[jira] [Created] (LOG4J2-1369) "xz" compression results in plaintext, uncompressed files.

["Alex Birch (JIRA)" <ji...@apache.org>]

Alex Birch created LOG4J2-1369:
----------------------------------

             Summary: "xz" compression results in plaintext, uncompressed files.
                 Key: LOG4J2-1369
                 URL: https://issues.apache.org/jira/browse/LOG4J2-1369
             Project: Log4j 2
          Issue Type: Bug
          Components: Appenders, Core, Documentation
    Affects Versions: 2.5
         Environment: Java SE 1.7
            Reporter: Alex Birch


_Note: see [associated StackOverflow problem](https://stackoverflow.com/questions/36695617/enabling-lzma2-i-e-xz-compression-in-log4j2)

## Current state of world

Currently our `RollingFileAppender` in `log4j2.xml` uses Gzip compression:

```
<RollingFile name="RollingFile"
             fileName="logs/engine.log"
             filePattern="logs/engine.log.%i.gz">
```

## Goal

I would like to switch to LZMA(2) (i.e. `.xz`) compression, to enjoy an improved compression ratio.

## Attempt

I have tried changing `engine.log.%i.gz` to `engine.log.%i.xz` — as per [the documentation](https://logging.apache.org/log4j/2.x/manual/appenders.html#DefaultRolloverStrategy):

> If the file pattern ends with `.gz`, `.zip`, `.bz2`, `.deflate`, `.pack200`, or `.xz` the resulting archive will be compressed using the compression scheme that matches the suffix. The formats bzip2, Deflate, Pack200 and XZ require Apache Commons Compress. In addition, XZ requires [XZ for Java](http://tukaani.org/xz/java.html).

Additionally I have ensured that I have a runtime dependency on [XZ for Java](http://tukaani.org/xz/java.html) — via `pom.xml`:

```
<dependency>
    <!-- Support Log4j2 Log compression schemes: ".gz", ".zip", ".bz2", ".deflate", ".pack200", [".xz" (part 1 of 2)] -->
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-compress</artifactId>
    <version>1.11</version>
</dependency>
<dependency>
    <!-- Support Log4j2 Log compression scheme [".xz" (part 2 of 2)] -->
    <groupId>org.tukaani</groupId>
    <artifactId>xz</artifactId>
    <version>1.5</version>
</dependency>
```

## Result

When the RollingFileAppender is triggered: the archive created is indeed _named_ `engines.log.1.xz` — as required.

**However**, its contents are incorrect:

### Expectation

`engines.log.1.xz` should contain LZMA(2) compressed text

### Actual

`engines.log.1.xz` instead contains plain, uncompressed text.

## Sanity checks

I confirm that the `org.tukaani:xz` and `org.apache.commons:commons-compress` successfully made it into the classpath of my jar:

```
🍔 jar tf mycooljar.jar | grep tukaani
org/tukaani/
org/tukaani/xz/
...

🍔 jar tf mycooljar.jar | grep org/apache/commons/compress
org/apache/commons/compress/
org/apache/commons/compress/changes/
...
```

This Java program is not deployed to a J2EE webserver. I believe its class loading is straightforward.

## Summary

I have correctly followed the instructions necessary to create `.gz` archives.

I believe the only additional step required to create `.xz` archives is: I must provide at runtime the [XZ for Java](http://tukaani.org/xz/java.html) artefact. I have done this.

Am I missing something here? I am tempted to believe one of the following:

 - The functionality is broken
 - The docs are incomplete/incorrect
 - log4j2 fails to discover the class at runtime

## Leads so far

I was able to find some evidence that perhaps I am expected to input `.xy` instead of `.xz`. If I use `.xy`: the log4j2 `RollingAppender` fails to produce archives. That is: it creates blank `.xy` files, and retains the unarchived plaintext as a `.log` file. It smells like a buggy implementation.

Here is the code I present as evidence from `org.apache.logging.log4j.core.appender.rolling.DefaultRolloverStrategy`:
```
static enum FileExtensions {
    XY(".xy") {
        @Override
        Action createCompressAction(final String renameTo, final String compressedName, final boolean deleteSource,
                 final int compressionLevel) {
             // One of "gz", "bzip2", "xz", "pack200", or "deflate".
             return new CommonsCompressAction("xy", source(renameTo), target(compressedName), deleteSource);
        }
    }
}
```



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