fix: apply code review suggestions

src/client.rs

@@ -45,7 +45,7 @@ impl Client {
         }
         if !cache_path.join(AUTHORITY_FILENAME).exists() {
             debug!("required file missing: {}", AUTHORITY_FILENAME);
-            return Err(Error::CacheCorruption("required files missing in cache").into());
+            return Err(Error::CacheCorruption("required file(s) missing in cache").into());
         }
         Ok(())
     }

src/flatfiledirmgr.rs

@@ -82,22 +82,18 @@ impl<R: Runtime> FlatFileDirMgr<R> {
 
     /// Check cache directory content.
     fn check_directory(cache_path: &Path) -> Result<()> {
-        let mut any_missing = false;
-        for filename in [
+        let missing_files: Vec<&&str> = [
             CONSENSUS_FILENAME,
             MICRODESCRIPTORS_FILENAME,
             CERTIFICATE_FILENAME,
             CHURN_FILENAME,
         ]
         .iter()
-        {
-            if !cache_path.join(filename).exists() {
-                any_missing = true;
-                debug!("required file missing: {filename}");
-            }
-        }
-        if any_missing {
-            return Err(Error::CacheCorruption("required files missing in cache"));
+        .filter(|filename| !cache_path.join(filename).exists())
+        .collect();
+        if !missing_files.is_empty() {
+            debug!("required file(s) missing: {missing_files:?}");
+            return Err(Error::CacheCorruption("required file(s) missing in cache"));
         }
         Ok(())
     }

tests/client.rs

@@ -120,7 +120,7 @@ async fn test_required_files_missing() {
         let root_cause = error.root_cause();
         assert_eq!(
             format!("{}", root_cause),
-            "Corrupt cache: required files missing in cache"
+            "Corrupt cache: required file(s) missing in cache"
         );
     }
 }