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SSL_CTX_sess_set_get_cb(3) OpenSSL SSL_CTX_sess_set_get_cb(3)
NAME
SSL_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
LIBRARY
libcrypto, -lcrypto
SYNOPSIS
#include <openssl/ssl.h>
void SSL_CTX_sess_set_new_cb(SSL_CTX *ctx,
int (*new_session_cb)(SSL *, SSL_SESSION *));
void SSL_CTX_sess_set_remove_cb(SSL_CTX *ctx,
void (*remove_session_cb)(SSL_CTX *ctx,
SSL_SESSION *));
void SSL_CTX_sess_set_get_cb(SSL_CTX *ctx,
SSL_SESSION (*get_session_cb)(SSL *,
const unsigned char *,
int, int *));
int (*SSL_CTX_sess_get_new_cb(SSL_CTX *ctx))(struct ssl_st *ssl,
SSL_SESSION *sess);
void (*SSL_CTX_sess_get_remove_cb(SSL_CTX *ctx))(struct ssl_ctx_st *ctx,
SSL_SESSION *sess);
SSL_SESSION *(*SSL_CTX_sess_get_get_cb(SSL_CTX *ctx))(struct ssl_st *ssl,
const unsigned char *data,
int len, int *copy);
DESCRIPTION
SSL_CTX_sess_set_new_cb() sets the callback function that is called
whenever a new session was negotiated.
SSL_CTX_sess_set_remove_cb() sets the callback function that is called
whenever a session is removed by the SSL engine. For example, this can
occur because a session is considered faulty or has become obsolete
because of exceeding the timeout value.
SSL_CTX_sess_set_get_cb() sets the callback function that is called
whenever a TLS client proposed to resume a session but the session
could not be found in the internal session cache (see
SSL_CTX_set_session_cache_mode(3)). (TLS server only.)
SSL_CTX_sess_get_new_cb(), SSL_CTX_sess_get_remove_cb(), and
SSL_CTX_sess_get_get_cb() retrieve the function pointers set by the
corresponding set callback functions. If a callback function has not
been set, the NULL pointer is returned.
NOTES
In order to allow external session caching, synchronization with the
internal session cache is realized via callback functions. Inside these
callback functions, session can be saved to disk or put into a database
using the d2i_SSL_SESSION(3) interface.
The new_session_cb() is called whenever a new session has been
negotiated and session caching is enabled (see
SSL_CTX_set_session_cache_mode(3)). The new_session_cb() is passed the
ssl connection and the nascent ssl session sess. Since sessions are
reference-counted objects, the reference count on the session is
incremented before the callback, on behalf of the application. If the
callback returns 0, the session will be immediately removed from the
internal cache and the reference count released. If the callback
returns 1, the application retains the reference (for an entry in the
application-maintained "external session cache"), and is responsible
for calling SSL_SESSION_free() when the session reference is no longer
in use.
Note that in TLSv1.3, sessions are established after the main handshake
has completed. The server decides when to send the client the session
information and this may occur some time after the end of the handshake
(or not at all). This means that applications should expect the
new_session_cb() function to be invoked during the handshake (for <=
TLSv1.2) or after the handshake (for TLSv1.3). It is also possible in
TLSv1.3 for multiple sessions to be established with a single
connection. In these case the new_session_cb() function will be invoked
multiple times.
In TLSv1.3 it is recommended that each SSL_SESSION object is only used
for resumption once. One way of enforcing that is for applications to
call SSL_CTX_remove_session(3) after a session has been used.
The remove_session_cb() is called whenever the SSL engine removes a
session from the internal cache. This can happen when the session is
removed because it is expired or when a connection was not shutdown
cleanly. It also happens for all sessions in the internal session cache
when SSL_CTX_free(3) is called. The remove_session_cb() is passed the
ctx and the ssl session sess. It does not provide any feedback.
The get_session_cb() is only called on SSL/TLS servers, and is given
the session id proposed by the client. The get_session_cb() is always
called, even when session caching was disabled. The get_session_cb() is
passed the ssl connection and the session id of length length at the
memory location data. By setting the parameter copy to 1, the callback
can require the SSL engine to increment the reference count of the
SSL_SESSION object; setting copy to 0 causes the reference count to
remain unchanged. If the get_session_cb() does not write to copy, the
reference count is incremented and the session must be explicitly freed
with SSL_SESSION_free(3).
RETURN VALUES
SSL_CTX_sess_get_new_cb(), SSL_CTX_sess_get_remove_cb() and
SSL_CTX_sess_get_get_cb() return different callback function pointers
respectively.
SEE ALSO
ssl(7), d2i_SSL_SESSION(3), SSL_CTX_set_session_cache_mode(3),
SSL_CTX_flush_sessions(3), SSL_SESSION_free(3), SSL_CTX_free(3)
COPYRIGHT
Copyright 2001-2020 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (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>.
3.0.12 2023-05-07 SSL_CTX_sess_set_get_cb(3)