1SSL_CTX_SESS_SET_GET_CB(3) OpenSSL SSL_CTX_SESS_SET_GET_CB(3)
2
6 SSL_CTX_sess_set_new_cb, SSL_CTX_sess_set_remove_cb,
7 SSL_CTX_sess_set_get_cb, SSL_CTX_sess_get_new_cb,
8 SSL_CTX_sess_get_remove_cb, SSL_CTX_sess_get_get_cb - provide callback
9 functions for server side external session caching
10
12 #include <openssl/ssl.h>
13 void SSL_CTX_sess_set_new_cb(SSL_CTX *ctx,
15 int (*new_session_cb)(SSL *, SSL_SESSION *));
16 void SSL_CTX_sess_set_remove_cb(SSL_CTX *ctx,
17 void (*remove_session_cb)(SSL_CTX *ctx,
18 SSL_SESSION *));
19 void SSL_CTX_sess_set_get_cb(SSL_CTX *ctx,
20 SSL_SESSION (*get_session_cb)(SSL *,
21 const unsigned char *,
22 int, int *));
23 int (*SSL_CTX_sess_get_new_cb(SSL_CTX *ctx))(struct ssl_st *ssl,
25 SSL_SESSION *sess);
26 void (*SSL_CTX_sess_get_remove_cb(SSL_CTX *ctx))(struct ssl_ctx_st *ctx,
27 SSL_SESSION *sess);
28 SSL_SESSION *(*SSL_CTX_sess_get_get_cb(SSL_CTX *ctx))(struct ssl_st *ssl,
29 const unsigned char *data,
30 int len, int *copy);
31
33 SSL_CTX_sess_set_new_cb() sets the callback function that is called
34 whenever a new session was negotiated.
35 SSL_CTX_sess_set_remove_cb() sets the callback function that is called
37 whenever a session is removed by the SSL engine. For example, this can
38 occur because a session is considered faulty or has become obsolete
39 because of exceeding the timeout value.
40 SSL_CTX_sess_set_get_cb() sets the callback function that is called
42 whenever a TLS client proposed to resume a session but the session
43 could not be found in the internal session cache (see
44 SSL_CTX_set_session_cache_mode(3)). (TLS server only.)
45 SSL_CTX_sess_get_new_cb(), SSL_CTX_sess_get_remove_cb(), and
47 SSL_CTX_sess_get_get_cb() retrieve the function pointers set by the
48 corresponding set callback functions. If a callback function has not
49 been set, the NULL pointer is returned.
50
52 In order to allow external session caching, synchronization with the
53 internal session cache is realized via callback functions. Inside these
54 callback functions, session can be saved to disk or put into a database
55 using the d2i_SSL_SESSION(3) interface.
56 The new_session_cb() is called whenever a new session has been
58 negotiated and session caching is enabled (see
59 SSL_CTX_set_session_cache_mode(3)). The new_session_cb() is passed the
60 ssl connection and the nascent ssl session sess. Since sessions are
61 reference-counted objects, the reference count on the session is
62 incremented before the callback, on behalf of the application. If the
63 callback returns 0, the session will be immediately removed from the
64 internal cache and the reference count released. If the callback
65 returns 1, the application retains the reference (for an entry in the
66 application-maintained "external session cache"), and is responsible
67 for calling SSL_SESSION_free() when the session reference is no longer
68 in use.
69 Note that in TLSv1.3, sessions are established after the main handshake
71 has completed. The server decides when to send the client the session
72 information and this may occur some time after the end of the handshake
73 (or not at all). This means that applications should expect the
74 new_session_cb() function to be invoked during the handshake (for <=
75 TLSv1.2) or after the handshake (for TLSv1.3). It is also possible in
76 TLSv1.3 for multiple sessions to be established with a single
77 connection. In these case the new_session_cb() function will be invoked
78 multiple times.
79 In TLSv1.3 it is recommended that each SSL_SESSION object is only used
81 for resumption once. One way of enforcing that is for applications to
82 call SSL_CTX_remove_session(3) after a session has been used.
83 The remove_session_cb() is called whenever the SSL engine removes a
85 session from the internal cache. This can happen when the session is
86 removed because it is expired or when a connection was not shutdown
87 cleanly. It also happens for all sessions in the internal session cache
88 when SSL_CTX_free(3) is called. The remove_session_cb() is passed the
89 ctx and the ssl session sess. It does not provide any feedback.
90 The get_session_cb() is only called on SSL/TLS servers, and is given
92 the session id proposed by the client. The get_session_cb() is always
93 called, even when session caching was disabled. The get_session_cb() is
94 passed the ssl connection and the session id of length length at the
95 memory location data. By setting the parameter copy to 1, the callback
96 can require the SSL engine to increment the reference count of the
97 SSL_SESSION object; setting copy to 0 causes the reference count to
98 remain unchanged. If the get_session_cb() does not write to copy, the
99 reference count is incremented and the session must be explicitly freed
100 with SSL_SESSION_free(3).
101
103 SSL_CTX_sess_get_new_cb(), SSL_CTX_sess_get_remove_cb() and
104 SSL_CTX_sess_get_get_cb() return different callback function pointers
105 respectively.
106
108 ssl(7), d2i_SSL_SESSION(3), SSL_CTX_set_session_cache_mode(3),
109 SSL_CTX_flush_sessions(3), SSL_SESSION_free(3), SSL_CTX_free(3)
110
112 Copyright 2001-2020 The OpenSSL Project Authors. All Rights Reserved.
113 Licensed under the OpenSSL license (the "License"). You may not use
115 this file except in compliance with the License. You can obtain a copy
116 in the file LICENSE in the source distribution or at
117 <https://www.openssl.org/source/license.html>.
1181.1.1i 2021-07-22 SSL_CTX_SESS_SET_GET_CB(3)