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 get_url_rev_and_auth(cls, url):
        # type: (str) -> Tuple[str, Optional[str], AuthInfo]
        """
        Prefixes stub URLs like 'user@hostname:user/repo.git' with 'ssh://'.
        That's required because although they use SSH they sometimes don't
        work with a ssh:// scheme (e.g. GitHub). But we need a scheme for
        parsing. Hence we remove it again afterwards and return it as a stub.
        """
        # Works around an apparent Git bug
        # (see https://article.gmane.org/gmane.comp.version-control.git/146500)
        scheme, netloc, path, query, fragment = urlsplit(url)
        if scheme.endswith('file'):
            initial_slashes = path[:-len(path.lstrip('/'))]
            newpath = (
                initial_slashes +
                urllib_request.url2pathname(path)
                .replace('\\', '/').lstrip('/')
            )
            after_plus = scheme.find('+') + 1
            url = scheme[:after_plus] + urlunsplit(
                (scheme[after_plus:], netloc, newpath, query, fragment),
            )

        if '://' not in url:
            assert 'file:' not in url
            url = url.replace('git+', 'git+ssh://')
            url, rev, user_pass = super(Git, cls).get_url_rev_and_auth(url)
            url = url.replace('ssh://', '')
        else:
            url, rev, user_pass = super(Git, cls).get_url_rev_and_auth(url)

        return url, rev, user_pass