The node:zlib module provides compression functionality implemented using\nGzip, Deflate/Inflate, Brotli, and Zstd.
To access it:
\nimport zlib from 'node:zlib';\nconst zlib = require('node:zlib');\nCompression and decompression are built around the Node.js Streams API.
\nCompressing or decompressing a stream (such as a file) can be accomplished by\npiping the source stream through a zlib Transform stream into a destination\nstream:
import {\n createReadStream,\n createWriteStream,\n} from 'node:fs';\nimport process from 'node:process';\nimport { createGzip } from 'node:zlib';\nimport { pipeline } from 'node:stream';\n\nconst gzip = createGzip();\nconst source = createReadStream('input.txt');\nconst destination = createWriteStream('input.txt.gz');\n\npipeline(source, gzip, destination, (err) => {\n if (err) {\n console.error('An error occurred:', err);\n process.exitCode = 1;\n }\n});\nconst {\n createReadStream,\n createWriteStream,\n} = require('node:fs');\nconst { createGzip } = require('node:zlib');\nconst { pipeline } = require('node:stream');\n\nconst gzip = createGzip();\nconst source = createReadStream('input.txt');\nconst destination = createWriteStream('input.txt.gz');\n\npipeline(source, gzip, destination, (err) => {\n if (err) {\n console.error('An error occurred:', err);\n process.exitCode = 1;\n }\n});\nOr, using the promise pipeline API:
import {\n createReadStream,\n createWriteStream,\n} from 'node:fs';\nimport { createGzip } from 'node:zlib';\nimport { pipeline } from 'node:stream/promises';\n\nasync function do_gzip(input, output) {\n const gzip = createGzip();\n const source = createReadStream(input);\n const destination = createWriteStream(output);\n await pipeline(source, gzip, destination);\n}\n\nawait do_gzip('input.txt', 'input.txt.gz');\nconst {\n createReadStream,\n createWriteStream,\n} = require('node:fs');\nconst { createGzip } = require('node:zlib');\nconst { pipeline } = require('node:stream/promises');\n\nasync function do_gzip(input, output) {\n const gzip = createGzip();\n const source = createReadStream(input);\n const destination = createWriteStream(output);\n await pipeline(source, gzip, destination);\n}\n\ndo_gzip('input.txt', 'input.txt.gz')\n .catch((err) => {\n console.error('An error occurred:', err);\n process.exitCode = 1;\n });\nIt is also possible to compress or decompress data in a single step:
\nimport process from 'node:process';\nimport { Buffer } from 'node:buffer';\nimport { deflate, unzip } from 'node:zlib';\n\nconst input = '.................................';\ndeflate(input, (err, buffer) => {\n if (err) {\n console.error('An error occurred:', err);\n process.exitCode = 1;\n }\n console.log(buffer.toString('base64'));\n});\n\nconst buffer = Buffer.from('eJzT0yMAAGTvBe8=', 'base64');\nunzip(buffer, (err, buffer) => {\n if (err) {\n console.error('An error occurred:', err);\n process.exitCode = 1;\n }\n console.log(buffer.toString());\n});\n\n// Or, Promisified\n\nimport { promisify } from 'node:util';\nconst do_unzip = promisify(unzip);\n\nconst unzippedBuffer = await do_unzip(buffer);\nconsole.log(unzippedBuffer.toString());\nconst { deflate, unzip } = require('node:zlib');\n\nconst input = '.................................';\ndeflate(input, (err, buffer) => {\n if (err) {\n console.error('An error occurred:', err);\n process.exitCode = 1;\n }\n console.log(buffer.toString('base64'));\n});\n\nconst buffer = Buffer.from('eJzT0yMAAGTvBe8=', 'base64');\nunzip(buffer, (err, buffer) => {\n if (err) {\n console.error('An error occurred:', err);\n process.exitCode = 1;\n }\n console.log(buffer.toString());\n});\n\n// Or, Promisified\n\nconst { promisify } = require('node:util');\nconst do_unzip = promisify(unzip);\n\ndo_unzip(buffer)\n .then((buf) => console.log(buf.toString()))\n .catch((err) => {\n console.error('An error occurred:', err);\n process.exitCode = 1;\n });\nAll zlib APIs, except those that are explicitly synchronous, use the Node.js\ninternal threadpool. This can lead to surprising effects and performance\nlimitations in some applications.
Creating and using a large number of zlib objects simultaneously can cause\nsignificant memory fragmentation.
\nimport zlib from 'node:zlib';\nimport { Buffer } from 'node:buffer';\n\nconst payload = Buffer.from('This is some data');\n\n// WARNING: DO NOT DO THIS!\nfor (let i = 0; i < 30000; ++i) {\n zlib.deflate(payload, (err, buffer) => {});\n}\nconst zlib = require('node:zlib');\n\nconst payload = Buffer.from('This is some data');\n\n// WARNING: DO NOT DO THIS!\nfor (let i = 0; i < 30000; ++i) {\n zlib.deflate(payload, (err, buffer) => {});\n}\nIn the preceding example, 30,000 deflate instances are created concurrently.\nBecause of how some operating systems handle memory allocation and\ndeallocation, this may lead to significant memory fragmentation.
\nIt is strongly recommended that the results of compression\noperations be cached to avoid duplication of effort.
", "displayName": "Threadpool usage and performance considerations" }, { "textRaw": "Compressing HTTP requests and responses", "name": "compressing_http_requests_and_responses", "type": "module", "desc": "The node:zlib module can be used to implement support for the gzip, deflate,\nbr, and zstd content-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\nimport fs from 'node:fs';\nimport zlib from 'node:zlib';\nimport http from 'node:http';\nimport process from 'node:process';\nimport { pipeline } from 'node:stream';\n\nconst request = http.get({ host: 'example.com',\n path: '/',\n port: 80,\n headers: { 'Accept-Encoding': 'br,gzip,deflate,zstd' } });\nrequest.on('response', (response) => {\n const output = fs.createWriteStream('example.com_index.html');\n\n const onError = (err) => {\n if (err) {\n console.error('An error occurred:', err);\n process.exitCode = 1;\n }\n };\n\n switch (response.headers['content-encoding']) {\n case 'br':\n pipeline(response, zlib.createBrotliDecompress(), output, onError);\n break;\n // Or, just use zlib.createUnzip() to handle both of the following cases:\n case 'gzip':\n pipeline(response, zlib.createGunzip(), output, onError);\n break;\n case 'deflate':\n pipeline(response, zlib.createInflate(), output, onError);\n break;\n case 'zstd':\n pipeline(response, zlib.createZstdDecompress(), output, onError);\n break;\n default:\n pipeline(response, output, onError);\n break;\n }\n});\n// Client request example\nconst zlib = require('node:zlib');\nconst http = require('node:http');\nconst fs = require('node:fs');\nconst { pipeline } = require('node:stream');\n\nconst request = http.get({ host: 'example.com',\n path: '/',\n port: 80,\n headers: { 'Accept-Encoding': 'br,gzip,deflate,zstd' } });\nrequest.on('response', (response) => {\n const output = fs.createWriteStream('example.com_index.html');\n\n const onError = (err) => {\n if (err) {\n console.error('An error occurred:', err);\n process.exitCode = 1;\n }\n };\n\n switch (response.headers['content-encoding']) {\n case 'br':\n pipeline(response, zlib.createBrotliDecompress(), output, onError);\n break;\n // Or, just use zlib.createUnzip() to handle both of the following cases:\n case 'gzip':\n pipeline(response, zlib.createGunzip(), output, onError);\n break;\n case 'deflate':\n pipeline(response, zlib.createInflate(), output, onError);\n break;\n case 'zstd':\n pipeline(response, zlib.createZstdDecompress(), output, onError);\n break;\n default:\n pipeline(response, output, onError);\n break;\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.\nimport zlib from 'node:zlib';\nimport http from 'node:http';\nimport fs from 'node:fs';\nimport { pipeline } from 'node:stream';\n\nhttp.createServer((request, response) => {\n const raw = fs.createReadStream('index.html');\n // Store both a compressed and an uncompressed version of the resource.\n response.setHeader('Vary', 'Accept-Encoding');\n const acceptEncoding = request.headers['accept-encoding'] || '';\n\n const onError = (err) => {\n if (err) {\n // If an error occurs, there's not much we can do because\n // the server has already sent the 200 response code and\n // some amount of data has already been sent to the client.\n // The best we can do is terminate the response immediately\n // and log the error.