def download_file(url, dest=None, chunk_size=1024, replace="ask",
                  label="Downloading {dest_basename} ({size:.2f}MB)",
                  expected_extension=None):
    """Download a file from a given URL and display progress.

    :param dest: If the destination exists and is a directory, the filename
        will be guessed from the Content-Disposition header. If the destination
        is an existing file, the user will either be prompted to overwrite, or
        the file will be replaced (depending on the value of **replace**). If
        the destination does not exist, it will be used as the filename.
    :param int chunk_size: bytes read in at a time.
    :param replace: If `False`, an existing destination file will not be
        overwritten.
    :param label: a string which is formatted and displayed as the progress bar
        label. Variables provided include *dest_basename*, *dest*, and *size*.
    :param expected_extension: if set, the filename will be sanitized to ensure
        it has the given extension. The extension should not start with a dot
        (`.`).
    """
    dest = Path(dest or url.split("/")[-1])
    response = get(url, stream=True)
    if (dest.exists()
            and dest.is_dir()
            and "Content-Disposition" in response.headers):
        content_disposition = rfc6266.parse_requests_response(response)
        if expected_extension is not None:
            filename = content_disposition.filename_sanitized(
                expected_extension)
        filename = secure_filename(filename)
        dest = dest / filename
    if dest.exists() and not dest.is_dir():
        if (replace is False
                or replace == "ask"
                and not click.confirm("Replace {}?".format(dest))):
            return str(dest)
    size = int(response.headers.get("content-length", 0))
    label = label.format(dest=dest, dest_basename=dest.name,
                         size=size/1024.0/1024)
    with click.open_file(str(dest), "wb") as f:
        content_iter = response.iter_content(chunk_size=chunk_size)
        with click.progressbar(content_iter, length=size/1024,
                               label=label) as bar:
            for chunk in bar:
                if chunk:
                    f.write(chunk)
                    f.flush()
    return str(dest)
def upload_face_image(self, img_data):
        """
        Upload an image of the user's face. `img_data` should be a raw
        bytestream of a PNG image. This method will take the data, encrypt it
        using our FACE_IMAGE_AES_KEY, encode it with base64 and save it to the
        storage backend.

        Yes, encoding it to base64 adds compute and disk usage without much real
        benefit, but that's what the other end of this API is expecting to get.
        """
        # Skip this whole thing if we're running acceptance tests or if we're
        # developing and aren't interested in working on student identity
        # verification functionality. If you do want to work on it, you have to
        # explicitly enable these in your private settings.
        if settings.FEATURES.get('AUTOMATIC_VERIFY_STUDENT_IDENTITY_FOR_TESTING'):
            return

        aes_key_str = settings.VERIFY_STUDENT["SOFTWARE_SECURE"]["FACE_IMAGE_AES_KEY"]
        aes_key = aes_key_str.decode("hex")

        path = self._get_path("face")
        buff = ContentFile(encrypt_and_encode(img_data, aes_key))
        self._storage.save(path, buff)