{ "source": "doc/api/zlib.md", "modules": [ { "textRaw": "Zlib", "name": "zlib", "stability": 2, "stabilityText": "Stable", "desc": "

You can access this module with:

\n
const zlib = require('zlib');\n

This provides bindings to Gzip/Gunzip, Deflate/Inflate, and\nDeflateRaw/InflateRaw classes. Each class takes the same options, and\nis a readable/writable Stream.

\n

Examples

\n

Compressing or decompressing a file can be done by piping an\nfs.ReadStream into a zlib stream, then into an fs.WriteStream.

\n
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
\n

Compressing or decompressing data in one step can be done by using\nthe convenience methods.

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

To use this module in an HTTP client or server, use the [accept-encoding][]\non requests, and the [content-encoding][] header on responses.

\n

Note: these examples are drastically simplified to show\nthe basic concept. Zlib encoding can be expensive, and the results\nought to be cached. See [Memory Usage Tuning][] for more information\non the speed/memory/compression tradeoffs involved in zlib usage.

\n
// client request example\nconst zlib = require('zlib');\nconst http = require('http');\nconst fs = require('fs');\nconst request = http.get({ host: 'izs.me',\n                         path: '/',\n                         port: 80,\n                         headers: { 'accept-encoding': 'gzip,deflate' } });\nrequest.on('response', (response) => {\n  var output = fs.createWriteStream('izs.me_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  var raw = fs.createReadStream('index.html');\n  var acceptEncoding = request.headers['accept-encoding'];\n  if (!acceptEncoding) {\n    acceptEncoding = '';\n  }\n\n  // Note: this is not a conformant accept-encoding parser.\n  // See http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.3\n  if (acceptEncoding.match(/\\bdeflate\\b/)) {\n    response.writeHead(200, { 'content-encoding': 'deflate' });\n    raw.pipe(zlib.createDeflate()).pipe(response);\n  } else if (acceptEncoding.match(/\\bgzip\\b/)) {\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
\n", "miscs": [ { "textRaw": "Memory Usage Tuning", "name": "Memory Usage Tuning", "type": "misc", "desc": "

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

\n

The memory requirements for deflate are (in bytes):

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

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

\n

For example, if you want to reduce\nthe default memory requirements from 256K to 128K, set the options to:

\n
{ windowBits: 14, memLevel: 7 }\n

Of course this will generally degrade compression (there's no free lunch).

\n

The memory requirements for inflate are (in bytes)

\n
1 << windowBits\n

that is, 32K for windowBits=15 (default value) plus a few kilobytes\nfor small objects.

\n

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

\n

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.

\n

In general, greater memory usage options will mean that node.js has to make\nfewer calls to zlib, since it'll be able to process more data in a\nsingle write operation. So, this is another factor that affects the\nspeed, at the cost of memory usage.

\n" }, { "textRaw": "Constants", "name": "Constants", "meta": { "added": [ "v0.5.8" ] }, "type": "misc", "desc": "

All of the constants defined in zlib.h are also defined on\nrequire('zlib').\nIn the normal course of operations, you will not need to ever set any of\nthese. They are documented here so that their presence is not\nsurprising. This section is taken almost directly from the\n[zlib documentation][]. See http://zlib.net/manual.html#Constants for more\ndetails.

\n

Allowed flush values.

\n\n

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

\n\n

Compression levels.

\n\n

Compression strategy.

\n\n

Possible values of the data_type field.

\n\n

The deflate compression method (the only one supported in this version).

\n\n

For initializing zalloc, zfree, opaque.

\n\n" }, { "textRaw": "Class Options", "name": "Class Options", "meta": { "added": [ "v0.11.1" ] }, "type": "misc", "desc": "

Each class takes an options object. All options are optional.

\n

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

\n\n

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

\n" }, { "textRaw": "Convenience Methods", "name": "Convenience Methods", "type": "misc", "desc": "

All of these take a [Buffer][] or string as the first argument, an optional second\nargument to supply options to the zlib classes and will call the supplied\ncallback with callback(error, result).

\n

Every method has a *Sync counterpart, which accept the same arguments, but\nwithout a callback.

\n", "methods": [ { "textRaw": "zlib.deflate(buf[, options], callback)", "type": "method", "name": "deflate", "meta": { "added": [ "v0.6.0" ] }, "desc": "

Compress a Buffer or string with Deflate.

\n", "signatures": [ { "params": [ { "name": "buf" }, { "name": "options", "optional": true } ] }, { "params": [ { "name": "buf" }, { "name": "options", "optional": true }, { "name": "callback" } ] } ] }, { "textRaw": "zlib.deflateSync(buf[, options])", "type": "method", "name": "deflateSync", "meta": { "added": [ "v0.11.12" ] }, "desc": "

Compress a Buffer or string with Deflate.