\n response.end();\n console.error('An error occurred:', err);\n }\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 pipeline(raw, zlib.createDeflate(), response, onError);\n } else if (/\\bgzip\\b/.test(acceptEncoding)) {\n response.writeHead(200, { 'Content-Encoding': 'gzip' });\n pipeline(raw, zlib.createGzip(), response, onError);\n } else if (/\\bbr\\b/.test(acceptEncoding)) {\n response.writeHead(200, { 'Content-Encoding': 'br' });\n pipeline(raw, zlib.createBrotliCompress(), response, onError);\n } else if (/\\bzstd\\b/.test(acceptEncoding)) {\n response.writeHead(200, { 'Content-Encoding': 'zstd' });\n pipeline(raw, zlib.createZstdCompress(), response, onError);\n } else {\n response.writeHead(200, {});\n pipeline(raw, response, onError);\n }\n}).listen(1337);\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('node:zlib');\nconst http = require('node:http');\nconst fs = require('node:fs');\nconst { pipeline } = require('node:stream');\n\nhttp.createServer((request, response) => {\n const raw = fs.createReadStream('index.html');\n // Store both a compressed and an uncompressed version of the resource.\n response.setHeader('Vary', 'Accept-Encoding');\n const acceptEncoding = request.headers['accept-encoding'] || '';\n\n const onError = (err) => {\n if (err) {\n // If an error occurs, there's not much we can do because\n // the server has already sent the 200 response code and\n // some amount of data has already been sent to the client.\n // The best we can do is terminate the response immediately\n // and log the error.\n response.end();\n console.error('An error occurred:', err);\n }\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 pipeline(raw, zlib.createDeflate(), response, onError);\n } else if (/\\bgzip\\b/.test(acceptEncoding)) {\n response.writeHead(200, { 'Content-Encoding': 'gzip' });\n pipeline(raw, zlib.createGzip(), response, onError);\n } else if (/\\bbr\\b/.test(acceptEncoding)) {\n response.writeHead(200, { 'Content-Encoding': 'br' });\n pipeline(raw, zlib.createBrotliCompress(), response, onError);\n } else if (/\\bzstd\\b/.test(acceptEncoding)) {\n response.writeHead(200, { 'Content-Encoding': 'zstd' });\n pipeline(raw, zlib.createZstdCompress(), response, onError);\n } else {\n response.writeHead(200, {});\n pipeline(raw, response, onError);\n }\n}).listen(1337);\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 // For Brotli, the equivalent is zlib.constants.BROTLI_OPERATION_FLUSH.\n // For Zstd, the equivalent is zlib.constants.ZSTD_e_flush.\n { finishFlush: zlib.constants.Z_SYNC_FLUSH },\n (err, buffer) => {\n if (err) {\n console.error('An error occurred:', err);\n process.exitCode = 1;\n }\n console.log(buffer.toString());\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.
", "displayName": "Compressing HTTP requests and responses" }, { "textRaw": "Flushing", "name": "flushing", "type": "module", "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:
import zlib from 'node:zlib';\nimport http from 'node:http';\nimport { pipeline } from 'node:stream';\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 let i;\n\n pipeline(output, response, (err) => {\n if (err) {\n // If an error occurs, there's not much we can do because\n // the server has already sent the 200 response code and\n // some amount of data has already been sent to the client.\n // The best we can do is terminate the response immediately\n // and log the error.\n clearInterval(i);\n response.end();\n console.error('An error occurred:', err);\n }\n });\n\n i = 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);\nconst zlib = require('node:zlib');\nconst http = require('node:http');\nconst { pipeline } = require('node:stream');\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 let i;\n\n pipeline(output, response, (err) => {\n if (err) {\n // If an error occurs, there's not much we can do because\n // the server has already sent the 200 response code and\n // some amount of data has already been sent to the client.\n // The best we can do is terminate the response immediately\n // and log the error.\n clearInterval(i);\n response.end();\n console.error('An error occurred:', err);\n }\n });\n\n i = 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);\nThe node:zlib/iter module provides compression and decompression transforms\nfor use with the node:stream/iter iterable streams API.
This module is available only when the --experimental-stream-iter CLI flag\nis enabled.
Each algorithm has both an async variant (stateful async generator, for use\nwith pull() and pipeTo()) and a sync variant (stateful sync\ngenerator, for use with pullSync() and pipeToSync()).
The async transforms run compression on the libuv threadpool, overlapping\nI/O with JavaScript execution. The sync transforms run compression directly\non the main thread.
\n\n\nNote: The defaults for these transforms are tuned for streaming throughput,\nand differ from the defaults in
\nnode:zlib. In particular, gzip/deflate\ndefault to level 4 (not 6) and memLevel 9 (not 8), and Brotli defaults to\nquality 6 (not 11). These choices match common HTTP server configurations\nand provide significantly faster compression with only a small reduction in\ncompression ratio. All defaults can be overridden via options.
import { from, pull, bytes, text } from 'node:stream/iter';\nimport { compressGzip, decompressGzip } from 'node:zlib/iter';\n\n// Async round-trip\nconst compressed = await bytes(pull(from('hello'), compressGzip()));\nconst original = await text(pull(from(compressed), decompressGzip()));\nconsole.log(original); // 'hello'\nconst { from, pull, bytes, text } = require('node:stream/iter');\nconst { compressGzip, decompressGzip } = require('node:zlib/iter');\n\nasync function run() {\n const compressed = await bytes(pull(from('hello'), compressGzip()));\n const original = await text(pull(from(compressed), decompressGzip()));\n console.log(original); // 'hello'\n}\n\nrun().catch(console.error);\nimport { fromSync, pullSync, textSync } from 'node:stream/iter';\nimport { compressGzipSync, decompressGzipSync } from 'node:zlib/iter';\n\n// Sync round-trip\nconst compressed = pullSync(fromSync('hello'), compressGzipSync());\nconst original = textSync(pullSync(compressed, decompressGzipSync()));\nconsole.log(original); // 'hello'\nconst { fromSync, pullSync, textSync } = require('node:stream/iter');\nconst { compressGzipSync, decompressGzipSync } = require('node:zlib/iter');\n\nconst compressed = pullSync(fromSync('hello'), compressGzipSync());\nconst original = textSync(pullSync(compressed, decompressGzipSync()));\nconsole.log(original); // 'hello'\nCreate a Brotli compression transform. Output is compatible with\nzlib.brotliDecompress() and decompressBrotli()/decompressBrotliSync().
Create a deflate compression transform. Output is compatible with\nzlib.inflate() and decompressDeflate()/decompressDeflateSync().
Create a gzip compression transform. Output is compatible with zlib.gunzip()\nand decompressGzip()/decompressGzipSync().
Create a Zstandard compression transform. Output is compatible with\nzlib.zstdDecompress() and decompressZstd()/decompressZstdSync().
Create a Brotli decompression transform.
" }, { "textRaw": "`decompressDeflate([options])`", "name": "decompressDeflate", "type": "method", "signatures": [ { "params": [ { "name": "options", "optional": true } ] } ] }, { "textRaw": "`decompressDeflateSync([options])`", "name": "decompressDeflateSync", "type": "method", "meta": { "added": [ "v25.9.0" ], "changes": [] }, "signatures": [ { "params": [ { "textRaw": "`options` {Object}", "name": "options", "type": "Object", "options": [ { "textRaw": "`chunkSize` {number} Output buffer size. **Default:** `65536` (64 KB).", "name": "chunkSize", "type": "number", "default": "`65536` (64 KB)", "desc": "Output buffer size." }, { "textRaw": "`windowBits` {number} **Default:** `Z_DEFAULT_WINDOWBITS` (15).", "name": "windowBits", "type": "number", "default": "`Z_DEFAULT_WINDOWBITS` (15)" }, { "textRaw": "`dictionary` {Buffer|TypedArray|DataView}", "name": "dictionary", "type": "Buffer|TypedArray|DataView" } ], "optional": true } ], "return": { "textRaw": "Returns: {Object} A stateful transform.", "name": "return", "type": "Object", "desc": "A stateful transform." } } ], "desc": "Create a deflate decompression transform.
