=head1 DESCRIPTION
-SSL_CTX_sess_set_new_cb() sets the callback function, which is automatically
+SSL_CTX_sess_set_new_cb() sets the callback function that is
called whenever a new session was negotiated.
-SSL_CTX_sess_set_remove_cb() 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.
+SSL_CTX_sess_set_remove_cb() sets the callback function that is
+called whenever a session is removed by the SSL engine. For example,
+this can occur because a session is considered faulty or has become obsolete
+because of exceeding the timeout value.
-SSL_CTX_sess_set_get_cb() sets the callback function which is called,
-whenever a SSL/TLS client proposed to resume a session but the session
+SSL_CTX_sess_set_get_cb() sets the callback function that is called
+whenever a TLS client proposed to resume a session but the session
could not be found in the internal session cache (see
L<SSL_CTX_set_session_cache_mode(3)>).
-(SSL/TLS server only.)
+(TLS server only.)
SSL_CTX_sess_get_new_cb(), SSL_CTX_sess_get_remove_cb(), and
SSL_CTX_sess_get_get_cb() retrieve the function pointers set by the
functions, session can be saved to disk or put into a database using the
L<d2i_SSL_SESSION(3)> interface.
-The new_session_cb() is called, whenever a new session has been negotiated
-and session caching is enabled (see
-L<SSL_CTX_set_session_cache_mode(3)>).
-The new_session_cb() is passed the B<ssl> connection and the ssl session
-B<sess>. If the callback returns B<0>, the session will be immediately
-removed again. Note that in TLSv1.3, sessions are established after the main
+The new_session_cb() is called whenever a new session has been negotiated and
+session caching is enabled (see L<SSL_CTX_set_session_cache_mode(3)>). The
+new_session_cb() is passed the B<ssl> connection and the nascent
+ssl session B<sess>.
+Since sessions are reference-counted objects, the reference count on the
+session is incremented before the callback, on behalf of the application. If
+the callback returns B<0>, the session will be immediately removed from the
+internal cache and the reference count released. If the callback returns B<1>,
+the application retains the reference (for an entry in the
+application-maintained "external session cache"), and is responsible for
+calling SSL_SESSION_free() when the session reference is no longer in use.
+
+Note that in TLSv1.3, sessions are established after the main
handshake has completed. The server decides when to send the client the session
information and this may occur some time after the end of the handshake (or not
at all). This means that applications should expect the new_session_cb()
resumption once. One way of enforcing that is for applications to call
L<SSL_CTX_remove_session(3)> after a session has been used.
-The remove_session_cb() is called, whenever the SSL engine removes a session
-from the internal cache. This happens when the session is removed because
+The remove_session_cb() is called whenever the SSL engine removes a session
+from the internal cache. This can happen 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
L<SSL_CTX_free(3)> is called. The remove_session_cb() is passed
the B<ctx> and the ssl session B<sess>. It does not provide any feedback.
-The get_session_cb() is only called on SSL/TLS servers with the session id
-proposed by the client. The get_session_cb() is always called, also when
+The get_session_cb() is only called on SSL/TLS servers, and is given
+the session id
+proposed by the client. The get_session_cb() is always called, even when
session caching was disabled. The get_session_cb() is passed the
-B<ssl> connection, the session id of length B<length> at the memory location
-B<data>. With the parameter B<copy> 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
+B<ssl> connection and the session id of length B<length> at the memory location
+B<data>. By setting the parameter B<copy> to B<1>, the callback can require the
+SSL engine to increment the reference count of the SSL_SESSION object;
+setting B<copy> to B<0> causes the reference count to remain unchanged.
+If the get_session_cb() does not write to B<copy>, the reference count
+is incremented and the session must be explicitly freed with
L<SSL_SESSION_free(3)>.
=head1 RETURN VALUES
projects / openssl.git / blobdiff