From: Pat Patterson <Andrew.Patterson@...>
Date: 2007-03-13T13:21:52+09:00
Subject: Ruby Newbie Problems with deflate, base64...

I'm implementing a spec that calls for messages to be deflated, then 
base64 encoded, then URL encoded, so they can be passed as parameters to 
an HTTP GET. In PHP, this is achieved with:

$encodedMsg = urlencode( base64_encode( gzdeflate( $msg ) ) )

Looking at the docs, the equivalent in Ruby would be something like:

require "cgi"
require "base64"
require "zlib"

encodedMsg = CGI::escape( Base64.encode64( Zlib::Deflate.deflate( msg ) ) )

But this gives me completely different output to my (working) PHP model.

Some googling later, it appears that Zlib::Deflate.deflate prepends and 
appends 'stuff' to the deflated data. Investigating, the PHP

$deflated = gzdeflate( "Hello world" );
echo bin2hex( $deflated );

Gives me

f348cdc9c95728cf2fca490100

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)

Notice the additional '9c' at the start of the string and '18ab043d00' 
at the end. OK - there seems to be a consistent amount of data prepended 
and appended, so I can slice those off.

But now Base 64 is acting weird. In PHP:

$base64Encoded = base64_encode( $deflated );
echo $base64Encoded;

Shows

80jNyclXKM8vykkBAA==

While, in Ruby

# Remove extra stuff from deflated string
deflated = deflated[1,deflated.length-6]
base64encoded = Base64.encode64( deflated )
puts base64encoded

Shows

nPNIzcnJVyjPL8pJAQ==

Completely different! Now, if I feed that back through PHP's 
base64_unencode, I get

9cf348cdc9c95728cf2fca4901

Notice, again '9c' prepended, but this time the trailing '00' has been 
removed.

What is going on here? Any ideas??? Am I missing something really 
obvious about string handling in Ruby?

(BTW - this is on ruby 1.8.4 (2005-12-24) [i486-linux])

Cheers,

Pat

-- 
Pat Patterson - pat.patterson@sun.com
Federation Architect,
Sun Microsystems, Inc.
http://blogs.sun.com/superpat