code: func HandleContext(ctx context.Context, handler Handler) {
  	format, _ := os.LookupEnv("FN_FORMAT")
  	if format != "" && format != "http-stream" {
  		log.Fatal("only http-stream format is supported, please set function.format=http-stream against your fn service")
  	}
  	path := os.Getenv("FN_LISTENER")
  	startHTTPServer(ctx, handler, path)
  }
docs: // HandleContext works the same as Handle, but takes a context that will
  // exit the handler loop when canceled/timed out.