" }, { "textRaw": "`decompressGzip([options])`", "name": "decompressGzip", "type": "method", "signatures": [ { "params": [ { "name": "options", "optional": true } ] } ] }, { "textRaw": "`decompressGzipSync([options])`", "name": "decompressGzipSync", "type": "method", "meta": { "added": [ "v25.9.0" ], "changes": [] }, "signatures": [ { "params": [ { "textRaw": "`options` {Object}", "name": "options", "type": "Object", "options": [ { "textRaw": "`chunkSize` {number} Output buffer size. **Default:** `65536` (64 KB).", "name": "chunkSize", "type": "number", "default": "`65536` (64 KB)", "desc": "Output buffer size." }, { "textRaw": "`windowBits` {number} **Default:** `Z_DEFAULT_WINDOWBITS` (15).", "name": "windowBits", "type": "number", "default": "`Z_DEFAULT_WINDOWBITS` (15)" }, { "textRaw": "`dictionary` {Buffer|TypedArray|DataView}", "name": "dictionary", "type": "Buffer|TypedArray|DataView" } ], "optional": true } ], "return": { "textRaw": "Returns: {Object} A stateful transform.", "name": "return", "type": "Object", "desc": "A stateful transform." } } ], "desc": "Create a gzip decompression transform.
" }, { "textRaw": "`decompressZstd([options])`", "name": "decompressZstd", "type": "method", "signatures": [ { "params": [ { "name": "options", "optional": true } ] } ] }, { "textRaw": "`decompressZstdSync([options])`", "name": "decompressZstdSync", "type": "method", "meta": { "added": [ "v25.9.0" ], "changes": [] }, "signatures": [ { "params": [ { "textRaw": "`options` {Object}", "name": "options", "type": "Object", "options": [ { "textRaw": "`chunkSize` {number} Output buffer size. **Default:** `65536` (64 KB).", "name": "chunkSize", "type": "number", "default": "`65536` (64 KB)", "desc": "Output buffer size." }, { "textRaw": "`params` {Object} Key-value object where keys and values are `zlib.constants` entries. Available decompressor parameters:", "name": "params", "type": "Object", "desc": "Key-value object where keys and values are `zlib.constants` entries. Available decompressor parameters:", "options": [ { "textRaw": "`ZSTD_d_windowLogMax` -- maximum window size (log2) the decompressor will allocate. Limits memory usage against malicious input. See the Zstd decompressor options in the zlib documentation for details.", "name": "ZSTD_d_windowLogMax", "desc": "- maximum window size (log2) the decompressor will allocate. Limits memory usage against malicious input. See the Zstd decompressor options in the zlib documentation for details." } ] }, { "textRaw": "`dictionary` {Buffer|TypedArray|DataView}", "name": "dictionary", "type": "Buffer|TypedArray|DataView" } ], "optional": true } ], "return": { "textRaw": "Returns: {Object} A stateful transform.", "name": "return", "type": "Object", "desc": "A stateful transform." } } ], "desc": "Create a Zstandard decompression transform.
" } ], "displayName": "Iterable Compression" } ], "miscs": [ { "textRaw": "Memory usage tuning", "name": "Memory usage tuning", "type": "misc", "miscs": [ { "textRaw": "For zlib-based streams", "name": "for_zlib-based_streams", "type": "misc", "desc": "From zlib/zconf.h, modified for Node.js usage:
The memory requirements for deflate are (in bytes):
\n(1 << (windowBits + 2)) + (1 << (memLevel + 9));\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 };\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.
There are equivalents to the zlib options for Brotli-based streams, although\nthese options have different ranges than the zlib ones:
\nlevel option matches Brotli's BROTLI_PARAM_QUALITY option.windowBits option matches Brotli's BROTLI_PARAM_LGWIN option.See below for more details on Brotli-specific options.
", "displayName": "For Brotli-based streams" }, { "textRaw": "For Zstd-based streams", "name": "for_zstd-based_streams", "type": "misc", "stability": 1, "stabilityText": "Experimental", "desc": "There are equivalents to the zlib options for Zstd-based streams, although\nthese options have different ranges than the zlib ones:
\nlevel option matches Zstd's ZSTD_c_compressionLevel option.windowBits option matches Zstd's ZSTD_c_windowLog option.See below for more details on Zstd-specific options.
", "displayName": "For Zstd-based streams" } ] }, { "textRaw": "Constants", "name": "Constants", "type": "misc", "meta": { "added": [ "v0.5.8" ], "changes": [] }, "miscs": [ { "textRaw": "zlib constants", "name": "zlib_constants", "type": "misc", "desc": "All of the constants defined in zlib.h are also defined on\nrequire('node:zlib').constants. In the normal course of operations, it will\nnot be necessary to use these constants. They are documented so that their\npresence is not surprising. This section is taken almost directly from the\nzlib documentation.
Previously, the constants were available directly from require('node:zlib'),\nfor instance zlib.Z_NO_FLUSH. Accessing the constants directly from the module\nis currently still possible but is deprecated.
Allowed flush values.
\nzlib.constants.Z_NO_FLUSHzlib.constants.Z_PARTIAL_FLUSHzlib.constants.Z_SYNC_FLUSHzlib.constants.Z_FULL_FLUSHzlib.constants.Z_FINISHzlib.constants.Z_BLOCKReturn codes for the compression/decompression functions. Negative\nvalues are errors, positive values are used for special but normal\nevents.
\nzlib.constants.Z_OKzlib.constants.Z_STREAM_ENDzlib.constants.Z_NEED_DICTzlib.constants.Z_ERRNOzlib.constants.Z_STREAM_ERRORzlib.constants.Z_DATA_ERRORzlib.constants.Z_MEM_ERRORzlib.constants.Z_BUF_ERRORzlib.constants.Z_VERSION_ERRORCompression levels.
\nzlib.constants.Z_NO_COMPRESSIONzlib.constants.Z_BEST_SPEEDzlib.constants.Z_BEST_COMPRESSIONzlib.constants.Z_DEFAULT_COMPRESSIONCompression strategy.
\nzlib.constants.Z_FILTEREDzlib.constants.Z_HUFFMAN_ONLYzlib.constants.Z_RLEzlib.constants.Z_FIXEDzlib.constants.Z_DEFAULT_STRATEGYThere are several options and other constants available for Brotli-based\nstreams:
", "modules": [ { "textRaw": "Flush operations", "name": "flush_operations", "type": "module", "desc": "The following values are valid flush operations for Brotli-based streams:
\nzlib.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\nThere are several options that can be set on Brotli encoders, affecting\ncompression efficiency and speed. Both the keys and the values can be accessed\nas properties of the zlib.constants object.
