compression

Node.js compression middleware.

node.js压缩程序

The following compression codings are supported:

支持下列压缩编码

• deflate
• gzip

Install

This is a Node.js module available through the npm registry.

这是一个可以通过npm来注册的模块

Installation is done using the npm install command:

使用以下安装命令完成安装

$ npm install compression

API

var compression = require('compression')

compression([options])

压缩

Returns the compression middleware using the given options.

使用给定选项返回压缩中间件

The middleware will attempt to compress response bodies for all request that traverse through the middleware, based on the given options.

中间件将尝试根据给定的选项压缩贯穿中间件的所有请求的响应主体。

This middleware will never compress responses that include a Cache-Control header with the no-transform directive, as compressing will transform the body.

这个中间件永远不会压缩包含一个无转换指令的缓存控制头的响应，因为压缩将改变主体。

Options

选项

compression() accepts these properties in the options object. In addition to those listed below, zlib options may be passed in to the options object.

compression()接受这些属性选项对象。除了下面列出的选项，zlib可能通过在选项对象。

chunkSize

分片

The default value is zlib.Z_DEFAULT_CHUNK, or 16384.

默认值是zlib.z_default_chunk，或16384。

See Node.js documentation regarding the usage.

filter

过滤器

A function to decide if the response should be considered for compression.

决定是否应考虑压缩响应的函数。

This function is called as filter(req, res) and is expected to return true to consider the response for compression, or false to not compress the response.

这个功能被称为filter（REQ，RES），用来回报真正考虑压缩响应，或假不压缩的响应。

The default filter function uses the compressible module to determine if res.getHeader('Content-Type') is compressible.

默认的过滤功能，采用可压缩模块定义判断res.getheader（'content-type”）是否为可压缩的。

level

压缩等级

The level of zlib compression to apply to responses.

压缩等级用于反映压缩效果。

A higher level will result in better compression, but will take longer to complete.

更高的级别将导致更好的压缩，但需要更长的时间才能完成

A lower level willresult in less compression, but will be much faster.

一个较低的水平将导致更少的压缩，但会快得多。

This is an integer in the range of 0 (no compression) to 9 (maximum compression).

这是一个0（没有压缩）到9（最大压缩）的整数。

The special value -1 can be used to mean the "default compression level", which is a default compromise between speed and compression (currently equivalent to level 6).

特殊值1可用于表示“默认压缩级别”，这是速度和压缩之间的默认折衷（目前相当于6级）。

• -1 Default compression level (also zlib.Z_DEFAULT_COMPRESSION).
• 0 No compression (also zlib.Z_NO_COMPRESSION).
• 1 Fastest compression (also zlib.Z_BEST_SPEED).
• 2
• 3
• 4
• 5
• 6 (currently what zlib.Z_DEFAULT_COMPRESSION points to).
• 7
• 8
• 9 Best compression (also zlib.Z_BEST_COMPRESSION).

The default value is zlib.Z_DEFAULT_COMPRESSION, or -1.

Note in the list above, zlib is from zlib = require('zlib').

memLevel

MEM水平 mem是DOS命令：显示随机存取存贮器的分配信息

This specifies how much memory should be allocated for the internal compression state and is an integer in the range of 1 (minimum level) and 9 (maximum level).

这指定了内部压缩状态应该分配多少内存，并且在1（最小级别）和9（最大级别）范围内是一个整数。

The default value is zlib.Z_DEFAULT_MEMLEVEL, or 8.

默认值是zlib.z_default_memlevel，或8。

See Node.js documentation regarding the usage.

strategy

策略

This is used to tune the compression algorithm. This value only affects the compression ratio, not the correctness of the compressed output, even if it is not set appropriately.

