[PATCH datacenter-manager] namespaced-cache: avoid double path construction and key verification

[Lukas Wagner <l.wagner@proxmox.com>]

Instead of calling set_impl from set_if_newer_impl, we now pull out
common parts into another function, set_at_path. This ensures that some
of work at the start of the set_impl and set_if_newer_impl is not done
twice (key verification, path construction).

Also, while at it, add a brief comment with regards to why the .unwrap()
is safe when accessing the parent directory of the cache file path.

Signed-off-by: Lukas Wagner <l.wagner@proxmox.com>
---
 server/src/namespaced_cache.rs | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/server/src/namespaced_cache.rs b/server/src/namespaced_cache.rs
index d7831dca..50c72da8 100644
--- a/server/src/namespaced_cache.rs
+++ b/server/src/namespaced_cache.rs
@@ -603,7 +603,7 @@ fn set_if_newer_impl<T: Serialize + DeserializeOwned>(
         Err(err) => return Err(err),
     }
 
-    set_impl(inner, key, value, timestamp).map(|()| None)
+    set_at_path(inner, &path, value, timestamp).map(|()| None)
 }
 
 fn set_impl<T: Serialize + DeserializeOwned>(
@@ -615,8 +615,22 @@ fn set_impl<T: Serialize + DeserializeOwned>(
     ensure_valid_key(key)?;
     let path = get_path(&inner.base_path, &inner.namespace, key);
 
+    set_at_path(inner, &path, value, timestamp)
+}
+
+fn set_at_path<T: Serialize + DeserializeOwned>(
+    inner: &WritableInner,
+    path: &Path,
+    value: T,
+    timestamp: i64,
+) -> Result<(), CacheError> {
+    // unwrap: A namespace directory is always a subdirectory of the base directory
+    // that was passed when initializing `NamespacedCache`, so `.parent()`
+    // always returns Some(...)
+    let namespace_dir = path.parent().unwrap();
+
     proxmox_sys::fs::create_path(
-        path.parent().unwrap(),
+        namespace_dir,
         Some(inner.dir_options),
         Some(inner.dir_options),
     )?;
-- 
2.47.3