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the (76), and (51), #decompressionstream (32), #format (31), for (29), compressionstream (26), this (25), chunk (20), enqueue (17), deflate (16), data (16), compression (15), algorithm (15), gzip (14), set (14), context (14), let (14), standard (13), uint8array (13), input (13), with (13), android (12), new (12), compress (12), are (12), not (12), buffer (12), array (11), must (11), non (10), decompress (10), empty (10), org (9), transform (9), into (9), const (9), opera (8), chrome (8), safari (8), firefox (8), edge (8), interface (8), url (8), https (8), streams (8), rfc (8), specification (8), terms (8), typeerror (8), runs (8), arrays (8), result (8), error (8), compressionformat (7), constructor (7), living (7), compressed (7), transformalgorithm (7), flushalgorithm (7), blob (7), object (7), then (7), throw (7), brotli (6), normative (6), references (6), whatwg (6), infra (6), flush (6), stream (6), which (6), steps (6), flag (6), described (6), section (6), generictransformstream (5), raw (5), web (5), rfc7932 (5), may (5), rfc1952 (5), rfc1951 (5), rfc1950 (5), each (5), defined (5), return (5), they (5), contents (5), end (5), these (5), has (5), one (5), field (5), node (4), mobile (4), samsung (4), internet (4), webview (4), ios (4), none (4), legacy (4), 113 (4), all (4), current (4), engines (4), mdn (4), exposed (4), includes (4), index (4), informational (4), www (4), editor (4), version (4), defines (4), buffersource (4), readablestream (4), dfn (4), output (4), value (4), given (4), splitting (4), more (4), pieces (4), converting (4), them (4), type (4), takes (4), argument (4), ignored (4), created (4), errors (4), compliant (4), idl (3), rfc7230 (3), webidl (3), spec (3), deutsch (3), 1996 (3), following (3), transformstream (3), under (3), license (3), writer (3), totalsize (3), concatenated (3), offset (3), any (3), from (3), there (3), additional (3), after (3), only (3), implementations (3), supported (3), apis (3), enum (2), http (2), adam (2), rice (2), file (2), zlib (2), domenic (2), denicola (2), writablestream (2), reference (2), support (2), review (2), view (2), google (2), work (2), licensed (2), portions (2), source (2), code (2), such (2), was (2), w3c (2), document (2), intellectual (2), property (2), rights (2), acknowledgments (2), pipethrough (2), function (2), bytelength (2), arraybuffer (2), examples (2), developers (2), platform (2), privacy (2), security (2), considerations (2), handles (2), been (2), reached (2), decompressing (2), finish (2), unsupported (2), associated (2), compressing (2), member (2), fields (2), that (2), valid (2), method (2), values (2), invalid (2), conforming (2), blocks (2), checksum (2), adler32 (2), implementation (2), formats (2), state (2), infrastructure (2), used (2), introduction (2), tests (2), github (2), commits (2), fielding, reschke, june, 2014, proposed, httpwg, specs, html, hypertext, transfer, protocol, message, syntax, routing, edgar, chen, timothy, alakuijala, szabadka, july, 2016, gailly, anne, van, kesteren, thanks, canon, mukai, yutaka, hirano, their, those, interested, patent, should, draft, copyright, apple, mozilla, microsoft, extent, incorporated, instead, bsd, clause, creative, commons, attribution, international, originally, developed, wicg, where, available, software, written, ricea, chromium, decompressblob, response, compressarraybuffer, writable, getwriter, write, close, readable, push, async, compressedreadablestream, inputreadablestream, however, have, pay, attention, situation, when, attackers, can, get, length, able, guess, api, doesn, add, privileges, fully, consumed, results, contain, match, decompressed, isize, crc32, xfl, mtime, except, verify, terminated, correctly, fcomment, fname, fextra, present, incorrect, fhcrc, ftext, final, block, indicated, bfinal, correct, flevel, will, fdict, part, cmf, referred, consistency, content, encodings, see, note, internal, maintained, decompression, depend, use, point, opaque, initially, start, anticipates, first, byte, represents, ordered, sequence, chunks, piece, case, accept, depends, specified, algorithms, widely, table, javascript, binary, abstract, 한국어, 日本語, 简体中文, translations, ongoing, compressionapi, snapshot, commit, chat, matrix, open, issues, issue, participate, last, updated, april, 2026,

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compression standard compression living standard last updated 20 april 2026 participate github whatwg compression new issue open issues chat on matrix commits github whatwg compression commits snapshot as of this commit compressionapi tests web platform tests compression ongoing work translations non normative 简体中文 日本語 한국어 abstract this document defines a set of javascript apis to compress and decompress streams of binary data table of contents 1 introduction 2 infrastructure 3 supported formats 4 interface compressionstream 5 interface decompressionstream 6 privacy and security considerations 7 examples 7 1 gzip compress a stream 7 2 deflate compress an arraybuffer to a uint8array 7 3 gzip decompress a blob to blob acknowledgments intellectual property rights index terms defined by this specification terms defined by reference references normative references non normative references idl index 1 introduction this section is non normative the apis specified in this specification are used to compress and decompress streams of data they support deflate deflate raw and gzip as compression algorithms they are widely used by web developers 2 infrastructure this specification depends on infra infra a chunk is a piece of data in the case of compressionstream and decompressionstream