EmitTimesInUnixFormatWhenSaving Property

DotNetZip

Ionic Zip Library v1.9.1.6 EmitTimesInUnixFormatWhenSaving Property

Specifies whether the Creation, Access, and Modified times for entries added to the zip file will be emitted in "Unix(tm) format" when the zip archive is saved.

Declaration Syntax

Visual Basic

Visual C++

public bool EmitTimesInUnixFormatWhenSaving { get; set; }

Public Property EmitTimesInUnixFormatWhenSaving As Boolean
	Get
	Set

public:
property bool EmitTimesInUnixFormatWhenSaving {
	bool get ();
	void set (bool value);
}

Remarks

An application creating a zip archive can use this flag to explicitly specify that the file times for the entries should or should not be stored in the zip archive in the format used by Unix. By default this flag is false, meaning the Unix-format times are not stored in the zip archive.

When adding an entry from a file or directory, the Creation (CreationTime), Access (AccessedTime), and Modified (ModifiedTime) times for the given entry are automatically set from the filesystem values. When adding an entry from a stream or string, all three values are implicitly set to DateTime.Now. Applications can also explicitly set those times by calling SetEntryTimes(DateTime, DateTime, DateTime).

PKWARE's zip specification describes multiple ways to format these times in a zip file. One is the format Windows applications normally use: 100ns ticks since January 1, 1601 UTC. The other is a format Unix applications typically use: seconds since January 1, 1970 UTC. Each format can be stored in an "extra field" in the zip entry when saving the zip archive. The former uses an extra field with a Header Id of 0x000A, while the latter uses a header ID of 0x5455, although you probably don't need to know that.

Not all tools and libraries can interpret these fields. Windows compressed folders is one that can read the Windows Format timestamps, while I believe the Infozip tools can read the Unix format timestamps. Some tools and libraries may be able to read only one or the other. DotNetZip can read or write times in either or both formats.

The times stored are taken from ModifiedTime, AccessedTime, and CreationTime.

This property is not mutually exclusive of the EmitTimesInWindowsFormatWhenSaving property. It is possible and legal and valid to produce a zip file that contains timestamps encoded in the Unix format as well as in the Windows format, in addition to the LastModified time attached to each entry in the zip archive, a time that is always stored in "DOS format". And, notwithstanding the names PKWare uses for these time formats, any of them can be read and written by any computer, on any operating system. But, there are no guarantees that a program running on Mac or Linux will gracefully handle a zip file with "Windows" formatted times, or that an application that does not use DotNetZip but runs on Windows will be able to handle file times in Unix format.

When in doubt, test. Sorry, I haven't got a complete list of tools and which sort of timestamps they can use and will tolerate. If you get any good information and would like to pass it on, please do so and I will include that information in this documentation.