SSL_shutdown(3)

     SSL_shutdown(3)        0.9.6h (2001-08-20)        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 connection).  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.

     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
     connection 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.
          When the application is the first party to send the "close
     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.
          If the peer already sent the "close notify" alert and it was

     Page 1                                         (printed 1/19/103)

     SSL_shutdown(3)        0.9.6h (2001-08-20)        SSL_shutdown(3)

          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 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 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 SSL_ERROR_WANT_READ or
          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.

          SSL_shutdown() can be modified to only set the connection 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_shutdown()
              for a second time, if a bidirectional shutdown 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

     Page 2                                         (printed 1/19/103)

     SSL_shutdown(3)        0.9.6h (2001-08-20)        SSL_shutdown(3)

              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)

     Page 3                                         (printed 1/19/103)