the output chunk type is uint8array they accept any buffersource type as input a stream represents an ordered sequence of chunks the terms readablestream and writablestream are defined in streams streams a compression context is the internal state maintained by a compression or decompression algorithm the contents of a compression context depend on the format algorithm and implementation in use from the point of view of this specification it is an opaque object a compression context is initially in a start state such that it anticipates the first byte of input 3 supported formats brotli brotli compressed data format rfc7932 implementation must be compliant as described in rfc7932 section 1 4 non rfc7932 conforming blocks must not be created by compressionstream and are errors for decompressionstream deflate zlib compressed data format rfc1950 note this format is referred to as deflate for consistency with http content encodings see rfc7230 section 4 2 2 implementations must be compliant as described in rfc1950 section 2 3 field values described as invalid in rfc1950 must not be created by compressionstream and are errors for decompressionstream the only valid value of the cm compression method part of the cmf field is 8 the fdict flag is not supported by these apis and will error the stream if set the flevel flag is ignored by decompressionstream it is an error for decompressionstream if the adler32 checksum is not correct it is an error if there is additional input data after the adler32 checksum deflate raw the deflate algorithm rfc1951 implementations must be compliant as described in rfc1951 section 1 4 non rfc1951 conforming blocks must not be created by compressionstream and are errors for decompressionstream it is an error if there is additional input data after the final block indicated by the bfinal flag gzip gzip file format rfc1952 implementations must be compliant as described in rfc1952 section 2 3 1 2 field values described as invalid in rfc1952 must not be created by compressionstream and are errors for decompressionstream the only valid value of the cm compression method field is 8 the ftext flag must be ignored by decompressionstream if the fhcrc field is present it is an error for it to be incorrect the contents of any fextra fname and fcomment fields must be ignored by decompressionstream except to verify that they are terminated correctly the contents of the mtime xfl and os fields must be ignored by decompressionstream it is an error if crc32 or isize do not match the decompressed data a gzip stream may only contain one member it is an error if there is additional input data after the end of the member 4 interface compressionstream enum compressionformat brotli deflate deflate raw gzip exposed interface compressionstream constructor compressionformat format compressionstream includes generictransformstream a compressionstream has an associated format and compression context context the new compressionstream format steps are if format is unsupported in compressionstream then throw a typeerror set this s format to format let transformalgorithm be an algorithm which takes a chunk argument and runs the compress and enqueue a chunk algorithm with this and chunk let flushalgorithm be an algorithm which takes no argument and runs the compress flush and enqueue algorithm with this set this s transform to a new transformstream set up this s transform with transformalgorithm set to transformalgorithm and flushalgorithm set to flushalgorithm the compress and enqueue a chunk algorithm given a compressionstream object cs and a chunk runs these steps if chunk is not a buffersource type then throw a typeerror let buffer be the result of compressing chunk with cs s format and context if buffer is empty return let arrays be the result of splitting buffer into one or more non empty pieces and converting them into uint8array s for each uint8array array of arrays enqueue array in cs s transform the compress flush and enqueue algorithm which handles the end of data from the input readablestream object given a compressionstream object cs runs these steps let buffer be the result of compressing an empty input with cs s format and context with the finish flag if buffer is empty return let arrays be the result of splitting buffer into one or more non empty pieces and converting them into uint8array s for each uint8array array of arrays enqueue array in cs s transform 5 interface decompressionstream exposed interface decompressionstream constructor compressionformat format decompressionstream includes generictransformstream a decompressionstream has an associated format and compression context context the new decompressionstream format steps are if format is unsupported in decompressionstream then throw a typeerror set this s format to format let transformalgorithm be an algorithm which takes a chunk argument and runs the decompress and enqueue a chunk algorithm with this and chunk let flushalgorithm be an algorithm which takes no argument and runs the decompress flush and enqueue algorithm with this set this s transform to a new transformstream set up this s transform with transformalgorithm set to transformalgorithm and flushalgorithm set to flushalgorithm the decompress and enqueue a chunk algorithm given a decompressionstream object ds and a chunk runs these steps if chunk is not a buffersource type then throw a typeerror let buffer be the result of decompressing chunk with ds s format and context if this results in an error then throw a typeerror if buffer is empty return let arrays be the result of splitting buffer into one or more non empty pieces and converting them into uint8array s for each uint8array array of