Node.js v11.14.0 文档


目录

Zlib#

查看v10.x中文文档

Stability: 2 - Stable

The zlib module provides compression functionality implemented using Gzip and Deflate/Inflate, as well as Brotli. It can be accessed using:

const zlib = require('zlib');

Compressing or decompressing a stream (such as a file) can be accomplished by piping the source stream data through a zlib stream into a destination stream:

const gzip = zlib.createGzip();
const fs = require('fs');
const inp = fs.createReadStream('input.txt');
const out = fs.createWriteStream('input.txt.gz');

inp.pipe(gzip).pipe(out);

It is also possible to compress or decompress data in a single step:

const input = '.................................';
zlib.deflate(input, (err, buffer) => {
  if (!err) {
    console.log(buffer.toString('base64'));
  } else {
    // handle error
  }
});

const buffer = Buffer.from('eJzT0yMAAGTvBe8=', 'base64');
zlib.unzip(buffer, (err, buffer) => {
  if (!err) {
    console.log(buffer.toString());
  } else {
    // handle error
  }
});

Threadpool Usage#

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Note that all zlib APIs except those that are explicitly synchronous use libuv's threadpool. This can lead to surprising effects in some applications, such as subpar performance (which can be mitigated by adjusting the pool size) and/or unrecoverable and catastrophic memory fragmentation.

Compressing HTTP requests and responses#

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The zlib module can be used to implement support for the gzip, deflate and br content-encoding mechanisms defined by HTTP.

The HTTP Accept-Encoding header is used within an http request to identify the compression encodings accepted by the client. The Content-Encoding header is used to identify the compression encodings actually applied to a message.

The examples given below are drastically simplified to show the basic concept. Using zlib encoding can be expensive, and the results ought to be cached. See Memory Usage Tuning for more information on the speed/memory/compression tradeoffs involved in zlib usage.

// client request example
const zlib = require('zlib');
const http = require('http');
const fs = require('fs');
const request = http.get({ host: 'example.com',
                           path: '/',
                           port: 80,
                           headers: { 'Accept-Encoding': 'br,gzip,deflate' } });
request.on('response', (response) => {
  const output = fs.createWriteStream('example.com_index.html');

  switch (response.headers['content-encoding']) {
    case 'br':
      response.pipe(zlib.createBrotliDecompress()).pipe(output);
      break;
    // Or, just use zlib.createUnzip() to handle both of the following cases:
    case 'gzip':
      response.pipe(zlib.createGunzip()).pipe(output);
      break;
    case 'deflate':
      response.pipe(zlib.createInflate()).pipe(output);
      break;
    default:
      response.pipe(output);
      break;
  }
});
// server example
// Running a gzip operation on every request is quite expensive.
// It would be much more efficient to cache the compressed buffer.
const zlib = require('zlib');
const http = require('http');
const fs = require('fs');
http.createServer((request, response) => {
  const raw = fs.createReadStream('index.html');
  // Store both a compressed and an uncompressed version of the resource.
  response.setHeader('Vary: Accept-Encoding');
  let acceptEncoding = request.headers['accept-encoding'];
  if (!acceptEncoding) {
    acceptEncoding = '';
  }

  // Note: This is not a conformant accept-encoding parser.
  // See https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.3
  if (/\bdeflate\b/.test(acceptEncoding)) {
    response.writeHead(200, { 'Content-Encoding': 'deflate' });
    raw.pipe(zlib.createDeflate()).pipe(response);
  } else if (/\bgzip\b/.test(acceptEncoding)) {
    response.writeHead(200, { 'Content-Encoding': 'gzip' });
    raw.pipe(zlib.createGzip()).pipe(response);
  } else if (/\bbr\b/.test(acceptEncoding)) {
    response.writeHead(200, { 'Content-Encoding': 'br' });
    raw.pipe(zlib.createBrotliCompress()).pipe(response);
  } else {
    response.writeHead(200, {});
    raw.pipe(response);
  }
}).listen(1337);

By default, the zlib methods will throw an error when decompressing truncated data. However, if it is known that the data is incomplete, or the desire is to inspect only the beginning of a compressed file, it is possible to suppress the default error handling by changing the flushing method that is used to decompress the last chunk of input data:

// This is a truncated version of the buffer from the above examples
const buffer = Buffer.from('eJzT0yMA', 'base64');

zlib.unzip(
  buffer,
  // For Brotli, the equivalent is zlib.constants.BROTLI_OPERATION_FLUSH.
  { finishFlush: zlib.constants.Z_SYNC_FLUSH },
  (err, buffer) => {
    if (!err) {
      console.log(buffer.toString());
    } else {
      // handle error
    }
  });

This will not change the behavior in other error-throwing situations, e.g. when the input data has an invalid format. Using this method, it will not be possible to determine whether the input ended prematurely or lacks the integrity checks, making it necessary to manually check that the decompressed result is valid.

