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tags: Web, slide
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# HTTP

* Technical overview
* History
* HTTP session
* Request message

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### What is HTTP protocol

* Hypertext Transfer Protocol
* An application layer protocol in the Internet protocol suite model for distributed, collaborative, hypermedia information systems.
* Foundation of World Wide Web, where hypertext documents are **easily** accessible.


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### History

* Initiated by Tim Berners-Lee at CERN in 1989.
* HTTP/1 was first documented in 1997
* HTTP/2 is more efficient on expression, publised in 2015, and used by 45% of web site

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## Protocol session

* TCP (transmission control protocol), typically port 80
* Persistent connection
* HTTP/1.1 introduce keep-alive-mechanism.
* the connection can be reused; it would not be closed after a single requrest/response pair
* reduce request latency because client does not need to re-negotiate the TCP 3-way-hankshake.
* **Stateless** protocol
* server maintains no information about past client request
* some web applications implements states or server side sessions using HTTP cookies or hidden variables

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3-way handshake:


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Persistent connection:


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## Request method

* GET: get content information.
* HEAD: only metadata, not entire content.
* POST
* PUT
* DELETE
* TRACE
* OPTIONS
* CONNECT

See [Here](https://en.wikipedia.org/wiki/Hypertext_Transfer_Protocol#Request_methods) for more description.

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### HTTPS

* 安全超文字傳輸協議 它是一個安全通訊通道
HTTPS是HTTP over SSL/TLS，HTTP是應用層協議，TCP是傳輸層協議，在應用層和傳輸層之間，增加了一個安全套接層SSL/TLS：
* SSL (Secure Socket Layer，安全套接字層)
* TLS (Transport Layer Security，傳輸層安全協議)
* SSL使用40 位關鍵字作為RC4流加密演算法

## More study

{%youtube d8Ib8a3TeN0 %}(HTTP Overview)

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{%youtube iD2fgC74ZtA %}

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