qstdweb.cpp

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// Copyright (C) 2025 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
// Qt-Security score:critical reason:data-parser
 
#include "qstdweb_p.h"
#include "qwasmsuspendresumecontrol_p.h"
#include "qwasmglobal_p.h"
 
#include <QtCore/qcoreapplication.h>
#include <QtCore/qfile.h>
#include <QtCore/qmimedata.h>
 
#include <emscripten/emscripten.h>
#include <emscripten/bind.h>
#include <emscripten/val.h>
#include <emscripten/html5.h>
#include <emscripten/threading.h>
 
#include <cstdint>
#include <iostream>
 
#include <unordered_map>
 
QT_BEGIN_NAMESPACE
 
using namespace Qt::StringLiterals;
using emscripten::val;
 
namespace qstdweb {
 
static void usePotentialyUnusedSymbols()
{
    // Using this adds a reference on JSEvents and specialHTMLTargets which are always exported.
    // This hack is needed as it is currently impossible to specify a dollar sign in
    // target_link_options. The following is impossible:
    // DEFAULT_LIBRARY_FUNCS_TO_INCLUDE=$JSEvents
    // TODO(mikolajboc): QTBUG-108444, review this when cmake gets fixed.
    // Volatile is to make this unoptimizable, so that the function is referenced, but is not
    // called at runtime.
    volatile bool doIt = false;
    if (doIt)
        emscripten_set_wheel_callback(EMSCRIPTEN_EVENT_TARGET_WINDOW, 0, 0, NULL);
}
 
Q_CONSTRUCTOR_FUNCTION(usePotentialyUnusedSymbols)
typedef double uint53_t; // see Number.MAX_SAFE_INTEGER
namespace {
// Reads file in chunks in order to avoid holding two copies in memory at the same time
struct ChunkedFileReader
{
public:
    static void read(File file, char *buffer, uint32_t offset, uint32_t end,
                     std::function<void()> onCompleted)
    {
        (new ChunkedFileReader(end, std::move(onCompleted), std::move(file)))
                ->readNextChunk(offset, buffer);
    }
 
private:
    ChunkedFileReader(uint32_t end, std::function<void()> onCompleted, File file)
        : end(end), onCompleted(std::move(onCompleted)), file(std::move(file))
    {
    }
 
    void readNextChunk(uint32_t chunkBegin, char *chunkBuffer)
    {
        // Copy current chunk from JS memory to Wasm memory
        qstdweb::ArrayBuffer result = fileReader.result();
        qstdweb::Uint8Array(result).copyTo(chunkBuffer);
 
        // Read next chunk if not at buffer end
        const uint32_t nextChunkBegin = std::min(chunkBegin + result.byteLength(), end);
        if (nextChunkBegin == end) {
            onCompleted();
            delete this;
            return;
        }
        char *nextChunkBuffer = chunkBuffer + result.byteLength();
        fileReader.onLoad([this, nextChunkBegin, nextChunkBuffer](emscripten::val) {
            readNextChunk(nextChunkBegin, nextChunkBuffer);
        });
        const uint32_t nextChunkEnd = std::min(nextChunkBegin + chunkSize, end);
        qstdweb::Blob blob = file.slice(nextChunkBegin, nextChunkEnd);
        fileReader.readAsArrayBuffer(blob);
    }
 
    static constexpr uint32_t chunkSize = 256 * 1024;
 
    qstdweb::FileReader fileReader;
    uint32_t end;
    std::function<void()> onCompleted;
    File file;
};
 
#if defined(QT_STATIC)
 
EM_JS(bool, jsHaveAsyncify, (), { return typeof Asyncify !== "undefined"; });
EM_JS(bool, jsHaveJspi, (),
      { return typeof Asyncify !== "undefined" && !!Asyncify.makeAsyncFunction && (!!WebAssembly.Function || !!WebAssembly.Suspending); });
 
