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by ymnk@jcraft.com, JCraft,Inc.
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http://www.jcraft.com/jzlib/
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Last modified: Wed Dec 20 05:47:39 UTC 2000
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JZlib is a re-implementation of zlib in pure Java.
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The first and final aim for hacking this stuff is
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to add the packet compression support to pure Java SSH systems.
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* README files all over the source tree have info related to the stuff
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* ChangeLog: what changed from the previous version?
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Directories & Files in the Source Tree
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======================================
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* com/ has source trees of JZlib.
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* example/ has some samples, which demonstrate the usages.
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* misc/ has some stuffs. At present, this directory includes
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a patch file for MindTerm v.1.2.1, which adds the packet compression
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* Needless to say, JZlib can inflate data, which is deflated by zlib and
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JZlib can generate deflated data, which is acceptable and inflated by zlib.
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* JZlib supports all compression level and all flushing mode in zlib.
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* JZlib does not support gzip file handling supports.
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* The performance has not been estimated yet, but it will be not so bad
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in deflating/inflating data stream on the low bandwidth network.
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* JZlib is under LGPL.
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* Any invention has not been done in developing JZlib.
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So, if zlib is patent free, JZlib is also not covered by any patents.
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Java Platform API provides packages 'java.util.zip.*' for
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accessing to zlib, but that support is very limited
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if you need to use the essence of zlib. For example,
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we needed to full access to zlib to add the packet compression
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support to pure Java SSH system, but they are useless for our requirements.
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The Internet draft, SSH Transport Layer Protocol, says in the section '4.2 Compression' as follows,
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The following compression methods are currently defined:
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none REQUIRED no compression
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zlib OPTIONAL GNU ZLIB (LZ77) compression
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The "zlib" compression is described in [RFC-1950] and in [RFC-1951]. The
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compression context is initialized after each key exchange, and is
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passed from one packet to the next with only a partial flush being
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performed at the end of each packet. A partial flush means that all data
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will be output, but the next packet will continue using compression
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tables from the end of the previous packet.
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To implement this functionality, the Z_PARTIAL_FLUSH mode of zlib must be
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used, however JDK does not permit us to do so. It seems that this problem has
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been well known and some people have already reported to
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JavaSoft's BugParade(for example, BugId:4255743),
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but any positive response has not been returned from JavaSoft,
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so this problem will not be solved forever.
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This is our motivation to hack JZlib.
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A unofficial patch for MindTerm v.1.2.1
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=======================================
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A unofficial patch file for MindTerm v.1.2.1 has included in 'misc' directory.
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It adds the packet compression support to MindTerm.
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Please refer to 'misc/README' file.
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Copyrights & Disclaimers
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========================
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JZlib is copyrighted by JCraft,Inc. and is licensed through the
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GNU Library General Public License.
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Read the COPYING file for the complete license.
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JZlib has been developed by ymnk@jcraft.com,
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but he has just re-implemented zlib in pure Java.
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So, all credit should go to authors
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Jean-loup Gailly(jloup@gzip.org) and Mark Adler(madler@alumni.caltech.edu)
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and contributors of zlib.
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If you have any comments, suggestions and questions, write us
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``SSH is a registered trademark and Secure Shell is a trademark of
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SSH Communications Security Corp (www.ssh.com)''.
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README
