1=pod
2
3=head1 NAME
4
5SSL_CTX_sess_set_new_cb, SSL_CTX_sess_set_remove_cb, SSL_CTX_sess_set_get_cb, SSL_CTX_sess_get_new_cb, SSL_CTX_sess_get_remove_cb, SSL_CTX_sess_get_get_cb - provide callback functions for server side external session caching
6
7=head1 SYNOPSIS
8
9 #include <openssl/ssl.h>
10
11 void SSL_CTX_sess_set_new_cb(SSL_CTX *ctx,
12                              int (*new_session_cb)(SSL *, SSL_SESSION *));
13 void SSL_CTX_sess_set_remove_cb(SSL_CTX *ctx,
14                                 void (*remove_session_cb)(SSL_CTX *ctx,
15                                                           SSL_SESSION *));
16 void SSL_CTX_sess_set_get_cb(SSL_CTX *ctx,
17                              SSL_SESSION (*get_session_cb)(SSL *,
18                                                            const unsigned char *,
19                                                            int, int *));
20
21 int (*SSL_CTX_sess_get_new_cb(SSL_CTX *ctx))(struct ssl_st *ssl,
22                                              SSL_SESSION *sess);
23 void (*SSL_CTX_sess_get_remove_cb(SSL_CTX *ctx))(struct ssl_ctx_st *ctx,
24                                                  SSL_SESSION *sess);
25 SSL_SESSION *(*SSL_CTX_sess_get_get_cb(SSL_CTX *ctx))(struct ssl_st *ssl,
26                                                       const unsigned char *data,
27                                                       int len, int *copy);
28
29=head1 DESCRIPTION
30
31SSL_CTX_sess_set_new_cb() sets the callback function, which is automatically
32called whenever a new session was negotiated.
33
34SSL_CTX_sess_set_remove_cb() sets the callback function, which is
35automatically called whenever a session is removed by the SSL engine,
36because it is considered faulty or the session has become obsolete because
37of exceeding the timeout value.
38
39SSL_CTX_sess_set_get_cb() sets the callback function which is called,
40whenever a SSL/TLS client proposed to resume a session but the session
41could not be found in the internal session cache (see
42L<SSL_CTX_set_session_cache_mode(3)>).
43(SSL/TLS server only.)
44
45SSL_CTX_sess_get_new_cb(), SSL_CTX_sess_get_remove_cb(), and
46SSL_CTX_sess_get_get_cb() retrieve the function pointers set by the
47corresponding set callback functions. If a callback function has not been
48set, the NULL pointer is returned.
49
50=head1 NOTES
51
52In order to allow external session caching, synchronization with the internal
53session cache is realized via callback functions. Inside these callback
54functions, session can be saved to disk or put into a database using the
55L<d2i_SSL_SESSION(3)> interface.
56
57The new_session_cb() is called, whenever a new session has been negotiated
58and session caching is enabled (see
59L<SSL_CTX_set_session_cache_mode(3)>).
60The new_session_cb() is passed the B<ssl> connection and the ssl session
61B<sess>. If the callback returns B<0>, the session will be immediately
62removed again. Note that in TLSv1.3, sessions are established after the main
63handshake has completed. The server decides when to send the client the session
64information and this may occur some time after the end of the handshake (or not
65at all). This means that applications should expect the new_session_cb()
66function to be invoked during the handshake (for <= TLSv1.2) or after the
67handshake (for TLSv1.3). It is also possible in TLSv1.3 for multiple sessions to
68be established with a single connection. In these case the new_session_cb()
69function will be invoked multiple times.
70
71In TLSv1.3 it is recommended that each SSL_SESSION object is only used for
72resumption once. One way of enforcing that is for applications to call
73L<SSL_CTX_remove_session(3)> after a session has been used.
74
75The remove_session_cb() is called, whenever the SSL engine removes a session
76from the internal cache. This happens when the session is removed because
77it is expired or when a connection was not shutdown cleanly. It also happens
78for all sessions in the internal session cache when
79L<SSL_CTX_free(3)> is called. The remove_session_cb() is passed
80the B<ctx> and the ssl session B<sess>. It does not provide any feedback.
81
82The get_session_cb() is only called on SSL/TLS servers with the session id
83proposed by the client. The get_session_cb() is always called, also when
84session caching was disabled. The get_session_cb() is passed the
85B<ssl> connection, the session id of length B<length> at the memory location
86B<data>. With the parameter B<copy> the callback can require the
87SSL engine to increment the reference count of the SSL_SESSION object,
88Normally the reference count is not incremented and therefore the
89session must not be explicitly freed with
90L<SSL_SESSION_free(3)>.
91
92=head1 RETURN VALUES
93
94SSL_CTX_sess_get_new_cb(), SSL_CTX_sess_get_remove_cb() and SSL_CTX_sess_get_get_cb()
95return different callback function pointers respectively.
96
97=head1 SEE ALSO
98
99L<ssl(7)>, L<d2i_SSL_SESSION(3)>,
100L<SSL_CTX_set_session_cache_mode(3)>,
101L<SSL_CTX_flush_sessions(3)>,
102L<SSL_SESSION_free(3)>,
103L<SSL_CTX_free(3)>
104
105=head1 COPYRIGHT
106
107Copyright 2001-2018 The OpenSSL Project Authors. All Rights Reserved.
108
109Licensed under the OpenSSL license (the "License").  You may not use
110this file except in compliance with the License.  You can obtain a copy
111in the file LICENSE in the source distribution or at
112L<https://www.openssl.org/source/license.html>.
113
114=cut
115