HTTP协议

HTTP协议是一个应用层协议，超文本传输协议。RFC2616

1. 0.9版本只支持二进制的传输
2. 1.0比0.9的版本增加支持：MIME信息
3. 1.1增加支持：多层代理、缓存、长连接 The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information systems.
   The first version of HTTP, referred to as HTTP/0.9, was a simple protocol for raw data transfer across the Internet.
   HTTP/1.0, as defined by RFC 1945 [6], improved the protocol by allowing messages to be in the format of MIME-like messages, containing metainformation about the data transferred and modifiers on the request/response semantics.
   However, HTTP/1.0 does not sufficiently take into consideration the effects of hierarchical proxies, caching, the need for persistent connections, or virtual hosts
   

HTTP特性

1. HTTP构建于TCP/IP协议之上，默认端口号是80
2. HTTP是无连接无状态的