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Unidirectional shutdown is allowed according to the RFC.

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This commit is contained in:
Lutz Jänicke 2001-08-17 09:08:32 +00:00
parent bb766a0ad6
commit b2ed462934
1 changed files with 18 additions and 6 deletions
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24
doc/ssl/SSL_shutdown.pod
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@ -23,16 +23,27 @@ a currently open session is considered closed and good and will be kept in the
session cache for further reuse. session cache for further reuse.
The shutdown procedure consists of 2 steps: the sending of the "close notify" 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 shutdown alert and the reception of the peer's "close notify" shutdown
alert: 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.
=over 4 =over 4
=item When the application is the first party to send the "close notify" =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 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 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 be kept in cache). SSL_shutdown() will then return with 0. If a unidirectional
complete the shutdown handshake, SSL_shutdown() must be called again. 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" 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 shutdown alert. On success, the second call to SSL_shutdown() will return
with 1. with 1.
@ -40,7 +51,7 @@ with 1.
=item If the peer already sent the "close notify" alert B<and> it was =item If the peer already sent the "close notify" alert B<and> it was
already processed implicitly inside another call of e.g. already processed implicitly inside another call of e.g.
B<SSL_read(3)|SSL_read(3)>, SSL_shutdown() will send the "close notify" B<SSL_read(3)|SSL_read(3)>, SSL_shutdown() will send the "close notify"
alert and will immediately return with 1. alert, set the SSL_SENT_SHUTDOWN flag and will immediately return with 1.
=back =back
@ -79,7 +90,8 @@ and the peer's "close notify" alert was received.
=item 0 =item 0
The shutdown is not yet finished. Call SSL_shutdown() for a second time. The shutdown is not yet finished. Call SSL_shutdown() for a second time,
if a bidirectional shutdown shall be performed.
The output of L<SSL_get_error(3)|SSL_get_error(3)> may be misleading, as an 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. erroneous SSL_ERROR_SYSCALL may be flagged even though no error occurred.