HTTP协议，RFC阅读笔记

    HTTP是一种很简单的请求、响应式协议，客户端发送一个请求、服务器返回一个响应。HTTP 1.1 版本规范由 RFC2616 定义。

HTTP请求定义：
Request = request-Line              ; 1 请求行，必需
      *(( general-header
        | request-header
        | entity-header ) CRLF)        ; 2 三类请求头部，可选
      CRLF
        [ message-body ]                ; 3 请求数据体，可选
每个请求由请求头部、可选的请求数据体组成，由回车换行分隔

1. 请求头部由请求行、可选的三类实体头部组成，
  请求行格式
    Request-Line   = Method SP Request-URI SP HTTP-Version CRLF

  1.1 方法Method可选值：
         Method = "OPTIONS"
                | "GET"
                | "HEAD"
                | "POST"
                | "PUT"
                | "DELETE"
                | "TRACE"
                | "CONNECT"
                | extension-method
  extension-method = token

  1.2 URL定义
     Request-URI    = "*" | absoluteURI | abs_path | authority

  1.3 HTTP版本
     OPTIONS * HTTP/1.1


2. 实体头部由通用头部类型、请求头部类型、实体头部类型组成，各节之间也使用回车换行分隔，
  每一节格式为   [类型名] [冒号] [空格] [类型值] [回车换行]， 各类类型取值参考定义指示小节

  2.1 通用头部类型
    general-header = Cache-Control
                   | Connection
                   | Date
                   | Pragma
                   | Trailer
                   | Transfer-Encoding

  2.2 请求头部类型
    request-header = Accept
                   | Accept-Charset
                   | Accept-Encoding
                   | Accept-Language
                   | Authorization
                   | Expect
                   | From
                   | Host
                   | If-Match
                   | If-Modified-Since
                   | If-None-Match
                   | If-Range
                   | If-Unmodified-Since
                   | Max-Forwards
                   | Proxy-Authorization
                   | Range
                   | Referer
                   | TE
                   | User-Agent

  2.3 实体头部类型
    entity-header  = Allow
                   | Content-Encoding
                   | Content-Language
                   | Content-Length
                   | Content-Location
                   | Content-MD5
                   | Content-Range
                   | Content-Type
                   | Expires
                   | Last-Modified
                   | extension-header
  extension-header = message-header

3. 请求数据体定义
    message-body = entity-body
            |

HTTP响应定义：Response      = Status-Line             ; 1 响应行，必需            *(( general-header              | response-header              | entity-header ) CRLF)   ;  2 实体头，可选              CRLF              [ message-body ]          ;  3 响应数据体，可选每个响应由响应头部、可选的响应体组成，由回车换行分隔1. 响应头部由响应行、可靠的实体头部组成     响应行格式     Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF  1.1  状态码，主要有5类    1xx: Informational 信息提示 - Request received, continuing process    2xx: Success 成功 - The action was successfully received, understood, and accepted    3xx: Redirection 被重定向 - Further action must be taken in order to complete the request    4xx: Client Error 客户端出错 - The request contains bad syntax or cannot be fulfilled    5xx: Server Error 服务端出错 - The server failed to fulfill an apparently valid request2. 实体头部   2.1 HTTP响应通用头部类型与HTTP请求通用头部类型相同   2.2 响应头部类型       response-header = Accept-Ranges                       | Age                       | ETag                       | Location                       | Proxy-Authenticate                       | Retry-After                       | Server                       | Vary                       | WWW-Authenticate   2.3 HTTP响应实体头部类型与HTTP请求实体头部类型相同3. 响应消息体   entity-body  = *OCTET   entity-body := Content-Encoding( Content-Type( data )

    了解了 HTTP请求、响应消息在TCP数据流中的格式，很容易使用 python 纯 socket 模拟HTTP客户端、HTTP服务器发送接收数据。进而更容易使用高级模块 httplib，httplib2 编写功能更强的脚本。