#else
 
bool jsHaveAsyncify() { return false; }
bool jsHaveJspi() { return false; }
 
#endif
} // namespace
 
ArrayBuffer::ArrayBuffer(uint32_t size)
{
    m_arrayBuffer = emscripten::val::global("ArrayBuffer").new_(size);
}
 
ArrayBuffer::ArrayBuffer(const emscripten::val &arrayBuffer)
    :m_arrayBuffer(arrayBuffer)
{
 
}
 
uint32_t ArrayBuffer::byteLength() const
{
    if (m_arrayBuffer.isUndefined() || m_arrayBuffer.isNull())
        return 0;
 
    return m_arrayBuffer["byteLength"].as<uint32_t>();
}
 
ArrayBuffer ArrayBuffer::slice(uint32_t begin, uint32_t end) const
{
    return ArrayBuffer(m_arrayBuffer.call<emscripten::val>("slice", begin, end));
}
 
emscripten::val ArrayBuffer::val() const
{
    return m_arrayBuffer;
}
 
Blob::Blob(const emscripten::val &blob)
    :m_blob(blob)
{
 
}
 
Blob Blob::fromArrayBuffer(const ArrayBuffer &arrayBuffer)
{
    auto array = emscripten::val::array();
    array.call<void>("push", arrayBuffer.val());
    return Blob(emscripten::val::global("Blob").new_(array));
}
 
uint32_t Blob::size() const
{
    return m_blob["size"].as<uint32_t>();
}
 
Blob Blob::copyFrom(const char *buffer, uint32_t size, std::string mimeType)
{
    Uint8Array contentCopy = Uint8Array::copyFrom(buffer, size);
 
    emscripten::val contentArray = emscripten::val::array();
    contentArray.call<void>("push", contentCopy.val());
    emscripten::val type = emscripten::val::object();
    type.set("type", std::move(mimeType));
    return Blob(emscripten::val::global("Blob").new_(contentArray, type));
}
 
// Copies content from the given buffer into a Blob object
Blob Blob::copyFrom(const char *buffer, uint32_t size)
{
    return copyFrom(buffer, size, "application/octet-stream");
}
 
Blob Blob::slice(uint32_t begin, uint32_t end) const
{
    return Blob(m_blob.call<emscripten::val>("slice", begin, end));
}
 
ArrayBuffer Blob::arrayBuffer_sync() const
{
    emscripten::val buffer;
    QList<uint32_t> handlers;
    qstdweb::Promise::make(
        handlers,
        m_blob,
        QStringLiteral("arrayBuffer"),
        {
            .thenFunc = [&buffer](emscripten::val arrayBuffer) {
                buffer = arrayBuffer;
        }
    });
    Promise::suspendExclusive(handlers);
    return ArrayBuffer(buffer);
}
 
emscripten::val Blob::val() const
{
    return m_blob;
}
 
File::File(const emscripten::val &file)
:m_file(file)
{
 
}
 
File::~File() = default;
 
File::File(const File &other) = default;
 
File::File(File &&other) = default;
 
File &File::operator=(const File &other) = default;
 
File &File::operator=(File &&other) = default;
 
 
Blob File::slice(uint64_t begin, uint64_t end) const
{
    return Blob(m_file.call<emscripten::val>("slice", uint53_t(begin), uint53_t(end)));
}
 
std::string File::name() const
{
    return m_file["name"].as<std::string>();
}
 
uint64_t File::size() const
{
    return uint64_t(m_file["size"].as<uint53_t>());
}
 
std::string Blob::type() const
{
    return m_blob["type"].as<std::string>();
}
 
// Streams partial file content into the given buffer asynchronously. The completed
// callback is called on completion.
void File::stream(uint32_t offset, uint32_t length, char *buffer,
                  std::function<void()> completed) const
{
    ChunkedFileReader::read(*this, buffer, offset, offset + length, std::move(completed));
}
 
