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.\"
.IX Title "SSL_CTX_sess_set_get_cb 3"
.TH SSL_CTX_sess_set_get_cb 3 2019-12-20 1.0.2u OpenSSL
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH 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
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 1
\& #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 *, 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, unsigned char *data, int len, int *copy);
\&
\& int (*new_session_cb)(struct ssl_st *ssl, SSL_SESSION *sess);
\& void (*remove_session_cb)(struct ssl_ctx_st *ctx, SSL_SESSION *sess);
\& SSL_SESSION *(*get_session_cb)(struct ssl_st *ssl, unsigned char *data,
\&               int len, int *copy);
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
\&\fBSSL_CTX_sess_set_new_cb()\fR sets the callback function, which is automatically
called whenever a new session was negotiated.
.PP
\&\fBSSL_CTX_sess_set_remove_cb()\fR sets the callback function, which is
automatically called whenever a session is removed by the SSL engine,
because it is considered faulty or the session has become obsolete because
of exceeding the timeout value.
.PP
\&\fBSSL_CTX_sess_set_get_cb()\fR sets the callback function which is called,
whenever a SSL/TLS client proposed to resume a session but the session
could not be found in the internal session cache (see
\&\fBSSL_CTX_set_session_cache_mode\fR\|(3)).
(SSL/TLS server only.)
.PP
\&\fBSSL_CTX_sess_get_new_cb()\fR, \fBSSL_CTX_sess_get_remove_cb()\fR, and
\&\fBSSL_CTX_sess_get_get_cb()\fR allow to retrieve the function pointers of the
provided callback functions. If a callback function has not been set,
the NULL pointer is returned.
.SH NOTES
.IX Header "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
\&\fBd2i_SSL_SESSION\fR\|(3) interface.
.PP
The \fBnew_session_cb()\fR is called, whenever a new session has been negotiated
and session caching is enabled (see
\&\fBSSL_CTX_set_session_cache_mode\fR\|(3)).
The \fBnew_session_cb()\fR is passed the \fBssl\fR connection and the ssl session
\&\fBsess\fR. If the callback returns \fB0\fR, the session will be immediately
removed again.
.PP
The \fBremove_session_cb()\fR is called, whenever the SSL engine removes a session
from the internal cache. This happens 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
\&\fBSSL_CTX_free\fR\|(3) is called. The \fBremove_session_cb()\fR is passed
the \fBctx\fR and the ssl session \fBsess\fR. It does not provide any feedback.
.PP
The \fBget_session_cb()\fR is only called on SSL/TLS servers with the session id
proposed by the client. The \fBget_session_cb()\fR is always called, also when
session caching was disabled. The \fBget_session_cb()\fR is passed the
\&\fBssl\fR connection, the session id of length \fBlength\fR at the memory location
\&\fBdata\fR. With the parameter \fBcopy\fR the callback can require the
SSL engine to increment the reference count of the SSL_SESSION object,
Normally the reference count is not incremented and therefore the
session must not be explicitly freed with
\&\fBSSL_SESSION_free\fR\|(3).
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBssl\fR\|(3), \fBd2i_SSL_SESSION\fR\|(3),
\&\fBSSL_CTX_set_session_cache_mode\fR\|(3),
\&\fBSSL_CTX_flush_sessions\fR\|(3),
\&\fBSSL_SESSION_free\fR\|(3),
\&\fBSSL_CTX_free\fR\|(3)