This is a legacy API retained for backwards compatibility. When possible, you should use
sni_callback instead. The given server_name_callback is similar to sni_callback, except that when the server hostname is an IDN-encoded internationalized domain name, the server_name_callback receives a decoded U-label (
If there is an decoding error on the server name, the TLS connection will terminate with an
ALERT_DESCRIPTION_INTERNAL_ERROR fatal TLS alert message to the client.
New in version 3.4.