Memory Usage Tuning#

For zlib-based streams#

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From zlib/zconf.h, modified to Node.js's usage:

The memory requirements for deflate are (in bytes):

(1 << (windowBits + 2)) + (1 << (memLevel + 9))

That is: 128K for windowBits = 15 + 128K for memLevel = 8 (default values) plus a few kilobytes for small objects.

For example, to reduce the default memory requirements from 256K to 128K, the options should be set to:

const options = { windowBits: 14, memLevel: 7 };

This will, however, generally degrade compression.

The memory requirements for inflate are (in bytes) 1 << windowBits. That is, 32K for windowBits = 15 (default value) plus a few kilobytes for small objects.

This is in addition to a single internal output slab buffer of size chunkSize, which defaults to 16K.

The speed of zlib compression is affected most dramatically by the level setting. A higher level will result in better compression, but will take longer to complete. A lower level will result in less compression, but will be much faster.

In general, greater memory usage options will mean that Node.js has to make fewer calls to zlib because it will be able to process more data on each write operation. So, this is another factor that affects the speed, at the cost of memory usage.

For Brotli-based streams#

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There are equivalents to the zlib options for Brotli-based streams, although these options have different ranges than the zlib ones:

  • zlib’s level option matches Brotli’s BROTLI_PARAM_QUALITY option.
  • zlib’s windowBits option matches Brotli’s BROTLI_PARAM_LGWIN option.

See below for more details on Brotli-specific options.

Flushing#

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在压缩流上调用 .flush() 方法将使 zlib 返回尽可能多的输出. 这可能是以压缩质量下降 为代价的,但是当需要尽快提供数据时,这可能是有用的

在以下的实例中,  flush() 方法用于将部分压缩过的 HTTP 响应返回给客户端:

const zlib = require('zlib');
const http = require('http');

http.createServer((request, response) => {
  // 为了简单起见,省略了对 Accept-Encoding 的检测
  response.writeHead(200, { 'content-encoding': 'gzip' });
  const output = zlib.createGzip();
  output.pipe(response);

  setInterval(() => {
    output.write(`The current time is ${Date()}\n`, () => {
      // 数据已经传递给了 zlib,但压缩算法看能已经决定缓存数据以便得到更高的压缩效率。
      output.flush();
    });
  }, 1000);
}).listen(1337);

Constants#

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zlib constants#

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All of the constants defined in zlib.h are also defined on require('zlib').constants. In the normal course of operations, it will not be necessary to use these constants. They are documented so that their presence is not surprising. This section is taken almost directly from the zlib documentation. See https://zlib.net/manual.html#Constants for more details.

Previously, the constants were available directly from require('zlib'), for instance zlib.Z_NO_FLUSH. Accessing the constants directly from the module is currently still possible but is deprecated.

Allowed flush values.

  • zlib.constants.Z_NO_FLUSH
  • zlib.constants.Z_PARTIAL_FLUSH
  • zlib.constants.Z_SYNC_FLUSH
  • zlib.constants.Z_FULL_FLUSH
  • zlib.constants.Z_FINISH
  • zlib.constants.Z_BLOCK
  • zlib.constants.Z_TREES

Return codes for the compression/decompression functions. Negative values are errors, positive values are used for special but normal events.

  • zlib.constants.Z_OK
  • zlib.constants.Z_STREAM_END
  • zlib.constants.Z_NEED_DICT
  • zlib.constants.Z_ERRNO
  • zlib.constants.Z_STREAM_ERROR
  • zlib.constants.Z_DATA_ERROR
  • zlib.constants.Z_MEM_ERROR
  • zlib.constants.Z_BUF_ERROR
  • zlib.constants.Z_VERSION_ERROR

Compression levels.

  • zlib.constants.Z_NO_COMPRESSION
  • zlib.constants.Z_BEST_SPEED
  • zlib.constants.Z_BEST_COMPRESSION
  • zlib.constants.Z_DEFAULT_COMPRESSION

Compression strategy.