The most important options are:
\nBROTLI_PARAM_MODE\nBROTLI_MODE_GENERIC (default)BROTLI_MODE_TEXT, adjusted for UTF-8 textBROTLI_MODE_FONT, adjusted for WOFF 2.0 fontsBROTLI_PARAM_QUALITY\nBROTLI_MIN_QUALITY to BROTLI_MAX_QUALITY,\nwith a default of BROTLI_DEFAULT_QUALITY.BROTLI_PARAM_SIZE_HINT\n0 for an unknown input size.The following flags can be set for advanced control over the compression\nalgorithm and memory usage tuning:
\nBROTLI_PARAM_LGWIN\nBROTLI_MIN_WINDOW_BITS to BROTLI_MAX_WINDOW_BITS,\nwith a default of BROTLI_DEFAULT_WINDOW, or up to\nBROTLI_LARGE_MAX_WINDOW_BITS if the BROTLI_PARAM_LARGE_WINDOW flag\nis set.BROTLI_PARAM_LGBLOCK\nBROTLI_MIN_INPUT_BLOCK_BITS to BROTLI_MAX_INPUT_BLOCK_BITS.BROTLI_PARAM_DISABLE_LITERAL_CONTEXT_MODELING\nBROTLI_PARAM_LARGE_WINDOW\nBROTLI_PARAM_NPOSTFIX\n0 to BROTLI_MAX_NPOSTFIX.BROTLI_PARAM_NDIRECT\n0 to 15 << NPOSTFIX in steps of 1 << NPOSTFIX.These advanced options are available for controlling decompression:
\nBROTLI_DECODER_PARAM_DISABLE_RING_BUFFER_REALLOCATION\nBROTLI_DECODER_PARAM_LARGE_WINDOW\nThere are several options and other constants available for Zstd-based\nstreams:
", "modules": [ { "textRaw": "Flush operations", "name": "flush_operations", "type": "module", "desc": "The following values are valid flush operations for Zstd-based streams:
\nzlib.constants.ZSTD_e_continue (default for all operations)zlib.constants.ZSTD_e_flush (default when calling .flush())zlib.constants.ZSTD_e_end (default for the last chunk)There are several options that can be set on Zstd encoders, affecting\ncompression efficiency and speed. Both the keys and the values can be accessed\nas properties of the zlib.constants object.
The most important options are:
\nZSTD_c_compressionLevel\nZSTD_c_strategy\nThe following constants can be used as values for the ZSTD_c_strategy\nparameter:
zlib.constants.ZSTD_fastzlib.constants.ZSTD_dfastzlib.constants.ZSTD_greedyzlib.constants.ZSTD_lazyzlib.constants.ZSTD_lazy2zlib.constants.ZSTD_btlazy2zlib.constants.ZSTD_btoptzlib.constants.ZSTD_btultrazlib.constants.ZSTD_btultra2Example:
\nconst stream = zlib.createZstdCompress({\n params: {\n [zlib.constants.ZSTD_c_strategy]: zlib.constants.ZSTD_btultra,\n },\n});\nIt's possible to specify the expected total size of the uncompressed input via\nopts.pledgedSrcSize, which must be a non-negative safe integer. If the size\ndoesn't match at the end of the input, compression will fail with the code\nZSTD_error_srcSize_wrong.
These advanced options are available for controlling decompression:
\nZSTD_d_windowLogMax\nEach zlib-based class takes an options object. No options are required.
Some options are only relevant when compressing and are\nignored by the decompression classes.
\nflush <integer> Default: zlib.constants.Z_NO_FLUSHfinishFlush <integer> Default: zlib.constants.Z_FINISHchunkSize <integer> Default: 16 * 1024windowBits <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.)maxOutputLength <integer> Limits output size when using convenience methods. Default: buffer.kMaxLengthrejectGarbageAfterEnd <boolean> If true, decompression fails when\ntrailing input is detected after the end of the compressed stream. This\nincludes unreadable bytes and, when decompressing gzip, additional gzip\nmembers following the first member. Default: falseSee the deflateInit2 and inflateInit2 documentation for more\ninformation.
Each Brotli-based class takes an options object. All options are optional.
flush <integer> Default: zlib.constants.BROTLI_OPERATION_PROCESSfinishFlush <integer> Default: zlib.constants.BROTLI_OPERATION_FINISHchunkSize <integer> Default: 16 * 1024params <Object> Key-value object containing indexed Brotli parameters.maxOutputLength <integer> Limits output size when using convenience methods. Default: buffer.kMaxLengthinfo <boolean> If true, returns an object with buffer and engine. Default: falserejectGarbageAfterEnd <boolean> If true, decompression fails when\ninput remains after the first complete compressed stream. Default: falseFor example:
\nconst stream = zlib.createBrotliCompress({\n chunkSize: 32 * 1024,\n params: {\n [zlib.constants.BROTLI_PARAM_MODE]: zlib.constants.BROTLI_MODE_TEXT,\n [zlib.constants.BROTLI_PARAM_QUALITY]: 4,\n [zlib.constants.BROTLI_PARAM_SIZE_HINT]: fs.statSync(inputFile).size,\n },\n});\nEach Zstd-based class takes an options object. All options are optional.
flush <integer> Default: zlib.constants.ZSTD_e_continuefinishFlush <integer> Default: zlib.constants.ZSTD_e_endchunkSize <integer> Default: 16 * 1024params <Object> Key-value object containing indexed Zstd parameters.maxOutputLength <integer> Limits output size when using convenience methods. Default: buffer.kMaxLengthinfo <boolean> If true, returns an object with buffer and engine. Default: falsedictionary <Buffer> | <TypedArray> | <DataView> | <ArrayBuffer> Optional dictionary used\nto improve compression efficiency when compressing or decompressing data that\nshares common patterns with the dictionary.rejectGarbageAfterEnd <boolean> If true, decompression fails when\ninput remains after the first complete compressed stream. Default: falseFor example:
\nconst stream = zlib.createZstdCompress({\n chunkSize: 32 * 1024,\n params: {\n [zlib.constants.ZSTD_c_compressionLevel]: 10,\n [zlib.constants.ZSTD_c_checksumFlag]: 1,\n },\n});\nAll of these take a <Buffer>, <TypedArray>, <DataView>, <ArrayBuffer>, or string\nas 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 BrotliCompress.
Decompress a chunk of data with BrotliDecompress.
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 a chunk of data with ZstdCompress.
Decompress a chunk of data with ZstdDecompress.
ZlibBaseCompress data using the Brotli algorithm.
" }, { "textRaw": "Class: `zlib.BrotliDecompress`", "name": "zlib.BrotliDecompress", "type": "class", "meta": { "added": [ "v11.7.0", "v10.16.0" ], "changes": [] }, "desc": "ZlibBaseDecompress data using the Brotli algorithm.
" }, { "textRaw": "Class: `zlib.Deflate`", "name": "zlib.Deflate", "type": "class", "meta": { "added": [ "v0.5.8" ], "changes": [] }, "desc": "ZlibBaseCompress data using deflate.
" }, { "textRaw": "Class: `zlib.DeflateRaw`", "name": "zlib.DeflateRaw", "type": "class", "meta": { "added": [ "v0.5.8" ], "changes": [] }, "desc": "ZlibBaseCompress data using deflate, and do not append a zlib header.
ZlibBaseDecompress a gzip stream.
" }, { "textRaw": "Class: `zlib.Gzip`", "name": "zlib.Gzip", "type": "class", "meta": { "added": [ "v0.5.8" ], "changes": [] }, "desc": "ZlibBaseCompress data using gzip.
" }, { "textRaw": "Class: `zlib.Inflate`", "name": "zlib.Inflate", "type": "class", "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": "ZlibBaseDecompress a deflate stream.
" }, { "textRaw": "Class: `zlib.InflateRaw`", "name": "zlib.InflateRaw", "type": "class", "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": "ZlibBaseDecompress a raw deflate stream.
" }, { "textRaw": "Class: `zlib.Unzip`", "name": "zlib.Unzip", "type": "class", "meta": { "added": [ "v0.5.8" ], "changes": [] }, "desc": "ZlibBaseDecompress either a Gzip- or Deflate-compressed stream by auto-detecting\nthe header.
" }, { "textRaw": "Class: `zlib.ZipBuffer`", "name": "zlib.ZipBuffer", "type": "class", "meta": { "added": [ "REPLACEME" ], "changes": [] }, "stability": 1, "stabilityText": "Early development", "desc": "The ZIP archive API is experimental. Using any part of it (this class among\nthem) emits an experimental warning the first time; merely importing\nnode:zlib does not.
An in-memory, zero-copy view over the entries of a ZIP archive already\nheld in a Buffer, TypedArray, DataView, or ArrayBuffer. Its set of\nentries can be edited - entries added or removed - but, unlike ZipFile,\nthose edits are not written into the source buffer: a newly added entry is\nheld as a separate in-memory ZipEntry (the passed buffer is a fixed-size\nview with no room to append to), and removal just drops the entry from\nZipBuffer's index. The original bytes are never modified.\nzipBuffer.toBuffer() serializes the current set of entries into a fresh\narchive.