// Streams file content into the given buffer asynchronously. The completed
// callback is called on completion.
void File::stream(char *buffer, std::function<void()> completed) const
{
    stream(0, size(), buffer, std::move(completed));
}
 
std::string File::type() const
{
    return m_file["type"].as<std::string>();
}
 
emscripten::val File::val() const
{
    return m_file;
}
 
FileUrlRegistration::FileUrlRegistration(File file)
{
    m_path = QString::fromStdString(emscripten::val::global("window")["URL"].call<std::string>(
        "createObjectURL", file.file()));
}
 
FileUrlRegistration::~FileUrlRegistration()
{
    emscripten::val::global("window")["URL"].call<void>("revokeObjectURL",
                                                        emscripten::val(m_path.toStdString()));
}
 
FileUrlRegistration::FileUrlRegistration(FileUrlRegistration &&other) = default;
 
FileUrlRegistration &FileUrlRegistration::operator=(FileUrlRegistration &&other) = default;
 
FileList::FileList(const emscripten::val &fileList)
    :m_fileList(fileList)
{
 
}
 
int FileList::length() const
{
    return m_fileList["length"].as<int>();
}
 
File FileList::item(int index) const
{
    return File(m_fileList[index]);
}
 
File FileList::operator[](int index) const
{
    return item(index);
}
 
emscripten::val FileList::val() const
{
    return m_fileList;
}
 
ArrayBuffer FileReader::result() const
{
    return ArrayBuffer(m_fileReader["result"]);
}
 
void FileReader::readAsArrayBuffer(const Blob &blob) const
{
    m_fileReader.call<void>("readAsArrayBuffer", blob.m_blob);
}
 
void FileReader::onLoad(const std::function<void(emscripten::val)> &onLoad)
{
    m_onLoad.reset();
    m_onLoad = std::make_unique<EventCallback>(m_fileReader, "load", onLoad);
}
 
void FileReader::onError(const std::function<void(emscripten::val)> &onError)
{
    m_onError.reset();
    m_onError = std::make_unique<EventCallback>(m_fileReader, "error", onError);
}
 
void FileReader::onAbort(const std::function<void(emscripten::val)> &onAbort)
{
    m_onAbort.reset();
    m_onAbort = std::make_unique<EventCallback>(m_fileReader, "abort", onAbort);
}
 
emscripten::val FileReader::val() const
{
    return m_fileReader;
}
 
// Constructs a Uint8Array which references the given emscripten::val, which must contain a JS Unit8Array
Uint8Array::Uint8Array(const emscripten::val &uint8Array)
: m_uint8Array(uint8Array)
{
 
}
 
// Constructs a Uint8Array which references an ArrayBuffer
Uint8Array::Uint8Array(const ArrayBuffer &buffer)
: m_uint8Array(Uint8Array::constructor_().new_(buffer.m_arrayBuffer))
{
 
}
 
// Constructs a Uint8Array which references a view into an ArrayBuffer
Uint8Array::Uint8Array(const ArrayBuffer &buffer, uint32_t offset, uint32_t length)
: m_uint8Array(Uint8Array::constructor_().new_(buffer.m_arrayBuffer, offset, length))
{
 
}
 
// Constructs a Uint8Array which references an area on the heap.
Uint8Array::Uint8Array(const char *buffer, uint32_t size)
:m_uint8Array(emscripten::typed_memory_view(size, buffer))
{
 
}
 
// Constructs a Uint8Array which allocates and references a new ArrayBuffer with the given size.
Uint8Array::Uint8Array(uint32_t size)
: m_uint8Array(Uint8Array::constructor_().new_(size))
{
 
}
 
ArrayBuffer Uint8Array::buffer() const
{
    return ArrayBuffer(m_uint8Array["buffer"]);
}
 
uint32_t Uint8Array::length() const
{
    return m_uint8Array["length"].as<uint32_t>();
}
 
void Uint8Array::set(const Uint8Array &source)
{
    m_uint8Array.call<void>("set", source.m_uint8Array); // copies source content
}
 
