set file permissions on Unix

[wfurt]

What's the problem?

fixes #357 Incorrect file permissions for ccache file

What's the solution?

When file is created it will have some default permissions on Unix. Depending on system configuration that can allow read access to anybody.

Describe the solution here.

There is no standard way how to set Unix permissions on File class - specialty when targeting Framework (not really applicable) or .NET Standard. .NET Core 7.0 introduced method to set permissions (essentially chmod) and this PR tries to use it on Unix via Reflection.

I was wondering where to put it @SteveSyfuhs and I put it to base file class instead of just the ccache. If there are files that should be readable or writable by others that may be the wrong place. The code also tries to create directory if needed and I'm not sure if we should be explicit there is well in case we end up creating it. (that is different from the example in /tmp where we should not touch the permissions)

• Includes unit tests
• Requires manual test

I'm not sure how to construct Unix specific test and how to verify the functionality in portable way. If you have sgesstions please let me know.

What issue is this related to, if any?

#357

[SteveSyfuhs]

I'm happy with this. It's the right spot and nothing else needs specific permissions. The only other writable thing is the configuration, which is generally going to be provided by an admin and also doesn't contain anything sensitive.

[SteveSyfuhs]

Build succeeded but failed a test. Its a flaky test so rerunning. Is probably fine.