\n", "signatures": [ { "params": [ { "name": "buf" }, { "name": "options", "optional": true } ] } ] }, { "textRaw": "zlib.deflateRaw(buf[, options], callback)", "type": "method", "name": "deflateRaw", "meta": { "added": [ "v0.6.0" ] }, "desc": "

Compress a Buffer or string with DeflateRaw.

\n", "signatures": [ { "params": [ { "name": "buf" }, { "name": "options", "optional": true } ] }, { "params": [ { "name": "buf" }, { "name": "options", "optional": true }, { "name": "callback" } ] } ] }, { "textRaw": "zlib.deflateRawSync(buf[, options])", "type": "method", "name": "deflateRawSync", "meta": { "added": [ "v0.11.12" ] }, "desc": "

Compress a Buffer or string with DeflateRaw.

\n", "signatures": [ { "params": [ { "name": "buf" }, { "name": "options", "optional": true } ] } ] }, { "textRaw": "zlib.gunzip(buf[, options], callback)", "type": "method", "name": "gunzip", "meta": { "added": [ "v0.6.0" ] }, "desc": "

Decompress a Buffer or string with Gunzip.

\n", "signatures": [ { "params": [ { "name": "buf" }, { "name": "options", "optional": true } ] }, { "params": [ { "name": "buf" }, { "name": "options", "optional": true }, { "name": "callback" } ] } ] }, { "textRaw": "zlib.gunzipSync(buf[, options])", "type": "method", "name": "gunzipSync", "meta": { "added": [ "v0.11.12" ] }, "desc": "

Decompress a Buffer or string with Gunzip.

\n", "signatures": [ { "params": [ { "name": "buf" }, { "name": "options", "optional": true } ] } ] }, { "textRaw": "zlib.gzip(buf[, options], callback)", "type": "method", "name": "gzip", "meta": { "added": [ "v0.6.0" ] }, "desc": "

Compress a Buffer or string with Gzip.

\n", "signatures": [ { "params": [ { "name": "buf" }, { "name": "options", "optional": true } ] }, { "params": [ { "name": "buf" }, { "name": "options", "optional": true }, { "name": "callback" } ] } ] }, { "textRaw": "zlib.gzipSync(buf[, options])", "type": "method", "name": "gzipSync", "meta": { "added": [ "v0.11.12" ] }, "desc": "

Compress a Buffer or string with Gzip.

\n", "signatures": [ { "params": [ { "name": "buf" }, { "name": "options", "optional": true } ] } ] }, { "textRaw": "zlib.inflate(buf[, options], callback)", "type": "method", "name": "inflate", "meta": { "added": [ "v0.6.0" ] }, "desc": "

Decompress a Buffer or string with Inflate.

\n", "signatures": [ { "params": [ { "name": "buf" }, { "name": "options", "optional": true } ] }, { "params": [ { "name": "buf" }, { "name": "options", "optional": true }, { "name": "callback" } ] } ] }, { "textRaw": "zlib.inflateSync(buf[, options])", "type": "method", "name": "inflateSync", "meta": { "added": [ "v0.11.12" ] }, "desc": "

Decompress a Buffer or string with Inflate.

\n", "signatures": [ { "params": [ { "name": "buf" }, { "name": "options", "optional": true } ] } ] }, { "textRaw": "zlib.inflateRaw(buf[, options], callback)", "type": "method", "name": "inflateRaw", "meta": { "added": [ "v0.6.0" ] }, "desc": "

Decompress a Buffer or string with InflateRaw.

\n", "signatures": [ { "params": [ { "name": "buf" }, { "name": "options", "optional": true } ] }, { "params": [ { "name": "buf" }, { "name": "options", "optional": true }, { "name": "callback" } ] } ] }, { "textRaw": "zlib.inflateRawSync(buf[, options])", "type": "method", "name": "inflateRawSync", "meta": { "added": [ "v0.11.12" ] }, "desc": "

Decompress a Buffer or string with InflateRaw.

\n", "signatures": [ { "params": [ { "name": "buf" }, { "name": "options", "optional": true } ] } ] }, { "textRaw": "zlib.unzip(buf[, options], callback)", "type": "method", "name": "unzip", "meta": { "added": [ "v0.6.0" ] }, "desc": "

Decompress a Buffer or string with Unzip.

\n", "signatures": [ { "params": [ { "name": "buf" }, { "name": "options", "optional": true } ] }, { "params": [ { "name": "buf" }, { "name": "options", "optional": true }, { "name": "callback" } ] } ] }, { "textRaw": "zlib.unzipSync(buf[, options])", "type": "method", "name": "unzipSync", "meta": { "added": [ "v0.11.12" ] }, "desc": "

Decompress a Buffer or string with Unzip.

\n", "signatures": [ { "params": [ { "name": "buf" }, { "name": "options", "optional": true } ] } ] } ] } ], "modules": [ { "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.

