Ciao, per la seguente ragione:
"I downloaded the ZIP archive but my archiver software says it's broken. What's this all about? Can't JoomlaPack produce valid ZIP archives?
This is not a yes or no question. The situation is somewhat complex and requires a little bit of technical explanation. If you want the executive summary, JoomlaPack is unable to produce valid-looking ZIP files under certain configurations. However, the data is intact and you can extract the archive if your archiver software can be set up to ignore CRC errors in the archive. Alternatively, you can use the unzip.php script from the JPA Utils package.
And here goes the technical explanation. The ZIP archive format specifies that a CRC32 checksum must be stored for each file included in the archive. PHP before version 5.1.2, only had a CRC32 calculation function for in-memory data. As a result, JoomlaPack had to read the entire file to memory to calculate its CRC32 hash. However, due to memory consumption limitations imposed by PHP configuration, this is usually not possible for large files. "Large files" for PHP usually means anything over around 1Mb. A workaround was attempted but it was not successful, since PHP is a typeless language and the required bitwise arithmetic could not be performed.
The effect of all of this is that a dummy CRC32 value is stored for those files. Archiver software, adhering to the ZIP standard, check the CRC32 for each file they try to extract and when they come to such a file with a dummy CRC32 they think that the archive is broken and omit the extraction of the offending file. In fact, the file data is correct, the CRC32 is wrong. Some archiver software can be configured to ignore CRC errors and the ZIP will extract just fine.
Since PHP 5.1.2 there was the hash extension available. This PHP extension provides a method for quickly and accurately calculating any file's CRC32 without having to read all of it in memory. In systems with PHP 5.1.2 or better with the hash extension available, JoomlaPack will produce correct ZIP files, adhering to the ZIP standard.
Please note that this is a PHP limitation, beyond our control. We are not irresponsible, releasing a software which doesn't work. The current behaviour is a compromise between required features and technical possibility.
If you really want to extract your ZIP archive you can use our unzip.php command-line script, or the desktop application JoomlaPack eXtract, available for Windows only."
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Comunque morale della favola bisogna utilizzare il loro tools per l'estrazione dei file di backup di JoomlaPack che troverete quì:
http://joomlacode.org/gf/project/jpack/frs/Si chiama JoomlaPackNativeTools.
