SSL_CTX_set_session_cache_mode.pod revision 89837
1=pod 2 3=head1 NAME 4 5SSL_CTX_set_session_cache_mode, SSL_CTX_get_session_cache_mode - enable/disable session caching 6 7=head1 SYNOPSIS 8 9 #include <openssl/ssl.h> 10 11 long SSL_CTX_set_session_cache_mode(SSL_CTX ctx, long mode); 12 long SSL_CTX_get_session_cache_mode(SSL_CTX ctx); 13 14=head1 DESCRIPTION 15 16SSL_CTX_set_session_cache_mode() enables/disables session caching 17by setting the operational mode for B<ctx> to <mode>. 18 19SSL_CTX_get_session_cache_mode() returns the currently used cache mode. 20 21=head1 NOTES 22 23The OpenSSL library can store/retrieve SSL/TLS sessions for later reuse. 24The sessions can be held in memory for each B<ctx>, if more than one 25SSL_CTX object is being maintained, the sessions are unique for each SSL_CTX 26object. 27 28In order to reuse a session, a client must send the session's id to the 29server. It can only send exactly one id. The server then decides whether it 30agrees in reusing the session or starts the handshake for a new session. 31 32A server will lookup up the session in its internal session storage. If 33the session is not found in internal storage or internal storage is 34deactivated, the server will try the external storage if available. 35 36Since a client may try to reuse a session intended for use in a different 37context, the session id context must be set by the server (see 38L<SSL_CTX_set_session_id_context(3)|SSL_CTX_set_session_id_context(3)>). 39 40The following session cache modes and modifiers are available: 41 42=over 4 43 44=item SSL_SESS_CACHE_OFF 45 46No session caching for client or server takes place. 47 48=item SSL_SESS_CACHE_CLIENT 49 50Client sessions are added to the session cache. As there is no reliable way 51for the OpenSSL library to know whether a session should be reused or which 52session to choose (due to the abstract BIO layer the SSL engine does not 53have details about the connection), the application must select the session 54to be reused by using the L<SSL_set_session(3)|SSL_set_session(3)> 55function. This option is not activated by default. 56 57=item SSL_SESS_CACHE_SERVER 58 59Server sessions are added to the session cache. When a client proposes a 60session to be reused, the session is looked up in the internal session cache. 61If the session is found, the server will try to reuse the session. 62This is the default. 63 64=item SSL_SESS_CACHE_BOTH 65 66Enable both SSL_SESS_CACHE_CLIENT and SSL_SESS_CACHE_SERVER at the same time. 67 68=item SSL_SESS_CACHE_NO_AUTO_CLEAR 69 70Normally the session cache is checked for expired sessions every 71255 connections using the 72L<SSL_CTX_flush_sessions(3)|SSL_CTX_flush_sessions(3)> function. Since 73this may lead to a delay which cannot be controlled, the automatic 74flushing may be disabled and 75L<SSL_CTX_flush_sessions(3)|SSL_CTX_flush_sessions(3)> can be called 76explicitly by the application. 77 78=item SSL_SESS_CACHE_NO_INTERNAL_LOOKUP 79 80By setting this flag sessions are cached in the internal storage but 81they are not looked up automatically. If an external session cache 82is enabled, sessions are looked up in the external cache. As automatic 83lookup only applies for SSL/TLS servers, the flag has no effect on 84clients. 85 86=back 87 88The default mode is SSL_SESS_CACHE_SERVER. 89 90=head1 RETURN VALUES 91 92SSL_CTX_set_session_cache_mode() returns the previously set cache mode. 93 94SSL_CTX_get_session_cache_mode() returns the currently set cache mode. 95 96 97=head1 SEE ALSO 98 99L<ssl(3)|ssl(3)>, L<SSL_set_session(3)|SSL_set_session(3)>, 100L<SSL_session_reused(3)|SSL_session_reused(3)>, 101L<SSL_CTX_sess_number(3)|SSL_CTX_sess_number(3)>, 102L<SSL_CTX_sess_set_cache_size(3)|SSL_CTX_sess_set_cache_size(3)>, 103L<SSL_CTX_sess_set_get_cb(3)|SSL_CTX_sess_set_get_cb(3)>, 104L<SSL_CTX_set_session_id_context(3)|SSL_CTX_set_session_id_context(3)>, 105L<SSL_CTX_set_timeout(3)|SSL_CTX_set_timeout(3)>, 106L<SSL_CTX_flush_sessions(3)|SSL_CTX_flush_sessions(3)> 107 108=cut 109