{ "type": "module", "source": "doc/api/zlib.md", "modules": [ { "textRaw": "Zlib", "name": "zlib", "introduced_in": "v0.10.0", "stability": 2, "stabilityText": "Stable", "desc": "
The zlib
module provides compression functionality implemented using Gzip and\nDeflate/Inflate. It can be accessed using:
const zlib = require('zlib');\n
\nCompressing or decompressing a stream (such as a file) can be accomplished by\npiping the source stream data through a zlib
stream into a destination stream:
const gzip = zlib.createGzip();\nconst fs = require('fs');\nconst inp = fs.createReadStream('input.txt');\nconst out = fs.createWriteStream('input.txt.gz');\n\ninp.pipe(gzip).pipe(out);\n
\nIt is also possible to compress or decompress data in a single step:
\nconst input = '.................................';\nzlib.deflate(input, (err, buffer) => {\n if (!err) {\n console.log(buffer.toString('base64'));\n } else {\n // handle error\n }\n});\n\nconst buffer = Buffer.from('eJzT0yMAAGTvBe8=', 'base64');\nzlib.unzip(buffer, (err, buffer) => {\n if (!err) {\n console.log(buffer.toString());\n } else {\n // handle error\n }\n});\n
",
"modules": [
{
"textRaw": "Threadpool Usage",
"name": "threadpool_usage",
"desc": "Note that all zlib APIs except those that are explicitly synchronous use libuv's\nthreadpool. This can lead to surprising effects in some applications, such as\nsubpar performance (which can be mitigated by adjusting the pool size)\nand/or unrecoverable and catastrophic memory fragmentation.
", "type": "module", "displayName": "Threadpool Usage" }, { "textRaw": "Compressing HTTP requests and responses", "name": "compressing_http_requests_and_responses", "desc": "The zlib
module can be used to implement support for the gzip
and deflate
\ncontent-encoding mechanisms defined by\nHTTP.
The HTTP Accept-Encoding
header is used within an http request to identify\nthe compression encodings accepted by the client. The Content-Encoding
\nheader is used to identify the compression encodings actually applied to a\nmessage.
The examples given below are drastically simplified to show the basic concept.\nUsing zlib
encoding can be expensive, and the results ought to be cached.\nSee Memory Usage Tuning for more information on the speed/memory/compression\ntradeoffs involved in zlib
usage.
// client request example\nconst zlib = require('zlib');\nconst http = require('http');\nconst fs = require('fs');\nconst request = http.get({ host: 'example.com',\n path: '/',\n port: 80,\n headers: { 'Accept-Encoding': 'gzip,deflate' } });\nrequest.on('response', (response) => {\n const output = fs.createWriteStream('example.com_index.html');\n\n switch (response.headers['content-encoding']) {\n // or, just use zlib.createUnzip() to handle both cases\n case 'gzip':\n response.pipe(zlib.createGunzip()).pipe(output);\n break;\n case 'deflate':\n response.pipe(zlib.createInflate()).pipe(output);\n break;\n default:\n response.pipe(output);\n break;\n }\n});\n
\n// server example\n// Running a gzip operation on every request is quite expensive.\n// It would be much more efficient to cache the compressed buffer.\nconst zlib = require('zlib');\nconst http = require('http');\nconst fs = require('fs');\nhttp.createServer((request, response) => {\n const raw = fs.createReadStream('index.html');\n let acceptEncoding = request.headers['accept-encoding'];\n if (!acceptEncoding) {\n acceptEncoding = '';\n }\n\n // Note: This is not a conformant accept-encoding parser.\n // See https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.3\n if (/\\bdeflate\\b/.test(acceptEncoding)) {\n response.writeHead(200, { 'Content-Encoding': 'deflate' });\n raw.pipe(zlib.createDeflate()).pipe(response);\n } else if (/\\bgzip\\b/.test(acceptEncoding)) {\n response.writeHead(200, { 'Content-Encoding': 'gzip' });\n raw.pipe(zlib.createGzip()).pipe(response);\n } else {\n response.writeHead(200, {});\n raw.pipe(response);\n }\n}).listen(1337);\n
\nBy default, the zlib
methods will throw an error when decompressing\ntruncated data. However, if it is known that the data is incomplete, or\nthe desire is to inspect only the beginning of a compressed file, it is\npossible to suppress the default error handling by changing the flushing\nmethod that is used to decompress the last chunk of input data:
// This is a truncated version of the buffer from the above examples\nconst buffer = Buffer.from('eJzT0yMA', 'base64');\n\nzlib.unzip(\n buffer,\n { finishFlush: zlib.constants.Z_SYNC_FLUSH },\n (err, buffer) => {\n if (!err) {\n console.log(buffer.toString());\n } else {\n // handle error\n }\n });\n
\nThis will not change the behavior in other error-throwing situations, e.g.\nwhen the input data has an invalid format. Using this method, it will not be\npossible to determine whether the input ended prematurely or lacks the\nintegrity checks, making it necessary to manually check that the\ndecompressed result is valid.
