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SSL_CTX_SET_SESSION_CACHE_MODE(3)   OpenSSL  SSL_CTX_SET_SESSION_CACHE_MODE(3)

NAME
       SSL_CTX_set_session_cache_mode, SSL_CTX_get_session_cache_mode -
       enable/disable session caching

SYNOPSIS
	#include <openssl/ssl.h>

	long SSL_CTX_set_session_cache_mode(SSL_CTX ctx, long mode);
	long SSL_CTX_get_session_cache_mode(SSL_CTX ctx);

DESCRIPTION
       SSL_CTX_set_session_cache_mode()	enables/disables session caching by
       setting the operational mode for	ctx to <mode>.

       SSL_CTX_get_session_cache_mode()	returns	the currently used cache mode.

NOTES
       The OpenSSL library can store/retrieve SSL/TLS sessions for later
       reuse.  The sessions can	be held	in memory for each ctx,	if more	than
       one SSL_CTX object is being maintained, the sessions are	unique for
       each SSL_CTX object.

       In order	to reuse a session, a client must send the session's id	to the
       server. It can only send	exactly	one id.	 The server then either	agrees
       to reuse	the session or it starts a full	handshake (to create a new
       session).

       A server	will look up the session in its	internal session storage. If
       the session is not found	in internal storage or lookups for the
       internal	storage	have been deactivated
       (SSL_SESS_CACHE_NO_INTERNAL_LOOKUP), the	server will try	the external
       storage if available.

       Since a client may try to reuse a session intended for use in a
       different context, the session id context must be set by	the server
       (see SSL_CTX_set_session_id_context(3)).

       The following session cache modes and modifiers are available:

       SSL_SESS_CACHE_OFF
	   No session caching for client or server takes place.

       SSL_SESS_CACHE_CLIENT
	   Client sessions are added to	the session cache. As there is no
	   reliable way	for the	OpenSSL	library	to know	whether	a session
	   should be reused or which session to	choose (due to the abstract
	   BIO layer the SSL engine does not have details about	the
	   connection),	the application	must select the	session	to be reused
	   by using the	SSL_set_session(3) function. This option is not
	   activated by	default.

       SSL_SESS_CACHE_SERVER
	   Server sessions are added to	the session cache. When	a client
	   proposes a session to be reused, the	server looks for the
	   corresponding session in (first) the	internal session cache (unless
	   SSL_SESS_CACHE_NO_INTERNAL_LOOKUP is	set), then (second) in the
	   external cache if available.	If the session is found, the server
	   will	try to reuse the session.  This	is the default.

       SSL_SESS_CACHE_BOTH
	   Enable both SSL_SESS_CACHE_CLIENT and SSL_SESS_CACHE_SERVER at the
	   same	time.

       SSL_SESS_CACHE_NO_AUTO_CLEAR
	   Normally the	session	cache is checked for expired sessions every
	   255 connections using the SSL_CTX_flush_sessions(3) function. Since
	   this	may lead to a delay which cannot be controlled,	the automatic
	   flushing may	be disabled and	SSL_CTX_flush_sessions(3) can be
	   called explicitly by	the application.

       SSL_SESS_CACHE_NO_INTERNAL_LOOKUP
	   By setting this flag, session-resume	operations in an SSL/TLS
	   server will not automatically look up sessions in the internal
	   cache, even if sessions are automatically stored there. If external
	   session caching callbacks are in use, this flag guarantees that all
	   lookups are directed	to the external	cache.	As automatic lookup
	   only	applies	for SSL/TLS servers, the flag has no effect on
	   clients.

       SSL_SESS_CACHE_NO_INTERNAL_STORE
	   Depending on	the presence of	SSL_SESS_CACHE_CLIENT and/or
	   SSL_SESS_CACHE_SERVER, sessions negotiated in an SSL/TLS handshake
	   may be cached for possible reuse.  Normally a new session is	added
	   to the internal cache as well as any	external session caching
	   (callback) that is configured for the SSL_CTX. This flag will
	   prevent sessions being stored in the	internal cache (though the
	   application can add them manually using SSL_CTX_add_session(3)).
	   Note: in any	SSL/TLS	servers	where external caching is configured,
	   any successful session lookups in the external cache	(ie. for
	   session-resume requests) would normally be copied into the local
	   cache before	processing continues - this flag prevents these
	   additions to	the internal cache as well.

       SSL_SESS_CACHE_NO_INTERNAL
	   Enable both SSL_SESS_CACHE_NO_INTERNAL_LOOKUP and
	   SSL_SESS_CACHE_NO_INTERNAL_STORE at the same	time.

       The default mode	is SSL_SESS_CACHE_SERVER.

RETURN VALUES
       SSL_CTX_set_session_cache_mode()	returns	the previously set cache mode.

       SSL_CTX_get_session_cache_mode()	returns	the currently set cache	mode.

SEE ALSO
       ssl(7), SSL_set_session(3), SSL_session_reused(3),
       SSL_CTX_add_session(3), SSL_CTX_sess_number(3),
       SSL_CTX_sess_set_cache_size(3), SSL_CTX_sess_set_get_cb(3),
       SSL_CTX_set_session_id_context(3), SSL_CTX_set_timeout(3),
       SSL_CTX_flush_sessions(3)

COPYRIGHT
       Copyright 2001-2016 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>.

1.1.1a				  2018-11-20 SSL_CTX_SET_SESSION_CACHE_MODE(3)

NAME | SYNOPSIS | DESCRIPTION | NOTES | RETURN VALUES | SEE ALSO | COPYRIGHT

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