How Do I Copy File Metadata to a New File?

help
1

How to use Rust to implement the cp -p function? I want to copy the file metadata when copying the file content. The std::fs::copy provided by the standard library ensures that the file permission remains unchanged, but the time attribute is not inherited.

2

You won't be able to do it with Rust's standard library. Different operating systems have different weird corners here, and you will need to use native OS-specific APIs for it.

So check how to implement it in C, and then use FFI or -sys crates to do it.

1 Like
3

Thank you. Is there a suitable API for modifying the file time attribute in UNIX?

4

You are probably looking for nix::sys::stat::utimes() from the nix crate. That crate has safe wrappers for a lot of Unix-specific functionality.

5

You can read it:

You can't write it yet:

1 Like
6

Thank you. After upgrading the rust version, I finally saw the API you said.

7

I found that the API for modifying file time is not stable. Are there any other stable APIs?

8

Doesn't seem to support the Windows platform.

9

Well you did ask for a UNIX solution.

If you want something that works with Windows, check out the windows::Win32::Storage::FileSystem::SetFileTime() function from the windows crate.

10

Our current scenario is Unix, but I want the code to be portable.

11

The best way to do that is by writing a cross-platform abstraction which calls into the right platform-specific API - kinda like what std does already.

For example,

pub fn copy_metadata(from: impl AsRef<Path>,  to: impl AsRef<Path>) -> Result<(), io::Error> {
  let from = from.as_ref();
  let to = to.as_ref();

  cfg_if! {
    if #[cfg(windows)] {
      windows::copy_metadata(from, to)
    } else if #[cfg(unix)] {
      unix::copy_metadata(from, to)
    } else {
      Err(io::ErrorKind::Unsupported.into())
    }
  }
}

#[cfg(windows)]
mod windows {
  pub(crate) fn copy_metadata(from: &Path, to: &Path) -> Result<(), io::Error> {
    // use windows::Win32::Storage::FileSystem::SetFileTime()
  }
}

#[cfg(unix)]
mod unix {
  pub(crate) fn copy_metadata(from: &Path, to: &Path) -> Result<(), io::Error> {
    // use nix::sys::stat::utimes()
  }
}

You could publish this as its own crate, or even make a PR to a crate like fs-extra which provides additional capabilities for working with the filesystem.

12

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