ZipBuffer does not copy the archive you hand it. It keeps a view onto that\nmemory and reads each entry's content lazily and directly from it, which is\nwhat makes construction cheap regardless of archive size. The trade-off is\nthat you must not modify or reuse that memory - including the\nArrayBuffer backing a TypedArray/DataView - while the ZipBuffer, or\nany ZipEntry obtained from it, is still in use: a later read would\nobserve the change and may fail or return corrupt data. Pass a copy (for\nexample Buffer.from(source)) if the source might be mutated or reused.
add() and toBuffer() each have a *Sync counterpart\n(addSync(), toBufferSync())\nthat performs the same compression work synchronously. As with the\nsynchronous node:fs APIs, these block the Node.js event loop and further\nJavaScript execution until the operation completes; use them only where\nsynchronous execution is appropriate (for example, short-lived scripts or\nstartup code), not in code that must stay responsive.
import { ZipBuffer } from 'node:zlib';\nimport { readFileSync, writeFileSync } from 'node:fs';\nimport { Buffer } from 'node:buffer';\n\nconst zip = new ZipBuffer(readFileSync('archive.zip'));\nfor (const [name, entry] of zip) {\n console.log(name, entry.size);\n}\nawait zip.add('hello.txt', Buffer.from('Hello, world!'));\nzip.delete('unwanted.txt');\nwriteFileSync('archive.zip', await zip.toBuffer());\nconst { ZipBuffer } = require('node:zlib');\nconst { readFileSync, writeFileSync } = require('node:fs');\n\nasync function main() {\n const zip = new ZipBuffer(readFileSync('archive.zip'));\n for (const [name, entry] of zip) {\n console.log(name, entry.size);\n }\n await zip.add('hello.txt', Buffer.from('Hello, world!'));\n zip.delete('unwanted.txt');\n writeFileSync('archive.zip', await zip.toBuffer());\n}\nmain();\nParses the archive's central directory. Throws an ERR_ZIP_INVALID_ARCHIVE\nor ERR_ZIP_UNSUPPORTED_FEATURE error if buffer is not a well-formed,\nsupported archive.
buffer is not copied: the ZipBuffer retains a zero-copy view of it (for\na TypedArray, DataView, or ArrayBuffer, of the underlying ArrayBuffer)\nand reads entry content directly from it on demand. Do not mutate or reuse that\nmemory while the ZipBuffer or any entry read from it is still live; pass a\ncopy if it might change.
Equivalent to zipBuffer.addEntry(await zlib.ZipEntry.create(filename, data, options)).
The synchronous version of zipBuffer.add(). Equivalent to\nzipBuffer.addEntry(zlib.ZipEntry.createSync(filename, data, options)).
Adds an already-built entry, keyed by its own zipEntry.name. Replaces\nany existing entry of that name.
Removes every entry.
" }, { "textRaw": "`zipBuffer.delete(name)`", "name": "delete", "type": "method", "meta": { "added": [ "REPLACEME" ], "changes": [] }, "signatures": [ { "params": [ { "textRaw": "`name` {string}", "name": "name", "type": "string" } ], "return": { "textRaw": "Returns: {boolean} `true` if an entry named `name` existed and was removed.", "name": "return", "type": "boolean", "desc": "`true` if an entry named `name` existed and was removed." } } ] }, { "textRaw": "`zipBuffer.entries()`", "name": "entries", "type": "method", "meta": { "added": [ "REPLACEME" ], "changes": [] }, "signatures": [ { "params": [], "return": { "textRaw": "Returns: {Iterator} of `[name, entry]` pairs, where `entry` is a `ZipEntry`.", "name": "return", "type": "Iterator", "desc": "of `[name, entry]` pairs, where `entry` is a `ZipEntry`." } } ] }, { "textRaw": "`zipBuffer.forEach(callback[, thisArg])`", "name": "forEach", "type": "method", "meta": { "added": [ "REPLACEME" ], "changes": [] }, "signatures": [ { "params": [ { "textRaw": "`callback` {Function}", "name": "callback", "type": "Function" }, { "textRaw": "`thisArg` {any}", "name": "thisArg", "type": "any", "optional": true } ] } ], "desc": "Calls callback once for each entry, in the order the archive lists them.
Throws ERR_ZIP_ENTRY_NOT_FOUND if the archive has no entry named name.
Serializes the current set of entries - in the order they were added or\nread - into a fresh archive, switching to Zip64 structures automatically as\nneeded (see zlib.createZipArchive()).
The synchronous version of zipBuffer.toBuffer() (see\nzlib.createZipArchiveSync()).
The archive-level comment, preserved byte-for-byte across\nzipBuffer.toBuffer() calls unless overridden. The bytes are decoded as\nUTF-8 when they are valid UTF-8 and as CP437 otherwise (the field carries no\nencoding flag of its own).
The number of entries in the archive.
" }, { "textRaw": "Type: {boolean}", "name": "writable", "type": "boolean", "meta": { "added": [ "REPLACEME" ], "changes": [] }, "desc": "Always true.
The ZIP archive API is experimental. Using any part of it (this class among\nthem) emits an experimental warning the first time; merely importing\nnode:zlib does not.
A single file or directory inside a ZIP archive. Instances are produced by\nZipBuffer and ZipFile, or created directly for writing with\nZipEntry.create()/ZipEntry.createStream().
create() and content() each have a *Sync counterpart (the streaming\ncontentIterator() does not). As with the synchronous node:fs APIs, these\nblock the\nNode.js event loop and further JavaScript execution until the operation\n(including any deflate/inflate pass) completes; use them only where\nsynchronous execution is appropriate (for example, short-lived scripts or\nstartup code), not in code that must stay responsive.
Compresses data (unless method is 'store', or compression would not\nreduce its size) and computes its CRC-32.
When the entry ends up stored uncompressed (because method is 'store',\nor because compression would not reduce the size), the entry retains a\nzero-copy view of data rather than a copy, and its CRC-32 has already been\nrecorded. Do not mutate data after creating the entry; pass a copy if it\nmight change.
The MS-DOS date/time fields ZIP uses for modified have 2-second resolution\nand no time zone. When modified does not fall on a whole 2-second\nboundary, an Info-ZIP extended-timestamp extra field is written as well,\nrecording the whole (UTC) second so the time round-trips more precisely (see\nzipEntry.modified). This applies to every entry-creation path.
Creates an entry whose content is compressed on the fly as it is serialized\nby zlib.createZipArchive(), without buffering source in memory. Its\nsize, compressedSize, and crc32 only become available once\nserialization has finished. There is no synchronous counterpart: streaming\nentries only make sense with an asynchronous, incrementally-produced\nsource.
source is drained exactly once, during serialization. Until that happens\nthe entry has no readable content, so zipEntry.content(),\nzipEntry.contentSync(), and zipEntry.contentIterator() throw\nERR_INVALID_STATE. If the entry is serialized by adding it to a writable\nZipFile with zipFile.addEntry() (or addEntrySync()), it is then\npromoted in place to a file-backed entry pointing at the copy just written,\nso it becomes readable (and can be serialized again) for as long as that\nZipFile stays open. Serializing it any other way (for example directly\nthrough zlib.createZipArchive()) leaves it spent and unreadable.
Because source may hold an operating-system resource (a file read stream,\nsay), a streaming entry is disposable: its Symbol.dispose and\nSymbol.asyncDispose methods destroy source if it has not been consumed.\nAn entry passed to an archive is disposed by that archive (see\nzlib.createZipArchive()); dispose an entry directly only when it was\nbuilt but never handed to one. Disposal is a no-op for non-streaming entries -\nin particular a file-backed entry never closes the ZipFile descriptor it\nborrows.
Creates a symbolic-link entry: a stored entry whose content is target and\nwhose Unix mode type bits mark it as a symlink, so zipEntry.isSymlink is\ntrue when it is read back. Extraction tools that honor symlink entries\nrecreate the link; treat target as untrusted (see zipEntry.name on\npath safety).
The synchronous version of zlib.ZipEntry.create().
Parses every entry out of buffer directly, without indexing it into a\nZipBuffer. Like ZipBuffer, the yielded entries hold zero-copy views\nof buffer rather than copies of their content, so the same rule applies: do\nnot mutate or reuse buffer while any of them is still in use.
true if the entry's content is stored in compressed form (any compression\nmethod, currently deflate or Zstandard); false if it is stored\nuncompressed.
