From: Raymond O'Connor <nappin713@...>
Date: 2007-12-01T08:46:09+09:00
Subject: Running GzipWriter on same input produces different output

Hi,

Is it normal that everytime I gzip the same contents, the output is
different?
For example, calling gzip writer on the same input twice, gives
different results:

>> strio = StringIO.open('','w')
>> gz = Zlib::GzipWriter.new(strio)
>> gz.write('foobar')
>> gz.close
>> Digest::MD5.hexdigest(strio.string)
=> "30888fba6a6fadd5b4006000e05c9d14"

>> strio = StringIO.open('','w')
>> gz = Zlib::GzipWriter.new(strio)
>> gz.write('foobar')
>> gz.close
>> Digest::MD5.hexdigest(strio.string)
=> "e09426945afb531b3db49733060b8d08"

I'm trying to compare 1 file that is unzipped versus another file that
is gzipped on a network store (to determine whether to update it or
not).  So I gzip the unzipped file, generate an md5 hash for it, and
then compare the md5 hash to the md5 of the gzip file on the server.
However, I soon noticed that calling gzipwriter on the same file
contents over and over produced a different md5 hash everytime.    Oddly
when I use the gzip system command I don't get this behavior.  The gzip
data it produces is the same each time.

Any help would be appreciated.
Thanks,
Ray
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