Uint8Array Uint8Array::subarray(uint32_t begin, uint32_t end)
{
    // Note: using uint64_t here errors with "Cannot convert a BigInt value to a number"
    // (see JS BigInt and Number types). Use uint32_t for now.
    return Uint8Array(m_uint8Array.call<emscripten::val>("subarray", begin, end));
}
 
// Copies the Uint8Array content to a destination on the heap
void Uint8Array::copyTo(char *destination) const
{
    Uint8Array(destination, length()).set(*this);
}
 
// Copies the Uint8Array content to a destination QByteArray
QByteArray Uint8Array::copyToQByteArray() const
{
    if (length() > std::numeric_limits<qsizetype>::max())
        return QByteArray();
 
    QByteArray destinationArray;
    destinationArray.resize(length());
    copyTo(destinationArray.data());
    return destinationArray;
}
 
// Copies the Uint8Array content to a destination on the heap
void Uint8Array::copy(char *destination, const Uint8Array &source)
{
    Uint8Array(destination, source.length()).set(source);
}
 
// Copies content from a source on the heap to a new Uint8Array object
Uint8Array Uint8Array::copyFrom(const char *buffer, uint32_t size)
{
    Uint8Array contentCopy(size);
    contentCopy.set(Uint8Array(buffer, size));
    return contentCopy;
}
 
// Copies content from a QByteArray to a new Uint8Array object
Uint8Array Uint8Array::copyFrom(const QByteArray &buffer)
{
    return copyFrom(buffer.constData(), buffer.size());
}
 
emscripten::val Uint8Array::val() const
{
    return m_uint8Array;
}
 
emscripten::val Uint8Array::constructor_()
{
    return emscripten::val::global("Uint8Array");
}
 
EventCallback::EventCallback(emscripten::val element, const std::string &name,
                             const std::function<void(emscripten::val)> &fn)
  :QWasmEventHandler(element, name, fn)
{
 
}
 
size_t qstdweb::Promise::State::s_numInstances = 0;
 
//
// When a promise settles, all attached handlers will be called in
// the order they where added.
//
// In particular a finally handler will be called according to its
// position in the call chain. Which is not necessarily at the end,
//
// This makes cleanup difficult. If we cleanup to early, we will remove
// handlers before they have a chance to be called. This would be the
// case if we add a finally handler in the Promise constructor.
//
// For correct cleanup it is necessary that it happens after the
// last handler has been called.
//
// We choose to implement this by making sure the last handler
// is always a finally handler.
//
// In this case we have multiple finally handlers, so any called
// handler checks if it is the last handler to be called.
// If it is, the cleanup is performed, otherwise cleanup
// is delayed to the last handler.
//
// We could try to let the handlers cleanup themselves, but this
// only works for finally handlers. A then or catch handler is not
// necessarily called, and would not cleanup itself.
//
// We could try to let a (then,catch) pair cleanup both handlers,
// under the assumption that one of them will always be called.
// This does not work in the case that we do not have both handlers,
// or if the then handler throws (both should be called in this case).
//
Promise& Promise::addThenFunction(std::function<void(emscripten::val)> thenFunc)
{
    QWasmSuspendResumeControl *suspendResume = QWasmSuspendResumeControl::get();
    Q_ASSERT(suspendResume);
 
    m_state->m_handlers.push_back(suspendResume->registerEventHandler(thenFunc));
    m_state->m_promise =
        m_state->m_promise.call<emscripten::val>(
            "then",
            suspendResume->jsEventHandlerAt(
                m_state->m_handlers.back()));
 
    addFinallyFunction([](){}); // Add a potential cleanup handler
    return (*this);
}
 