The entry's raw general-purpose bit flag.
" }, { "textRaw": "Type: {boolean}", "name": "isDirectory", "type": "boolean", "meta": { "added": [ "REPLACEME" ], "changes": [] }, "desc": "true if the entry is a directory (its name ends with /).
true if the entry is a regular file — that is, neither a directory nor a\nsymbolic link.
true if the entry is a symbolic link (its Unix mode type bits are\nS_IFLNK); its content is the link target. Always false for archives not\nwritten on a Unix-like system. When extracting, treat a symlink's target as\nuntrusted — see zipEntry.name on path safety.
The entry's Unix mode permission bits, including the setuid, setgid, and\nsticky bits (the low 12 bits, 0o7777), or 0 if the archive was not written\non a Unix-like system. The file-type bits are not included here; use\nzipEntry.isDirectory / zipEntry.isSymlink for the type.
The entry's last-modification time. When the archive carries a higher-fidelity\ntimestamp in an extra field — an NTFS (0x000a), Info-ZIP extended (0x5455),\nor Info-ZIP Unix (0x5855) field, as most modern tools write — that absolute\n(UTC) time is used; otherwise the coarse, local-time MS-DOS date/time field\n(2-second resolution) is used.
Some tools store their high-fidelity timestamp only in the local file header,\nso on a file-backed entry (one returned by zipFile.get()) the first read\nof this property may perform a small synchronous positioned disk read to\nresolve that header. If that read fails, the value silently falls back to the\ncentral-directory data.
The entry's raw compression method: 0 for stored, 8 for deflate, 93\nfor Zstandard.
The entry's name, decoded from the central directory, which is treated as\nauthoritative — a local file header that disagrees is ignored, so a\nmismatched-header (\"ZIP-confusion\") archive cannot make name disagree with\nwhat is read. The bytes are decoded from a valid Info-ZIP Unicode Path extra\nfield (0x7075) when one is present; otherwise as UTF-8 when the\nlanguage-encoding flag (general-purpose bit 11) is set or the bytes are\nvalid UTF-8 (plenty of tools wrote UTF-8 names without ever setting the\nflag); and as CP437 — the historical default — only when they are not.\nSee zipEntry.nameBuffer for the raw bytes.
The name is returned verbatim: it is never normalized, and a name\ncontaining .., a leading /, a drive letter, or backslashes is neither\nrewritten nor rejected. A ZipFile/ZipBuffer never writes to disk, so\nguarding against path traversal (\"Zip Slip\") when extracting is the caller's\nresponsibility.
The entry's raw name bytes, before any character decoding. Useful when the\narchive's names are in an encoding other than UTF-8 or CP437 and the caller\nwants to decode them itself.
" }, { "textRaw": "Type: {Buffer|null}", "name": "rawContent", "type": "Buffer|null", "meta": { "added": [ "REPLACEME" ], "changes": [] }, "desc": "The entry's raw (still compressed, if applicable) content when it is held in\nmemory, or null when there is no in-memory buffer to expose - for an entry\ncreated with zlib.ZipEntry.createStream(), or a file-backed entry\nreturned by zipFile.get(), whose bytes are read from disk on demand\nrather than retained. Use zipEntry.content() or\nzipEntry.contentIterator() to read a file-backed entry.
The entry's uncompressed size, in bytes.
" } ], "methods": [ { "textRaw": "`zipEntry.content([options])`", "name": "content", "type": "method", "meta": { "added": [ "REPLACEME" ], "changes": [] }, "signatures": [ { "params": [ { "textRaw": "`options` {Object}", "name": "options", "type": "Object", "options": [ { "textRaw": "`verify` {boolean} Verify the entry's CRC-32 checksum. **Default:** `true`.", "name": "verify", "type": "boolean", "default": "`true`", "desc": "Verify the entry's CRC-32 checksum." }, { "textRaw": "`maxSize` {number} Reject content declaring more than this many uncompressed bytes, before allocating anything. **Default:** `zlib.getMaxZipContentSize()`.", "name": "maxSize", "type": "number", "default": "`zlib.getMaxZipContentSize()`", "desc": "Reject content declaring more than this many uncompressed bytes, before allocating anything." } ], "optional": true } ], "return": { "textRaw": "Returns: {Promise} Fulfilled with a {Buffer} containing the entry's decompressed content. The buffer is a fresh copy that shares no memory with the archive or with data the entry was created from.", "name": "return", "type": "Promise", "desc": "Fulfilled with a {Buffer} containing the entry's decompressed content. The buffer is a fresh copy that shares no memory with the archive or with data the entry was created from." } } ], "desc": "Throws an ERR_ZIP_ENTRY_TOO_LARGE error if the entry's declared size\nexceeds maxSize, an ERR_ZIP_ENTRY_CORRUPT error if the content fails\nCRC-32 verification or does not match its declared size, and an\nERR_INVALID_STATE error for a streaming entry\n(zlib.ZipEntry.createStream()) whose content is not yet available (see\nthat method for when a streaming entry becomes readable).
The synchronous version of zipEntry.content().
Unlike zipEntry.content(), this does not buffer the whole member in\nmemory. For a file-backed entry (one returned by zipFile.get()) the\ncompressed bytes are read from disk as the iterator is consumed and nothing is\nretained; the entry is valid only while its ZipFile is open.
Because streaming is the bounded-memory path for arbitrarily large members, it\nis not capped by zlib.getMaxZipContentSize() the way\nzipEntry.content() is - that default guards a single large allocation,\nwhich streaming never makes. Output is still bounded per chunk to the declared\nuncompressed size; pass maxSize to impose an explicit ceiling.
For an in-memory entry stored without compression, the yielded chunks are\nzero-copy views of the entry's retained content (see\nzipEntry.rawContent); do not mutate them.
The yielded chunks are provisional until the iterator completes. CRC-32\nverification (and the final declared-size check) can only run once every byte\nhas been read, so a corrupt or truncated entry is reported by the iterator\nthrowing after the last chunk, not before the first. Each chunk is still\nbounded so the total never exceeds the declared size or maxSize, but a\nconsumer that must not act on unverified bytes should buffer them (or use\nzipEntry.content(), which verifies before returning anything) rather than\nprocessing chunks as they arrive.
The ZIP archive API is experimental. Using any part of it (this class among\nthem) emits an experimental warning the first time; merely importing\nnode:zlib does not.
A random-access view over the entries of a ZIP archive on disk. Only the\narchive's tail and central directory are read up front; member content is\nread from disk lazily, on demand. Writable when opened with\n{ writable: true }: zipFile.addEntry()/zipFile.add() append the\nnew member's data where the central directory used to be, then rewrite the\ncentral directory immediately after it; zipFile.delete() just rewrites\nthe central directory. Both mean the file is altered as soon as the method's\nreturned Promise fulfills. Deleted or replaced members are left behind as\ndead space; zipFile.compact() produces a stream with none.
These in-place edits are not crash-atomic. Rewriting the central directory\nhappens in place, so a write that fails partway - the disk fills, the device\ndisconnects, the process is killed - can leave the archive on disk with a\npartial or missing central directory, i.e. unreadable, even though the member\ndata before it is intact. The rejected call surfaces the underlying error and\nthe ZipFile object is left usable (its in-memory view is not discarded, so a\ncaller can attempt recovery - for example re-writing the entries elsewhere with\nzipFile.compact()), but that in-memory view may no longer match the bytes\non disk. Write to a copy, or compact() into a fresh file, when durability\nacross a failure matters.
