fix(api): descriptive InvalidArgument reason for Windows-unsupported object keys (#4947)

fix(api): return descriptive InvalidArgument reason for Windows-unsupported object keys

On Windows hosts object keys containing NTFS-reserved characters or
Win32-unaddressable path segments are rejected up front, but the client
only saw a bare "Invalid argument" (issue #3299). Attach an explicit
reason to these rejections and surface non-empty InvalidArgument reasons
through the S3 error message.

rustfs/src/error.rs

@@ -276,6 +276,13 @@ impl From<StorageError> for ApiError {
 
         let message = if code == S3ErrorCode::InternalError {
             err.to_string()
+        } else if let StorageError::InvalidArgument(_, _, reason) = &err
+            && !reason.is_empty()
+        {
+            // Argument-validation rejections carry a client-actionable reason
+            // (e.g. object keys unsupported on Windows hosts, issue #3299);
+            // a bare "Invalid argument" gives the caller nothing to fix.
+            format!("Invalid argument: {reason}")
         } else {
             ApiError::error_code_to_message(&code)
         };
@@ -397,6 +404,26 @@ mod tests {
         }
     }
 
+    #[test]
+    fn test_api_error_surfaces_invalid_argument_reason() {
+        let err = StorageError::InvalidArgument(
+            "bucket".into(),
+            "a:b*c".into(),
+            "object key contains characters unsupported on Windows hosts".into(),
+        );
+        let api_error: ApiError = err.into();
+        assert_eq!(api_error.code, S3ErrorCode::InvalidArgument);
+        assert_eq!(
+            api_error.message,
+            "Invalid argument: object key contains characters unsupported on Windows hosts"
+        );
+
+        // An empty reason falls back to the generic message.
+        let err = StorageError::InvalidArgument("bucket".into(), "object".into(), String::new());
+        let api_error: ApiError = err.into();
+        assert_eq!(api_error.message, "Invalid argument");
+    }
+
     #[test]
     fn test_api_error_other_function() {
         let custom_error = "Custom API error";