SSL_client_version, SSL_get_version, SSL_is_dtls, SSL_version - get the protocol
  information of a connection
 #include <openssl/ssl.h>
 int SSL_client_version(const SSL *s);
 const char *SSL_get_version(const SSL *ssl);
 int SSL_is_dtls(const SSL *ssl);
 int SSL_version(const SSL *s);
SSL_client_version() returns the numeric protocol version advertised by
  the client in the legacy_version field of the ClientHello when initiating the
  connection. Note that, for TLS, this value will never indicate a version
  greater than TLSv1.2 even if TLSv1.3 is subsequently negotiated.
  SSL_get_version() returns the name of the protocol used for the
  connection. SSL_version() returns the numeric protocol version used for
  the connection. They should only be called after the initial handshake has
  been completed. Prior to that the results returned from these functions may be
  unreliable.
SSL_is_dtls() returns one if the connection is using DTLS,
    zero if not.
SSL_get_version() returns one of the following strings:
  - SSLv3
- The connection uses the SSLv3 protocol.
- TLSv1
- The connection uses the TLSv1.0 protocol.
- TLSv1.1
- The connection uses the TLSv1.1 protocol.
- TLSv1.2
- The connection uses the TLSv1.2 protocol.
- TLSv1.3
- The connection uses the TLSv1.3 protocol.
- unknown
- This indicates an unknown protocol version.
SSL_version() and SSL_client_version() return an
    integer which could include any of the following:
  - SSL3_VERSION
- The connection uses the SSLv3 protocol.
- TLS1_VERSION
- The connection uses the TLSv1.0 protocol.
- TLS1_1_VERSION
- The connection uses the TLSv1.1 protocol.
- TLS1_2_VERSION
- The connection uses the TLSv1.2 protocol.
- TLS1_3_VERSION
- The connection uses the TLSv1.3 protocol (never returned for
      SSL_client_version()).
The SSL_is_dtls() function was added in OpenSSL 1.1.0.
Copyright 2001-2018 The OpenSSL Project Authors. All Rights Reserved.Licensed under the Apache License 2.0 (the "License").
    You may not use this file except in compliance with the License. You can
    obtain a copy in the file LICENSE in the source distribution or at
    <https://www.openssl.org/source/license.html>.