Fix /model_info serialization when a config value is a class (#39237)

Co-authored-by: Lianmin Zheng <lianminzheng@gmail.com>

python/sglang/srt/entrypoints/http_server.py

@@ -785,7 +785,7 @@ async def model_info():
             config=resolving_view(_global_state.tokenizer_manager.server_args),
             model_config=model_config,
         )
-    return result
+    return msgspec_to_builtins(result)
 
 
 @app.get("/get_weight_version")

python/sglang/srt/utils/msgspec_utils.py

@@ -49,6 +49,9 @@ def msgspec_to_builtins(obj: Any) -> Any:
             for f in dataclasses.fields(obj)
         }
 
+    if isinstance(obj, type):
+        return f"{obj.__module__}.{obj.__qualname__}"
+
     if isinstance(obj, dict):
         return {key: msgspec_to_builtins(value) for key, value in obj.items()}