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doc: more accurate zlib windowBits information
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Fixes: nodejs/node#14847
PR-URL: nodejs/node#16511
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
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addaleax authored and Qard committed Nov 2, 2017
1 parent de45915 commit 6711946
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Showing 2 changed files with 7 additions and 7 deletions.
11 changes: 5 additions & 6 deletions doc/api/zlib.md
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Expand Up @@ -459,12 +459,11 @@ added: v0.5.8
Creates and returns a new [DeflateRaw][] object with the given [options][].

*Note*: An upgrade of zlib from 1.2.8 to 1.2.11 changed behavior when windowBits
is set to 8 for raw deflate streams. zlib does not have a working implementation
of an 8-bit Window for raw deflate streams and would automatically set windowBit
to 9 if initially set to 8. Newer versions of zlib will throw an exception.
This creates a potential DOS vector, and as such the behavior ahs been reverted
in Node.js 8, 6, and 4. Node.js version 9 and higher will throw when windowBits
is set to 8.
is set to 8 for raw deflate streams. zlib would automatically set windowBits
to 9 if was initially set to 8. Newer versions of zlib will throw an exception,
so Node.js restored the original behavior of upgrading a value of 8 to 9,
since passing `windowBits = 9` to zlib actually results in a compressed stream
that effectively uses an 8-bit window only.

## zlib.createGunzip([options])
<!-- YAML
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3 changes: 2 additions & 1 deletion test/parallel/test-zlib.js
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Expand Up @@ -166,7 +166,8 @@ assert.doesNotThrow(() => {
// value of the matching deflate’s windowBits. However, inflate raw with
// windowBits = 8 should be able to handle compressed data from a source
// that does not know about the silent 8-to-9 upgrade of windowBits
// that older versions of zlib/Node perform.
// that most versions of zlib/Node perform, and which *still* results in
// a valid 8-bit-window zlib stream.
node.pipe(zlib.createDeflateRaw({ windowBits: 9 }))
.pipe(zlib.createInflateRaw({ windowBits: 8 }))
.on('data', (chunk) => reinflated.push(chunk))
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