Promise& Promise::addCatchFunction(std::function<void(emscripten::val)> catchFunc)
{
    QWasmSuspendResumeControl *suspendResume = QWasmSuspendResumeControl::get();
    Q_ASSERT(suspendResume);
 
    m_state->m_handlers.push_back(suspendResume->registerEventHandler(catchFunc));
    m_state->m_promise =
        m_state->m_promise.call<emscripten::val>(
            "catch",
            suspendResume->jsEventHandlerAt(
                m_state->m_handlers.back()));
 
    addFinallyFunction([](){}); // Add a potential cleanup handler
    return (*this);
}
 
Promise& Promise::addFinallyFunction(std::function<void()> finallyFunc)
{
    QWasmSuspendResumeControl *suspendResume = QWasmSuspendResumeControl::get();
    Q_ASSERT(suspendResume);
 
    auto thisHandler = std::make_shared<uint32_t>((uint32_t)(-1));
    auto state = m_state;
 
    std::function<void(emscripten::val)> func =
        [state, thisHandler, finallyFunc](emscripten::val element) {
            Q_UNUSED(element);
 
            finallyFunc();
 
            // See comment at top, we can only do the cleanup
            // if we are the last handler in the handler chain
            if (state->m_handlers.back() == *thisHandler) {
                auto guard = state; // removeEventHandler will remove also this function
                QWasmSuspendResumeControl *suspendResume = QWasmSuspendResumeControl::get();
                Q_ASSERT(suspendResume);
                for (int i = 0; i < guard->m_handlers.size(); ++i) {
                    suspendResume->removeEventHandler(guard->m_handlers[i]);
                    guard->m_handlers[i] = (uint32_t)(-1);
                }
            }
        };
 
    *thisHandler = suspendResume->registerEventHandler(func);
    m_state->m_handlers.push_back(*thisHandler);
    m_state->m_promise =
        m_state->m_promise.call<emscripten::val>(
            "finally",
            suspendResume->jsEventHandlerAt(
                m_state->m_handlers.back()));
 
    return (*this);
}
 
void Promise::suspendExclusive()
{
    Promise::suspendExclusive(m_state->m_handlers);
}
 
emscripten::val Promise::getPromise() const
{
    return m_state->m_promise;
}
 
uint32_t Promise::adoptPromise(emscripten::val promise, PromiseCallbacks callbacks, QList<uint32_t> *handlers)
{
    Q_ASSERT_X(!!callbacks.catchFunc || !!callbacks.finallyFunc || !!callbacks.thenFunc,
        "Promise::adoptPromise", "must provide at least one callback function");
 
    QWasmSuspendResumeControl *suspendResume = QWasmSuspendResumeControl::get();
    Q_ASSERT(suspendResume);
 
    // Registers a possibly-empty callback with suspendresumecontrol. Returns
    // the the handler index if there was a valid callback, or nullopt.
    auto registerCallback = [suspendResume](std::function<void(emscripten::val)> cb) -> std::optional<uint32_t>{
        if (!cb)
            return std::nullopt;
        return std::optional<uint32_t>{suspendResume->registerEventHandler(std::move(cb))};
    };
 
    // Register callbacks with suspendresumecontrol, so that it can
    // resume the wasm instance when the promise resolves. The finally
    // callback is sepecial, since we remove the event handlers there
    // as cleanup, including the event handler for the cleanup function
    // itself.
    std::optional<uint32_t> thenIndex = registerCallback(std::move(callbacks.thenFunc));
    std::optional<uint32_t> catchIndex = registerCallback(std::move(callbacks.catchFunc));
    std::shared_ptr<uint32_t> finallyIndex = std::make_shared<uint32_t>();;
    auto finallyFunc = callbacks.finallyFunc;
 
    // 'Finally' callback which performs clean-up and calls the user-provided finally.
    auto finally = [suspendResume, thenIndex, catchIndex, finallyIndex, finallyFunc](emscripten::val){
 
