How to decompress Gzip string in ruby?

Question

Zlib::GzipReader can take "an IO, or IO-like, object." as it's input, as stated in docs.

Zlib::GzipReader.open('hoge.gz') {|gz|
  print gz.read
}

File.open('hoge.gz') do |f|
  gz = Zlib::GzipReader.new(f)
  print gz.read
  gz.close
end

How should I ungzip a string?

score 130 · Accepted Answer · edited Mar 30 '15 at 16:34

130

The above method didn't work for me.
I kept getting incorrect header check (Zlib::DataError) error. Apparently it assumes you have a header by default, which may not always be the case.

The work around that I implemented was:

require 'zlib'
require 'stringio'
gz = Zlib::GzipReader.new(StringIO.new(resp.body.to_s))    
uncompressed_string = gz.read

edited Mar 30 '15 at 16:34

rogerdpack

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answered Sep 02 '09 at 06:59

Garth

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3

Thank you, I was getting the same error and this solved my problem! – Matt Huggins Mar 24 '13 at 01:07
is calling body.to_s redundant? – Blaskovicz Jun 26 '14 at 17:50

score 19 · Answer 2 · answered Nov 15 '09 at 19:03

Zlib by default asumes that your compressed data contains a header. If your data does NOT contain a header it will fail by raising a Zlib::DataError.

You can tell Zlib to assume the data has no header via the following workaround:

def inflate(string)
  zstream = Zlib::Inflate.new(-Zlib::MAX_WBITS)
  buf = zstream.inflate(string)
  zstream.finish
  zstream.close
  buf
end

dimus · Answer 3 · 2009-09-01T11:36:20.963

16

You need Zlib::Inflate for decompression of a string and Zlib::Deflate for compression

  def inflate(string)
    zstream = Zlib::Inflate.new
    buf = zstream.inflate(string)
    zstream.finish
    zstream.close
    buf
  end

edited Sep 01 '09 at 11:36

answered Sep 01 '09 at 11:30

dimus

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score 16 · Answer 4 · answered Nov 12 '15 at 21:10

16

In Rails you can use:

ActiveSupport::Gzip.compress("my string")
ActiveSupport::Gzip.decompress().

answered Nov 12 '15 at 21:10

Tyler

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score 7 · Answer 5 · answered Jan 16 '14 at 05:09

7

zstream = Zlib::Inflate.new(16+Zlib::MAX_WBITS)

answered Jan 16 '14 at 05:09

BearPy

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Nice one. From [the docs](http://www.ruby-doc.org/stdlib-2.1.5/libdoc/zlib/rdoc/Zlib/Inflate.html) "or add 16 to decode only the gzip format (a Zlib::DataError will be raised for a non-gzip stream)" – ian Dec 10 '14 at 13:39

score 5 · Answer 6 · edited Sep 25 '11 at 01:05

5

Using (-Zlib::MAX_WBITS), I got ERROR: invalid code lengths set and ERROR: invalid block type
The only following works for me, too.

Zlib::GzipReader.new(StringIO.new(response_body)).read

edited Sep 25 '11 at 01:05

Nakilon

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answered Dec 26 '09 at 04:34

john

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score 3 · Answer 7 · answered Sep 18 '12 at 09:59

3

We don't need any extra parameters these days. There are deflate and inflate class methods which allow for quick oneliners like these:

>> data = "Hello, Zlib!"
>> compressed = Zlib::Deflate.deflate(data)
=> "x\234\363H\315\311\311\327Q\210\312\311LR\004\000\032\305\003\363"
>> uncompressed = Zlib::Inflate.inflate(compressed)
=> "Hello, Zlib!"

I think it answers the question "How should I ungzip a string?" the best. :)

answered Sep 18 '12 at 09:59

Alex Fortuna

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If you compress and decompress then this will be fine, but it will not be gzip compressed. Just running Zlib::Inflate.inflate(compressed) on gzip compressed data will assume the wrong compression and throw a "incorrect header check" exception. – philwhln Nov 04 '12 at 22:20

score 3 · Answer 8 · answered Mar 30 '11 at 20:15

I used the answer above to use a Zlib::Deflate

I kept getting broken files (for small files) and it took many hours to figure out that the problem can be fixed using:

buf = zstream.deflate(string,Zlib::FINISH)

without the the zstream.finish line!

def self.deflate(string)
    zstream = Zlib::Deflate.new
    buf = zstream.deflate(string,Zlib::FINISH)
    zstream.close
    buf
end

score 3 · Answer 9 · answered Oct 18 '11 at 09:28

3

To gunzip content, use following code (tested on 1.9.2)

Zlib::GzipReader.new(StringIO.new(content), :external_encoding => content.encoding).read

Beware of encoding problems

answered Oct 18 '11 at 09:28

pinguin666

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How to decompress Gzip string in ruby?

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