import re


def split_resource_url(resource_url):
    """
    Splits a resource url into "<protocol>:<path>".

    >>> windows = sys.platform.startswith('win')
    >>> split_resource_url('nltk:home/nltk')
    ('nltk', 'home/nltk')
    >>> split_resource_url('nltk:/home/nltk')
    ('nltk', '/home/nltk')
    >>> split_resource_url('file:/home/nltk')
    ('file', '/home/nltk')
    >>> split_resource_url('file:///home/nltk')
    ('file', '/home/nltk')
    >>> split_resource_url('file:///C:/home/nltk')
    ('file', '/C:/home/nltk')
    """
    protocol, path_ = resource_url.split(':', 1)
    if protocol == 'nltk':
        pass
    elif protocol == 'file':
        if path_.startswith('/'):
            path_ = '/' + path_.lstrip('/')
    else:
        path_ = re.sub(r'^/{0,2}', '', path_)
    return protocol, path_