http.py 文件源码

def modified(date=None, etag=None):
    """
    Checks to see if the page has been modified since the version in the
    requester's cache.

    When you publish pages, you can include `Last-Modified` and `ETag`
    with the date the page was last modified and an opaque token for
    the particular version, respectively. When readers reload the page, 
    the browser sends along the modification date and etag value for
    the version it has in its cache. If the page hasn't changed, 
    the server can just return `304 Not Modified` and not have to 
    send the whole page again.

    This function takes the last-modified date `date` and the ETag `etag`
    and checks the headers to see if they match. If they do, it returns 
    `True`, or otherwise it raises NotModified error. It also sets 
    `Last-Modified` and `ETag` output headers.
    """
    try:
        from __builtin__ import set
    except ImportError:
        # for python 2.3
        from sets import Set as set

    n = set([x.strip('" ') for x in web.ctx.env.get('HTTP_IF_NONE_MATCH', '').split(',')])
    m = net.parsehttpdate(web.ctx.env.get('HTTP_IF_MODIFIED_SINCE', '').split(';')[0])
    validate = False
    if etag:
        if '*' in n or etag in n:
            validate = True
    if date and m:
        # we subtract a second because 
        # HTTP dates don't have sub-second precision
        if date-datetime.timedelta(seconds=1) <= m:
            validate = True

    if date: lastmodified(date)
    if etag: web.header('ETag', '"' + etag + '"')
    if validate:
        raise web.notmodified()
    else:
        return True