Use read_link to cope with broken symlinks

Signed-off-by: James Rhodes <[email protected]>

crates/common/tedge_utils/src/fs.rs

@@ -48,12 +48,11 @@ pub fn atomically_write_file_sync(
     dest: impl AsRef<Path>,
     mut reader: impl Read,
 ) -> Result<(), AtomFileError> {
-    // resolve path (including valid symlinks that point to an existing file)
-    let dest = dest
-        .as_ref()
-        .canonicalize()
-        .unwrap_or_else(|_| dest.as_ref().to_path_buf());
-    let dest_dir = parent_dir(dest.as_ref());
+    let dest = dest.as_ref();
+    // resolve path (including symlinks)
+    // if the symlink doesn't exist, (attempt to) create the file it points to
+    let dest = std::fs::read_link(dest).unwrap_or_else(|_| dest.to_path_buf());
+    let dest_dir = parent_dir(&dest);
 
     // removed on drop
     let mut file = tempfile::Builder::new()
@@ -94,15 +93,21 @@ pub fn atomically_write_file_sync(
     )?;
 
     // Move the temp file to its destination
-    file.persist(&dest)
-        .with_context(|| "could not write to destination file".to_string(), &dest)?;
+    file.persist(&dest).with_context(
+        || "could not write to destination file".to_string(),
+        &dest,
+    )?;
 
     // Ensure the new name reach the disk
-    let dir = std::fs::File::open(dest_dir)
-        .with_context(|| "could not open the directory".to_string(), &dest)?;
+    let dir = std::fs::File::open(dest_dir).with_context(
+        || "could not open the directory".to_string(),
+        &dest,
+    )?;
 
-    dir.sync_all()
-        .with_context(|| "could not save the file to disk".to_string(), &dest)?;
+    dir.sync_all().with_context(
+        || "could not save the file to disk".to_string(),
+        &dest,
+    )?;
 
     Ok(())
 }
@@ -257,4 +262,22 @@ mod tests {
             panic!("failed to read the new file");
         }
     }
+
+    #[test]
+    fn atomically_write_file_file_sync_with_broken_symlink() {
+        let temp_dir = tempdir().unwrap();
+        let link_path = temp_dir.path().join("test-link");
+        let destination_path = temp_dir.path().join("test-orig");
+        let _ = std::os::unix::fs::symlink(destination_path.clone(), link_path.clone());
+
+        let content = "test_data";
+
+        let () = atomically_write_file_sync(link_path.clone(), content.as_bytes()).unwrap();
+
+        if let Ok(destination_content) = std::fs::read(destination_path) {
+            assert_eq!(destination_content, content.as_bytes());
+        } else {
+            panic!("failed to read the new file");
+        }
+    }
 }