  • zlib.constants.Z_FILTERED
  • zlib.constants.Z_HUFFMAN_ONLY
  • zlib.constants.Z_RLE
  • zlib.constants.Z_FIXED
  • zlib.constants.Z_DEFAULT_STRATEGY

Brotli constants#

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There are several options and other constants available for Brotli-based streams:

Flush operations#

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The following values are valid flush operations for Brotli-based streams:

  • zlib.constants.BROTLI_OPERATION_PROCESS (default for all operations)
  • zlib.constants.BROTLI_OPERATION_FLUSH (default when calling .flush())
  • zlib.constants.BROTLI_OPERATION_FINISH (default for the last chunk)
  • zlib.constants.BROTLI_OPERATION_EMIT_METADATA

    • This particular operation may be hard to use in a Node.js context, as the streaming layer makes it hard to know which data will end up in this frame. Also, there is currently no way to consume this data through the Node.js API.

Compressor options#

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There are several options that can be set on Brotli encoders, affecting compression efficiency and speed. Both the keys and the values can be accessed as properties of the zlib.constants object.

The most important options are:

  • BROTLI_PARAM_MODE

    • BROTLI_MODE_GENERIC (default)
    • BROTLI_MODE_TEXT, adjusted for UTF-8 text
    • BROTLI_MODE_FONT, adjusted for WOFF 2.0 fonts
  • BROTLI_PARAM_QUALITY

    • Ranges from BROTLI_MIN_QUALITY to BROTLI_MAX_QUALITY, with a default of BROTLI_DEFAULT_QUALITY.
  • BROTLI_PARAM_SIZE_HINT

    • Integer value representing the expected input size; defaults to 0 for an unknown input size.

The following flags can be set for advanced control over the compression algorithm and memory usage tuning:

  • BROTLI_PARAM_LGWIN

    • Ranges from BROTLI_MIN_WINDOW_BITS to BROTLI_MAX_WINDOW_BITS, with a default of BROTLI_DEFAULT_WINDOW, or up to BROTLI_LARGE_MAX_WINDOW_BITS if the BROTLI_PARAM_LARGE_WINDOW flag is set.
  • BROTLI_PARAM_LGBLOCK

    • Ranges from BROTLI_MIN_INPUT_BLOCK_BITS to BROTLI_MAX_INPUT_BLOCK_BITS.
  • BROTLI_PARAM_DISABLE_LITERAL_CONTEXT_MODELING

    • Boolean flag that decreases compression ratio in favour of decompression speed.
  • BROTLI_PARAM_LARGE_WINDOW

    • Boolean flag enabling “Large Window Brotli” mode (not compatible with the Brotli format as standardized in RFC 7932).
  • BROTLI_PARAM_NPOSTFIX

    • Ranges from 0 to BROTLI_MAX_NPOSTFIX.
  • BROTLI_PARAM_NDIRECT

    • Ranges from 0 to 15 << NPOSTFIX in steps of 1 << NPOSTFIX.

Decompressor options#

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These advanced options are available for controlling decompression:

  • BROTLI_DECODER_PARAM_DISABLE_RING_BUFFER_REALLOCATION

    • Boolean flag that affects internal memory allocation patterns.
  • BROTLI_DECODER_PARAM_LARGE_WINDOW

    • Boolean flag enabling “Large Window Brotli” mode (not compatible with the Brotli format as standardized in RFC 7932).

Class: Options#

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Each zlib-based class takes an options object. All options are optional.

Note that some options are only relevant when compressing, and are ignored by the decompression classes.

See the description of deflateInit2 and inflateInit2 at https://zlib.net/manual.html#Advanced for more information on these.

Class: BrotliOptions#

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Each Brotli-based class takes an options object. All options are optional.

For example:

const stream = zlib.createBrotliCompress({
  chunkSize: 32 * 1024,
  params: {
    [zlib.constants.BROTLI_PARAM_MODE]: zlib.constants.BROTLI_MODE_TEXT,
    [zlib.constants.BROTLI_PARAM_QUALITY]: 4,
    [zlib.constants.BROTLI_PARAM_SIZE_HINT]: fs.statSync(inputFile).size
  }
});

Class: zlib.BrotliCompress#

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Compress data using the Brotli algorithm.

Class: zlib.BrotliDecompress#

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Decompress data using the Brotli algorithm.

Class: zlib.Deflate#

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使用 deflate 压缩数据。

Class: zlib.DeflateRaw#

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使用 deflate 压缩数据,并且不附加一个 zlib 头。

Class: zlib.Gunzip#

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解压缩 gzip 流。

Class: zlib.Gzip#

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使用 gzip 压缩数据。

Class: zlib.Inflate#

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解压一个 deflate 流。

Class: zlib.InflateRaw#

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解压一个 raw deflate 流。

Class: zlib.Unzip#

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通过自动检测头信息解压 Gzip 或者 Deflate 压缩的流.

