Document session caching, first step.

=pod

=head1 NAME

SSL_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

=head1 SYNOPSIS

 #include <openssl/ssl.h>

 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 SSL_CTX_sess_set_get_cb(SSL_CTX *ctx,

	   SSL_SESSION (*get_session-cb)(SSL *, 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, 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);

=head1 DESCRIPTION

SSL_CTX_sess_set_new_cb() sets the callback function, which is automatically

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_get_cb() sets the callback function which is called,

whenever a SSL/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_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 funtion pointers of the

provided callback functions. If a callback function has not been set,

the NULL pointer is returned.

=head1 NOTES

In order to allow external session caching, synchronization with the internal

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)|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)|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 immediatly

removed again.

The remove_session_cb() is called, whenever the SSL engine removes a session

from the internal cache. This happens if the session is removed because

it is expired or when a connection was not shutdown cleanly. 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

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.

=head1 SEE ALSO

L<ssl(3)|ssl(3)>, L<d2i_SSL_SESSION(3)|d2i_SSL_SESSION(3)>,

L<SSL_CTX_set_session_cache_mode(3)|SSL_CTX_set_session_cache_mode(3)>

=cut

=pod

=head1 NAME

SSL_CTX_set_session_cache_mode - enable/disable session caching

=head1 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);

=head1 DESCRIPTION

SSL_CTX_set_session_cache_mode() enables/disables session caching

by setting the operational mode for B<ctx> to <mode>.

SSL_CTX_get_session_cache_mode() returns the currently used cache mode.

=head1 NOTES

The OpenSSL library can store/retrieve SSL/TLS sessions for later reuse.

The sessions can be held in memory for each B<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 decides whether it

agrees in reusing the session or starts the handshake for 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 internal storage is

deactivated, 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

L<SSL_CTX_set_session_id_context(3)|SSL_CTX_set_session_id_context(3)>).

The following session cache modes and modifiers are available:

=over 4

=item SSL_SESS_CACHE_OFF

No session caching for client or server takes place.

=item 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 using the L<SSL_set_session(3)|SSL_set_session(3)>

function. This option is not activated by default.

=item SSL_SESS_CACHE_SERVER

Server sessions are added to the session cache. When a client proposes a

session to be reused, the session is looked up in the internal session cache.

If the session is found, the server will try to reuse the session.

This is the default.

=item SSL_SESS_CACHE_BOTH

Enable both SSL_SESS_CACHE_CLIENT and SSL_SESS_CACHE_SERVER at the same time.

=item SSL_SESS_CACHE_NO_AUTO_CLEAR

Normally the session cache is checked for expired sessions every

255 connections using the SSL_CTX_flush_sessions() function. Since

this may lead to a delay which cannot be controlled, the automatic

flushing may be disabled and SSL_CTX_flush_sessions() can be called

explicitly by the application.

=item SSL_SESS_CACHE_NO_INTERNAL_LOOKUP

By setting this flag sessions are cached in the internal storage but

they are not looked up automatically. If an external session cache

is enabled, sessions are looked up in the external cache. As automatic

lookup only applies for SSL/TLS servers, the flag has no effect on

clients.

=back

The default mode is SSL_SESS_CACHE_SERVER.

=head1 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.

=head1 SEE ALSO

L<ssl(3)|ssl(3)>, L<SSL_set_session(3)|SSL_set_session(3)>,

L<SSL_CTX_sess_set_get_cb(3)|SSL_CTX_sess_set_get_cb(3)>,

L<SSL_CTX_set_session_id_context(3)|SSL_CTX_set_session_id_context(3)>

=cut

=head1 SEE ALSO

L<ssl(3)|ssl(3)>, L<SSL_SESSION_free(3)|SSL_SESSION_free(3)>

L<ssl(3)|ssl(3)>, L<SSL_SESSION_free(3)|SSL_SESSION_free(3)>,

L<SSL_CTX_set_session_cache_mode(3)|SSL_CTX_set_session_cache_mode(3)>

=cut

=pod

=head1 NAME

d2i_SSL_SESSION, i2d_SSL_SESSION - convert SSL_SESSION object from/to ASN1 representation