", "type": "module", "displayName": "Compressing HTTP requests and responses" }, { "textRaw": "Flushing", "name": "flushing", "desc": "Calling .flush()
on a compression stream will make zlib
return as much\noutput as currently possible. This may come at the cost of degraded compression\nquality, but can be useful when data needs to be available as soon as possible.
In the following example, flush()
is used to write a compressed partial\nHTTP response to the client:
const zlib = require('zlib');\nconst http = require('http');\n\nhttp.createServer((request, response) => {\n // For the sake of simplicity, the Accept-Encoding checks are omitted.\n response.writeHead(200, { 'content-encoding': 'gzip' });\n const output = zlib.createGzip();\n output.pipe(response);\n\n setInterval(() => {\n output.write(`The current time is ${Date()}\\n`, () => {\n // The data has been passed to zlib, but the compression algorithm may\n // have decided to buffer the data for more efficient compression.\n // Calling .flush() will make the data available as soon as the client\n // is ready to receive it.\n output.flush();\n });\n }, 1000);\n}).listen(1337);\n
",
"type": "module",
"displayName": "Flushing"
}
],
"miscs": [
{
"textRaw": "Memory Usage Tuning",
"name": "Memory Usage Tuning",
"type": "misc",
"desc": "From zlib/zconf.h
, modified to Node.js's usage:
The memory requirements for deflate are (in bytes):
\n\n(1 << (windowBits + 2)) + (1 << (memLevel + 9))\n
\nThat is: 128K for windowBits
= 15 + 128K for memLevel
= 8\n(default values) plus a few kilobytes for small objects.
For example, to reduce the default memory requirements from 256K to 128K, the\noptions should be set to:
\nconst options = { windowBits: 14, memLevel: 7 };\n
\nThis will, however, generally degrade compression.
\nThe memory requirements for inflate are (in bytes) 1 << windowBits
.\nThat is, 32K for windowBits
= 15 (default value) plus a few kilobytes\nfor small objects.
This is in addition to a single internal output slab buffer of size\nchunkSize
, which defaults to 16K.
The speed of zlib
compression is affected most dramatically by the\nlevel
setting. A higher level will result in better compression, but\nwill take longer to complete. A lower level will result in less\ncompression, but will be much faster.
In general, greater memory usage options will mean that Node.js has to make\nfewer calls to zlib
because it will be able to process more data on\neach write
operation. So, this is another factor that affects the\nspeed, at the cost of memory usage.
All of the constants defined in zlib.h
are also defined on\nrequire('zlib').constants
. In the normal course of operations, it will not be\nnecessary to use these constants. They are documented so that their presence is\nnot surprising. This section is taken almost directly from the\nzlib documentation. See https://zlib.net/manual.html#Constants for more\ndetails.
Previously, the constants were available directly from require('zlib')
, for\ninstance zlib.Z_NO_FLUSH
. Accessing the constants directly from the module is\ncurrently still possible but is deprecated.
Allowed flush values.
\nzlib.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\nvalues are errors, positive values are used for special but normal\nevents.
\nzlib.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.
\nzlib.constants.Z_NO_COMPRESSION
zlib.constants.Z_BEST_SPEED
zlib.constants.Z_BEST_COMPRESSION
zlib.constants.Z_DEFAULT_COMPRESSION
Compression strategy.
\nzlib.constants.Z_FILTERED
zlib.constants.Z_HUFFMAN_ONLY
zlib.constants.Z_RLE
zlib.constants.Z_FIXED
zlib.constants.Z_DEFAULT_STRATEGY
Each class takes an options
object. All options are optional.
Note that some options are only relevant when compressing, and are\nignored by the decompression classes.
\nflush
<integer> Default: zlib.constants.Z_NO_FLUSH
finishFlush
<integer> Default: zlib.constants.Z_FINISH
chunkSize
<integer> Default: 16 * 1024
windowBits
<integer>level
<integer> (compression only)memLevel
<integer> (compression only)strategy
<integer> (compression only)dictionary
<Buffer> | <TypedArray> | <DataView> | <ArrayBuffer> (deflate/inflate only,\nempty dictionary by default)info
<boolean> (If true
, returns an object with buffer
and engine
.)See the description of deflateInit2
and inflateInit2
at\nhttps://zlib.net/manual.html#Advanced for more information on these.
All of these take a Buffer
, TypedArray
, DataView
,\nArrayBuffer
or string as the first argument, an optional second argument\nto supply options to the zlib
classes and will call the supplied callback\nwith callback(error, result)
.
Every method has a *Sync
counterpart, which accept the same arguments, but\nwithout a callback.
Compress a chunk of data with Deflate
.
Compress a chunk of data with DeflateRaw
.
Decompress a chunk of data with Gunzip
.
Compress a chunk of data with Gzip
.
Decompress a chunk of data with Inflate
.
Decompress a chunk of data with InflateRaw
.
Decompress a chunk of data with Unzip
.
Compress data using deflate.
" }, { "textRaw": "Class: zlib.DeflateRaw", "type": "class", "name": "zlib.DeflateRaw", "meta": { "added": [ "v0.5.8" ], "changes": [] }, "desc": "Compress data using deflate, and do not append a zlib
header.
Decompress a gzip stream.
