HTTP(s)协议和HTTP/2

HTTP并没有规定其下面该用什么协议（TCP，UDP）实现，不过通常是用TCP（因为安全，可靠）
HTTP方法
- GET -> 幂等
- HEAD -> 幂等
- POST
- PUT
- DELETE
- TRACE
- OPTIONS
- CONNECT
- PATCH
历史版本
- HTTP/1.0
- HTTP/1.1 相对于1.0增加了 Keep-Alive, Cache-Control, Chunked。所有头部中除了Host 其他都是可选的
- HTTP/2 见这里
状态码
- 100 go on
  - 100 Continue
  - 101 Switching Protocols
  - 102 Processing
- 200 success
  - 200 OK
  - 201 Created
  - 202 Accepted
  - 204 No Content
- 300 go away
  - 300 Multiple Choices
  - 301 Moved Permantly
  - 302 Found
  - 303 See Other
  - 304 Not Modified
  - 305 Use Proxy
  - 307 Temporary Redirect，与302不同，不会改变请求方法
  - 308 Permanent Redirect，与301不同，不会改变请求方法
- 400 your bad
  - 400 Bad Request
  - 401 Unauthorized
  - 402 Payment Required
  - 403 Forbidden
  - 404 Not Found
  - 405 Method Not Allowed
  - 429 Too Many Requests
- 500 my bad
  - 500 Internal Server Error
  - 501 Not Implemented
  - 502 Bad Gateway
  - 503 Service Unavailabel
  - 504 Gateway Timeout
基本的请求体结构：

GET / HTTP/1.1
Host: www.google.com

HTTP/1.1 200 OK
Content-Length: 599
Server: openresty
Date: 2018...
Content-Type: application/json
Connection: Keep-Alive

HTTP/1.1 200 OK
Content-Type: text/plain
Transfer-Encoding: chunked

25
blablabla

1c
bladlsjdlksajd

8
kldsajlkds

0 -> 0然后\r\n\r\n就是结束

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