.worker.js:208 TypeError: Cannot read properties of undefined
>>> (reading 'createElement')
>>>     at methodCaller_emscripten$$val_$std$$string$ (eval at new_
>>> (47933e67-c694-46fe-af70-91dc8b50859c:8694:27), <anonymous>:5:20)
>>>     at __emval_call_method (47933e67-c694-46fe-af70-91dc8b50859c:9267:14)
>>>     at emscripten::internal::MethodCaller<emscripten::val,
>>> std::__2::basic_string<char, std::__2::char_traits<char>,
>>> std::__2::allocator<char> > >::call(emscripten::internal::_EM_VAL*, char
>>> const*, std::__2::basic_string<char, std::__2::char_traits<char>,
>>> std::__2::allocator<char>
>>> emscripten::internal::MethodCaller<emscripten::val,
>>> std::__2::basic_string<char, std::__2::char_traits<char>,
>>> std::__2::allocator<char> > >::call(emscripten::internal::_EM_VAL*, char
>>> const*, std::__2::basic_string<char, std::__2::char_traits<char>,
>>> std::__2::allocator<char> >&&) (val.h:278)
>>>     at emscripten::val emscripten::val::call<emscripten::val,
>>> std::__2::basic_string<char, std::__2::char_traits<char>,
>>> std::__2::allocator<char> > >(char const*, std::__2::basic_string<char,
>>> std::__2::char_traits<char>, std::__2::allocator<char> >&&) emscripten::val
>>> emscripten::val::call<emscripten::val, std::__2::basic_string<char,
>>> std::__2::char_traits<char>, std::__2::allocator<char> > >(char const*,
>>> std::__2::basic_string<char, std::__2::char_traits<char>,
>>> std::__2::allocator<char> >&&) const (val.h:498)
>>>     at QWasmLocalFileAccess::openFileDialog(std::__2::basic_string<char,
>>> std::__2::char_traits<char>, std::__2::allocator<char> > const&,
>>> QWasmLocalFileAccess::FileSelectMode, std::__2::function<void
>>> (qstdweb::FileList const&)>
>>> QWasmLocalFileAccess::openFileDialog(std::__2::basic_string<char,
>>> std::__2::char_traits<char>, std::__2::allocator<char> > const&,
>>> QWasmLocalFileAccess::FileSelectMode, std::__2::function<void
>>> (qstdweb::FileList const&)> const&) (qwasmlocalfileaccess.cpp:131)
>>>     at QWasmLocalFileAccess::openFiles(std::__2::basic_string<char,
>>> std::__2::char_traits<char>, std::__2::allocator<char> > const&,
>>> QWasmLocalFileAccess::FileSelectMode, std::__2::function<void (int)>
>>> const&, std::__2::function<char* (unsigned long long,
>>> std::__2::basic_string<char, std::__2::char_traits<char>,
>>> std::__2::allocator<char> >)> const&, std::__2::function<void ()>
>>> QWasmLocalFileAccess::openFiles(std::__2::basic_string<char,
>>> std::__2::char_traits<char>, std::__2::allocator<char> > const&,
>>> QWasmLocalFileAccess::FileSelectMode, std::__2::function<void (int)>
>>> const&, std::__2::function<char* (unsigned long long,
>>> std::__2::basic_string<char, std::__2::char_traits<char>,
>>> std::__2::allocator<char> >)> const&, std::__2::function<void ()> const&)
>>> (qwasmlocalfileaccess.cpp:156)
>>>     at QWasmLocalFileAccess::openFile(std::__2::basic_string<char,
>>> std::__2::char_traits<char>, std::__2::allocator<char> > const&,
>>> std::__2::function<void (bool)> const&, std::__2::function<char* (unsigned
>>> long long, std::__2::basic_string<char, std::__2::char_traits<char>,
>>> std::__2::allocator<char> >)> const&, std::__2::function<void ()>
>>> QWasmLocalFileAccess::openFile(std::__2::basic_string<char,
>>> std::__2::char_traits<char>, std::__2::allocator<char> > const&,
>>> std::__2::function<void (bool)> const&, std::__2::function<char* (unsigned
>>> long long, std::__2::basic_string<char, std::__2::char_traits<char>,
>>> std::__2::allocator<char> >)> const&, std::__2::function<void ()> const&)
>>> (qwasmlocalfileaccess.cpp:169)
>>>     at QFileDialog::getOpenFileContent(QString const&,
>>> std::__2::function<void (QString const&, QByteArray const&)>
>>> QFileDialog::getOpenFileContent(QString const&, std::__2::function<void
