Does ouch support permissions like --xattrs?

[RyanGreenup]

Discussed in #625

^{Originally posted by RyanGreenup February 10, 2024}
It's common to use tar to backup up a home directory like so:

mount LABEL=ROOT -o subvol=@ /mnt

# use bsdar if gnu tar compiled without xattrs or acls
cd /mnt
x=/root-tarball.tar.gz
bsdtar --acls --xattrs --preserve-permissions -cvaf ${x} .

Users can later extract this with:

bsdtar --acls --xattrs  --numeric-owner -xpzf ${x} /mnt

Is there any support for those properties in Ouch? It would be convenient, atleast for me, if there was a command line flag like -P / --preserve-all-permissions, then one could more simply:

# Compress
cd /mnt
ouch compress -P . ${x}

# Decompress
cd /
ouch decompress -P ${x} .

I had a look at the:

• tar crate
  • See also Tar - Extended File Attributes Docs.

and the crate documentation suggests the following functions:

• --xattrs
  • set_unpack_xattrs
• --preserve-permissions
  • set_preserve_permissions
• --acls
  • I couldn't find anything for this, I'll have a look through the docs, it may have a different name.
• --numeric-owner
  • This could be important for Docker containers
  • set_preserve_ownerships

We'd probably need to add this somewhere around src/archive/tar.rs

If you could offer some guidance, I can try and put together a PR if you'd like?

[RyanGreenup]

These are all the functions I could find under Archive:: with the set_ prefix:

• tar::Archive::set_mask
• tar::Archive::set_overwrite
• tar::Archive::set_ignore_zeros
• tar::Archive::set_unpack_xattrs
• tar::Archive::set_preserve_mtime
• tar::Archive::set_preserve_ownerships
• tar::Archive::set_preserve_permissions

There's also a set_mode which might be the --acls

[RyanGreenup]

Tar.rs logic

It seems like the work flow of tar is:

Compress

1. Make a
   builder
   objectwith a
   Header::new_gnu(),
   • this object uses builder.append(&mut
     header)
     to add files
   • that header will by default have
     HeaderMode::Complete
     to include everything like mod/access times and ownership
     • (although it could be modified by it's
       set_metadata
       method)
       • TODO does this include acls by default?
2. Use builder.append to add files

Decompress

1. Create an archive and set
   • set_unpackxattrs
   • set_{preservepermissions}
   • set_{preserveownerships}
   • set_acls
     • TODO is there a way to set acls?
2. Unpack the archive

Examples

1. Compressing

   For Compressing the example in the
   documentation
   is something like:

   use tar::{Builder, Header};
   
   let mut header = Header::new_gnu();
   
   let mut data: &[u8] = &[1, 2, 3, 4];
   
   let mut builder = Builder::new(Vec::new());
   builder.append(&header, data).unwrap();
   let data = builder.into_inner().unwrap();

   We just need to ensure acls are pulled in.

2. Decompressing

   This could then be decompressed with unpack_archive like so:

   pub fn unpack_archive(reader: Box<dyn Read>, output_folder: &Path, quiet: bool) -> crate::Result<usize> {
       assert!(output_folder.read_dir().expect("dir exists").count() == 0);
       let mut archive = tar::Archive::new(reader);
   
       // --xattrs
       archive.set_unpack_xattrs(true);
       // --preserver-permissions
       archive.set_preserve_permissions();
       // --numeric-ownership
       archive.set_preserve_ownerships();
   
       // --acls
       // TODO
   
       let mut files_unpacked = 0;
       for file in archive.entries()? {
           let mut file = file?;
   
           file.unpack_in(output_folder)?;
       }
   
       Ok(files_unpacked)
   }

   Does that seem right?

[RyanGreenup]

I created an issue with tar-rs asking about acls:

• tar-rs #353

Further resources:

• Wikipedia - Table of archive Formats supporting ACLs
• RHEL - Archiving File Systems With ACLs

[marcospb19]

If you could offer some guidance, I can try and put together a PR if you'd like?

Sorry for the late response. Unfortunately, I don't think I have the time to give guidance on how to approach this, but we could iterate on the solution in the PR review process.

You're right, Ouch doesn't support --xattrs atm.

---

I like your idea of having a -P/--preserve-all-permissions flag that covers it all.

In the --help message we also have to explain that these permissions apply for Tar but not for Zip archives 🤔, and state that CLS is not supported yet.

In conclusion, I approve this feature request and a PR (from you or someone else) would be welcomed for reviewing 👍.