openssl/doc/ssl/SSL_CTX_add_session.pod
Geoff Thorpe e0db2eed8d Correct and enhance the behaviour of "internal" session caching as it
relates to SSL_CTX flags and the use of "external" session caching. The
existing flag, "SSL_SESS_CACHE_NO_INTERNAL_LOOKUP" remains but is
supplemented with a complimentary flag, "SSL_SESS_CACHE_NO_INTERNAL_STORE".
The bitwise OR of the two flags is also defined as
"SSL_SESS_CACHE_NO_INTERNAL" and is the flag that should be used by most
applications wanting to implement session caching *entirely* by its own
provided callbacks. As the documented behaviour contradicted actual
behaviour up until recently, and since that point behaviour has itself been
inconsistent anyway, this change should not introduce any compatibility
problems. I've adjusted the relevant documentation to elaborate about how
this works.

Kudos to "Nadav Har'El" <nyh@math.technion.ac.il> for diagnosing these
anomalies and testing this patch for correctness.

PR: 311
2002-10-29 00:33:04 +00:00

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=pod
=head1 NAME
SSL_CTX_add_session, SSL_add_session, SSL_CTX_remove_session, SSL_remove_session - manipulate session cache
=head1 SYNOPSIS
#include <openssl/ssl.h>
int SSL_CTX_add_session(SSL_CTX *ctx, SSL_SESSION *c);
int SSL_add_session(SSL_CTX *ctx, SSL_SESSION *c);
int SSL_CTX_remove_session(SSL_CTX *ctx, SSL_SESSION *c);
int SSL_remove_session(SSL_CTX *ctx, SSL_SESSION *c);
=head1 DESCRIPTION
SSL_CTX_add_session() adds the session B<c> to the context B<ctx>. The
reference count for session B<c> is incremented by 1. If a session with
the same session id already exists, the old session is removed by calling
L<SSL_SESSION_free(3)|SSL_SESSION_free(3)>.
SSL_CTX_remove_session() removes the session B<c> from the context B<ctx>.
L<SSL_SESSION_free(3)|SSL_SESSION_free(3)> is called once for B<c>.
SSL_add_session() and SSL_remove_session() are synonyms for their
SSL_CTX_*() counterparts.
=head1 NOTES
When adding a new session to the internal session cache, it is examined
whether a session with the same session id already exists. In this case
it is assumed that both sessions are identical. If the same session is
stored in a different SSL_SESSION object, The old session is
removed and replaced by the new session. If the session is actually
identical (the SSL_SESSION object is identical), SSL_CTX_add_session()
is a no-op, and the return value is 0.
If a server SSL_CTX is configured with the SSL_SESS_CACHE_NO_INTERNAL_STORE
flag then the internal cache will not be populated automatically by new
sessions negotiated by the SSL/TLS implementation, even though the internal
cache will be searched automatically for session-resume requests (the
latter can be surpressed by SSL_SESS_CACHE_NO_INTERNAL_LOOKUP). So the
application can use SSL_CTX_add_session() directly to have full control
over the sessions that can be resumed if desired.
=head1 RETURN VALUES
The following values are returned by all functions:
=over 4
=item 0
The operation failed. In case of the add operation, it was tried to add
the same (identical) session twice. In case of the remove operation, the
session was not found in the cache.
=item 1
The operation succeeded.
=back
=head1 SEE ALSO
L<ssl(3)|ssl(3)>,
L<SSL_CTX_set_session_cache_mode(3)|SSL_CTX_set_session_cache_mode(3)>,
L<SSL_SESSION_free(3)|SSL_SESSION_free(3)>
=cut