        // Clean up event handlers
        if (thenIndex)
            suspendResume->removeEventHandler(*thenIndex);
        if (catchIndex)
            suspendResume->removeEventHandler(*catchIndex);
 
        // Call user finally
        if (finallyFunc)
            finallyFunc();
 
        // Remove the finally (this) event handler last
        suspendResume->removeEventHandler(*finallyIndex);
    };
 
    *finallyIndex = suspendResume->registerEventHandler(std::move(finally));
 
    // Set handlers on the promise
    if (thenIndex)
        promise =
                promise.call<emscripten::val>("then", suspendResume->jsEventHandlerAt(*thenIndex));
 
    if (catchIndex)
        promise = promise.call<emscripten::val>("catch",
                                                suspendResume->jsEventHandlerAt(*catchIndex));
 
    promise = promise.call<emscripten::val>("finally",
                                            suspendResume->jsEventHandlerAt(*finallyIndex));
 
    if (handlers) {
        if (thenIndex)
            handlers->push_back(*thenIndex);
        if (catchIndex)
            handlers->push_back(*catchIndex);
        handlers->push_back(*finallyIndex);
    }
    return *finallyIndex;
}
 
void Promise::suspendExclusive(QList<uint32_t> handlerIndices)
{
    QWasmSuspendResumeControl *suspendResume = QWasmSuspendResumeControl::get();
    Q_ASSERT(suspendResume);
    suspendResume->suspendExclusive(handlerIndices);
    suspendResume->sendPendingEvents();
}
 
void Promise::all(std::vector<emscripten::val> promises, PromiseCallbacks callbacks)
{
    auto arr = emscripten::val::array(promises);
    auto all = val::global("Promise").call<emscripten::val>("all", arr);
    adoptPromise(all, callbacks);
}
 
//  Asyncify and thread blocking: Normally, it's not possible to block the main
//  thread, except if asyncify is enabled. Secondary threads can always block.
//
//  haveAsyncify(): returns true if the main thread can block on QEventLoop::exec(),
//      if either asyncify 1 or 2 (JSPI) is available.
//
//  haveJspi(): returns true if asyncify 2 (JSPI) is available.
//
//  canBlockCallingThread(): returns true if the calling thread can block on
//      QEventLoop::exec(), using either asyncify or as a seconarday thread.
bool haveJspi()
{
    static bool HaveJspi = jsHaveJspi();
    return HaveJspi;
}
 
bool haveAsyncify()
{
    static bool HaveAsyncify = jsHaveAsyncify() || haveJspi();
    return HaveAsyncify;
}
 
bool canBlockCallingThread()
{
    return haveAsyncify() || !emscripten_is_main_runtime_thread();
}
 
BlobIODevice::BlobIODevice(Blob blob)
    : m_blob(blob)
{
 
}
 
bool BlobIODevice::open(QIODevice::OpenMode mode)
{
    if (mode.testFlag(QIODevice::WriteOnly))
        return false;
    return QIODevice::open(mode);
}
 
bool BlobIODevice::isSequential() const
{
    return false;
}
 
qint64 BlobIODevice::size() const
{
    return m_blob.size();
}
 
bool BlobIODevice::seek(qint64 pos)
{
    if (pos >= size())
        return false;
    return QIODevice::seek(pos);
}
 
qint64 BlobIODevice::readData(char *data, qint64 maxSize)
{
    uint64_t begin = QIODevice::pos();
    uint64_t end = std::min<uint64_t>(begin + maxSize, size());
    uint64_t size = end - begin;
    if (size > 0) {
        qstdweb::ArrayBuffer buffer = m_blob.slice(begin, end).arrayBuffer_sync();
        qstdweb::Uint8Array(buffer).copyTo(data);
    }
    return size;
}
 
