Ionic Zip Library v1.9.1.6
Zip64Option Enumeration
ReferenceIonic.ZipZip64Option
Options for using ZIP64 extensions when saving zip archives.
Declaration Syntax
C#Visual BasicVisual C++
public enum Zip64Option
Public Enumeration Zip64Option
public enum class Zip64Option
Members
MemberDescription
Default The default behavior, which is "Never". (For COM clients, this is a 0 (zero).)
Never Do not use ZIP64 extensions when writing zip archives. (For COM clients, this is a 0 (zero).)
AsNecessary Use ZIP64 extensions when writing zip archives, as necessary. For example, when a single entry exceeds 0xFFFFFFFF in size, or when the archive as a whole exceeds 0xFFFFFFFF in size, or when there are more than 65535 entries in an archive. (For COM clients, this is a 1.)
Always Always use ZIP64 extensions when writing zip archives, even when unnecessary. (For COM clients, this is a 2.)
Remarks

Designed many years ago, the original zip specification from PKWARE allowed for 32-bit quantities for the compressed and uncompressed sizes of zip entries, as well as a 32-bit quantity for specifying the length of the zip archive itself, and a maximum of 65535 entries. These limits are now regularly exceeded in many backup and archival scenarios. Recently, PKWare added extensions to the original zip spec, called "ZIP64 extensions", to raise those limitations. This property governs whether DotNetZip will use those extensions when writing zip archives. The use of these extensions is optional and explicit in DotNetZip because, despite the status of ZIP64 as a bona fide standard, many other zip tools and libraries do not support ZIP64, and therefore a zip file with ZIP64 extensions may be unreadable by some of those other tools.

Set this property to Always to always use ZIP64 extensions when saving, regardless of whether your zip archive needs it. Suppose you add 5 files, each under 100k, to a ZipFile. If you specify Always for this flag, you will get a ZIP64 archive, though the archive does not need to use ZIP64 because none of the original zip limits had been exceeded.

Set this property to Never to tell the DotNetZip library to never use ZIP64 extensions. This is useful for maximum compatibility and interoperability, at the expense of the capability of handling large files or large archives. NB: Windows Explorer in Windows XP and Windows Vista cannot currently extract files from a zip64 archive, so if you want to guarantee that a zip archive produced by this library will work in Windows Explorer, use Never. If you set this property to Never, and your application creates a zip that would exceed one of the Zip limits, the library will throw an exception while saving the zip file.

Set this property to AsNecessary to tell the DotNetZip library to use the ZIP64 extensions when required by the entry. After the file is compressed, the original and compressed sizes are checked, and if they exceed the limits described above, then zip64 can be used. That is the general idea, but there is an additional wrinkle when saving to a non-seekable device, like the ASP.NET Response.OutputStream, or Console.Out. When using non-seekable streams for output, the entry header - which indicates whether zip64 is in use - is emitted before it is known if zip64 is necessary. It is only after all entries have been saved that it can be known if ZIP64 will be required. On seekable output streams, after saving all entries, the library can seek backward and re-emit the zip file header to be consistent with the actual ZIP64 requirement. But using a non-seekable output stream, the library cannot seek backward, so the header can never be changed. In other words, the archive's use of ZIP64 extensions is not alterable after the header is emitted. Therefore, when saving to non-seekable streams, using AsNecessary is the same as using Always: it will always produce a zip archive that uses ZIP64 extensions.

Assembly: Ionic.Zip (Module: Ionic.Zip) Version: 1.9.1.6 (1.9.1.6)