Zlib | Node.js v17.3.1 Documentation

Source Code: lib/zlib.js
The zlib module provides compaction functionality implemented using Gzip, Deflate/Inflate, and Brotli.

To access it :

 const zlib =  want( 'zlib ');

compression and decompression are built around the Node.js Streams API .
Compressing or decompressing a current ( such as a file ) can be accomplished by piping the informant stream through a zlib Transform stream into a finish stream :

 const { createGzip } =  want( 'zlib ');
 const { pipeline } =  ask( 'stream ');
 const {
  createReadStream,
  createWriteStream
} =  command( 'fs ');

 const gzip =  createGzip();
 const source =  createReadStream( 'input.txt ');
 const destination =  createWriteStream( 'input.txt.gz ');

 pipeline(source, gzip, destination,  ( 
err
 ) = > {
   if (err) {
     console. error( 'An error occurred : ', err);
    process. exitCode =  1;
  }
});

 

 const { promisify } =  want( 'util ');
 const pipe =  promisify(pipeline);

 async  routine  do_gzip( input, end product) {
   const gzip =  createGzip();
   const source =  createReadStream(input);
   const destination =  createWriteStream(output);
   expect  shriek(source, gzip, destination);
}

 do_gzip( 'input.txt ',  'input.txt.gz ')
 . catch( ( 
err
 ) = > {
     console table. error( 'An error occurred : ', err);
    process. exitCode =  1;
  });

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

 const { deflate, unzip } =  ask( 'zlib ');

 const input =  ' ... ... ... ... ... ... ... ... ... ... ... ';
 deflate(input,  ( 
err, buffer
 ) = > {
   if (err) {
     cabinet. error( 'An error occurred : ', err);
    process. exitCode =  1;
  }
   console. log(buffer. toString( 'base64 '));
});

 const buffer =  buff. from( 'eJzT0yMAAGTvBe8= ',  'base64 ');
 unzip(buffer,  ( 
err, buffer
 ) = > {
   if (err) {
     console. error( 'An error occurred : ', err);
    process. exitCode =  1;
  }
   comfort. log(buffer. toString());
});

 

 const { promisify } =  want( 'util ');
 const do_unzip =  promisify(unzip);

 do_unzip(buffer)
 . then( ( 
buf
 ) = >  console. logarithm(buf. toString()))
 . catch( ( 
err
 ) = > {
     console table. mistake( 'An error occurred : ', err);
    process. exitCode =  1;
  });

Threadpool usage and performance considerations#

All zlib APIs, except those that are explicitly synchronous, use the Node.js inner threadpool. This can lead to surprising effects and performance limitations in some applications .
Creating and using a large phone number of zlib objects simultaneously can cause significant memory fragmentation .

 const zlib =  ask( 'zlib ');

 const payload =  buff. from( 'This is some data ');

 
 for ( let i =  0; i <  30000; ++i) {
  zlib. deflate(payload,  ( 
err, buffer
 ) = > {});
}

In the preceding model, 30,000 deflate instances are created concurrently. Because of how some operating systems manage memory allotment and deallocation, this may lead to to significant memory fragmentation .
It is powerfully recommended that the results of compression operations be cached to avoid duplicate of feat .

Compressing HTTP requests and responses#

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 hypertext transfer protocol request to identify the compression encodings accepted by the node. The Content-Encoding heading is used to identify the compaction encodings actually applied to a message .
The examples given below are drastically simplified to show the basic concept. Using zlib encode 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 custom .

 
 const zlib =  ask( 'zlib ');
 const http =  ask( 'http ');
 const fs =  ask( 'fs ');
 const { pipeline } =  want( 'stream ');

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

   const  onError = ( err) => {
     if (err) {
       comfort. error( 'An error occurred : ', err);
      process. exitCode =  1;
    }
  };

   switch (response. headers[ 'content-encoding ']) {
     case  'br ':
       pipeline(response, zlib. createBrotliDecompress(), output, onError);
       rupture;
     
     encase  'gzip ':
       grapevine(response, zlib. createGunzip(), output, onError);
       break;
     font  'deflate ':
       grapevine(response, zlib. createInflate(), output, onError);
       break;
     default:
       grapevine(response, output, onError);
       break;
  }
});

 
 
 
 const zlib =  want( 'zlib ');
 const http =  command( 'http ');
 const fs =  want( 'fs ');
 const { pipeline } =  ask( 'stream ');

http. createServer( ( 
request, response
 ) = > {
   const raw = fs. createReadStream( 'index.html ');
   
  response. setHeader( 'Vary ',  'Accept-Encoding ');
   let acceptEncoding = request. headers[ 'accept-encoding '];
   if (!acceptEncoding) {
    acceptEncoding =  '';
  }

   const  onError = ( stray) => {
     if (err) {
       
       
       