Every method has a *Sync counterpart. As with the synchronous node:fs\nAPIs, these block the Node.js event loop and further JavaScript execution\nuntil the operation completes; use them only where synchronous execution is\nappropriate (for example, short-lived scripts or startup code), not in code\nthat must stay responsive. A synchronous method throws ERR_INVALID_STATE\nif called while an asynchronous add(), addEntry(), delete(), or\nclose() on the same ZipFile has not settled yet, since letting the two\ninterleave could corrupt the archive.
import { ZipFile } from 'node:zlib';\nimport { Buffer } from 'node:buffer';\n\nconst zip = await ZipFile.open('archive.zip', { writable: true });\ntry {\n const entry = await zip.get('member.txt');\n console.log((await entry.content()).toString());\n for await (const chunk of await zip.stream('huge.bin')) {\n // Process each chunk without buffering the whole member.\n }\n await zip.add('new.txt', Buffer.from('hello'));\n await zip.delete('unwanted.txt');\n} finally {\n await zip.close();\n}\nconst { ZipFile } = require('node:zlib');\n\nasync function main() {\n const zip = await ZipFile.open('archive.zip', { writable: true });\n try {\n const entry = await zip.get('member.txt');\n console.log((await entry.content()).toString());\n for await (const chunk of await zip.stream('huge.bin')) {\n // Process each chunk without buffering the whole member.\n }\n await zip.add('new.txt', Buffer.from('hello'));\n await zip.delete('unwanted.txt');\n } finally {\n await zip.close();\n }\n}\nmain();\nThrows an ERR_ZIP_ARCHIVE_TOO_LARGE error if the archive's central\ndirectory is too large to buffer in memory.
The synchronous version of zlib.ZipFile.open().
Equivalent to zipFile.addEntry(await zlib.ZipEntry.create(filename, data, options)).
Writes entry where the central directory currently starts, then rewrites\nthe central directory to include it, replacing any existing entry of the\nsame name. Throws ERR_ZIP_NOT_WRITABLE if the ZipFile was not opened\nwith { writable: true }.
The returned (same) entry is left readable: a streaming entry created with\nzlib.ZipEntry.createStream(), which would otherwise be spent once\nserialized, is promoted in place to a file-backed entry pointing at the copy\njust written (valid while this ZipFile is open). In-memory entries keep their\nown buffer unchanged.
The synchronous version of zipFile.addEntry(). entry must not be a\npending streaming entry (one created with\nzlib.ZipEntry.createStream()) - there is no synchronous way to drain\nits asynchronous source.
The synchronous version of zipFile.add(). Equivalent to\nzipFile.addEntrySync(zlib.ZipEntry.createSync(filename, data, options)).
Closes the underlying file handle.
\nClosing does not invalidate outstanding objects: ZipEntry objects previously\nreturned by zipFile.get() and the ZipFile's own methods will fail with\nsystem-level errors (for example EBADF) if used after close, rather than a\ndedicated Node.js error code. The same applies to zipFile.closeSync().
The synchronous version of zipFile.close().
Does not modify the open file; pipe the result into a new one:
\nimport { createWriteStream } from 'node:fs';\nzip.compact().pipe(createWriteStream('compacted.zip'));\nThe synchronous version of zipFile.compact(). Does not modify the\nopen file.
Rewrites the central directory without writing any new content - the\narchive does not grow. Throws ERR_ZIP_NOT_WRITABLE if the ZipFile was\nnot opened with { writable: true }.
The synchronous version of zipFile.delete().
The synchronous version of zipFile.entries().
The synchronous version of zipFile.forEach(): callback is invoked\nwith a resolved ZipEntry instead of a Promise.
Returns a lazy, file-backed ZipEntry for name. Nothing is read from\ndisk here and no content is buffered: the returned entry reads (and, for\nzipEntry.content(), decompresses) its member straight from the file on\neach access, and the ZipFile retains no member content. The entry is valid\nonly while this ZipFile is open. Reading its content later may throw\nERR_ZIP_ENTRY_TOO_LARGE if the member is too large to hold in a single\nbuffer; use zipEntry.contentIterator() (or zipFile.stream())\ninstead. Throws ERR_ZIP_ENTRY_NOT_FOUND if the archive has no entry\nnamed name.
The synchronous version of zipFile.get(). Like get(), it reads\nnothing up front and only builds the lazy handle, so it does not itself block\non I/O - but reads performed later through the returned entry (such as\nzipEntry.contentSync()) do; see the note above on synchronous methods.
Convenience wrapper that resolves to a Readable over\nzipEntry.contentIterator() of zipFile.get()(name); the\ncompressed bytes are read from disk as the stream is consumed. The returned\npromise rejects with ERR_ZIP_ENTRY_NOT_FOUND if the archive has no entry\nnamed name.
The synchronous version of zipFile.values().
The archive-level comment, preserved byte-for-byte across\nzipFile.addEntry()/zipFile.delete() calls. The bytes are decoded\nas UTF-8 when they are valid UTF-8 and as CP437 otherwise (the field carries\nno encoding flag of its own).
The number of entries in the archive.
" }, { "textRaw": "Type: {boolean}", "name": "writable", "type": "boolean", "meta": { "added": [ "REPLACEME" ], "changes": [] }, "desc": "Whether this ZipFile was opened with { writable: true }.
stream.TransformNot exported by the node:zlib module. It is documented here because it is the\nbase class of the compressor/decompressor classes.
This class inherits from stream.Transform, allowing node:zlib objects to\nbe used in pipes and similar stream operations.
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)`", "name": "flush", "type": "method", "meta": { "added": [ "v0.5.8" ], "changes": [] }, "signatures": [ { "params": [ { "name": "kind", "optional": true }, { "name": "callback" } ] } ], "desc": "kind Default: zlib.constants.Z_FULL_FLUSH for zlib-based streams,\nzlib.constants.BROTLI_OPERATION_FLUSH for Brotli-based streams.callback <Function>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.
This function is only available for zlib-based streams, i.e. not Brotli.
\nDynamically update the compression level and compression strategy.\nOnly applicable to deflate algorithm.
" }, { "textRaw": "`zlib.reset()`", "name": "reset", "type": "method", "meta": { "added": [ "v0.7.0" ], "changes": [] }, "signatures": [ { "params": [] } ], "desc": "Reset the compressor/decompressor to factory defaults. Only applicable to\nthe inflate and deflate algorithms.
" } ] }, { "textRaw": "Class: `zlib.ZstdCompress`", "name": "zlib.ZstdCompress", "type": "class", "meta": { "added": [ "v23.8.0", "v22.15.0" ], "changes": [] }, "stability": 1, "stabilityText": "Experimental", "desc": "Compress data using the Zstd algorithm.
" }, { "textRaw": "Class: `zlib.ZstdDecompress`", "name": "zlib.ZstdDecompress", "type": "class", "meta": { "added": [ "v23.8.0", "v22.15.0" ], "changes": [] }, "stability": 1, "stabilityText": "Experimental", "desc": "Decompress data using the Zstd algorithm.
" } ], "properties": [ { "textRaw": "`zlib.constants`", "name": "constants", "type": "property", "meta": { "added": [ "v7.0.0" ], "changes": [] }, "desc": "Provides an object enumerating Zlib-related constants.
" } ], "methods": [ { "textRaw": "`zlib.crc32(data[, value])`", "name": "crc32", "type": "method", "meta": { "added": [ "v22.2.0", "v20.15.0" ], "changes": [] }, "signatures": [ { "params": [ { "textRaw": "`data` {string|Buffer|TypedArray|DataView} When `data` is a string, it will be encoded as UTF-8 before being used for computation.", "name": "data", "type": "string|Buffer|TypedArray|DataView", "desc": "When `data` is a string, it will be encoded as UTF-8 before being used for computation." }, { "textRaw": "`value` {integer} An optional starting value. It must be a 32-bit unsigned integer. **Default:** `0`", "name": "value", "type": "integer", "default": "`0`", "desc": "An optional starting value. It must be a 32-bit unsigned integer.", "optional": true } ], "return": { "textRaw": "Returns: {integer} A 32-bit unsigned integer containing the checksum.", "name": "return", "type": "integer", "desc": "A 32-bit unsigned integer containing the checksum." } } ], "desc": "Computes a 32-bit Cyclic Redundancy Check checksum of data. If\nvalue is specified, it is used as the starting value of the checksum,\notherwise, 0 is used as the starting value.
The CRC algorithm is designed to compute checksums and to detect error\nin data transmission. It's not suitable for cryptographic authentication.