arrays enqueue array in ds s transform if the end of the compressed input has been reached and ds s context has not fully consumed chunk then throw a typeerror the decompress flush and enqueue algorithm which handles the end of data from the input readablestream object given a decompressionstream object ds runs these steps let buffer be the result of decompressing an empty input with ds s format and context with the finish flag if buffer is not empty let arrays be the result of splitting buffer into one or more non empty pieces and converting them into uint8array s for each uint8array array of arrays enqueue array in ds s transform if the end of the compressed input has not been reached then throw a typeerror 6 privacy and security considerations the api doesn t add any new privileges to the web platform however web developers have to pay attention to the situation when attackers can get the length of the data if so they may be able to guess the contents of the data 7 examples 7 1 gzip compress a stream const compressedreadablestream inputreadablestream pipethrough new compressionstream gzip 7 2 deflate compress an arraybuffer to a uint8array async function compressarraybuffer input const cs new compressionstream deflate const writer cs writable getwriter writer write input writer close const output let totalsize 0 for const chunk of cs readable output push value totalsize value bytelength const concatenated new uint8array totalsize let offset 0 for const array of output concatenated set array offset offset array bytelength return concatenated 7 3 gzip decompress a blob to blob function decompressblob blob const ds new decompressionstream gzip const decompressionstream blob stream pipethrough ds return new response decompressionstream blob acknowledgments thanks to canon mukai domenic denicola and yutaka hirano for their support this standard is written by adam rice google ricea chromium org intellectual property rights this living standard was originally developed in the w3c wicg where it was available under the w3c software and document license copyright whatwg apple google mozilla microsoft this work is licensed under a creative commons attribution 4 0 international license to the extent portions of it are incorporated into source code such portions in the source code are licensed under the bsd 3 clause license instead this is the living standard those interested in the patent review version should view the living standard review draft index terms defined by this specification brotli in 4 compress and enqueue a chunk in 4 compress flush and enqueue in 4 compression context in 2 compressionformat in 4 compressionstream in 4 compressionstream format in 4 constructor format constructor for compressionstream in 4 constructor for decompressionstream in 5 context dfn for compressionstream in 4 dfn for decompressionstream in 5 decompress and enqueue a chunk in 5 decompress flush and enqueue in 5 decompressionstream in 5 decompressionstream format in 5 deflate in 4 deflate raw in 4 format dfn for compressionstream in 4 dfn for decompressionstream in 5 gzip in 4 terms defined by reference infra defines the following terms for each streams defines the following terms generictransformstream readablestream transformstream writablestream enqueue flushalgorithm set up transform transformalgorithm webidl defines the following terms buffersource typeerror uint8array new this references normative references infra anne van kesteren domenic denicola infra standard living standard url https infra spec whatwg org rfc1950 p deutsch j l gailly zlib compressed data format specification version 3 3 may 1996 informational url https www rfc editor org rfc rfc1950 rfc1951 p deutsch deflate compressed data format specification version 1 3 may 1996 informational url https www rfc editor org rfc rfc1951 rfc1952 p deutsch gzip file format specification version 4 3 may 1996 informational url https www rfc editor org rfc rfc1952 rfc7932 j alakuijala z szabadka brotli compressed data format july 2016 informational url https www rfc editor org rfc rfc7932 streams adam rice et al streams standard living standard url https streams spec whatwg org webidl edgar chen timothy gu web idl standard living standard url https webidl spec whatwg org non normative references rfc7230 r fielding ed j reschke ed hypertext transfer protocol http 1 1 message syntax and routing june 2014 proposed standard url https httpwg org specs rfc7230 html idl index enum compressionformat brotli deflate deflate raw gzip exposed interface compressionstream constructor compressionformat format compressionstream includes generictransformstream exposed interface decompressionstream constructor compressionformat format decompressionstream includes generictransformstream mdn compressionstream compressionstream in all current engines firefox 113 safari 16 4 chrome 80 opera edge 80 edge legacy ie none firefox for android ios safari chrome for android android webview samsung internet opera mobile node js 17 0 0 mdn compressionstream in all current engines firefox 113 safari 16 4 chrome 80 opera edge 80 edge legacy ie none firefox for android ios safari chrome for android android webview samsung internet opera mobile node js 18 0 0 mdn decompressionstream decompressionstream in all current engines firefox 113 safari 16 4 chrome 80 opera edge 80 edge legacy ie none firefox for android ios safari chrome for android android webview samsung internet opera mobile node js 17 0 0 mdn decompressionstream in all current engines firefox 113 safari 16 4 chrome 80 opera edge 80 edge legacy ie none firefox for android ios safari chrome for android android webview samsung internet opera mobile node js 18 0 0