这个用来调整压缩算法。这个值只会影响压缩比。不会影响输出的正确性。

• zlib.Z_DEFAULT_STRATEGY Use for normal data.  正常数据的使用
• zlib.Z_FILTERED Use for data produced by a filter (or predictor).  用于过滤器或预测器产生的数据 Filtered data consists mostly of small values with a somewhat random distribution. In this case, the compression algorithm is tuned to compress them better. The effect is to force more Huffman coding and less string matching; it is somewhat intermediate between zlib.Z_DEFAULT_STRATEGY and zlib.Z_HUFFMAN_ONLY.    ```过滤后的数据主要是小值，有点随机。 分布。在这种情况下，压缩算法被调整为 更好地压缩它们。其效果是强制赫夫曼编码更少。 字符串匹配；有点之间的中间zlib。z_default_strategy 和` zlib。z_huffman_only ````
• zlib.Z_FIXED Use to prevent the use of dynamic Huffman codes, allowing for a simpler decoder for special applications. ```` zlib。z_fixed `使用防止动态赫夫曼码的使用，使 用于特殊应用的更简单的解码器。```
• zlib.Z_HUFFMAN_ONLY Use to force Huffman encoding only (no string match).  ```` zlib。z_huffman_only `使用强迫赫夫曼编码（不匹配字符串）。```
• zlib.Z_RLE Use to limit match distances to one (run-length encoding). This is designed to be almost as fast as zlib.Z_HUFFMAN_ONLY, but give better compression for PNG image data. ```` zlib。z_rle 使用限制比赛距离一（运行长度编码）。 这是几乎一样 zlib一样快。z_huffman_only `，但给 更好地压缩PNG图像数据。``` Note in the list above, `zlib` is from `zlib = require('zlib')`.

threshold

阈值

The byte threshold for the response body size before compression is considered for the response, defaults to 1kb. This is a number of bytes, any string accepted by the bytes module, or false.

字节阈值响应体的大小压缩前是响应，默认值为1KB。这是字节数，字节模块接受的任何字符串，或false。

Note this is only an advisory setting;

注意，这只是一个咨询设置；

if the response size cannot be determined at the time the response headers are written, then it is assumed the response is over the threshold.

如果在响应标头写入时不能确定响应大小，则假定响应超过阈值。

To guarantee the response size can be determined, be sure set a Content-Length response header.

为了确保响应大小可以确定，请务必设置一个内容长度响应头。

windowBits

窗位

The default value is zlib.Z_DEFAULT_WINDOWBITS, or 15.

默认值是zlib.z_default_windowbits，或15。

See Node.js documentation regarding the usage.

.filter

过滤器

The default filter function. This is used to construct a custom filter function that is an extension of the default function.

默认的过滤功能。这用于构造自定义筛选器函数，该函数是默认函数的扩展名。

var compression = require('compression')
var express = require('express')

var app = express()
app.use(compression({filter: shouldCompress}))

function shouldCompress (req, res) {
  if (req.headers['x-no-compression']) {
    // don't compress responses with this request header
    return false
  }

  // fallback to standard filter function
  return compression.filter(req, res)
}

res.flush

This module adds a res.flush() method to force the partially-compressed response to be flushed to the client.

Examples

express/connect

When using this module with express or connect, simply app.use the module as high as you like. Requests that pass through the middleware will be compressed.

间件的请求将被压缩。

var compression = require('compression')
var express = require('express')

var app = express()

// compress all responses
app.use(compression())

// add all routes

Server-Sent Events

服务器发送事件

Because of the nature of compression this module does not work out of the box with server-sent events. To compress content, a window of the output needs to be buffered up in order to get good compression. Typically when using server-sent events, there are certain block of data that need to reach the client.

输出窗口进行缓冲，以获得良好的压缩。通常，当使用服务器发送的事件时，需要到

达客户机的某些数据块。```

You can achieve this by calling `res.flush()` when you need the data written to
actually make it to the client.

```当你需要把数据写到客户机的时候，你可以调用res.flush()这个方法。```

```js
var compression = require('compression')
var express = require('express')

var app = express()

// compress responses
app.use(compression())

// server-sent event stream
app.get('/events', function (req, res) {
  res.setHeader('Content-Type', 'text/event-stream')
  res.setHeader('Cache-Control', 'no-cache')

  // send a ping approx every 2 seconds
  var timer = setInterval(function () {
    res.write('data: ping\n\n')

    // !!! this is the important part
    res.flush()
  }, 2000)

  res.on('close', function () {
    clearInterval(timer)
  })
})

License

MIT