zlib.error: Error -3 while decompressing: incorrect header check
Update: dnozay's answer explains the problem and should be the accepted answer.
Try the gzip
module, code below is straight from the python docs.
import gzip
f = gzip.open('/home/joe/file.txt.gz', 'rb')
file_content = f.read()
f.close()
You have this error:
zlib.error: Error -3 while decompressing: incorrect header check
Which is most likely because you are trying to check headers that are not there, e.g. your data follows RFC 1951
(deflate
compressed format) rather than RFC 1950
(zlib
compressed format) or RFC 1952
(gzip
compressed format).
choosing windowBits
But zlib
can decompress all those formats:
- to (de-)compress
deflate
format, usewbits = -zlib.MAX_WBITS
- to (de-)compress
zlib
format, usewbits = zlib.MAX_WBITS
- to (de-)compress
gzip
format, usewbits = zlib.MAX_WBITS | 16
See documentation in http://www.zlib.net/manual.html#Advanced (section inflateInit2
)
examples
test data:
>>> deflate_compress = zlib.compressobj(9, zlib.DEFLATED, -zlib.MAX_WBITS)
>>> zlib_compress = zlib.compressobj(9, zlib.DEFLATED, zlib.MAX_WBITS)
>>> gzip_compress = zlib.compressobj(9, zlib.DEFLATED, zlib.MAX_WBITS | 16)
>>>
>>> text = '''test'''
>>> deflate_data = deflate_compress.compress(text) + deflate_compress.flush()
>>> zlib_data = zlib_compress.compress(text) + zlib_compress.flush()
>>> gzip_data = gzip_compress.compress(text) + gzip_compress.flush()
>>>
obvious test for zlib
:
>>> zlib.decompress(zlib_data)
'test'
test for deflate
:
>>> zlib.decompress(deflate_data)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
zlib.error: Error -3 while decompressing data: incorrect header check
>>> zlib.decompress(deflate_data, -zlib.MAX_WBITS)
'test'
test for gzip
:
>>> zlib.decompress(gzip_data)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
zlib.error: Error -3 while decompressing data: incorrect header check
>>> zlib.decompress(gzip_data, zlib.MAX_WBITS|16)
'test'
the data is also compatible with gzip
module:
>>> import gzip
>>> import StringIO
>>> fio = StringIO.StringIO(gzip_data) # io.BytesIO for Python 3
>>> f = gzip.GzipFile(fileobj=fio)
>>> f.read()
'test'
>>> f.close()
automatic header detection (zlib or gzip)
adding 32
to windowBits
will trigger header detection
>>> zlib.decompress(gzip_data, zlib.MAX_WBITS|32)
'test'
>>> zlib.decompress(zlib_data, zlib.MAX_WBITS|32)
'test'
using gzip
instead
or you can ignore zlib
and use gzip
module directly; but please remember that under the hood, gzip
uses zlib
.
fh = gzip.open('abc.gz', 'rb')
cdata = fh.read()
fh.close()