qint64 BlobIODevice::writeData(const char *, qint64)
{
    Q_UNREACHABLE();
}
 
Uint8ArrayIODevice::Uint8ArrayIODevice(Uint8Array array)
    : m_array(array)
{
 
}
 
bool Uint8ArrayIODevice::open(QIODevice::OpenMode mode)
{
    return QIODevice::open(mode);
}
 
bool Uint8ArrayIODevice::isSequential() const
{
    return false;
}
 
qint64 Uint8ArrayIODevice::size() const
{
    return m_array.length();
}
 
bool Uint8ArrayIODevice::seek(qint64 pos)
{
    if (pos >= size())
        return false;
    return QIODevice::seek(pos);
}
 
qint64 Uint8ArrayIODevice::readData(char *data, qint64 maxSize)
{
    uint64_t begin = QIODevice::pos();
    uint64_t end = std::min<uint64_t>(begin + maxSize, size());
    uint64_t size = end - begin;
    if (size > 0)
        m_array.subarray(begin, end).copyTo(data);
    return size;
}
 
qint64 Uint8ArrayIODevice::writeData(const char *data, qint64 maxSize)
{
    uint64_t begin = QIODevice::pos();
    uint64_t end = std::min<uint64_t>(begin + maxSize, size());
    uint64_t size = end - begin;
    if (size > 0)
        m_array.subarray(begin, end).set(Uint8Array(data, size));
    return size;
}
 
FileSystemWritableFileStreamIODevice::FileSystemWritableFileStreamIODevice(FileSystemWritableFileStream stream)
    : m_stream(std::move(stream))
{
}
 
bool FileSystemWritableFileStreamIODevice::open(QIODevice::OpenMode mode)
{
    if (mode.testFlag(QIODevice::ReadOnly))
        return false;
    return QIODevice::open(mode);
}
 
void FileSystemWritableFileStreamIODevice::close()
{
    if (!isOpen()) {
        QIODevice::close();
        return;
    }
 
    QList<uint32_t> handlers;
    Promise::make(handlers, m_stream.val(), QStringLiteral("close"), {
        .thenFunc = [](emscripten::val) {
        }
    });
    Promise::suspendExclusive(handlers);
 
    QIODevice::close();
}
 
bool FileSystemWritableFileStreamIODevice::isSequential() const
{
    return false;
}
 
qint64 FileSystemWritableFileStreamIODevice::size() const
{
    return m_size;
}
 
bool FileSystemWritableFileStreamIODevice::seek(qint64 pos)
{
    bool success = false;
 
    emscripten::val seekParams = emscripten::val::object();
    seekParams.set("type", std::string("seek"));
    seekParams.set("position", static_cast<double>(pos));
    QList<uint32_t> handlers;
    Promise::make(handlers, m_stream.val(), QStringLiteral("write"), {
        .thenFunc = [&success](emscripten::val) {
            success = true;
        },
        .catchFunc = [](emscripten::val) {
        }
    }, seekParams);
    Promise::suspendExclusive(handlers);
 
    if (!success)
        return false;
 
    return QIODevice::seek(pos);
}
 
qint64 FileSystemWritableFileStreamIODevice::readData(char *, qint64)
{
    Q_UNREACHABLE();
}
 
qint64 FileSystemWritableFileStreamIODevice::writeData(const char *data, qint64 size)
{
    bool success = false;
 
    Uint8Array array = Uint8Array::copyFrom(data, size);
    QList<uint32_t> handlers;
    Promise::make(handlers, m_stream.val(), QStringLiteral("write"), {
        .thenFunc = [&success](emscripten::val) {
            success = true;
        },
        .catchFunc = [](emscripten::val) {
        }
    }, array.val());
    Promise::suspendExclusive(handlers);
 
    if (success) {
        qint64 newPos = pos() + size;
        m_size = std::max(m_size, newPos);
        return size;
    }
    return -1;
}
 
FileSystemWritableFileStream::FileSystemWritableFileStream(const emscripten::val &writableStream)
    : m_writableStream(writableStream)
{
}
 
emscripten::val FileSystemWritableFileStream::val() const
{
    return m_writableStream;
}
 
