@UnstableApi
    public ServerBuilder successFunction(SuccessFunction successFunction) {
        virtualHostTemplate.successFunction(requireNonNull(successFunction, "successFunction"));
        return this;
    }
Sets a {@link SuccessFunction} that determines whether a request was handled successfully or not.
If unspecified, {@link SuccessFunction#ofDefault()} is used.
core/src/main/java/com/linecorp/armeria/server/ServerBuilder.java