SSL_shutdown(3)             OpenSSL             SSL_shutdown(3)





NAME
       SSL_shutdown - shut down a TLS/SSL connection

SYNOPSIS
        #include <openssl/ssl.h>

        int SSL_shutdown(SSL *ssl);

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

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 reception
       of the peer's "close notify" shutdown alert. According
       to the TLS standard, it is acceptable for an application
       to only send its shutdown alert and then close the
       underlying connection without waiting for the peer's
       response (this way resources can be saved, as the
       process can already terminate or serve another connec-
       tion).  When the underlying connection shall be used for
       more communications, the complete shutdown procedure
       (bidirectional "close notify" alerts) must be performed,
       so that the peers stay synchronized.

       SSL_shutdown() supports both uni- and bidirectional
       shutdown by its 2 step behaviour.

       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. If a
       unidirectional shutdown is enough (the underlying con-
       nection shall be closed anyway), this first call to
       SSL_shutdown() is sufficient. In order to complete the
       bidirectional 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.
       If the peer already sent the "close notify" alert and it
       was already processed implicitly inside another function
       (SSL_read(3)), the SSL_RECEIVED_SHUTDOWN flag is set.
       SSL_shutdown() will send the "close notify" alert, set
       the SSL_SENT_SHUTDOWN flag and will immediately return
       with 1. Whether SSL_RECEIVED_SHUTDOWN is already set can
       be checked using the SSL_get_shutdown() (see also
       SSL_set_shutdown(3) call.

       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 spe-
       cially 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 blocking, SSL_shutdown() will
       only return once the handshake step has been finished or
       an error occurred.

       If the underlying BIO is non-blocking, SSL_shutdown()
       will also return when the underlying BIO could not sat-
       isfy the needs of SSL_shutdown() to continue the hand-
       shake. In this case a call to SSL_get_error() with the
       return value of SSL_shutdown() will yield
       SSL_ERROR_WANT_READ or SSL_ERROR_WANT_WRITE. The calling
       process then must repeat the call after taking appropri-
       ate 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.

       SSL_shutdown() can be modified to only set the connec-
       tion to "shutdown" state but not actually send the
       "close notify" alert messages, see
       SSL_CTX_set_quiet_shutdown(3).  When "quiet shutdown" is
       enabled, SSL_shutdown() will always succeed and return
       1.

RETURN VALUES
       The following return values can occur:

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

       o   The shutdown is not yet finished. Call SSL_shut-
           down() for a second time, if a bidirectional shut-
           down shall be performed.  The output of
           SSL_get_error(3) may be misleading, as an erroneous
           SSL_ERROR_SYSCALL may be flagged even though no
           error occurred.

       -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 SSL_get_error(3) with the
           return value ret to find out the reason.

SEE ALSO
       SSL_get_error(3), SSL_connect(3), SSL_accept(3),
       SSL_set_shutdown(3), SSL_CTX_set_quiet_shutdown(3),
       SSL_clear(3), SSL_free(3), ssl(3), bio(3)



0.9.7c                     2001-08-20           SSL_shutdown(3)
