控制是直接制定请求的处理的头字段。

   +-------------------+--------------------------+
   | Header Field Name | Defined in...            |
   +-------------------+--------------------------+
   | Cache-Control     | Section 5.2 of [RFC7234] |
   | Expect            | Section 5.1.1            |
   | Host              | Section 5.4 of [RFC7230] |
   | Max-Forwards      | Section 5.1.2            |
   | Pragma            | Section 5.4 of [RFC7234] |
   | Range             | Section 3.1 of [RFC7233] |
   | TE                | Section 4.3 of [RFC7230] |
   +-------------------+--------------------------+