Cryptography and SSL/TLS Toolkit



SSL_SESSION_get0_hostname, SSL_SESSION_set1_hostname, SSL_SESSION_get0_alpn_selected, SSL_SESSION_set1_alpn_selected - get and set SNI and ALPN data associated with a session


#include <openssl/ssl.h>

const char *SSL_SESSION_get0_hostname(const SSL_SESSION *s);
int SSL_SESSION_set1_hostname(SSL_SESSION *s, const char *hostname);

void SSL_SESSION_get0_alpn_selected(const SSL_SESSION *s,
                                    const unsigned char **alpn,
                                    size_t *len);
int SSL_SESSION_set1_alpn_selected(SSL_SESSION *s, const unsigned char *alpn,
                                   size_t len);


SSL_SESSION_get0_hostname() retrieves the SNI value that was sent by the client when the session was created if it was accepted by the server and TLSv1.2 or below was negotiated. Otherwise NULL is returned. Note that in TLSv1.3 the SNI hostname is negotiated with each handshake including resumption handshakes and is therefore never associated with the session.

The value returned is a pointer to memory maintained within s and should not be free'd.

SSL_SESSION_set1_hostname() sets the SNI value for the hostname to a copy of the string provided in hostname.

SSL_SESSION_get0_alpn_selected() retrieves the selected ALPN protocol for this session and its associated length in bytes. The returned value of *alpn is a pointer to memory maintained within s and should not be free'd.

SSL_SESSION_set1_alpn_selected() sets the ALPN protocol for this session to the value in alpn which should be of length len bytes. A copy of the input value is made, and the caller retains ownership of the memory pointed to by alpn.


SSL_SESSION_get0_hostname() returns either a string or NULL based on if there is the SNI value sent by client.

SSL_SESSION_set1_hostname() returns 1 on success or 0 on error.

SSL_SESSION_set1_alpn_selected() returns 1 on success or 0 on error.


ssl(7), d2i_SSL_SESSION(3), SSL_SESSION_get_time(3), SSL_SESSION_free(3)


The SSL_SESSION_set1_hostname(), SSL_SESSION_get0_alpn_selected() and SSL_SESSION_set1_alpn_selected() functions were added in OpenSSL 1.1.1.

Copyright 2016-2020 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