" }, { "textRaw": "Class: zlib.Gzip", "type": "class", "name": "zlib.Gzip", "meta": { "added": [ "v0.5.8" ], "changes": [] }, "desc": "Compress data using gzip.
" }, { "textRaw": "Class: zlib.Inflate", "type": "class", "name": "zlib.Inflate", "meta": { "added": [ "v0.5.8" ], "changes": [ { "version": "v5.0.0", "pr-url": "https://github.com/nodejs/node/pull/2595", "description": "A truncated input stream will now result in an `'error'` event." } ] }, "desc": "Decompress a deflate stream.
" }, { "textRaw": "Class: zlib.InflateRaw", "type": "class", "name": "zlib.InflateRaw", "meta": { "added": [ "v0.5.8" ], "changes": [ { "version": "v6.8.0", "pr-url": "https://github.com/nodejs/node/pull/8512", "description": "Custom dictionaries are now supported by `InflateRaw`." }, { "version": "v5.0.0", "pr-url": "https://github.com/nodejs/node/pull/2595", "description": "A truncated input stream will now result in an `'error'` event." } ] }, "desc": "Decompress a raw deflate stream.
" }, { "textRaw": "Class: zlib.Unzip", "type": "class", "name": "zlib.Unzip", "meta": { "added": [ "v0.5.8" ], "changes": [] }, "desc": "Decompress either a Gzip- or Deflate-compressed stream by auto-detecting\nthe header.
" }, { "textRaw": "Class: zlib.Zlib", "type": "class", "name": "zlib.Zlib", "meta": { "added": [ "v0.5.8" ], "changes": [] }, "desc": "Not exported by the zlib
module. It is documented here because it is the base\nclass of the compressor/decompressor classes.
This class inherits from stream.Transform
, allowing zlib
objects to be\nused in pipes and similar stream operations.
Deprecated alias for zlib.bytesWritten
. This original name was chosen\nbecause it also made sense to interpret the value as the number of bytes\nread by the engine, but is inconsistent with other streams in Node.js that\nexpose values under these names.
The zlib.bytesWritten
property specifies the number of bytes written to\nthe engine, before the bytes are processed (compressed or decompressed,\nas appropriate for the derived class).
Close the underlying handle.
" }, { "textRaw": "zlib.flush([kind, ]callback)", "type": "method", "name": "flush", "meta": { "added": [ "v0.5.8" ], "changes": [] }, "signatures": [ { "params": [ { "textRaw": "`kind` **Default:** `zlib.constants.Z_FULL_FLUSH`", "name": "kind", "default": "`zlib.constants.Z_FULL_FLUSH`", "optional": true }, { "textRaw": "`callback` {Function}", "name": "callback", "type": "Function" } ] } ], "desc": "Flush pending data. Don't call this frivolously, premature flushes negatively\nimpact the effectiveness of the compression algorithm.
\nCalling this only flushes data from the internal zlib
state, and does not\nperform flushing of any kind on the streams level. Rather, it behaves like a\nnormal call to .write()
, i.e. it will be queued up behind other pending\nwrites and will only produce output when data is being read from the stream.
Dynamically update the compression level and compression strategy.\nOnly applicable to deflate algorithm.
" }, { "textRaw": "zlib.reset()", "type": "method", "name": "reset", "meta": { "added": [ "v0.7.0" ], "changes": [] }, "signatures": [ { "params": [] } ], "desc": "Reset the compressor/decompressor to factory defaults. Only applicable to\nthe inflate and deflate algorithms.
" } ] } ], "properties": [ { "textRaw": "zlib.constants", "name": "constants", "meta": { "added": [ "v7.0.0" ], "changes": [] }, "desc": "Provides an object enumerating Zlib-related constants.
" } ], "methods": [ { "textRaw": "zlib.createDeflate([options])", "type": "method", "name": "createDeflate", "meta": { "added": [ "v0.5.8" ], "changes": [] }, "signatures": [ { "params": [ { "textRaw": "`options` {zlib options}", "name": "options", "type": "zlib options", "optional": true } ] } ], "desc": "Creates and returns a new Deflate
object.
Creates and returns a new DeflateRaw
object.
An upgrade of zlib from 1.2.8 to 1.2.11 changed behavior when windowBits
\nis set to 8 for raw deflate streams. zlib would automatically set windowBits
\nto 9 if was initially set to 8. Newer versions of zlib will throw an exception,\nso Node.js restored the original behavior of upgrading a value of 8 to 9,\nsince passing windowBits = 9
to zlib actually results in a compressed stream\nthat effectively uses an 8-bit window only.
Creates and returns a new Gunzip
object.
Creates and returns a new Gzip
object.
Creates and returns a new Inflate
object.
Creates and returns a new InflateRaw
object.
Creates and returns a new Unzip
object.
Compress a chunk of data with Deflate
.
Compress a chunk of data with DeflateRaw
.
Decompress a chunk of data with Gunzip
.
Compress a chunk of data with Gzip
.
Decompress a chunk of data with Inflate
.
Decompress a chunk of data with InflateRaw
.
Decompress a chunk of data with Unzip
.