>>> (QString const&, QByteArray const&)> const&)::$_2::operator()()
>>> (qfiledialog.cpp:2444)
>>>     at
>>> decltype(std::__2::forward<QFileDialog::getOpenFileContent(QString const&,
>>> std::__2::function<void (QString const&, QByteArray const&)>
>>> const&)::$_2&>(fp)())
>>> std::__2::__invoke<QFileDialog::getOpenFileContent(QString const&,
>>> std::__2::function<void (QString const&, QByteArray const&)>
>>> const&)::$_2&>(QFileDialog::getOpenFileContent(QString const&,
>>> std::__2::function<void (QString const&, QByteArray const&)>
>>> decltype(std::__2::forward<QFileDialog::getOpenFileContent(QString const&,
>>> std::__2::function<void (QString const&, QByteArray const&)>
>>> const&)::$_2&>(fp)())
>>> std::__2::__invoke<QFileDialog::getOpenFileContent(QString const&,
>>> std::__2::function<void (QString const&, QByteArray const&)>
>>> const&)::$_2&>(QFileDialog::getOpenFileContent(QString const&,
>>> std::__2::function<void (QString const&, QByteArray const&)> const&)::$_2&)
>>> (type_traits:3694)
>>>     at void std::__2::__invoke_void_return_wrapper<void,
>>> true>::__call<QFileDialog::getOpenFileContent(QString const&,
>>> std::__2::function<void (QString const&, QByteArray const&)>
>>> const&)::$_2&>(QFileDialog::getOpenFileContent(QString const&,
>>> std::__2::function<void (QString const&, QByteArray const&)> void
>>> std::__2::__invoke_void_return_wrapper<void,
>>> true>::__call<QFileDialog::getOpenFileContent(QString const&,
>>> std::__2::function<void (QString const&, QByteArray const&)>
>>> const&)::$_2&>(QFileDialog::getOpenFileContent(QString const&,
>>> std::__2::function<void (QString const&, QByteArray const&)> const&)::$_2&)
>>> (__functional_base:348)worker.js onmessage() captured an uncaught
>>> exception: TypeError: Cannot read properties of undefined (reading
>>> 'createElement')
>>> self.onmessage @ soffice.worker.js:207
>>> soffice.worker.js:208 TypeError: Cannot read properties of undefined
>>> (reading 'createElement')
>>>     at methodCaller_emscripten$$val_$std$$string$ (eval at new_
>>> (47933e67-c694-46fe-af70-91dc8b50859c:8694:27), <anonymous>:5:20)
>>>     at __emval_call_method (47933e67-c694-46fe-af70-91dc8b50859c:9267:14)
>>>     at emscripten::internal::MethodCaller<emscripten::val,
>>> std::__2::basic_string<char, std::__2::char_traits<char>,
>>> std::__2::allocator<char> > >::call(emscripten::internal::_EM_VAL*, char
>>> const*, std::__2::basic_string<char, std::__2::char_traits<char>,
>>> std::__2::allocator<char>
>>> emscripten::internal::MethodCaller<emscripten::val,
>>> std::__2::basic_string<char, std::__2::char_traits<char>,
>>> std::__2::allocator<char> > >::call(emscripten::internal::_EM_VAL*, char
>>> const*, std::__2::basic_string<char, std::__2::char_traits<char>,
>>> std::__2::allocator<char> >&&) (val.h:278)
>>>     at emscripten::val emscripten::val::call<emscripten::val,
>>> std::__2::basic_string<char, std::__2::char_traits<char>,
>>> std::__2::allocator<char> > >(char const*, std::__2::basic_string<char,
>>> std::__2::char_traits<char>, std::__2::allocator<char> >&&) emscripten::val
>>> emscripten::val::call<emscripten::val, std::__2::basic_string<char,
>>> std::__2::char_traits<char>, std::__2::allocator<char> > >(char const*,
>>> std::__2::basic_string<char, std::__2::char_traits<char>,
>>> std::__2::allocator<char> >&&) const (val.h:498)
>>>     at QWasmLocalFileAccess::openFileDialog(std::__2::basic_string<char,
>>> std::__2::char_traits<char>, std::__2::allocator<char> > const&,
>>> QWasmLocalFileAccess::FileSelectMode, std::__2::function<void
>>> (qstdweb::FileList const&)>
>>> QWasmLocalFileAccess::openFileDialog(std::__2::basic_string<char,
>>> std::__2::char_traits<char>, std::__2::allocator<char> > const&,
>>> QWasmLocalFileAccess::FileSelectMode, std::__2::function<void
