Better description of the behaviour of SSL_shutdown() as it is now, broken

a currently open session is considered closed and good and will be kept in the

session cache for further reuse.

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

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 has been finished or an error occurred.

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()

=item 1

The shutdown was successfully completed.

The shutdown was successfully completed. The "close notify" alert was sent

and the peer's "close notify" alert was received.

=item 0

The shutdown was not successful. Call SSL_get_error() with the return

value B<ret> to find out the reason.

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 of

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 SSL_get_error() with the return value B<ret> to find out the reason.

Call L<SSL_get_error(3)|SSL_get_error(3)> with the return value B<ret>

to find out the reason.

=back