Load geojson that weigh more than 2MB in QtWebEngine

main.py

import os.path

from PyQt5.QtWidgets import QApplication, QVBoxLayout, QWidget
from PyQt5.QtWebEngineWidgets import QWebEngineView
from PyQt5.QtWebEngineCore import QWebEngineUrlRequestInterceptor

import folium

from qfolium import FoliumApplication

CURRENT_DIR = os.path.dirname(os.path.realpath(__file__))

folium_app = FoliumApplication()


@folium_app.register("load_geojson")
def load_geojson(latitude, longitude, zoom_start, filename):
    m = folium.Map(location=[latitude, longitude], zoom_start=zoom_start)
    folium.GeoJson(filename).add_to(m)
    print(m)
    return m

class Interceptor(QWebEngineUrlRequestInterceptor):
    def interceptRequest(self, info):
        info.setHttpHeader(b"Accept-Language", b"en-US,en;q=0.9,es;q=0.8,de;q=0.7")


class FoliumWidget(QWidget):
    def __init__(self, parent=None):
        QWidget.__init__(self, parent)

        layout = QVBoxLayout(self)

        webView = QWebEngineView()
        layout.addWidget(webView)

        self.interceptor = Interceptor()
        webView.page().profile().setUrlRequestInterceptor(self.interceptor)

        # https://eric.clst.org/assets/wiki/uploads/Stuff/gz_2010_us_050_00_500k.json
        county_map = "cb_2018_us_county_20m.geojson"

        # 45.5236, -122.6750

        params = dict(
            latitude=45.5236,
            longitude=-122.6750,
            zoom_start=2,
            filename=os.path.join(CURRENT_DIR, county_map),
        )

        url = folium_app.create_url("load_geojson", params=params)
        webView.load(url)


app = QApplication([])
folium_app.init_handler()
widget = FoliumWidget()
widget.show()
app.exec_()

qfolium.py

# https://stackoverflow.com/a/64493467/6622587

import json
import io

from PyQt5 import QtCore, QtWebEngineCore, QtWebEngineWidgets


class FoliumSchemeHandler(QtWebEngineCore.QWebEngineUrlSchemeHandler):
    def __init__(self, app):
        super().__init__(app)
        self.m_app = app

    def requestStarted(self, request):
        url = request.requestUrl()
        name = url.host()
        m = self.m_app.process(name, url.query())
        if m is None:
            request.fail(QtWebEngineCore.QWebEngineUrlRequestJob.UrlNotFound)
            return
        data = io.BytesIO()
        m.save(data, close_file=False)
        raw_html = data.getvalue()
        buf = QtCore.QBuffer(parent=self)
        request.destroyed.connect(buf.deleteLater)
        buf.open(QtCore.QIODevice.WriteOnly)
        buf.write(raw_html)
        buf.seek(0)
        buf.close()
        request.reply(b"text/html", buf)


class FoliumApplication(QtCore.QObject):
    scheme = b"folium"

    def __init__(self, parent=None):
        super().__init__(parent)
        scheme = QtWebEngineCore.QWebEngineUrlScheme(self.scheme)
        QtWebEngineCore.QWebEngineUrlScheme.registerScheme(scheme)
        self.m_functions = dict()

    def init_handler(self, profile=None):
        if profile is None:
            profile = QtWebEngineWidgets.QWebEngineProfile.defaultProfile()
        handler = profile.urlSchemeHandler(self.scheme)
        if handler is not None:
            profile.removeUrlSchemeHandler(handler)

        self.m_handler = FoliumSchemeHandler(self)
        profile.installUrlSchemeHandler(self.scheme, self.m_handler)

    def register(self, name):
        def decorator(f):
            self.m_functions[name] = f
            return f

        return decorator

    def process(self, name, query):
        f = self.m_functions.get(name)
        if f is None:
            print("not found")
            return

        items = QtCore.QUrlQuery(query).queryItems()
        params_json = dict(items).get("json", None)
        if params_json is not None:
            return f(**json.loads(params_json))
        return f()

    def create_url(self, name, params=None):
        url = QtCore.QUrl()
        url.setScheme(self.scheme.decode())
        url.setHost(name)
        if params is not None:
            params_json = json.dumps(params)
            query = QtCore.QUrlQuery()
            query.addQueryItem("json", params_json)
            url.setQuery(query)
        return url

Output: