1=pod 2 3=head1 NAME 4 5SSL_get_handshake_rtt 6- get round trip time for SSL Handshake 7 8=head1 SYNOPSIS 9 10 #include <openssl/ssl.h> 11 12 int SSL_get_handshake_rtt(const SSL *s, uint64_t *rtt); 13 14=head1 DESCRIPTION 15 16SSL_get_handshake_rtt() retrieves the round-trip time (RTT) for I<ssl>. 17 18This metric is represented in microseconds (us) as a uint64_t data type. 19 20=head1 NOTES 21 22This metric is created by taking two timestamps during the handshake and 23providing the difference between these two times. 24 25When acting as the server, one timestamp is taken when the server is finished 26writing to the client. This is during the ServerFinished in TLS 1.3 and 27ServerHelloDone in TLS 1.2. The other timestamp is taken when the server is 28done reading the client's response. This is after the client has responded 29with ClientFinished. 30 31When acting as the client, one timestamp is taken when the client is finished 32writing the ClientHello and early data (if any). The other is taken when 33client is done reading the server's response. This is after ServerFinished in 34TLS 1.3 and after ServerHelloDone in TLS 1.2. 35 36In addition to network propagation delay and network stack overhead, this 37metric includes processing time on both endpoints, as this is based on TLS 38protocol-level messages and the TLS protocol is not designed to measure 39network timings. In some cases the processing time can be significant, 40especially when the processing includes asymmetric cryptographic operations. 41 42=head1 RETURN VALUES 43 44Returns 1 if the TLS handshake RTT is successfully retrieved. 45Returns 0 if the TLS handshake RTT cannot be determined yet. 46Returns -1 if, while retrieving the TLS handshake RTT, an error occurs. 47 48=head1 HISTORY 49 50This function was added in OpenSSL 3.2. 51 52=head1 COPYRIGHT 53 54Copyright 2023-2024 The OpenSSL Project Authors. All Rights Reserved. 55 56Licensed under the Apache License 2.0 (the "License"). You may not use 57this file except in compliance with the License. You can obtain a copy 58in the file LICENSE in the source distribution or at 59L<https://www.openssl.org/source/license.html>. 60 61=cut 62