doc/man3/SSL_CTX_set_session_cache_mode.pod - third_party/openssl - Git at Google

 =pod

 =head1 NAME

 SSL_CTX_set_session_cache_mode, SSL_CTX_get_session_cache_mode - enable/disable session caching

 =head1 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);

 =head1 DESCRIPTION

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

 SSL_CTX_get_session_cache_mode() returns the currently used cache mode.

 =head1 NOTES

 The OpenSSL library can store/retrieve SSL/TLS sessions for later reuse.
 The sessions can be held in memory for each B<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
 L<SSL_CTX_set_session_id_context(3)>).

 The following session cache modes and modifiers are available:

 =over 4

 =item SSL_SESS_CACHE_OFF

 No session caching for client or server takes place.

 =item 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 L<SSL_set_session(3)>
 function. This option is not activated by default.

 =item 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.

 =item SSL_SESS_CACHE_BOTH

 Enable both SSL_SESS_CACHE_CLIENT and SSL_SESS_CACHE_SERVER at the same time.

 =item SSL_SESS_CACHE_NO_AUTO_CLEAR

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

 =item 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.

 =item 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 L<SSL_CTX_add_session(3)>). Note:
 in any SSL/TLS servers where external caching is configured, any successful
 session lookups in the external cache (i.e. 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.

 =item SSL_SESS_CACHE_NO_INTERNAL

 Enable both SSL_SESS_CACHE_NO_INTERNAL_LOOKUP and
 SSL_SESS_CACHE_NO_INTERNAL_STORE at the same time.

 =item SSL_SESS_CACHE_UPDATE_TIME

 Updates the timestamp of the session when it is used, increasing the lifespan
 of the session. The session timeout applies to last use, rather then creation
 time.

 =back

 The default mode is SSL_SESS_CACHE_SERVER.

 =head1 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.


 =head1 SEE ALSO

 L<ssl(7)>, L<SSL_set_session(3)>,
 L<SSL_session_reused(3)>,
 L<SSL_CTX_add_session(3)>,
 L<SSL_CTX_sess_number(3)>,
 L<SSL_CTX_sess_set_cache_size(3)>,
 L<SSL_CTX_sess_set_get_cb(3)>,
 L<SSL_CTX_set_session_id_context(3)>,
 L<SSL_CTX_set_timeout(3)>,
 L<SSL_CTX_flush_sessions(3)>

 =head1 COPYRIGHT

 Copyright 2001-2021 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
 L<https://www.openssl.org/source/license.html>.

 =cut
	=pod

	=head1 NAME

	SSL_CTX_set_session_cache_mode, SSL_CTX_get_session_cache_mode - enable/disable session caching

	=head1 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);

	=head1 DESCRIPTION

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

	SSL_CTX_get_session_cache_mode() returns the currently used cache mode.

	=head1 NOTES

	The OpenSSL library can store/retrieve SSL/TLS sessions for later reuse.
	The sessions can be held in memory for each B<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
	L<SSL_CTX_set_session_id_context(3)>).

	The following session cache modes and modifiers are available:

	=over 4

	=item SSL_SESS_CACHE_OFF

	No session caching for client or server takes place.

	=item 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 L<SSL_set_session(3)>
	function. This option is not activated by default.

	=item 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.

	=item SSL_SESS_CACHE_BOTH

	Enable both SSL_SESS_CACHE_CLIENT and SSL_SESS_CACHE_SERVER at the same time.

	=item SSL_SESS_CACHE_NO_AUTO_CLEAR

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

	=item 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.

	=item 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 L<SSL_CTX_add_session(3)>). Note:
	in any SSL/TLS servers where external caching is configured, any successful
	session lookups in the external cache (i.e. 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.

	=item SSL_SESS_CACHE_NO_INTERNAL

	Enable both SSL_SESS_CACHE_NO_INTERNAL_LOOKUP and
	SSL_SESS_CACHE_NO_INTERNAL_STORE at the same time.

	=item SSL_SESS_CACHE_UPDATE_TIME

	Updates the timestamp of the session when it is used, increasing the lifespan
	of the session. The session timeout applies to last use, rather then creation
	time.

	=back

	The default mode is SSL_SESS_CACHE_SERVER.

	=head1 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.


	=head1 SEE ALSO

	L<ssl(7)>, L<SSL_set_session(3)>,
	L<SSL_session_reused(3)>,
	L<SSL_CTX_add_session(3)>,
	L<SSL_CTX_sess_number(3)>,
	L<SSL_CTX_sess_set_cache_size(3)>,
	L<SSL_CTX_sess_set_get_cb(3)>,
	L<SSL_CTX_set_session_id_context(3)>,
	L<SSL_CTX_set_timeout(3)>,
	L<SSL_CTX_flush_sessions(3)>

	=head1 COPYRIGHT

	Copyright 2001-2021 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
	L<https://www.openssl.org/source/license.html>.

	=cut