1=pod 2 3=head1 NAME 4 5SSL_get_session, SSL_get0_session, SSL_get1_session - retrieve TLS/SSL session data 6 7=head1 SYNOPSIS 8 9 #include <openssl/ssl.h> 10 11 SSL_SESSION *SSL_get_session(const SSL *ssl); 12 SSL_SESSION *SSL_get0_session(const SSL *ssl); 13 SSL_SESSION *SSL_get1_session(SSL *ssl); 14 15=head1 DESCRIPTION 16 17SSL_get_session() returns a pointer to the B<SSL_SESSION> actually used in 18B<ssl>. The reference count of the B<SSL_SESSION> is not incremented, so 19that the pointer can become invalid by other operations. 20 21SSL_get0_session() is the same as SSL_get_session(). 22 23SSL_get1_session() is the same as SSL_get_session(), but the reference 24count of the B<SSL_SESSION> is incremented by one. 25 26=head1 NOTES 27 28The ssl session contains all information required to re-establish the 29connection without a full handshake for SSL versions up to and including 30TLSv1.2. In TLSv1.3 the same is true, but sessions are established after the 31main handshake has occurred. The server will send the session information to the 32client at a time of its choosing, which may be some while after the initial 33connection is established (or never). Calling these functions on the client side 34in TLSv1.3 before the session has been established will still return an 35SSL_SESSION object but that object cannot be used for resuming the session. See 36L<SSL_SESSION_is_resumable(3)> for information on how to determine whether an 37SSL_SESSION object can be used for resumption or not. 38 39Additionally, in TLSv1.3, a server can send multiple messages that establish a 40session for a single connection. In that case, on the client side, the above 41functions will only return information on the last session that was received. On 42the server side they will only return information on the last session that was 43sent, or if no session tickets were sent then the session for the current 44connection. 45 46The preferred way for applications to obtain a resumable SSL_SESSION object is 47to use a new session callback as described in L<SSL_CTX_sess_set_new_cb(3)>. 48The new session callback is only invoked when a session is actually established, 49so this avoids the problem described above where an application obtains an 50SSL_SESSION object that cannot be used for resumption in TLSv1.3. It also 51enables applications to obtain information about all sessions sent by the 52server. 53 54A session will be automatically removed from the session cache and marked as 55non-resumable if the connection is not closed down cleanly, e.g. if a fatal 56error occurs on the connection or L<SSL_shutdown(3)> is not called prior to 57L<SSL_free(3)>. 58 59In TLSv1.3 it is recommended that each SSL_SESSION object is only used for 60resumption once. 61 62SSL_get0_session() returns a pointer to the actual session. As the 63reference counter is not incremented, the pointer is only valid while 64the connection is in use. If L<SSL_clear(3)> or 65L<SSL_free(3)> is called, the session may be removed completely 66(if considered bad), and the pointer obtained will become invalid. Even 67if the session is valid, it can be removed at any time due to timeout 68during L<SSL_CTX_flush_sessions(3)>. 69 70If the data is to be kept, SSL_get1_session() will increment the reference 71count, so that the session will not be implicitly removed by other operations 72but stays in memory. In order to remove the session 73L<SSL_SESSION_free(3)> must be explicitly called once 74to decrement the reference count again. 75 76SSL_SESSION objects keep internal link information about the session cache 77list, when being inserted into one SSL_CTX object's session cache. 78One SSL_SESSION object, regardless of its reference count, must therefore 79only be used with one SSL_CTX object (and the SSL objects created 80from this SSL_CTX object). 81 82=head1 RETURN VALUES 83 84The following return values can occur: 85 86=over 4 87 88=item NULL 89 90There is no session available in B<ssl>. 91 92=item Pointer to an SSL_SESSION 93 94The return value points to the data of an SSL session. 95 96=back 97 98=head1 SEE ALSO 99 100L<ssl(7)>, L<SSL_free(3)>, 101L<SSL_clear(3)>, 102L<SSL_SESSION_free(3)> 103 104=head1 COPYRIGHT 105 106Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved. 107 108Licensed under the Apache License 2.0 (the "License"). You may not use 109this file except in compliance with the License. You can obtain a copy 110in the file LICENSE in the source distribution or at 111L<https://www.openssl.org/source/license.html>. 112 113=cut 114
