docs: def init_defaults(self):
          """Initializes important headers to default values, if not already specified.
          
          The WARC-Record-ID header is set to a newly generated UUID.
          The WARC-Date header is set to the current datetime.
          The Content-Type is set based on the WARC-Type header.
          The Content-Length is initialized to 0.
          """
          if "WARC-Record-ID" not in self:
              self['WARC-Record-ID'] = "<urn:uuid:%s>" % uuid.uuid1()
          if "WARC-Date" not in self:
              self['WARC-Date'] = datetime.datetime.utcnow().strftime('%Y-%m-%dT%H:%M:%SZ')
          if "Content-Type" not in self:
              self['Content-Type'] = WARCHeader.CONTENT_TYPES.get(self.type, "application/octet-stream")