fix: stabilize head metadata responses and heal tests (#1732)

Signed-off-by: LoganZ2 <103290230+LoganZ2@users.noreply.github.com>
Co-authored-by: houseme <housemecn@gmail.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

rustfs/src/storage/concurrency.rs

@@ -426,8 +426,19 @@ impl Drop for GetObjectGuard {
     /// This ensures accurate tracking even in error/panic scenarios, as Drop
     /// is called during stack unwinding (unless explicitly forgotten).
     fn drop(&mut self) {
-        // Decrement concurrent request counter
-        ACTIVE_GET_REQUESTS.fetch_sub(1, Ordering::Relaxed);
+        // Decrement concurrent request counter without underflow.
+        // If the counter is already 0, `checked_sub` returns None and `fetch_update`
+        // yields Err(previous). We treat that as a lifecycle bug (e.g., unmatched drop)
+        // and surface it in debug builds instead of silently discarding it.
+        if let Err(previous) =
+            ACTIVE_GET_REQUESTS.fetch_update(Ordering::Relaxed, Ordering::Relaxed, |current| current.checked_sub(1))
+        {
+            debug_assert_eq!(
+                previous, 0,
+                "ACTIVE_GET_REQUESTS underflow attempt in GetObjectGuard::drop; previous value = {}",
+                previous
+            );
+        }
 
         // Record Prometheus metrics for monitoring and alerting
         #[cfg(feature = "metrics")]

rustfs/src/storage/ecfs.rs

@@ -3428,6 +3428,30 @@ impl S3 for FS {
         // takes precedence for these read operations.
         let mut response = wrap_response_with_cors(&bucket, &req.method, &req.headers, output).await;
 
+        if let Some(content_disposition) = metadata_map.get("content-disposition") {
+            // Only set Content-Disposition from metadata if it has not already been set
+            if response.headers.get(http::header::CONTENT_DISPOSITION).is_none() {
+                match HeaderValue::from_str(content_disposition) {
+                    Ok(header_value) => {
+                        response.headers.insert(http::header::CONTENT_DISPOSITION, header_value);
+                    }
+                    Err(err) => {
+                        warn!(
+                            "Failed to parse content-disposition metadata value `{}` into HeaderValue: {}",
+                            content_disposition, err
+                        );
+                    }
+                }
+            }
+        }
+
+        if !response.headers.contains_key(http::header::CONTENT_TYPE)
+            && let Some(content_type) = metadata_map.get("content-type")
+            && let Ok(header_value) = HeaderValue::from_str(content_type)
+        {
+            response.headers.insert(http::header::CONTENT_TYPE, header_value);
+        }
+
         // Add x-amz-tagging-count header if object has tags
         // Per S3 API spec, this header should be present in HEAD object response when tags exist
         if tag_count > 0 {

rustfs/src/storage/options.rs

@@ -390,12 +390,16 @@ pub fn extract_metadata_from_mime_with_object_name(
 }
 
 pub(crate) fn filter_object_metadata(metadata: &HashMap<String, String>) -> Option<HashMap<String, String>> {
-    // Standard HTTP headers that should NOT be returned in the Metadata field
-    // These are returned as separate response headers, not user metadata
+    // HTTP headers that should NOT be returned in the Metadata field.
+    // These headers are returned as separate response headers, not user metadata.
+    //
+    // Note: content-type and content-disposition are intentionally NOT excluded here.
+    // They remain in the filtered metadata so they can continue to be exposed via
+    // x-amz-meta-* style user metadata for backward compatibility, while the HEAD
+    // implementation also mirrors their values into the standard Content-Type and
+    // Content-Disposition response headers where appropriate.
     const EXCLUDED_HEADERS: &[&str] = &[
-        "content-type",
         "content-encoding",
-        "content-disposition",
         "content-language",
         "cache-control",
         "expires",
@@ -432,7 +436,8 @@ pub(crate) fn filter_object_metadata(metadata: &HashMap<String, String>) -> Opti
             continue;
         }
 
-        // Skip standard HTTP headers (they are returned as separate headers, not metadata)
+        // Skip excluded HTTP headers (they are returned as separate headers, not metadata)
+        // Note: content-type and content-disposition are NOT excluded and will be treated as user metadata
         if EXCLUDED_HEADERS.contains(&lower_key.as_str()) {
             continue;
         }