       
       
      response. end 
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();
       comfort. mistake( 'An error occurred : ', err);
    }
  };

   
   
   if ( /\bdeflate\b/. trial(acceptEncoding)) {
    response. writeHead( 200, {  'Content-Encoding ':  'deflate ' });
     pipeline(raw, zlib. createDeflate(), response, onError);
  }  else  if ( /\bgzip\b/. trial(acceptEncoding)) {
    response. writeHead( 200, {  'Content-Encoding ':  'gzip ' });
     pipeline(raw, zlib. createGzip(), response, onError);
  }  else  if ( /\bbr\b/. test(acceptEncoding)) {
    response. writeHead( 200, {  'Content-Encoding ':  'br ' });
     pipeline(raw, zlib. createBrotliCompress(), response, onError);
  }  else {
    response. writeHead( 200, {});
     pipeline(raw, response, onError);
  }
}). heed( 1337);

By default, the zlib methods will throw an error when decompressing truncated data. however, if it is known that the datum is incomplete, or the hope is to inspect only the begin of a compressed file, it is possible to suppress the default erroneousness manage by changing the flushing method acting that is used to decompress the last lump of remark data :

 
 const buffer =  buffer. from( 'eJzT0yMA ',  'base64 ');

zlib. unzip(
  buffer,
   
  {  finishFlush: zlib. constants. Z_SYNC_FLUSH },
   ( 
err, buffer
 ) = > {
     if (err) {
       console. erroneousness( 'An error occurred : ', err);
      process. exitCode =  1;
    }
     console table. log(buffer. toString());
  });

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

Memory usage tuning#

For zlib-based streams#

From zlib/zconf.h, modified for Node.js custom :
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 exemplar, 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, by and large degrade compaction .
The memory requirements for balloon are ( in bytes ) 1 << windowBits. That is, 32K for windowBits = 15 ( nonpayment prize ) plus a few kilobytes for little objects .
This is in summation to a single home output slab buffer zone of size chunkSize, which defaults to 16K .
The speed of zlib compression is affected most dramatically by the level jell. A higher tied will result in better compression, but will take longer to complete. A lower level will result in less compaction, but will be much faster .
In general, greater memory custom 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. thus, this is another divisor that affects the rush, at the monetary value of memory usage .

For Brotli-based streams#

There are equivalents to the zlib options for Brotli-based streams, although these options have unlike 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#

Calling .flush() on a compression pour will make zlib return as a lot output ampere presently possible. This may come at the cost of degrade compression choice, but can be utilitarian when data needs to be available angstrom soon as possible .
In the postdate case, flush() is used to write a compressed overtone HTTP response to the customer :

 const zlib =  want( 'zlib ');
 const http =  want( 'http ');
 const { pipeline } =  want( 'stream ');

http. createServer( ( 
request, response
 ) = > {
   
  response. writeHead( 200, {  'content-encoding ':  'gzip ' });
   const output = zlib. createGzip();
   let i;

   pipeline(output, response,  ( 
err
 ) = > {
     if (err) {
       
       
       
       
       
       clearInterval(i);
      response. end();
       console. error( 'An error occurred : ', err);
    }
  });

  i =  setInterval( ( ) = > {
    output. publish( `The stream time is 
${
Date
()}
 \n`,  ( ) = > {
       
       
       
       
      output. bloom();
    });
  },  1000);
}). listen( 1337);

Constants#

Added in: v0.5.8

zlib constants#

All of the constants defined in zlib.h are besides 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 surprise. This part is taken about immediately from the zlib documentation .
previously, the constants were available immediately from require('zlib'), for example zlib.Z_NO_FLUSH. Accessing the constants directly from the module is presently distillery 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. minus values are errors, positive values are used for especial 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

compaction levels .

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

compression scheme .

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

Brotli constants#

Added in: v11.7.0, v10.16.0

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

Flush operations#

The come 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#

There are respective options that can be set on Brotli encoders, affecting compression efficiency and focal ratio. Both the key 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 follow flags can be set for advance see over the compression algorithm and memory use 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#

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#

History

Version	Changes
v14.5.0, v12.19.0	The maxOutputLength choice is supported now .
v9.4.0	The dictionary choice can be an ArrayBuffer .
v8.0.0	The dictionary choice can be an Uint8Array now .
v5.11.0	The finishFlush option is supported now .
v0.11.1	Added in : v0.11.1

Each zlib-based class takes an options aim. No options are required .
Some options are only relevant when compress and are ignored by the decompression classes .

