You can prevent deflate from generating the header by passing in -
MAX_WBITS to the options for Deflate.new.  The following method
emulates gzdeflate from php:

def gzdeflate(s)
  Zlib::Deflate.new(nil, -Zlib::MAX_WBITS).deflate(s, Zlib::FINISH)
end

puts gzdeflate("Hello World").unpack('H*').first
# => f348cdc9c95708cf2fca490100

On Mar 14, 8:16 am, Pat Patterson <Andrew.Patter... / Sun.COM> wrote:
> OK - so now I know what is happening...
>
> Zlib::Deflate.deflate implements ZLIB compression according to RFC 1950.
> ZLIB defines a 2 byte header containing a variety of flags and a 4 byte
> trailer containing an Adler-32 checksum. Just out of interest, the
> header that I'm seeing translates as 'compression method = deflate,
> windows size = 32k, no preset dictionary, default compression level',
> which makes perfect sense. Deflate compression itself is defined by RFC
> 1951.
>
> So - if you want 'raw' deflated data (which is called for in many
> situations), cutting off the leading 2 and trailing 4 bytes is exactly
> what you need to do.
>
> Cheers,
>
> Pat
>
>
>
> Pat Patterson wrote:
> > Thanks, Brian! That revealed an obvious bug in the code I was using to
> > examine the deflated data (should have been 0.upto(deflated.length-1)).
>
> > So Base64 /is/ working correctly. Deflate prepends 2 bytes (seems to
> > be constant 0x789c for default deflate level) and appends 4 bytes
> > (rather than 1 and 5 as I thought) to the deflated data. When I cut
> > those off, I can get Ruby to work the same as PHP.
>
> > Still - it would be nice if deflate worked the same as on Java, PHP, ...
>
> > Cheers,
>
> > Pat
>
> > Brian Candler wrote:
> >> On Tue, Mar 13, 2007 at 01:21:52PM +0900, Pat Patterson wrote:
>
> >>> While the Ruby
>
> >>> deflated = Zlib::Deflate.deflate( "Hello world" )
> >>> myhex = ""
> >>> 1.upto(deflated.length) { |i| myhex << "%02x" % deflated[i] }
> >>> puts myhex
>
> >>> Shows
>
> >>> 9cf348cdc9c95728cf2fca49010018ab043d00
>
> >>> (BTW - if anyone knows a more succinct way to hex encode a string in
> >>> Ruby, that would be useful)
>
> >> str = "\001\377"
> >> puts str.unpack("H*")
>
> --
> Pat Patterson - pat.patter... / sun.com
> Federation Architect,
> Sun Microsystems, Inc.http://blogs.sun.com/superpat