1=pod 2 3=head1 NAME 4 5SSL_CTX_sess_set_new_cb, SSL_CTX_sess_set_remove_cb, SSL_CTX_sess_set_get_cb, SSL_CTX_sess_get_new_cb, SSL_CTX_sess_get_remove_cb, SSL_CTX_sess_get_get_cb - provide callback functions for server side external session caching 6 7=head1 SYNOPSIS 8 9 #include <openssl/ssl.h> 10 11 void SSL_CTX_sess_set_new_cb(SSL_CTX *ctx, 12 int (*new_session_cb)(SSL *, SSL_SESSION *)); 13 void SSL_CTX_sess_set_remove_cb(SSL_CTX *ctx, 14 void (*remove_session_cb)(SSL_CTX *ctx, 15 SSL_SESSION *)); 16 void SSL_CTX_sess_set_get_cb(SSL_CTX *ctx, 17 SSL_SESSION (*get_session_cb)(SSL *, 18 const unsigned char *, 19 int, int *)); 20 21 int (*SSL_CTX_sess_get_new_cb(SSL_CTX *ctx))(struct ssl_st *ssl, 22 SSL_SESSION *sess); 23 void (*SSL_CTX_sess_get_remove_cb(SSL_CTX *ctx))(struct ssl_ctx_st *ctx, 24 SSL_SESSION *sess); 25 SSL_SESSION *(*SSL_CTX_sess_get_get_cb(SSL_CTX *ctx))(struct ssl_st *ssl, 26 const unsigned char *data, 27 int len, int *copy); 28 29=head1 DESCRIPTION 30 31SSL_CTX_sess_set_new_cb() sets the callback function, which is automatically 32called whenever a new session was negotiated. 33 34SSL_CTX_sess_set_remove_cb() sets the callback function, which is 35automatically called whenever a session is removed by the SSL engine, 36because it is considered faulty or the session has become obsolete because 37of exceeding the timeout value. 38 39SSL_CTX_sess_set_get_cb() sets the callback function which is called, 40whenever a SSL/TLS client proposed to resume a session but the session 41could not be found in the internal session cache (see 42L<SSL_CTX_set_session_cache_mode(3)>). 43(SSL/TLS server only.) 44 45SSL_CTX_sess_get_new_cb(), SSL_CTX_sess_get_remove_cb(), and 46SSL_CTX_sess_get_get_cb() retrieve the function pointers set by the 47corresponding set callback functions. If a callback function has not been 48set, the NULL pointer is returned. 49 50=head1 NOTES 51 52In order to allow external session caching, synchronization with the internal 53session cache is realized via callback functions. Inside these callback 54functions, session can be saved to disk or put into a database using the 55L<d2i_SSL_SESSION(3)> interface. 56 57The new_session_cb() is called, whenever a new session has been negotiated 58and session caching is enabled (see 59L<SSL_CTX_set_session_cache_mode(3)>). 60The new_session_cb() is passed the B<ssl> connection and the ssl session 61B<sess>. If the callback returns B<0>, the session will be immediately 62removed again. Note that in TLSv1.3, sessions are established after the main 63handshake has completed. The server decides when to send the client the session 64information and this may occur some time after the end of the handshake (or not 65at all). This means that applications should expect the new_session_cb() 66function to be invoked during the handshake (for <= TLSv1.2) or after the 67handshake (for TLSv1.3). It is also possible in TLSv1.3 for multiple sessions to 68be established with a single connection. In these case the new_session_cb() 69function will be invoked multiple times. 70 71In TLSv1.3 it is recommended that each SSL_SESSION object is only used for 72resumption once. One way of enforcing that is for applications to call 73L<SSL_CTX_remove_session(3)> after a session has been used. 74 75The remove_session_cb() is called, whenever the SSL engine removes a session 76from the internal cache. This happens when the session is removed because 77it is expired or when a connection was not shutdown cleanly. It also happens 78for all sessions in the internal session cache when 79L<SSL_CTX_free(3)> is called. The remove_session_cb() is passed 80the B<ctx> and the ssl session B<sess>. It does not provide any feedback. 81 82The get_session_cb() is only called on SSL/TLS servers with the session id 83proposed by the client. The get_session_cb() is always called, also when 84session caching was disabled. The get_session_cb() is passed the 85B<ssl> connection, the session id of length B<length> at the memory location 86B<data>. With the parameter B<copy> the callback can require the 87SSL engine to increment the reference count of the SSL_SESSION object, 88Normally the reference count is not incremented and therefore the 89session must not be explicitly freed with 90L<SSL_SESSION_free(3)>. 91 92=head1 RETURN VALUES 93 94SSL_CTX_sess_get_new_cb(), SSL_CTX_sess_get_remove_cb() and SSL_CTX_sess_get_get_cb() 95return different callback function pointers respectively. 96 97=head1 SEE ALSO 98 99L<ssl(7)>, L<d2i_SSL_SESSION(3)>, 100L<SSL_CTX_set_session_cache_mode(3)>, 101L<SSL_CTX_flush_sessions(3)>, 102L<SSL_SESSION_free(3)>, 103L<SSL_CTX_free(3)> 104 105=head1 COPYRIGHT 106 107Copyright 2001-2018 The OpenSSL Project Authors. All Rights Reserved. 108 109Licensed under the OpenSSL license (the "License"). You may not use 110this file except in compliance with the License. You can obtain a copy 111in the file LICENSE in the source distribution or at 112L<https://www.openssl.org/source/license.html>. 113 114=cut 115