=pod

=head1 NAME

SSL_shutdown - shut down a TLS/SSL connection

=head1 SYNOPSIS

 #include <openssl/ssl.h>

 int SSL_shutdown(SSL *ssl);

=head1 DESCRIPTION

SSL_shutdown() shuts down an active TLS/SSL connection. It sends the 
"close notify" shutdown alert to the peer.

=head1 NOTES

SSL_shutdown() tries to send the "close notify" shutdown alert to the peer.
Whether the operation succeeds or not, the SSL_SENT_SHUTDOWN flag is set and
a currently open session is considered closed and good and will be kept in the
session cache for further reuse.

The shutdown procedure consists of 2 steps: the sending of the "close notify"
shutdown alert and the receipt ion of the peer's "close notify" shutdown
alert:

=over 4

=item When the application is the first party to send the "close notify"
alert, SSL_shutdown() will only send the alert and the set the
SSL_SENT_SHUTDOWN flag (so that the session is considered good and will
be kept in cache). SSL_shutdown() will then return with 0. In order to
complete the shutdown handshake, SSL_shutdown() must be called again.
The second call will make SSL_shutdown() wait for the peer's "close notify"
shutdown alert. On success, the second call to SSL_shutdown() will return
with 1.

=item If the peer already sent the "close notify" alert B<and> it was
already processed implicitly inside another call of e.g.
B<SSL_read(3)|SSL_read(3)>, SSL_shutdown() will send the "close notify"
alert and will immediately return with 1.

=back

It is therefore recommended, to check the return value of SSL_shutdown()
and call SSL_shutdown() again, if the bidirectional shutdown is not yet
complete (return value of the first call is 0). As the shutdown is not
specially handled in the SSLv2 protocol, SSL_shutdown() will succeed on
the first call.

The behaviour of SSL_shutdown() additionally depends on the underlying BIO. 

If the underlying BIO is B<blocking>, SSL_shutdown() will only return once the
handshake step has been finished or an error occurred.

If the underlying BIO is B<non-blocking>, SSL_shutdown() will also return
when the underlying BIO could not satisfy the needs of SSL_shutdown()
to continue the handshake. In this case a call to SSL_get_error() with the
return value of SSL_shutdown() will yield B<SSL_ERROR_WANT_READ> or
B<SSL_ERROR_WANT_WRITE>. The calling process then must repeat the call after
taking appropriate action to satisfy the needs of SSL_shutdown().
The action depends on the underlying BIO. When using a non-blocking socket,
nothing is to be done, but select() can be used to check for the required
condition. When using a buffering BIO, like a BIO pair, data must be written
into or retrieved out of the BIO before being able to continue.

=head1 RETURN VALUES

The following return values can occur:

=over 4

=item 1

The shutdown was successfully completed. The "close notify" alert was sent
and the peer's "close notify" alert was received.

=item 0

The shutdown is not yet finished. Call SSL_shutdown() for a second time.
The output of L<SSL_get_error(3)|SSL_get_error(3)> may be misleading, as an
erroneous SSL_ERROR_SYSCALL may be flagged even though no error occurred.

=item -1

The shutdown was not successful because a fatal error occurred either
at the protocol level or a connection failure occurred. It can also occur if
action is need to continue the operation for non-blocking BIOs.
Call L<SSL_get_error(3)|SSL_get_error(3)> with the return value B<ret>
to find out the reason.

=back

=head1 SEE ALSO

L<SSL_get_error(3)|SSL_get_error(3)>, L<SSL_connect(3)|SSL_connect(3)>,
L<SSL_accept(3)|SSL_accept(3)>, L<SSL_set_shutdown(3)|SSL_set_shutdown(3)>,
L<SSL_clear(3)|SSL_clear(3)>, L<SSL_free(3)|SSL_free(3)>,
L<ssl(3)|ssl(3)>, L<bio(3)|bio(3)>

=cut