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SSL_GET_SESSION(3) OpenSSL SSL_GET_SESSION(3)
SSL_get_session, SSL_get0_session, SSL_get1_session - retrieve TLS/SSL
SSL_SESSION *SSL_get_session(const SSL *ssl);
SSL_SESSION *SSL_get0_session(const SSL *ssl);
SSL_SESSION *SSL_get1_session(SSL *ssl);
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.
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, on the
client side, the above functions will only return information on the
last session that was received. On the server side they will only
return information on the last session that was sent, or if no session
tickets were sent then the session for the current connection.
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).
The following return values can occur:
There is no session available in ssl.
Pointer to an SSL_SESSION
The return value points to the data of an SSL session.
ssl(7), SSL_free(3), SSL_clear(3), SSL_SESSION_free(3)
Copyright 2000-2021 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
1.1.1t 2023-02-07 SSL_GET_SESSION(3)