tools/fs: add scan_subdir helper

This filters the results of read_subdir with a regex.

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>

src/tools/fs.rs

@@ -35,3 +35,29 @@ pub fn read_subdir<P: ?Sized + nix::NixPath>(dirfd: RawFd, path: &P) -> Result<R
     });
     Ok(ReadDir { iter })
 }
+
+/// Scan through a directory with a regular expression. This is simply a shortcut filtering the
+/// results of `read_subdir`. Non-UTF8 comaptible file names are silently ignored.
+pub fn scan_subdir<'a, P: ?Sized + nix::NixPath>(
+    dirfd: RawFd,
+    path: &P,
+    regex: &'a regex::Regex,
+) -> Result<impl Iterator<Item = Result<nix::dir::Entry, Error>> + 'a, Error> {
+    Ok(read_subdir(dirfd, path)?.filter_map(move |entry| {
+        match entry {
+            Ok(entry) => match entry.file_name().to_str() {
+                Ok(name) => {
+                    if regex.is_match(name) {
+                        Some(Ok(entry))
+                    } else {
+                        None // Skip values not matching the regex
+                    }
+                }
+                // Skip values which aren't valid utf-8
+                Err(_) => None,
+            },
+            // Propagate errors through
+            Err(e) => Some(Err(Error::from(e))),
+        }
+    }))
+}