\nTo be consistent with other APIs, if the data is a string, it will\nbe encoded with UTF-8 before being used for computation. If users only\nuse Node.js to compute and match the checksums, this works well with\nother APIs that uses the UTF-8 encoding by default.
Some third-party JavaScript libraries compute the checksum on a\nstring based on str.charCodeAt() so that it can be run in browsers.\nIf users want to match the checksum computed with this kind of library\nin the browser, it's better to use the same library in Node.js\nif it also runs in Node.js. If users have to use zlib.crc32() to\nmatch the checksum produced by such a third-party library:
Uint8Array as input, use TextEncoder\nin the browser to encode the string into a Uint8Array with UTF-8\nencoding, and compute the checksum based on the UTF-8 encoded string\nin the browser.str.charCodeAt(), on the Node.js side, convert the string into\na buffer using Buffer.from(str, 'utf16le').import zlib from 'node:zlib';\nimport { Buffer } from 'node:buffer';\n\nlet crc = zlib.crc32('hello'); // 907060870\ncrc = zlib.crc32('world', crc); // 4192936109\n\ncrc = zlib.crc32(Buffer.from('hello', 'utf16le')); // 1427272415\ncrc = zlib.crc32(Buffer.from('world', 'utf16le'), crc); // 4150509955\nconst zlib = require('node:zlib');\nconst { Buffer } = require('node:buffer');\n\nlet crc = zlib.crc32('hello'); // 907060870\ncrc = zlib.crc32('world', crc); // 4192936109\n\ncrc = zlib.crc32(Buffer.from('hello', 'utf16le')); // 1427272415\ncrc = zlib.crc32(Buffer.from('world', 'utf16le'), crc); // 4150509955\nCreates and returns a new BrotliCompress object.
Creates and returns a new BrotliDecompress object.
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.\nSee example.
Creates and returns a new Inflate object.
Creates and returns a new InflateRaw object.
Creates and returns a new Unzip object.
The ZIP archive API is experimental. Using any part of it (this function among\nthem) emits an experimental warning the first time; merely importing\nnode:zlib does not.
Serializes entries into a ZIP archive, switching to Zip64 structures\nautomatically once the entry count, or any offset or size, exceeds what the\nclassic 32-/16-bit ZIP fields can hold. The returned Readable is also an\nAsyncIterable of the same <Buffer> chunks it streams.
Entries are written in iteration order and nothing deduplicates names: an\niterable that yields two entries with the same name produces an archive\ncontaining both, and most extraction tools keep the one that appears later.\nZipBuffer and ZipFile add() methods replace entries by name\ninstead.
The entries are owned by the returned stream: each is consumed as the archive\nis produced and must not be reused afterwards. This matters for streaming\nentries (from zlib.ZipEntry.createStream()), which hold an underlying\nsource such as a file read stream. If the returned stream is destroyed before\nit is fully consumed - for example, the destination of a pipeline()\nfails - it disposes the entry it was serializing and every entry still queued\nbehind it, destroying their sources so no descriptor leaks. Consume the stream\nto the end, or destroy it (directly, through a failed pipeline(), or with\nawait using), to guarantee this cleanup; a stream that is neither consumed\nnor destroyed cannot release anything. A ZipEntry that is never handed to\nan archive can be released directly with Symbol.dispose / Symbol.asyncDispose.
Throws an ERR_ZIP_ARCHIVE_TOO_LARGE error if the archive comment\nexceeds 65,535 bytes when encoded as UTF-8.
import { createWriteStream } from 'node:fs';\nimport { pipeline } from 'node:stream/promises';\nimport { Buffer } from 'node:buffer';\nimport { ZipEntry, createZipArchive } from 'node:zlib';\n\nconst entries = [\n await ZipEntry.create('hello.txt', Buffer.from('Hello, world!')),\n await ZipEntry.create('data/', Buffer.alloc(0)),\n];\nawait pipeline(\n createZipArchive(entries, 'created by node:zlib'),\n createWriteStream('archive.zip'),\n);\nconst { createWriteStream } = require('node:fs');\nconst { pipeline } = require('node:stream/promises');\nconst { ZipEntry, createZipArchive } = require('node:zlib');\n\nasync function main() {\n const entries = [\n await ZipEntry.create('hello.txt', Buffer.from('Hello, world!')),\n await ZipEntry.create('data/', Buffer.alloc(0)),\n ];\n await pipeline(\n createZipArchive(entries, 'created by node:zlib'),\n createWriteStream('archive.zip'),\n );\n}\nmain();\nPassing options.baseOffset produces an archive that is valid immediately\nwhen placed after other content in the same file, without relying on a\nreader's self-extracting-archive detection to compensate for the shift:
import { createWriteStream } from 'node:fs';\nimport { Buffer } from 'node:buffer';\nimport { ZipEntry, createZipArchive } from 'node:zlib';\n\nconst prefix = Buffer.from('#!/bin/sh\\nexit 0\\n');\nconst entries = [await ZipEntry.create('hello.txt', Buffer.from('Hello, world!'))];\nconst out = createWriteStream('self-extracting.zip');\nout.write(prefix);\ncreateZipArchive(entries, { baseOffset: prefix.byteLength }).pipe(out);\nThe ZIP archive API is experimental. Using any part of it (this function among\nthem) emits an experimental warning the first time; merely importing\nnode:zlib does not.
The synchronous version of zlib.createZipArchive(). Blocks the\nNode.js event loop and further JavaScript execution until the whole\narchive (including any deflate passes) has been produced; use only where\nsynchronous execution is appropriate (for example, short-lived scripts or\nstartup code), not in code that must stay responsive. entries must be a\nplain (synchronous) Iterable - a streaming entry created with\nzlib.ZipEntry.createStream() throws when its turn to serialize comes\nup, since draining its asynchronous source has no synchronous equivalent.
As with zlib.createZipArchive(), the entries are owned by the returned\niterator and must not be reused. If iteration stops early - including the\nthrow on a streaming entry - the entry that stopped it and every entry still\nqueued behind it are disposed, releasing any sources they hold.
The ZIP archive API is experimental. Using any part of it (this function among\nthem) emits an experimental warning the first time; merely importing\nnode:zlib does not.
Builds an archive from files on disk. For each [sourcePath, entryName] pair\nit reads sourcePath and adds an entry named entryName, capturing the file's\nUnix mode and modification time. A directory becomes a directory entry; a\nregular file's contents are streamed in (as a zlib.ZipEntry.createStream()\nentry) without being buffered in memory. Directory contents are not walked\nrecursively — list each path you want included.
When followSymlinks is true (the default) a symbolic link is resolved and\narchived as its target file; when it is false the link itself is stored as a\nsymbolic-link entry whose content is the target path (see\nzlib.ZipEntry.createSymlink()).
import { zipFiles } from 'node:zlib';\nimport { createWriteStream } from 'node:fs';\nimport { pipeline } from 'node:stream/promises';\n\nawait pipeline(\n zipFiles([\n ['/data/report.pdf', 'report.pdf'],\n ['/data/notes.txt', 'docs/notes.txt'],\n ]),\n createWriteStream('archive.zip'),\n);\nCreates and returns a new ZstdCompress object.
Creates and returns a new ZstdDecompress object.
The ZIP archive API is experimental. Using any part of it (this function among\nthem) emits an experimental warning the first time; merely importing\nnode:zlib does not.
The current default ceiling, in bytes, applied by zipEntry.content()\nwhen no explicit maxSize is given. Default: 268435456 (256 MiB).
The ZIP archive API is experimental. Using any part of it (this function among\nthem) emits an experimental warning the first time; merely importing\nnode:zlib does not.
Sets the default ceiling used by zipEntry.content() when no explicit\nmaxSize option is given. This is a guard against zip bombs: an archive\nwhose central directory declares a member larger than this is rejected\nbefore allocating memory for it. Streaming reads\n(zipEntry.contentIterator(), zipFile.stream()) are bounded-memory\nby design and are not affected by this setting.
Compress a chunk of data with BrotliCompress.
Decompress a chunk of data with BrotliDecompress.
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 a chunk of data with ZstdCompress.
Decompress a chunk of data with ZstdDecompress.