=head1 SYNOPSIS

 #include <openssl/ssl.h>

 SSL_SESSION *d2i_SSL_SESSION(SSL_SESSION **a, unsigned char **pp, long length); int i2d_SSL_SESSION(SSL_SESSION *in, unsigned char **pp);

=head1 DESCRIPTION

d2i_SSL_SESSION() transforms the external ASN1 representation of an SSL/TLS

session, stored as binary data at location B<pp> with length B<length>, into

an SSL_SESSION object.

i2d_SSL_SESSION() transforms the SSL_SESSION object B<in> into the ASN1

representation and stores it into the memory location pointed to by B<pp>.

The length of the resulting ASN1 representation is returned. If B<pp> is

the NULL pointer, only the length is calculated and returned.

=head1 NOTES

The SSL_SESSION object is built from several malloc()ed parts, it can

therefore not be moved, copied or stored directly. In order to store

session data on disk or into a database, it must be transformed into

a binary ASN1 representation.

When using d2i_SSL_SESSION(), the SSL_SESSION object is automatically

allocated.

When using i2d_SSL_SESSION(), the memory location pointed to by B<pp> must be

large enough to hold the binary representation of the session. There is no

known limit on the size of the created ASN1 representation, so the necessary

amount of space should be obtained by first calling i2d_SSL_SESSION() with

B<pp=NULL>, and obtain the size needed, then allocate the memory and

call i2d_SSL_SESSION() again.

=head1 RETURN VALUES

d2i_SSL_SESSION() returns a pointer to the newly allocated SSL_SESSION

object. In case of failure the NULL-pointer is returned and the error message

can be retrieved from the error stack.

i2d_SSL_SESSION() returns the size of the ASN1 representation in bytes.

When the session is not valid, B<0> is returned and no operation is performed.

=head1 SEE ALSO

L<ssl(3)|ssl(3)>,

L<SSL_CTX_sess_set_get_cb(3)|SSL_CTX_sess_set_get_cb(3)>

=cut

L<SSL_CTX_get_verify_mode(3)|SSL_CTX_get_verify_mode(3)>,

L<SSL_CTX_load_verify_locations(3)|SSL_CTX_load_verify_locations(3)>

L<SSL_CTX_new(3)|SSL_CTX_new(3)>,

L<SSL_CTX_sess_set_get_cb(3)|SSL_CTX_sess_set_get_cb(3)>,

L<SSL_CTX_set_client_CA_list(3)|SSL_CTX_set_client_CA_list(3)>,

L<SSL_CTX_set_default_passwd_cb(3)|SSL_CTX_set_default_passwd_cb(3)>,

L<SSL_CTX_set_session_cache_mode(3)|SSL_CTX_set_session_cache_mode(3)>,

L<SSL_CTX_set_session_id_context(3)|SSL_CTX_set_session_id_context(3)>,

L<SSL_CTX_set_ssl_version(3)|SSL_CTX_set_ssl_version(3)>,

L<SSL_CTX_set_verify(3)|SSL_CTX_set_verify(3)>,

L<SSL_set_session(3)|SSL_set_session(3)>,

L<SSL_shutdown(3)|SSL_shutdown(3)>, L<SSL_write(3)|SSL_write(3)>,

L<SSL_SESSION_free(3)|SSL_SESSION_free(3)>,

L<SSL_SESSION_get_ex_new_index(3)|SSL_SESSION_get_ex_new_index(3)>

L<SSL_SESSION_get_ex_new_index(3)|SSL_SESSION_get_ex_new_index(3)>,

L<d2i_SSL_SESSION(3)|d2i_SSL_SESSION(3)>

=head1 HISTORY