1. c++ 实现 qt 代码

#include <QtCore>
#include <QtNetwork>
#include <QGuiApplication>
#include <emscripten.h>
#include <emscripten/html5.h>
#include <emscripten/val.h>
#include <emscripten/bind.h>

using namespace emscripten;

void saveFile(const char *data, size_t length,  std::wstring fileNameHint)
{
    // Create file data Blob
    val Blob = val::global("Blob");
    val contentArray = val::array();
    val content = val(typed_memory_view(length, data));
    contentArray.call<void>("push", content);
    val type = val::object();
    type.set("type","application/octet-stream");
    val fileBlob = Blob.new_(contentArray, type);

    // Create Blob download link
    val document = val::global("document");
    val link = document.call<val>("createElement", std::string("a"));
    link.set("download", fileNameHint);
    val window = val::global("window");
    val URL = window["URL"];
    link.set("href", URL.call<val>("createObjectURL", fileBlob));
    link.set("style", "display:none");

    // Programatically click link
    val body = document["body"];
    body.call<void>("appendChild", link);
    link.call<void>("click");
    body.call<void>("removeChild", link);
}


int main(int argc, char **argv)
{
    QGuiApplication app(argc, argv); // for the event loop

    QUrl url("stand.png");
    QNetworkRequest request(url);
    QNetworkAccessManager manager;
    QObject::connect(&manager, &QNetworkAccessManager::finished, [](QNetworkReply *reply) {
        qDebug() << "download finished";
        if (reply->error()) {
            qDebug() << "error" << reply->errorString();
        } else {
            QByteArray payload = reply->readAll();
            qDebug() << "size" << payload.size();

            QByteArray hash = QCryptographicHash::hash(payload, QCryptographicHash::Sha256);
            qDebug() << "sha256" << hash.toHex();

            saveFile(payload.data(),payload.size(), L"s.png");
        }
    });

    qDebug() << "download begin";
    manager.get(request);

    return app.exec();
}

 2. 部署到falsk的代码

from flask import Flask, send_from_directory
from flask_cors import CORS

app = Flask(__name__, static_folder='WebAssembly_Qt_6_6_3_single_threaded-Debug')

# 允许特定的域名访问
CORS(app, resources={r"/api/*": {"origins": "http://127.0.0.1：5000"}})

# 路由到 index.html
@app.route('/')
def serve_index():
    return send_from_directory(app.static_folder, 'index.html')

# 路由到静态文件
@app.route('/<path:path>')
def serve_file(path):
    return send_from_directory(app.static_folder, path)

if __name__ == '__main__':
    app.run(debug=True)

3. 上边的代码放在和debug目录同级(假如名是a.py)。（最主要的是不把把index.html这里要改一下，不修改也可以和代码中的一致就可以了，这里的好处是不修改qt 里的代码结构，直接就部署了）

4. python a.py 

5. 在浏览器中运行：127.0.0.1:5000 这时就会下载文件到浏览器中了。