Zlib Deflate to java.util.zip inflate problem


#1

Hello, I’m a total ruby newbie and am developing a simple app that
tests an existing web app. Part of the request I need to post
contains data that needs to be compressed as the web app will
uncompress it. Currently, the java app just uses simple
java.util.zip.Inflater to do this, and I’ve been able to do this from
cocoa to java no problem. Using Ruby to craft the data and post
request has presented a problem: when the web app gets the request,
I’m getting exceptions from java.utl.zip Unkown Compression format I
can’t change the back end, only the ruby client side. Does anybody
know how to properly use the ruby zlib library to deflate data such
that java’s built in classes can inflate it? Sorry if this is a basic
question; I’ve googled this to death and hit nothing but dead ends.
Here’s the call that compresses:

compressedBroadcast = Zlib::Deflate.new(nil, -
Zlib::MAX_WBITS).deflate(binaryBroadcastData, Zlib::FINISH)

Other than this, I’m very much enjoying the other Ruby bits. Thanks
for any pointers.

Dom


#2

Anything, anybody? Little help here…:wink:


#3

Dom wrote:

that java’s built in classes can inflate it? Sorry if this is a basic
question; I’ve googled this to death and hit nothing but dead ends.

Did you find rubyzip? It doesn’t seem to work under Ruby 1.9, but it
does have an interface supposedly modeled on java.util.zip:

 http://rubyzip.sourceforge.net/

It’s hard to believe this didn’t come up when you Googled.


#4

Dom wrote:

Sorry, should have been more clear, I’m not creating files. I did
find it, but it seems entirely focused on zip files; I’m just using
the deflate/inflate to squeeze some data before sending it over the
wire. Being that they’re both based on zlib, you’d think that deflated
from one would be inflatable by the other and I was hoping that
perhaps I’m just missing a setting or not using a correct parameter to
one of the ruby calls. But, I’ve pretty much tried every permutation
and cannot get the server to inflate the data. I’d think somebody’s
doing this somewhere with success.

Could it be that your java side is expecting the new zlib format?

As could be seen in your first post, you are using -MAX_WBITS, which
enables old (headerless? don’t know what it’s called) zlib format, that
has no gzip header and no checksum. Maybe you should be using +MAX_WBITS
(the default), which adds necessary header and checksum.


#5

On Apr 5, 2009, at 02:48, Alexey B. wrote:

Could it be that your java side is expecting the new zlib format?

As could be seen in your first post, you are using -MAX_WBITS, which
enables old (headerless? don’t know what it’s called) zlib format,
that
has no gzip header and no checksum. Maybe you should be using
+MAX_WBITS
(the default), which adds necessary header and checksum.

Agreed, you probably only want -MAX_WBITS when implementing a gzip
stream.


#6

On Apr 4, 2009, at 09:45, Dom wrote:

compressedBroadcast = Zlib::Deflate.new(nil, -
Zlib::MAX_WBITS).deflate(binaryBroadcastData, Zlib::FINISH)

I think you’re asking for a gzip stream here with your -MAX_WBITS


#7

Thanks for the reply,

Sorry, should have been more clear, I’m not creating files. I did
find it, but it seems entirely focused on zip files; I’m just using
the deflate/inflate to squeeze some data before sending it over the
wire. Being that they’re both based on zlib, you’d think that deflated
from one would be inflatable by the other and I was hoping that
perhaps I’m just missing a setting or not using a correct parameter to
one of the ruby calls. But, I’ve pretty much tried every permutation
and cannot get the server to inflate the data. I’d think somebody’s
doing this somewhere with success.