FileSystemFileHandle::FileSystemFileHandle(const emscripten::val &fileHandle)
    : m_fileHandle(fileHandle)
{
}
 
std::string FileSystemFileHandle::name() const
{
    return m_fileHandle["name"].as<std::string>();
}
 
std::string FileSystemFileHandle::kind() const
{
    return m_fileHandle["kind"].as<std::string>();
}
 
emscripten::val FileSystemFileHandle::val() const
{
    return m_fileHandle;
}
 
FileSystemFileIODevice::FileSystemFileIODevice(FileSystemFileHandle fileHandle)
    : m_fileHandle(fileHandle)
{
}
 
bool FileSystemFileIODevice::open(QIODevice::OpenMode mode)
{
    if (isOpen())
        return false;
 
    // Read mode: get the File and create a BlobIODevice
    if (mode & QIODevice::ReadOnly) {
        File file;
        bool success = false;
 
        QList<uint32_t> handlers;
        Promise::make(handlers, m_fileHandle.val(), QStringLiteral("getFile"), {
            .thenFunc = [&file, &success](emscripten::val fileVal) {
                file = File(fileVal);
                success = true;
            },
            .catchFunc = [](emscripten::val) {
            }
        });
        Promise::suspendExclusive(handlers);
 
        if (success) {
            m_blobDevice = std::make_unique<BlobIODevice>(file.slice(0, file.size()));
            m_size = file.size();
 
            if (!m_blobDevice->open(mode))
                return false;
        } else {
            return false;
        }
    }
 
    // Write mode: create a writable stream
    if (mode & QIODevice::WriteOnly) {
        FileSystemWritableFileStream writableStream;
        bool success = false;
 
        QList<uint32_t> handlers;
        Promise::make(handlers, m_fileHandle.val(), QStringLiteral("createWritable"), {
            .thenFunc = [&writableStream, &success](emscripten::val writable) {
                writableStream = FileSystemWritableFileStream(writable);
                success = true;
            },
            .catchFunc = [](emscripten::val) {
            }
        });
        Promise::suspendExclusive(handlers);
 
        if (success) {
            m_writableDevice = std::make_unique<FileSystemWritableFileStreamIODevice>(writableStream);
            if (!m_writableDevice->open(mode))
                return false;
        } else {
            return false;
        }
    }
 
    return QIODevice::open(mode);
}
 
void FileSystemFileIODevice::close()
{
    if (!isOpen()) {
        QIODevice::close();
        return;
    }
 
    if (m_writableDevice) {
        m_writableDevice->close();
        m_writableDevice.reset();
    }
    if (m_blobDevice) {
        m_blobDevice->close();
        m_blobDevice.reset();
    }
 
    QIODevice::close();
}
 
bool FileSystemFileIODevice::isSequential() const
{
    return false;
}
 
qint64 FileSystemFileIODevice::size() const
{
    return m_size;
}
 
bool FileSystemFileIODevice::seek(qint64 pos)
{
    if (m_blobDevice) {
        if (!m_blobDevice->seek(pos))
            return false;
    }
    if (m_writableDevice) {
        if (!m_writableDevice->seek(pos))
            return false;
    }
    return QIODevice::seek(pos);
}
 
qint64 FileSystemFileIODevice::readData(char *data, qint64 maxSize)
{
    if (!m_blobDevice)
        return -1;
 
    return m_blobDevice->read(data, maxSize);
}
 
qint64 FileSystemFileIODevice::writeData(const char *data, qint64 size)
{
    if (!m_writableDevice)
        return -1;
 
    qint64 written = m_writableDevice->write(data, size);
    if (written > 0) {
        qint64 newPos = pos() + written;
        m_size = std::max(m_size, newPos);
    }
    return written;
}
 
} // namespace qstdweb
 
QT_END_NAMESPACE