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SSL_GET_SESSION(3)                  OpenSSL                 SSL_GET_SESSION(3)
NAME
       SSL_get_session, SSL_get0_session, SSL_get1_session - retrieve TLS/SSL
       session data
SYNOPSIS
        #include <openssl/ssl.h>
        SSL_SESSION *SSL_get_session(const SSL *ssl);
        SSL_SESSION *SSL_get0_session(const SSL *ssl);
        SSL_SESSION *SSL_get1_session(SSL *ssl);
DESCRIPTION
       SSL_get_session() returns a pointer to the SSL_SESSION actually used in
       ssl. The reference count of the SSL_SESSION is not incremented, so that
       the pointer can become invalid by other operations.
       SSL_get0_session() is the same as SSL_get_session().
       SSL_get1_session() is the same as SSL_get_session(), but the reference
       count of the SSL_SESSION is incremented by one.
NOTES
       The ssl session contains all information required to re-establish the
       connection without a full handshake for SSL versions up to and
       including TLSv1.2. In TLSv1.3 the same is true, but sessions are
       established after the main handshake has occurred. The server will send
       the session information to the client at a time of its choosing, which
       may be some while after the initial connection is established (or
       never). Calling these functions on the client side in TLSv1.3 before
       the session has been established will still return an SSL_SESSION
       object but that object cannot be used for resuming the session. See
       SSL_SESSION_is_resumable(3) for information on how to determine whether
       an SSL_SESSION object can be used for resumption or not.
       Additionally, in TLSv1.3, a server can send multiple messages that
       establish a session for a single connection. In that case the above
       functions will only return information on the last session that was
       received.
       The preferred way for applications to obtain a resumable SSL_SESSION
       object is to use a new session callback as described in
       SSL_CTX_sess_set_new_cb(3).  The new session callback is only invoked
       when a session is actually established, so this avoids the problem
       described above where an application obtains an SSL_SESSION object that
       cannot be used for resumption in TLSv1.3. It also enables applications
       to obtain information about all sessions sent by the server.
       A session will be automatically removed from the session cache and
       marked as non-resumable if the connection is not closed down cleanly,
       e.g. if a fatal error occurs on the connection or SSL_shutdown(3) is
       not called prior to SSL_free(3).
       In TLSv1.3 it is recommended that each SSL_SESSION object is only used
       for resumption once.
       SSL_get0_session() returns a pointer to the actual session. As the
       reference counter is not incremented, the pointer is only valid while
       the connection is in use. If SSL_clear(3) or SSL_free(3) is called, the
       session may be removed completely (if considered bad), and the pointer
       obtained will become invalid. Even if the session is valid, it can be
       removed at any time due to timeout during SSL_CTX_flush_sessions(3).
       If the data is to be kept, SSL_get1_session() will increment the
       reference count, so that the session will not be implicitly removed by
       other operations but stays in memory. In order to remove the session
       SSL_SESSION_free(3) must be explicitly called once to decrement the
       reference count again.
       SSL_SESSION objects keep internal link information about the session
       cache list, when being inserted into one SSL_CTX object's session
       cache.  One SSL_SESSION object, regardless of its reference count, must
       therefore only be used with one SSL_CTX object (and the SSL objects
       created from this SSL_CTX object).
RETURN VALUES
       The following return values can occur:
       NULL
           There is no session available in ssl.
       Pointer to an SSL_SESSION
           The return value points to the data of an SSL session.
SEE ALSO
       ssl(7), SSL_free(3), SSL_clear(3), SSL_SESSION_free(3)
COPYRIGHT
       Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved.
       Licensed under the OpenSSL license (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
       <https://www.openssl.org/source/license.html>;.
1.1.1k                            2021-03-25                SSL_GET_SESSION(3)