functions for manipulating symlinks

libcitadel/src/symlink.rs

@@ -0,0 +1,66 @@
+use std::fs;
+use std::path::{Path,PathBuf};
+use std::os::unix;
+
+use crate::Result;
+
+pub fn read(path: impl AsRef<Path>) -> Option<PathBuf> {
+    let path = path.as_ref();
+
+    if !fs::symlink_metadata(path).is_ok() {
+        return None;
+    }
+
+    match fs::read_link(path) {
+        Ok(target) => Some(target),
+        Err(err) => {
+            warn!("error reading {} symlink: {}", path.display(), err);
+            None
+        }
+    }
+}
+
+// write symlink atomically and if tmp_in_parent is set, create the tmp link in parent directory
+// This is used so that the directory /run/citadel/realms/current can be monitored for changes
+// without inotify firing when the tmp link is created.
+pub fn write(target: impl AsRef<Path>, link: impl AsRef<Path>, tmp_in_parent: bool) -> Result<()> {
+    let link = link.as_ref();
+    let target = target.as_ref();
+    let tmp = write_tmp_path(link, tmp_in_parent);
+
+    if let Some(parent) = link.parent() {
+        if !parent.exists() {
+            fs::create_dir_all(parent)?;
+        }
+    }
+
+    if tmp.exists() {
+        fs::remove_file(&tmp)?;
+    }
+
+    unix::fs::symlink(target, &tmp)?;
+    fs::rename(&tmp, link)?;
+    Ok(())
+}
+
+fn write_tmp_path(link: &Path, tmp_in_parent: bool) -> PathBuf {
+    let skip = if tmp_in_parent { 2 } else { 1 };
+    let tmp_dir = link.ancestors().skip(skip).next()
+        .expect("No parent directory in write_symlink");
+
+    let mut tmp_fname = link.file_name()
+        .expect("No filename in write_symlink()")
+        .to_os_string();
+
+    tmp_fname.push(".tmp");
+
+    tmp_dir.join(tmp_fname)
+}
+
+pub fn remove(path: impl AsRef<Path>) -> Result<()> {
+    let path = path.as_ref();
+    if fs::symlink_metadata(path).is_ok() {
+        fs::remove_file(path)?;
+    }
+    Ok(())
+}