Update SSL_CTX_sess_set_new_cb(3) docs for refcounts

[openssl.git] / doc / man3 / SSL_CTX_sess_set_get_cb.pod

diff --git a/doc/man3/SSL_CTX_sess_set_get_cb.pod b/doc/man3/SSL_CTX_sess_set_get_cb.pod
index d0caa8a1552a4c71bed9ca4d614bbaae3eda6958..98fbfb57bfd1a9269c64df02103012d17ff711d2 100644 (file)
--- a/doc/man3/SSL_CTX_sess_set_get_cb.pod
+++ b/doc/man3/SSL_CTX_sess_set_get_cb.pod
@@ -11,18 +11,20 @@ SSL_CTX_sess_set_new_cb, SSL_CTX_sess_set_remove_cb, SSL_CTX_sess_set_get_cb, SS
  void SSL_CTX_sess_set_new_cb(SSL_CTX *ctx,
                               int (*new_session_cb)(SSL *, SSL_SESSION *));
  void SSL_CTX_sess_set_remove_cb(SSL_CTX *ctx,
-           void (*remove_session_cb)(SSL_CTX *ctx, SSL_SESSION *));
+                                 void (*remove_session_cb)(SSL_CTX *ctx,
+                                                           SSL_SESSION *));
  void SSL_CTX_sess_set_get_cb(SSL_CTX *ctx,
-           SSL_SESSION (*get_session_cb)(SSL *, const unsigned char *, int, int *));
-
- int (*SSL_CTX_sess_get_new_cb(SSL_CTX *ctx))(struct ssl_st *ssl, SSL_SESSION *sess);
- void (*SSL_CTX_sess_get_remove_cb(SSL_CTX *ctx))(struct ssl_ctx_st *ctx, SSL_SESSION *sess);
- SSL_SESSION *(*SSL_CTX_sess_get_get_cb(SSL_CTX *ctx))(struct ssl_st *ssl, const unsigned char *data, int len, int *copy);
-
- int (*new_session_cb)(struct ssl_st *ssl, SSL_SESSION *sess);
- void (*remove_session_cb)(struct ssl_ctx_st *ctx, SSL_SESSION *sess);
- SSL_SESSION *(*get_session_cb)(struct ssl_st *ssl, unsigned char *data,
-               int len, int *copy);
+                              SSL_SESSION (*get_session_cb)(SSL *,
+                                                            const unsigned char *,
+                                                            int, int *));
+
+ int (*SSL_CTX_sess_get_new_cb(SSL_CTX *ctx))(struct ssl_st *ssl,
+                                              SSL_SESSION *sess);
+ void (*SSL_CTX_sess_get_remove_cb(SSL_CTX *ctx))(struct ssl_ctx_st *ctx,
+                                                  SSL_SESSION *sess);
+ SSL_SESSION *(*SSL_CTX_sess_get_get_cb(SSL_CTX *ctx))(struct ssl_st *ssl,
+                                                       const unsigned char *data,
+                                                       int len, int *copy);
 
 =head1 DESCRIPTION
 
@@ -41,9 +43,9 @@ L<SSL_CTX_set_session_cache_mode(3)>).
 (SSL/TLS server only.)
 
 SSL_CTX_sess_get_new_cb(), SSL_CTX_sess_get_remove_cb(), and
-SSL_CTX_sess_get_get_cb() allow to retrieve the function pointers of the
-provided callback functions. If a callback function has not been set,
-the NULL pointer is returned.
+SSL_CTX_sess_get_get_cb() retrieve the function pointers set by the
+corresponding set callback functions. If a callback function has not been
+set, the NULL pointer is returned.
 
 =head1 NOTES
 
@@ -52,12 +54,18 @@ session cache is realized via callback functions. Inside these callback
 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 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()
@@ -67,7 +75,8 @@ be established with a single connection. In these case the new_session_cb()
 function will be invoked multiple times.
 
 In TLSv1.3 it is recommended that each SSL_SESSION object is only used for
-resumption once.
+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
@@ -86,6 +95,11 @@ Normally the reference count is not incremented and therefore the
 session must not be explicitly freed with
 L<SSL_SESSION_free(3)>.
 
+=head1 RETURN VALUES
+
+SSL_CTX_sess_get_new_cb(), SSL_CTX_sess_get_remove_cb() and SSL_CTX_sess_get_get_cb()
+return different callback function pointers respectively.
+
 =head1 SEE ALSO
 
 L<ssl(7)>, L<d2i_SSL_SESSION(3)>,
@@ -96,9 +110,9 @@ L<SSL_CTX_free(3)>
 
 =head1 COPYRIGHT
 
-Copyright 2001-2016 The OpenSSL Project Authors. All Rights Reserved.
+Copyright 2001-2018 The OpenSSL Project Authors. All Rights Reserved.
 
-Licensed under the OpenSSL license (the "License").  You may not use
+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>.