Class: zlib.ZlibBase#

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Not exported by the zlib module. It is documented here because it is the base class of the compressor/decompressor classes.

This class inherits from stream.Transform, allowing zlib objects to be used in pipes and similar stream operations.

zlib.bytesRead#

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zlib.bytesRead 属性指的是压缩引擎处理之前读取的字节数 (压缩或者解压, 适用于派生类)。

zlib.bytesWritten#

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The zlib.bytesWritten property specifies the number of bytes written to the engine, before the bytes are processed (compressed or decompressed, as appropriate for the derived class).

zlib.close([callback])#

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Close the underlying handle.

zlib.flush([kind, ]callback)#

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  • kind Default: zlib.constants.Z_FULL_FLUSH for zlib-based streams, zlib.constants.BROTLI_OPERATION_FLUSH for Brotli-based streams.
  • callback <Function>

Flush pending data. Don't call this frivolously, premature flushes negatively impact the effectiveness of the compression algorithm.

Calling this only flushes data from the internal zlib state, and does not perform flushing of any kind on the streams level. Rather, it behaves like a normal call to .write(), i.e. it will be queued up behind other pending writes and will only produce output when data is being read from the stream.

zlib.params(level, strategy, callback)#

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This function is only available for zlib-based streams, i.e. not Brotli.

Dynamically update the compression level and compression strategy. Only applicable to deflate algorithm.

zlib.reset()#

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重置 compressor/decompressor 为默认值。仅适用于 inflate 和 deflate 算法。

zlib.constants#

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Provides an object enumerating Zlib-related constants.

zlib.createBrotliCompress([options])#

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Creates and returns a new BrotliCompress object.

zlib.createBrotliDecompress([options])#

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Creates and returns a new BrotliDecompress object.

zlib.createDeflate([options])#

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Creates and returns a new Deflate object.

zlib.createDeflateRaw([options])#

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Creates and returns a new DeflateRaw object.

An upgrade of zlib from 1.2.8 to 1.2.11 changed behavior when windowBits is set to 8 for raw deflate streams. zlib would automatically set windowBits to 9 if was initially set to 8. Newer versions of zlib will throw an exception, so Node.js restored the original behavior of upgrading a value of 8 to 9, since passing windowBits = 9 to zlib actually results in a compressed stream that effectively uses an 8-bit window only.

zlib.createGunzip([options])#

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Creates and returns a new Gunzip object.

zlib.createGzip([options])#

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Creates and returns a new Gzip object.

zlib.createInflate([options])#

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Creates and returns a new Inflate object.

zlib.createInflateRaw([options])#

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Creates and returns a new InflateRaw object.

zlib.createUnzip([options])#

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Creates and returns a new Unzip object.

Convenience Methods#

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所有这些方法都将 Buffer, [TypeArray][], DataView, 或者字符串作为第一个 参数, 一个回调函数作为可选的第二个参数提供给 zlib 类, 会在 callback(error, result) 中调用.

每一个方法相对应的都有一个接受相同参数, 但是没有回调的 *Sync 版本.

zlib.brotliCompress(buffer[, options], callback)#

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zlib.brotliCompressSync(buffer[, options])#

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Compress a chunk of data with BrotliCompress.

zlib.brotliDecompress(buffer[, options], callback)#

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zlib.brotliDecompressSync(buffer[, options])#

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Decompress a chunk of data with BrotliDecompress.

zlib.deflate(buffer[, options], callback)#

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zlib.deflateSync(buffer[, options])#

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Compress a chunk of data with Deflate.

zlib.deflateRaw(buffer[, options], callback)#

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zlib.deflateRawSync(buffer[, options])#

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Compress a chunk of data with DeflateRaw.

zlib.gunzip(buffer[, options], callback)#

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zlib.gunzipSync(buffer[, options])#

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Decompress a chunk of data with Gunzip.

zlib.gzip(buffer[, options], callback)#

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zlib.gzipSync(buffer[, options])#

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Compress a chunk of data with Gzip.

zlib.inflate(buffer[, options], callback)#

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zlib.inflateSync(buffer[, options])#

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Decompress a chunk of data with Inflate.

zlib.inflateRaw(buffer[, options], callback)#

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zlib.inflateRawSync(buffer[, options])#

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Decompress a chunk of data with InflateRaw.

zlib.unzip(buffer[, options], callback)#

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zlib.unzipSync(buffer[, options])#

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Decompress a chunk of data with Unzip.