SSL_CTX_set_session_cache_mode(3)

     SSL_CTX_set_session_cac0.<I>99.6he(2SSL_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 lookup 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

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     SSL_CTX_set_session_cac0.<I>99.6he(2SSL_CTX_set_session_cache_mode(3)

              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

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     SSL_CTX_set_session_cac0.<I>99.6he(2SSL_CTX_set_session_cache_mode(3)

              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(3), 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)

     HISTORY
          SSL_SESS_CACHE_NO_INTERNAL_STORE and
          SSL_SESS_CACHE_NO_INTERNAL were introduced in OpenSSL
          0.9.6h.

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