ProFTPD module mod_deflate

## ProFTPD module `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/

## Author

Please contact TJ Saunders <tj at castaglia.org> with any questions, concerns, or suggestions regarding this module.

## Directives

- DeflateEngine
- DeflatefLog

### DeflateEngine

Syntax: DeflateEngine on|off
Default: off
Context: server config, `<VirtualHost>`, `<Global>`
Module: mod_deflate
Compatibility: 1.3.0rc1 and later

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.

### DeflateLog

Syntax: DeflateLog path|"none"
Default: None
Context: server config, `<VirtualHost>`, `<Global>`
Module: mod_deflate
Compatibility: 1.3.0rc1 and later

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.

## Installation

The `mod_deflate` module is distributed with ProFTPD. Follow the usual steps for using third-party modules in ProFTPD:

      $ ./configure --with-modules=mod_deflate

To build `mod_deflate` as a DSO module:

      $ ./configure --enable-dso --with-shared=mod_deflate

Then 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

## Usage

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:

- deflate

Thus for trace logging, to aid in debugging, you would use the following in your `proftpd.conf`:

      TraceLog /path/to/ftpd/trace.log
      Trace deflate:20

This 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 `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.

If `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.

The solution is make sure that the client uploads (and downloads) non-ASCII files as binary files, not as ASCII files.

© Copyright 2006-2017 TJ Saunders
All Rights Reserved