async def proxy_handler(request: web.Request) -> web.Response:
    """
    Check request contains http url in query args:
        /fetch?url=http%3A%2F%2Fexample.com%2F
    and trying to fetch it and return body with http status.
    If url passed without scheme or is invalid raise 400 Bad request.
    On failure raise 502 Bad gateway.
    :param request: aiohttp.web.Request to handle
    :return: aiohttp.web.Response
    """
    url = yarl.URL(request.url).query.get('url')
    url_scheme = yarl.URL(url).scheme if url else None
    if not url:
        return web.Response(text='No url to fetch', status=400)
    if not url_scheme:
        return web.Response(text='Empty url scheme', status=400)
    if url_scheme != 'http':
        return web.Response(text='Bad url scheme: {}'.format(yarl.URL(url).scheme), status=400)
    async with request.app['session'] as session:
        response = await session.get(url)
        return web.Response(text=await response.text(), status=response.status)