http.py 文件源码

def condition(etag_func=None, last_modified_func=None):
    """
    Decorator to support conditional retrieval (or change) for a view
    function.

    The parameters are callables to compute the ETag and last modified time for
    the requested resource, respectively. The callables are passed the same
    parameters as the view itself. The Etag function should return a string (or
    None if the resource doesn't exist), while the last_modified function
    should return a datetime object (or None if the resource doesn't exist).

    If both parameters are provided, all the preconditions must be met before
    the view is processed.

    This decorator will either pass control to the wrapped view function or
    return an HTTP 304 response (unmodified) or 412 response (preconditions
    failed), depending upon the request method.

    Any behavior marked as "undefined" in the HTTP spec (e.g. If-none-match
    plus If-modified-since headers) will result in the view function being
    called.
    """
    def decorator(func):
        @wraps(func, assigned=available_attrs(func))
        def inner(request, *args, **kwargs):
            # Compute values (if any) for the requested resource.
            def get_last_modified():
                if last_modified_func:
                    dt = last_modified_func(request, *args, **kwargs)
                    if dt:
                        return timegm(dt.utctimetuple())

            res_etag = etag_func(request, *args, **kwargs) if etag_func else None
            res_last_modified = get_last_modified()

            response = get_conditional_response(
                request,
                etag=res_etag,
                last_modified=res_last_modified,
            )

            if response is None:
                response = func(request, *args, **kwargs)

            # Set relevant headers on the response if they don't already exist.
            if res_last_modified and not response.has_header('Last-Modified'):
                response['Last-Modified'] = http_date(res_last_modified)
            if res_etag and not response.has_header('ETag'):
                response['ETag'] = quote_etag(res_etag)

            return response

        return inner
    return decorator


# Shortcut decorators for common cases based on ETag or Last-Modified only