#1432 7ZFM can't recognize UNIX timestamps in .ZIP archive

[quanta]

In the file fonts_ycc.zip[1], the local and central headers of each file contains the Type 1 Info-ZIP Unix Extra Field, which contains last access time and last modification time information. However, 7-Zip File Manager shows modification time from the main header's 'last mod file date' field in 7ZFM's 'Modified' field, while the 'Accessed' field remains empty.

According to Info-Zip's annotated version of .ZIP File Format Specification[2], it shows a guideline for handling timestamps within the extra field. Specifically, the timestamps from the Type 1 Info-ZIP Unix Extra Field should be used for the purpose of extraction, updating, freshening, creation, and conversion. However, the behaviour of listing the archive header contents is undefined.

To decide the proper behaviour in such scenario, the archive was processed with SecureZIP 9. SecureZIP 9 recognizes the presence of Info-Zip extra field in both headers of each file in fonts_ycc.zip[1], but never interpret the field in detail. However, after viewing the file/folder's properies in Properties dialogue, the object's Created, Modified, and Accessed dates all incorrectly changed to '1969/12/31 20:00:00' (local time, GMT=1970/01/01 00:00:00) after exiting Properties dialogue and switching tasks, but the Created field in the file list remains empty, and the changes are kept only if the archive is saved afterwards. After saving the archive within SecureZIP 9 with above mentioned timestamp change, reopening the archive shows SecureZIP 9 only modifies the extra field type to 0D (UNIX Extra Field) in central directory and converts the timestamps in the original archive in that place. Extra field within local headers, the last mod file time and last mod file date fields in the main local file header and central directory file header, are unchanged from the original archive. Opening the converted archive in 7-Zip File Manager shows 7ZFM does not recognize Unix timestamps, even after converting the extra field to the official Unix type.

The official PKWARE specifications document lists the Info-Zip extra field type but does not describe it in detail, but the Info-Zip's guideline does not contradict PKWARE's document. Therefore, 7-Zip File Manager should show the the last modified and last accessed timestamp from the Unix extra fields in the respective 'Modified' and 'Accessed' fields inside 7ZFM file list, following the guidelines for the corresponding extra field type in the Info-Zip's annotated specification[2]. Guideline aside, the central headers for each file indicates it was created in Unix environment, so there is no reason why the Unix timestamp in extra field doesn't overrule the main header's timestamp.

This bug also exposes the need for 7-Zip (File Manager) to list the archive contents and properties in further details than it currently supports in order to properly handle archive (format) with extended header contents. For the 7ZFM, it means adding extra detailed properties dialogue/window pane/tab. For the command line tools, extra command line switches should be implemented. For either version of 7-Zip, there should be customizable views for listing detailed properties of each object stored in an archive.

[1] http://web.archive.org/web/20110404064350/http://www.youngcreativechevrolet.eu/app/webroot/uploads/fonts_ycc.zip
[2] http://www.info-zip.org/doc/appnote-iz-latest.zip