Ability to mimic a zip file created by a Linux file-system.

[bjorg]

Use Case

Create a zip archive with specific permissions, such as the executable flag, using the ExternalAttributes property. The Linux unzip command only applies such permissions if the zip entry indicates the file was added by a Linux host-system.

Solution

Expose the more specific ZipEntry constructors that allow controlling the version number and host-system information. Ensure this information is used when creating the zip archive.

Changes:

1. Changed access level from internal to public on constructors for ZipEntry. This allows setting the madeByInfo value.
2. Changed VersionMadeBy property to return the entire ushort. This is required by ZipFile and ZipOutputStream to write the correct value.
3. Fixed HostSystem property to clear out the upper byte where the host system information is stored.
4. Changed ZipFile and ZipOutputStream to respect the VersionMadeBy value of the ZipEntry instance instead of hard-coding it.

Agreement

I certify that I own, and have sufficient rights to contribute, all source code and related material intended to be compiled or integrated with the source code for the SharpZipLib open source product (the "Contribution"). My Contribution is licensed under the MIT License.

[piksel]

I would prefer to add this by having a "host OS override" that can be set and which in turn sets the top version byte.

[bjorg]

There is a HostSystem property that might fit the bill. It had a bug where it cleared out the high-byte instead of the low-byte (see diff).

The big problem, IMO, is the VersionMadeBy property. As implemented, it always truncates the high-byte (see diff). Fixing that could potentially be a breaking change since dependent code may not expect the high-byte to have a value.

If VersionMadeBy cannot be fixed, then another property needs to be added that holds both the OS and zip version information. This information is later needed by ZipFile.WriteCentralDirectoryHeader(...) (see diff) and by ZipOutputStream.Finish(...) (see diff).

Let me know how you would like me to proceed and I'll update the pull-request. Thanks!

[piksel]

So, wouldn't just fixing the HostSystem property be enough then?
And using HostSystem + VersionMadeBy in ZipFile and ZipOutputStream?

[bjorg]

I think so, yes. That would probably work. Let me give it a shot and update the pull-request.

[bjorg]

@piksel
I updated the code. It now just fixes the HostSystem property bug and then ORs it with VersionMadeBy property in-lieu of the ZipConstants.VersionMadeBy constant.

[piksel]

As it turns out, it's not possible to set the HostSystem property of an entry using ZipFile (unless the file is empty).
I made some tests and added this functionality in a new PR.