diff --git a/WeChatFerry/spy/fill_response.h b/WeChatFerry/spy/fill_response.h
new file mode 100644
index 0000000..2cf1ddb
--- /dev/null
+++ b/WeChatFerry/spy/fill_response.h
@@ -0,0 +1,60 @@
+#pragma once
+
+#include <unordered_map>
+
+#include "log.hpp"
+#include "pb_encode.h"
+#include "pb_types.h"
+
+static const std::unordered_map<Functions, int> rpc_function_map
+    = { { Functions_FUNC_IS_LOGIN, Response_status_tag },
+        { Functions_FUNC_GET_SELF_WXID, Response_str_tag },
+        { Functions_FUNC_GET_USER_INFO, Response_ui_tag },
+        { Functions_FUNC_GET_MSG_TYPES, Response_types_tag },
+        { Functions_FUNC_GET_CONTACTS, Response_contacts_tag },
+        { Functions_FUNC_GET_DB_NAMES, Response_dbs_tag },
+        { Functions_FUNC_GET_DB_TABLES, Response_tables_tag },
+        { Functions_FUNC_GET_AUDIO_MSG, Response_str_tag },
+        { Functions_FUNC_SEND_TXT, Response_status_tag },
+        { Functions_FUNC_SEND_IMG, Response_status_tag },
+        { Functions_FUNC_SEND_FILE, Response_status_tag },
+        { Functions_FUNC_SEND_RICH_TXT, Response_status_tag },
+        { Functions_FUNC_SEND_PAT_MSG, Response_status_tag },
+        { Functions_FUNC_FORWARD_MSG, Response_status_tag },
+        { Functions_FUNC_SEND_EMOTION, Response_status_tag },
+        { Functions_FUNC_ENABLE_RECV_TXT, Response_status_tag },
+        { Functions_FUNC_DISABLE_RECV_TXT, Response_status_tag },
+        { Functions_FUNC_EXEC_DB_QUERY, Response_rows_tag },
+        { Functions_FUNC_REFRESH_PYQ, Response_status_tag },
+        { Functions_FUNC_DOWNLOAD_ATTACH, Response_status_tag },
+        { Functions_FUNC_RECV_TRANSFER, Response_status_tag },
+        { Functions_FUNC_REVOKE_MSG, Response_status_tag },
+        { Functions_FUNC_REFRESH_QRCODE, Response_str_tag },
+        { Functions_FUNC_DECRYPT_IMAGE, Response_str_tag },
+        { Functions_FUNC_EXEC_OCR, Response_ocr_tag },
+        { Functions_FUNC_ADD_ROOM_MEMBERS, Response_status_tag },
+        { Functions_FUNC_DEL_ROOM_MEMBERS, Response_status_tag },
+        { Functions_FUNC_INV_ROOM_MEMBERS, Response_status_tag } };
+
+template <Functions FuncType, typename AssignFunc> bool fill_response(uint8_t *out, size_t *len, AssignFunc assign)
+{
+    Response rsp = Response_init_default;
+    rsp.func     = FuncType;
+
+    auto it = rpc_function_map.find(FuncType);
+    if (it == rpc_function_map.end()) {
+        LOG_ERROR("Unknown function type: {}", FuncType);
+        return false;
+    }
+    rsp.which_msg = it->second;
+
+    assign(rsp);
+
+    pb_ostream_t stream = pb_ostream_from_buffer(out, *len);
+    if (!pb_encode(&stream, Response_fields, &rsp)) {
+        LOG_ERROR("Encoding failed: {}", PB_GET_ERROR(&stream));
+        return false;
+    }
+    *len = stream.bytes_written;
+    return true;
+}