mod_deflate
The mod_deflate module is designed to provide support for
MODE Z commands, which allows FTP clients and servers to
compress data for transfer.
This module is contained in the mod_deflate.c file for
ProFTPD 1.3.x, and is not compiled by default.  Installation instructions
are discussed here.  Detailed documentation on
mod_deflate usage can be found here.
The most current version of mod_deflate can be found at:
http://www.castaglia.org/proftpd/
Please contact TJ Saunders <tj at castaglia.org> with any questions, concerns, or suggestions regarding this module.
<VirtualHost>, <Global>
The DeflateEngine directive enables or disables the
mod_deflate compression functionality.  If set to on,
then mod_deflate will advertise support for MODE Z
compression via the FEAT command, and handle MODE Z
requests appropriately.
<VirtualHost>, <Global>
The DeflateLog directive is used to specify a log file for
mod_deflate reporting and debugging. The path parameter
must be the full path to the file to use for logging.  Note that this path must
not be to a world-writable directory and, unless
AllowLogSymlinks is explicitly set to on
(generally a bad idea), the path must not be a symbolic link.
If path is "none", no logging will be done at all.
mod_deflate module is distributed with ProFTPD.  Follow the
usual steps for using third-party modules in ProFTPD:
$ ./configure --with-modules=mod_deflateTo build
mod_deflate as a DSO module:
$ ./configure --enable-dso --with-shared=mod_deflateThen follow the usual steps:
$ make $ make install
For those with an existing ProFTPD installation, you can use the
prxs tool to add mod_deflate, as a DSO module, to
your existing server:
$ prxs -c -i -d mod_deflate.c
Example mod_deflate configuration:
  <IfModule mod_deflate.c>
    DeflateEngine on
    DeflateLog /var/log/proftpd/deflate.log
  </IfModule>
Sites that run proftpd 1.3.0 should disable sendfile use
when using mod_deflate, as the two features do not interoperate
well:
  <IfModule mod_deflate.c>
    DeflateEngine on
    DeflateLog /var/log/proftpd/deflate.log
    UseSendfile off
  </IfModule>
Logging
The mod_deflate module supports different forms of logging.  The
main module logging is done via the DeflateLog directive.
For debugging purposes, the module also uses trace logging, via the module-specific log channels:
proftpd.conf:
TraceLog /path/to/ftpd/trace.log Trace deflate:20This trace logging can generate large files; it is intended for debugging use only, and should be removed from any production configuration.
Frequently Asked Questions 
Question: I'm uploading a file using  
If  
The solution is make sure that the client uploads (and downloads) non-ASCII
files as binary files, not as ASCII files.
 
MODE Z,
but the upload always fails.  In the DeflateLog, I see:
 error inflating data: [-3] Data error
What is going wrong?  It is a mod_deflate bug?
Answer: The most common cause of this error is when
the client is trying to upload a binary file (e.g. PDF, MPG, etc)
in ASCII mode.
MODE Z is not used in cases like this, the upload succeeds,
but the uploaded file on the server is corrupted.  When MODE Z
is in effect, the corruption (translation of newlines inappropriately) is
detected earlier (since mod_deflate can't uncompress the
compressed data properly, hence the report of a "Data error"), and the
upload fails.
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 All Rights Reserved