mongoose/docs/c-api/http.h/mg_printf_websocket_frame.md

title	decl_name	symbol_kind	signature
mg_printf_websocket_frame()	mg_printf_websocket_frame	func	void mg_printf_websocket_frame(struct mg_connection *nc, int op_and_flags, const char *fmt, ...);

Sends WebSocket frame to the remote end.

Like mg_send_websocket_frame(), but allows to create formatted messages with printf()-like semantics.