1SSL_GET_SESSION(3)                  OpenSSL                 SSL_GET_SESSION(3)
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NAME

6       SSL_get_session, SSL_get0_session, SSL_get1_session - retrieve TLS/SSL
7       session data
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SYNOPSIS

10        #include <openssl/ssl.h>
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12        SSL_SESSION *SSL_get_session(const SSL *ssl);
13        SSL_SESSION *SSL_get0_session(const SSL *ssl);
14        SSL_SESSION *SSL_get1_session(SSL *ssl);
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DESCRIPTION

17       SSL_get_session() returns a pointer to the SSL_SESSION actually used in
18       ssl. The reference count of the SSL_SESSION is not incremented, so that
19       the pointer can become invalid by other operations.
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21       SSL_get0_session() is the same as SSL_get_session().
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23       SSL_get1_session() is the same as SSL_get_session(), but the reference
24       count of the SSL_SESSION is incremented by one.
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NOTES

27       The ssl session contains all information required to re-establish the
28       connection without a full handshake for SSL versions up to and
29       including TLSv1.2. In TLSv1.3 the same is true, but sessions are
30       established after the main handshake has occurred. The server will send
31       the session information to the client at a time of its choosing, which
32       may be some while after the initial connection is established (or
33       never). Calling these functions on the client side in TLSv1.3 before
34       the session has been established will still return an SSL_SESSION
35       object but that object cannot be used for resuming the session. See
36       SSL_SESSION_is_resumable(3) for information on how to determine whether
37       an SSL_SESSION object can be used for resumption or not.
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39       Additionally, in TLSv1.3, a server can send multiple messages that
40       establish a session for a single connection. In that case the above
41       functions will only return information on the last session that was
42       received.
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44       The preferred way for applications to obtain a resumable SSL_SESSION
45       object is to use a new session callback as described in
46       SSL_CTX_sess_set_new_cb(3).  The new session callback is only invoked
47       when a session is actually established, so this avoids the problem
48       described above where an application obtains an SSL_SESSION object that
49       cannot be used for resumption in TLSv1.3. It also enables applications
50       to obtain information about all sessions sent by the server.
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52       A session will be automatically removed from the session cache and
53       marked as non-resumable if the connection is not closed down cleanly,
54       e.g. if a fatal error occurs on the connection or SSL_shutdown(3) is
55       not called prior to SSL_free(3).
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57       In TLSv1.3 it is recommended that each SSL_SESSION object is only used
58       for resumption once.
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60       SSL_get0_session() returns a pointer to the actual session. As the
61       reference counter is not incremented, the pointer is only valid while
62       the connection is in use. If SSL_clear(3) or SSL_free(3) is called, the
63       session may be removed completely (if considered bad), and the pointer
64       obtained will become invalid. Even if the session is valid, it can be
65       removed at any time due to timeout during SSL_CTX_flush_sessions(3).
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67       If the data is to be kept, SSL_get1_session() will increment the
68       reference count, so that the session will not be implicitly removed by
69       other operations but stays in memory. In order to remove the session
70       SSL_SESSION_free(3) must be explicitly called once to decrement the
71       reference count again.
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73       SSL_SESSION objects keep internal link information about the session
74       cache list, when being inserted into one SSL_CTX object's session
75       cache.  One SSL_SESSION object, regardless of its reference count, must
76       therefore only be used with one SSL_CTX object (and the SSL objects
77       created from this SSL_CTX object).
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RETURN VALUES

80       The following return values can occur:
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82       NULL
83           There is no session available in ssl.
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85       Pointer to an SSL_SESSION
86           The return value points to the data of an SSL session.
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SEE ALSO

89       ssl(7), SSL_free(3), SSL_clear(3), SSL_SESSION_free(3)
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92       Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved.
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94       Licensed under the OpenSSL license (the "License").  You may not use
95       this file except in compliance with the License.  You can obtain a copy
96       in the file LICENSE in the source distribution or at
97       <https://www.openssl.org/source/license.html>.
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1011.1.1l                            2021-09-15                SSL_GET_SESSION(3)
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