fix(s3): add x-amz-tagging-count header to HEAD object response (#1568)

Co-authored-by: houseme <housemecn@gmail.com>

rustfs/src/storage/ecfs.rs

@@ -116,7 +116,7 @@ use rustfs_utils::{
     http::{
         AMZ_BUCKET_REPLICATION_STATUS, AMZ_CHECKSUM_MODE, AMZ_CHECKSUM_TYPE,
         headers::{
-            AMZ_DECODED_CONTENT_LENGTH, AMZ_OBJECT_TAGGING, AMZ_RESTORE_EXPIRY_DAYS, AMZ_RESTORE_REQUEST_DATE,
+            AMZ_DECODED_CONTENT_LENGTH, AMZ_OBJECT_TAGGING, AMZ_RESTORE_EXPIRY_DAYS, AMZ_RESTORE_REQUEST_DATE, AMZ_TAG_COUNT,
             RESERVED_METADATA_PREFIX, RESERVED_METADATA_PREFIX_LOWER,
         },
     },
@@ -3040,6 +3040,15 @@ impl S3 for FS {
         let content_language = metadata_map.get("content-language").cloned();
         let expires = info.expires.map(Timestamp::from);
 
+        // Calculate tag count from user_tags already in ObjectInfo
+        // This avoids an additional API call since user_tags is already populated by get_object_info
+        let tag_count = if !info.user_tags.is_empty() {
+            let tag_set = decode_tags(&info.user_tags);
+            tag_set.len()
+        } else {
+            0
+        };
+
         let output = HeadObjectOutput {
             content_length: Some(content_length),
             content_type,
@@ -3076,7 +3085,19 @@ impl S3 for FS {
         // interact with objects (PUT/POST/DELETE/LIST, etc.) rely on the system-level
         // CORS layer instead. In case both are applicable, this bucket-level CORS logic
         // takes precedence for these read operations.
-        let response = wrap_response_with_cors(&bucket, &req.method, &req.headers, output).await;
+        let mut response = wrap_response_with_cors(&bucket, &req.method, &req.headers, output).await;
+
+        // 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 {
+            let header_name = http::HeaderName::from_static(AMZ_TAG_COUNT);
+            if let Ok(header_value) = tag_count.to_string().parse::<http::HeaderValue>() {
+                response.headers.insert(header_name, header_value);
+            } else {
+                warn!("Failed to parse x-amz-tagging-count header value, skipping");
+            }
+        }
+
         let result = Ok(response);
         let _ = helper.complete(&result);