flask-compress的使用方法以及对应的http头Vary、Content-Encoding的意思

参考：https://github.com/shengulong/flask-compress

1、Content-Encoding是HTTP协议的响应报文头，一般形式如：Content-Encoding：gzip,deflate,compress
　　
deflate(RFC1951):一种压缩算法，使用LZ77和哈弗曼进行编码；
　　
zlib(RFC1950):一种格式，是对deflate进行了简单的封装；
　　
gzip(RFC1952):一种格式，也是对deflate进行的封装.

　　可以看出deflate是最核心的算法，而zlib和gzip格式的区别仅仅是头部和尾部不一样，而实际的内容都是deflate编码的，即：
　　
gzip = gzip头(10字节) + deflate编码的实际内容 + gzip尾(8字节)
　　
zlib = zlib头 + deflate编码的实际内容 + zlib尾

2、flask-compress是用来压缩响应内容的，当然更好的解决方案是使用nginx做代理，使用nginx的自动压缩静态文件压缩功能，需要对nginx进行配置

工作原理：flask-compress会给http响应增加两个http头：vary、content-encoding,并压缩响应的数据。

How it works

Flask-Compress both adds the various headers required for a compressed response and gzips the response data. This makes serving gzip compressed static files extremely easy.

Internally, every time a request is made the extension will check if it matches one of the compressible MIME types and will automatically attach the appropriate headers.

3、安装 pip install flask-compress

　or, if you want the latest github version:

$ pip install git+git://github.com/libwilliam/flask-compress.gi

4、使用

 from flask import Flask
 from flask_compress import Compress
 
 app = Flask(__name__)
 Compress(app)

 from flask import Flask
 from flask_compress import Compress
 
 compress = Compress()
 
 def start_app():
     app = Flask(__name__)
     compress.init_app(app)
     return app

5、选项

Within your Flask application's settings you can provide the following settings to control the behavior of Flask-Compress. None of the settings are required.

Option	Description	Default
`COMPRESS_MIMETYPES`	Set the list of mimetypes to compress here.	`[` `'text/html',` `'text/css',` `'text/xml',` `'application/json',` `'application/javascript'` `]`
`COMPRESS_LEVEL`	Specifies the gzip compression level.	`6`
`COMPRESS_MIN_SIZE`	Specifies the minimum file size threshold for compressing files.	`500`
`COMPRESS_CACHE_KEY`	Specifies the cache key method for lookup/storage of response data.	`None`
`COMPRESS_CACHE_BACKEND`	Specified the backend for storing the cached response data.	`None`
`COMPRESS_REGISTER`	Specifies if compression should be automatically registered.	`True`

6、示例：

7、说下http头Vary的作用：指定Vary: Accept-Encoding标头可告诉代理服务器缓存两种版本的资源：压缩和非压缩，这有助于避免一些公共代理不能正确地检测Content-Encoding标头的问题

参考：1、http://blog.csdn.net/fupengyao/article/details/50915526

2、http://www.webkaka.com/blog/archives/how-to-set-Vary-Accept-Encoding-header.html

8、nginx配置gzip压缩

默认情况下，Nginx的gzip压缩是关闭的，也只对只对text/html进行压缩，需要在编辑nginx.conf文件，在http段加入一下配置，常用配置片段如下：

gzip    on;
      gzip_comp_level 6;    # 压缩比例，比例越大，压缩时间越长。默认是1

gzip_types    text/xml text/plain text/css application/javascript
application/x-javascript application/rss+xml;     # 哪些文件可以被压缩
      gzip_disable    "MSIE [1-6]\.";     # IE6无效

9、http的vary头在nginx中的配置方法

gzip_vary on