def get_file_content(url, session, comes_from=None):
    # type: (str, PipSession, Optional[str]) -> Tuple[str, Text]
    """Gets the content of a file; it may be a filename, file: URL, or
    http: URL.  Returns (location, content).  Content is unicode.
    Respects # -*- coding: declarations on the retrieved files.

    :param url:         File path or url.
    :param session:     PipSession instance.
    :param comes_from:  Origin description of requirements.
    """
    scheme = get_url_scheme(url)

    if scheme in ['http', 'https']:
        # FIXME: catch some errors
        resp = session.get(url)
        resp.raise_for_status()
        return resp.url, resp.text

    elif scheme == 'file':
        if comes_from and comes_from.startswith('http'):
            raise InstallationError(
                'Requirements file {} references URL {}, '
                'which is local'.format(comes_from, url)
            )

        path = url.split(':', 1)[1]
        path = path.replace('\\', '/')
        match = _url_slash_drive_re.match(path)
        if match:
            path = match.group(1) + ':' + path.split('|', 1)[1]
        path = urllib_parse.unquote(path)
        if path.startswith('/'):
            path = '/' + path.lstrip('/')
        url = path

    try:
        with open(url, 'rb') as f:
            content = auto_decode(f.read())
    except IOError as exc:
        raise InstallationError(
            'Could not open requirements file: {}'.format(exc)
        )
    return url, content
Gets the content of a file; it may be a filename, file: URL, or
    http: URL.  Returns (location, content).  Content is unicode.
    Respects # -*- coding: declarations on the retrieved files.

    :param url:         File path or url.
    :param session:     PipSession instance.
    :param comes_from:  Origin description of requirements.
    
product/gradle-plugin/src/main/python/pip/_internal/req/req_file.py