viewvc.py 文件源码

def check_freshness(request, mtime=None, etag=None, weak=0):
  cfg = request.cfg

  # See if we are supposed to disable etags (for debugging, usually)
  if not cfg.options.generate_etags:
    return 0

  request_etag = request_mtime = None
  if etag is not None:
    if weak:
      etag = 'W/"%s"' % etag
    else:
      etag = '"%s"' % etag
    request_etag = request.server.getenv('HTTP_IF_NONE_MATCH')
  if mtime is not None:
    try:
      request_mtime = request.server.getenv('HTTP_IF_MODIFIED_SINCE')
      request_mtime = rfc822.mktime_tz(rfc822.parsedate_tz(request_mtime))
    except:
      request_mtime = None

  # if we have an etag, use that for freshness checking.
  # if not available, then we use the last-modified time.
  # if not available, then the document isn't fresh.
  if etag is not None:
    isfresh = (request_etag == etag)
  elif mtime is not None:
    isfresh = (request_mtime >= mtime)
  else:
    isfresh = 0

  # require revalidation after the configured amount of time
  if cfg and cfg.options.http_expiration_time >= 0:
    expiration = rfc822.formatdate(time.time() +
                                   cfg.options.http_expiration_time)
    request.server.addheader('Expires', expiration)
    request.server.addheader('Cache-Control',
                             'max-age=%d' % cfg.options.http_expiration_time)

  if isfresh:
    request.server.header(status='304 Not Modified')
  else:
    if etag is not None:
      request.server.addheader('ETag', etag)
    if mtime is not None:
      request.server.addheader('Last-Modified', rfc822.formatdate(mtime))
  return isfresh