Bug #10101
closedZlib::GzipReader produce different outputs for different methods applied
Description
The methods read
, readbyte
and each_byte
are producing different outputs. Comparing with the unziped file, only the result of readbyte is correct according to the size but comparing byte per byte with the original file sometimes gives differences at the same positions.
This part of the differences I couldn't reproduce in a way that I could share on the internet because the original file is a magnetic resonance image subject to confidentiality.
But fortunately I was able to reproduce the bug on input size. I've attached a script that illustrates the problem and here is the link for the file that I've used for the following sample output:
https://drive.google.com/file/d/0B3O0CbLN-q0TcmhGR0RGeWM2UHM/edit?usp=sharing
Sorry about the size, but I couldn't produce a smaller file.
[manzo@WALL-A gz_debug]$ ruby -v
ruby 2.1.2p95 (2014-05-08 revision 45877) [x86_64-linux]
[manzo@WALL-A gz_debug]$ ruby test1.rb sample.gz
Size of read: 45102570
Size of each_byte: 4668
Size of readbyte: 45158752
I hope I'm right on this report and thank you a lot for your time!
Files
Updated by nagachika (Tomoyuki Chikanaga) about 10 years ago
- Backport changed from 2.0.0: UNKNOWN, 2.1: UNKNOWN to 2.0.0: REQUIRED, 2.1: REQUIRED
Hello, Rafael.
Thank you for your report.
I can reproduce with your sample on 2.0.0p433 and 2.1.2, and it can be easily reproduced similar case with large gzip'ed file as follows.
$ dd if=/dev/zero of=foo count=5000
$ gzip foo
$ ruby test1.rb foo.gz
Size of read: 2560000
Size of each_byte: 2097151
Size of readbyte: 2560000
In this case, only `each_byte' returns wrong value. I suspect there are several different cause.
I don't have time to investigate this right now.
And zlib has no maintainer according to https://bugs.ruby-lang.org/projects/ruby/wiki/MaintainersStdlib
Are there anyone who can handle this?
Updated by cremno (cremno phobia) about 10 years ago
read
returns a string with external encoding. In your case it seems to be UTF-8
. The encodings of the given IO
object are ignored. Using Zlib::GzipReader.open
doesn't work either, by the way. It still ignores the b, but as a workaround you can change the encoding of the returned string, pass
external_encoding: Encoding::ASCII_8BITas new argument, call
String#bytesize`, etc.
After some rearranging and duplicating of the remaining two cases, I can't say why each_byte
sometimes fails. But with the following lines, [-2048, 1]
(2048 looks interesting) is printed by f_gz.rewind
when it fails.
def f.seek(*args)
p args
super
end
Updated by Anonymous about 10 years ago
- Status changed from Open to Closed
- % Done changed from 0 to 100
Applied in changeset r47327.
zlib: GzipReader#rewind preserves ZSTREAM_FLAG_GZFILE
-
ext/zlib/zlib.c (gzfile_reset): preserve ZSTREAM_FLAG_GZFILE
[Bug #10101] -
test/zlib/test_zlib.rb (test_rewind): test each_byte
We must preserve the ZSTREAM_FLAG_GZFILE flag to prevent
zstream_detach_buffer from:
a) returning Qnil and breaking out of the `each_byte' loop
b) yielding a large string to each_byte
Note: the test case in bug report takes a long time. I found this
bug because I noticed the massive time descrepancy between
each_byte' and
readbyte' loop before this patch. With this patch,
each_byte' and
readbyte' both take very long.
Updated by normalperson (Eric Wong) about 10 years ago
nagachika00@gmail.com wrote:
I don't have time to investigate this right now.
And zlib has no maintainer according to
https://bugs.ruby-lang.org/projects/ruby/wiki/MaintainersStdlib
Are there anyone who can handle this?
Hi, r47327 should fix this:¶
r47327 | normal | 2014-08-30 23:53:28 +0000 (Sat, 30 Aug 2014) | 18 lines
zlib: GzipReader#rewind preserves ZSTREAM_FLAG_GZFILE
-
ext/zlib/zlib.c (gzfile_reset): preserve ZSTREAM_FLAG_GZFILE
[Bug #10101] -
test/zlib/test_zlib.rb (test_rewind): test each_byte
We must preserve the ZSTREAM_FLAG_GZFILE flag to prevent
zstream_detach_buffer from:
a) returning Qnil and breaking out of the `each_byte' loop
b) yielding a large string to each_byte
Note: the test case in bug report takes a long time. I found this
bug because I noticed the massive time descrepancy between
each_byte' and
readbyte' loop before this patch. With this patch,
each_byte' and
readbyte' both take very long.
I should be able to help out on zlib in the future (and many bugs
reproducible without graphical or proprietary dependency).
Updated by nagachika (Tomoyuki Chikanaga) almost 10 years ago
- Backport changed from 2.0.0: REQUIRED, 2.1: REQUIRED to 2.0.0: REQUIRED, 2.1: DONE
Thank you Eric! It is a great insight.
Backported into ruby_2_1
at r47419.
Updated by usa (Usaku NAKAMURA) almost 10 years ago
- Backport changed from 2.0.0: REQUIRED, 2.1: DONE to 2.0.0: DONE, 2.1: DONE
backported into ruby_2_0_0
at r47500.