• flush Default: zlib.constants.Z_NO_FLUSH
• finishFlush Default: zlib.constants.Z_FINISH
• chunkSize Default: 16 * 1024
• windowBits
• level (compression only)
• memLevel (compression only)
• strategy (compression only)
• dictionary | | | (deflate/inflate only,
  empty dictionary by default)
• info (If true, returns an object with buffer and engine.)
• maxOutputLength Limits output size when using
  convenience methods. Default: buffer.kMaxLength

See the deflateInit2 and inflateInit2 documentation for more information .

Class: BrotliOptions#

History

Version	Changes
v14.5.0, v12.19.0	The maxOutputLength option is supported nowadays .
v11.7.0	Added in : v11.7.0

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

• flush Default: zlib.constants.BROTLI_OPERATION_PROCESS
• finishFlush Default: zlib.constants.BROTLI_OPERATION_FINISH
• chunkSize Default: 16 * 1024
• params Key-value object containing indexed Brotli parameters.
• maxOutputLength Limits output size when using
  convenience methods. Default: buffer.kMaxLength

For exercise :

 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#

Added in: v11.7.0, v10.16.0

Compress data using the Brotli algorithm .

Class: zlib.BrotliDecompress#

Added in: v11.7.0, v10.16.0

Decompress data using the Brotli algorithm .

Class: zlib.Deflate#

Added in: v0.5.8

Compress data using deflate .

Class: zlib.DeflateRaw#

Added in: v0.5.8

Compress data using deflate, and do not append a zlib header .

Class: zlib.Gunzip#

History

Version	Changes
v6.0.0	Trailing drivel at the end of the input pour will now result in an 'error' event .
v5.9.0	Multiple concatenated gzip file members are supported now .
v5.0.0	A truncate input flow will nowadays result in an 'error' event .
v0.5.8	Added in : v0.5.8

Decompress a gzip stream .

Class: zlib.Gzip#

Added in: v0.5.8

Compress data using gzip .

Class: zlib.Inflate#

History

Version	Changes
v5.0.0	A truncate input stream will immediately result in an 'error' event .
v0.5.8	Added in : v0.5.8

Decompress a deflate pour .

Class: zlib.InflateRaw#

History

Version	Changes
v6.8.0	Custom dictionaries are now supported by InflateRaw .
v5.0.0	A truncate remark stream will now result in an 'error' event .
v0.5.8	Added in : v0.5.8

Decompress a raw deflate pour .

Class: zlib.Unzip#

Added in: v0.5.8

Decompress either a Gzip- or Deflate-compressed stream by auto-detecting the header .

Class: zlib.ZlibBase#

History

Version	Changes
v11.7.0, v10.16.0	This class was renamed from Zlib to ZlibBase .
v0.5.8	Added in : v0.5.8

not exported by the zlib module. It is documented here because it is the base classify of the compressor/decompressor classes .
This class inherits from stream.Transform, allowing zlib objects to be used in pipes and alike flow operations .

zlib.bytesRead#

Added in: v8.1.0

Deprecated since: v10.0.0

Stability: 0 - Deprecated: Use zlib.bytesWritten instead.

Deprecated alias for zlib.bytesWritten. This original name was chosen because it besides made sense to interpret the respect as the number of bytes read by the locomotive, but is discrepant with other streams in Node.js that debunk values under these names .

zlib.bytesWritten#

Added in: v10.0.0

The zlib.bytesWritten property specifies the issue of bytes written to the engine, before the bytes are processed ( compressed or decompressed, as allow for the derive course ) .

zlib.close([callback])#

Added in: v0.9.4

• callback

close the underlying manage .

zlib.flush([kind, ]callback)#

Added in: v0.5.8

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

blush pending data. Do n't call this frivolously, previous flushes negatively impact the effectiveness of the compaction algorithm .
Calling this only flushes data from the home zlib state, and does not perform blush of any kind on the stream degree. quite, it behaves like a convention margin call to .write(), i.e. it will be queued up behind other pending writes and will only produce output signal when datum is being read from the stream .

zlib.params(level, strategy, callback)#

Added in: v0.11.4

• level
• strategy
• callback

This function is only available for zlib-based streams, i.e. not Brotli .
dynamically update the compaction level and compression strategy. only applicable to deflate algorithm .

zlib.reset()#

Added in: v0.7.0

Reset the compressor/decompressor to factory defaults. entirely applicable to the inflate and deflate algorithms .

zlib.constants#

Added in: v7.0.0

Provides an object enumerating Zlib-related constants .

zlib.createDeflateRaw([options])#

Added in: v0.5.8

• options

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 crude 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 demeanor of upgrading a rate of 8 to 9, since passing windowBits = 9 to zlib actually results in a compress stream that efficaciously uses an 8-bit windowpane only .

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