>>> (qstdweb::FileList const&)> const&) (qwasmlocalfileaccess.cpp:131)
>>>     at QWasmLocalFileAccess::openFiles(std::__2::basic_string<char,
>>> std::__2::char_traits<char>, std::__2::allocator<char> > const&,
>>> QWasmLocalFileAccess::FileSelectMode, std::__2::function<void (int)>
>>> const&, std::__2::function<char* (unsigned long long,
>>> std::__2::basic_string<char, std::__2::char_traits<char>,
>>> std::__2::allocator<char> >)> const&, std::__2::function<void ()>
>>> QWasmLocalFileAccess::openFiles(std::__2::basic_string<char,
>>> std::__2::char_traits<char>, std::__2::allocator<char> > const&,
>>> QWasmLocalFileAccess::FileSelectMode, std::__2::function<void (int)>
>>> const&, std::__2::function<char* (unsigned long long,
>>> std::__2::basic_string<char, std::__2::char_traits<char>,
>>> std::__2::allocator<char> >)> const&, std::__2::function<void ()> const&)
>>> (qwasmlocalfileaccess.cpp:156)
>>>     at QWasmLocalFileAccess::openFile(std::__2::basic_string<char,
>>> std::__2::char_traits<char>, std::__2::allocator<char> > const&,
>>> std::__2::function<void (bool)> const&, std::__2::function<char* (unsigned
>>> long long, std::__2::basic_string<char, std::__2::char_traits<char>,
>>> std::__2::allocator<char> >)> const&, std::__2::function<void ()>
>>> QWasmLocalFileAccess::openFile(std::__2::basic_string<char,
>>> std::__2::char_traits<char>, std::__2::allocator<char> > const&,
>>> std::__2::function<void (bool)> const&, std::__2::function<char* (unsigned
>>> long long, std::__2::basic_string<char, std::__2::char_traits<char>,
>>> std::__2::allocator<char> >)> const&, std::__2::function<void ()> const&)
>>> (qwasmlocalfileaccess.cpp:169)
>>>     at QFileDialog::getOpenFileContent(QString const&,
>>> std::__2::function<void (QString const&, QByteArray const&)>
>>> QFileDialog::getOpenFileContent(QString const&, std::__2::function<void
>>> (QString const&, QByteArray const&)> const&)::$_2::operator()()
>>> (qfiledialog.cpp:2444)
>>>     at
>>> decltype(std::__2::forward<QFileDialog::getOpenFileContent(QString const&,
>>> std::__2::function<void (QString const&, QByteArray const&)>
>>> const&)::$_2&>(fp)())
>>> std::__2::__invoke<QFileDialog::getOpenFileContent(QString const&,
>>> std::__2::function<void (QString const&, QByteArray const&)>
>>> const&)::$_2&>(QFileDialog::getOpenFileContent(QString const&,
>>> std::__2::function<void (QString const&, QByteArray const&)>
>>> decltype(std::__2::forward<QFileDialog::getOpenFileContent(QString const&,
>>> std::__2::function<void (QString const&, QByteArray const&)>
>>> const&)::$_2&>(fp)())
>>> std::__2::__invoke<QFileDialog::getOpenFileContent(QString const&,
>>> std::__2::function<void (QString const&, QByteArray const&)>
>>> const&)::$_2&>(QFileDialog::getOpenFileContent(QString const&,
>>> std::__2::function<void (QString const&, QByteArray const&)> const&)::$_2&)
>>> (type_traits:3694)
>>>     at void std::__2::__invoke_void_return_wrapper<void,
>>> true>::__call<QFileDialog::getOpenFileContent(QString const&,
>>> std::__2::function<void (QString const&, QByteArray const&)>
>>> const&)::$_2&>(QFileDialog::getOpenFileContent(QString const&,
>>> std::__2::function<void (QString const&, QByteArray const&)> void
>>> std::__2::__invoke_void_return_wrapper<void,
>>> true>::__call<QFileDialog::getOpenFileContent(QString const&,
>>> std::__2::function<void (QString const&, QByteArray const&)>
>>> const&)::$_2&>(QFileDialog::getOpenFileContent(QString const&,
>>> std::__2::function<void (QString const&, QByteArray const&)> const&)::$_2&)
>>> (__functional_base:348)
>>>
>>> Thanks in advance,
>>> Balazs
>>>
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Re: emscripten and qt5 for wasm reading files from the local file system

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