\n

In the following example, flush() is used to write a compressed partial\nHTTP response to the client:

\n
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
\n", "type": "module", "displayName": "Flushing" } ], "meta": { "added": [ "v0.5.8" ] }, "classes": [ { "textRaw": "Class: zlib.Deflate", "type": "class", "name": "zlib.Deflate", "meta": { "added": [ "v0.5.8" ] }, "desc": "

Compress data using deflate.

\n" }, { "textRaw": "Class: zlib.DeflateRaw", "type": "class", "name": "zlib.DeflateRaw", "meta": { "added": [ "v0.5.8" ] }, "desc": "

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

\n" }, { "textRaw": "Class: zlib.Gunzip", "type": "class", "name": "zlib.Gunzip", "meta": { "added": [ "v0.5.8" ] }, "desc": "

Decompress a gzip stream.

\n" }, { "textRaw": "Class: zlib.Gzip", "type": "class", "name": "zlib.Gzip", "meta": { "added": [ "v0.5.8" ] }, "desc": "

Compress data using gzip.

\n" }, { "textRaw": "Class: zlib.Inflate", "type": "class", "name": "zlib.Inflate", "meta": { "added": [ "v0.5.8" ] }, "desc": "

Decompress a deflate stream.

\n" }, { "textRaw": "Class: zlib.InflateRaw", "type": "class", "name": "zlib.InflateRaw", "meta": { "added": [ "v0.5.8" ] }, "desc": "

Decompress a raw deflate stream.

\n" }, { "textRaw": "Class: zlib.Unzip", "type": "class", "name": "zlib.Unzip", "meta": { "added": [ "v0.5.8" ] }, "desc": "

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

\n" }, { "textRaw": "Class: zlib.Zlib", "type": "class", "name": "zlib.Zlib", "meta": { "added": [ "v0.5.8" ] }, "desc": "

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

\n", "methods": [ { "textRaw": "zlib.flush([kind], callback)", "type": "method", "name": "flush", "meta": { "added": [ "v0.5.8" ] }, "desc": "

kind defaults to zlib.Z_FULL_FLUSH.

\n

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

\n

Calling 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.

\n", "signatures": [ { "params": [ { "name": "kind", "optional": true }, { "name": "callback" } ] } ] }, { "textRaw": "zlib.params(level, strategy, callback)", "type": "method", "name": "params", "meta": { "added": [ "v0.11.4" ] }, "desc": "

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

\n", "signatures": [ { "params": [ { "name": "level" }, { "name": "strategy" }, { "name": "callback" } ] } ] }, { "textRaw": "zlib.reset()", "type": "method", "name": "reset", "meta": { "added": [ "v0.7.0" ] }, "desc": "

Reset the compressor/decompressor to factory defaults. Only applicable to\nthe inflate and deflate algorithms.

\n", "signatures": [ { "params": [] } ] } ] } ], "methods": [ { "textRaw": "zlib.createDeflate([options])", "type": "method", "name": "createDeflate", "meta": { "added": [ "v0.5.8" ] }, "desc": "

Returns a new [Deflate][] object with an [options][].

\n", "signatures": [ { "params": [ { "name": "options", "optional": true } ] } ] }, { "textRaw": "zlib.createDeflateRaw([options])", "type": "method", "name": "createDeflateRaw", "meta": { "added": [ "v0.5.8" ] }, "desc": "

Returns a new [DeflateRaw][] object with an [options][].

\n", "signatures": [ { "params": [ { "name": "options", "optional": true } ] } ] }, { "textRaw": "zlib.createGunzip([options])", "type": "method", "name": "createGunzip", "meta": { "added": [ "v0.5.8" ] }, "desc": "

Returns a new [Gunzip][] object with an [options][].

\n", "signatures": [ { "params": [ { "name": "options", "optional": true } ] } ] }, { "textRaw": "zlib.createGzip([options])", "type": "method", "name": "createGzip", "meta": { "added": [ "v0.5.8" ] }, "desc": "

Returns a new [Gzip][] object with an [options][].

\n", "signatures": [ { "params": [ { "name": "options", "optional": true } ] } ] }, { "textRaw": "zlib.createInflate([options])", "type": "method", "name": "createInflate", "meta": { "added": [ "v0.5.8" ] }, "desc": "

Returns a new [Inflate][] object with an [options][].

\n", "signatures": [ { "params": [ { "name": "options", "optional": true } ] } ] }, { "textRaw": "zlib.createInflateRaw([options])", "type": "method", "name": "createInflateRaw", "meta": { "added": [ "v0.5.8" ] }, "desc": "

Returns a new [InflateRaw][] object with an [options][].

\n", "signatures": [ { "params": [ { "name": "options", "optional": true } ] } ] }, { "textRaw": "zlib.createUnzip([options])", "type": "method", "name": "createUnzip", "meta": { "added": [ "v0.5.8" ] }, "desc": "

Returns a new [Unzip][] object with an [options][].

\n", "signatures": [ { "params": [ { "name": "options", "optional": true } ] } ] } ], "type": "module", "displayName": "Zlib" } ] }