+/*-
+ * The servername extension is treated as follows:
+ *
+ * - Only the hostname type is supported with a maximum length of 255.
+ * - The servername is rejected if too long or if it contains zeros,
+ * in which case an fatal alert is generated.
+ * - The servername field is maintained together with the session cache.
+ * - When a session is resumed, the servername call back invoked in order
+ * to allow the application to position itself to the right context.
+ * - The servername is acknowledged if it is new for a session or when
+ * it is identical to a previously used for the same session.
+ * Applications can control the behaviour. They can at any time
+ * set a 'desirable' servername for a new SSL object. This can be the
+ * case for example with HTTPS when a Host: header field is received and
+ * a renegotiation is requested. In this case, a possible servername
+ * presented in the new client hello is only acknowledged if it matches
+ * the value of the Host: field.
+ * - Applications must use SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION
+ * if they provide for changing an explicit servername context for the
+ * session, i.e. when the session has been established with a servername
+ * extension.
+ * - On session reconnect, the servername extension may be absent.
+ */
+int tls_parse_ctos_server_name(SSL *s, PACKET *pkt, int *al)