mongoose/docs/c-api/net.h/mg_event_handler_t.md

title	decl_name	symbol_kind	signature
mg_event_handler_t	mg_event_handler_t	typedef	typedef void (*mg_event_handler_t)(struct mg_connection *, int ev, void *);

Callback function (event handler) prototype. Must be defined by the user. Mongoose calls the event handler, passing the events defined below.