| SSL_shutdown.pod (79998) | SSL_shutdown.pod (89837) |
|---|---|
| 1=pod 2 3=head1 NAME 4 5SSL_shutdown - shut down a TLS/SSL connection 6 7=head1 SYNOPSIS 8 --- 8 unchanged lines hidden (view full) --- 17 18=head1 NOTES 19 20SSL_shutdown() tries to send the "close notify" shutdown alert to the peer. 21Whether the operation succeeds or not, the SSL_SENT_SHUTDOWN flag is set and 22a currently open session is considered closed and good and will be kept in the 23session cache for further reuse. 24 | 1=pod 2 3=head1 NAME 4 5SSL_shutdown - shut down a TLS/SSL connection 6 7=head1 SYNOPSIS 8 --- 8 unchanged lines hidden (view full) --- 17 18=head1 NOTES 19 20SSL_shutdown() tries to send the "close notify" shutdown alert to the peer. 21Whether the operation succeeds or not, the SSL_SENT_SHUTDOWN flag is set and 22a currently open session is considered closed and good and will be kept in the 23session cache for further reuse. 24 |
| 25The behaviour of SSL_shutdown() depends on the underlying BIO. | 25The shutdown procedure consists of 2 steps: the sending of the "close notify" 26shutdown alert and the reception of the peer's "close notify" shutdown 27alert. According to the TLS standard, it is acceptable for an application 28to only send its shutdown alert and then close the underlying connection 29without waiting for the peer's response (this way resources can be saved, 30as the process can already terminate or serve another connection). 31When the underlying connection shall be used for more communications, the 32complete shutdown procedure (bidirectional "close notify" alerts) must be 33performed, so that the peers stay synchronized. |
| 26 | 34 |
| 35SSL_shutdown() supports both uni- and bidirectional shutdown by its 2 step 36behaviour. 37 38=over 4 39 40=item When the application is the first party to send the "close notify" 41alert, SSL_shutdown() will only send the alert and the set the 42SSL_SENT_SHUTDOWN flag (so that the session is considered good and will 43be kept in cache). SSL_shutdown() will then return with 0. If a unidirectional 44shutdown is enough (the underlying connection shall be closed anyway), this 45first call to SSL_shutdown() is sufficient. In order to complete the 46bidirectional shutdown handshake, SSL_shutdown() must be called again. 47The second call will make SSL_shutdown() wait for the peer's "close notify" 48shutdown alert. On success, the second call to SSL_shutdown() will return 49with 1. 50 51=item If the peer already sent the "close notify" alert B<and> it was 52already processed implicitly inside another function 53(L<SSL_read(3)|SSL_read(3)>), the SSL_RECEIVED_SHUTDOWN flag is set. 54SSL_shutdown() will send the "close notify" alert, set the SSL_SENT_SHUTDOWN 55flag and will immediately return with 1. 56Whether SSL_RECEIVED_SHUTDOWN is already set can be checked using the 57SSL_get_shutdown() (see also L<SSL_set_shutdown(3)|SSL_set_shutdown(3)> call. 58 59=back 60 61It is therefore recommended, to check the return value of SSL_shutdown() 62and call SSL_shutdown() again, if the bidirectional shutdown is not yet 63complete (return value of the first call is 0). As the shutdown is not 64specially handled in the SSLv2 protocol, SSL_shutdown() will succeed on 65the first call. 66 67The behaviour of SSL_shutdown() additionally depends on the underlying BIO. 68 |
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| 27If the underlying BIO is B<blocking>, SSL_shutdown() will only return once the | 69If the underlying BIO is B<blocking>, SSL_shutdown() will only return once the |
| 28handshake has been finished or an error occurred. | 70handshake step has been finished or an error occurred. |
| 29 30If the underlying BIO is B<non-blocking>, SSL_shutdown() will also return 31when the underlying BIO could not satisfy the needs of SSL_shutdown() 32to continue the handshake. In this case a call to SSL_get_error() with the 33return value of SSL_shutdown() will yield B<SSL_ERROR_WANT_READ> or 34B<SSL_ERROR_WANT_WRITE>. The calling process then must repeat the call after 35taking appropriate action to satisfy the needs of SSL_shutdown(). 36The action depends on the underlying BIO. When using a non-blocking socket, 37nothing is to be done, but select() can be used to check for the required 38condition. When using a buffering BIO, like a BIO pair, data must be written 39into or retrieved out of the BIO before being able to continue. 40 | 71 72If the underlying BIO is B<non-blocking>, SSL_shutdown() will also return 73when the underlying BIO could not satisfy the needs of SSL_shutdown() 74to continue the handshake. In this case a call to SSL_get_error() with the 75return value of SSL_shutdown() will yield B<SSL_ERROR_WANT_READ> or 76B<SSL_ERROR_WANT_WRITE>. The calling process then must repeat the call after 77taking appropriate action to satisfy the needs of SSL_shutdown(). 78The action depends on the underlying BIO. When using a non-blocking socket, 79nothing is to be done, but select() can be used to check for the required 80condition. When using a buffering BIO, like a BIO pair, data must be written 81into or retrieved out of the BIO before being able to continue. 82 |
| 83SSL_shutdown() can be modified to only set the connection to "shutdown" 84state but not actually send the "close notify" alert messages, 85see L<SSL_CTX_set_quiet_shutdown(3)|SSL_CTX_set_quiet_shutdown(3)>. 86When "quiet shutdown" is enabled, SSL_shutdown() will always succeed 87and return 1. 88 |
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| 41=head1 RETURN VALUES 42 43The following return values can occur: 44 45=over 4 46 47=item 1 48 | 89=head1 RETURN VALUES 90 91The following return values can occur: 92 93=over 4 94 95=item 1 96 |
| 49The shutdown was successfully completed. | 97The shutdown was successfully completed. The "close notify" alert was sent 98and the peer's "close notify" alert was received. |
| 50 51=item 0 52 | 99 100=item 0 101 |
| 53The shutdown was not successful. Call SSL_get_error() with the return 54value B<ret> to find out the reason. | 102The shutdown is not yet finished. Call SSL_shutdown() for a second time, 103if a bidirectional shutdown shall be performed. 104The output of L<SSL_get_error(3)|SSL_get_error(3)> may be misleading, as an 105erroneous SSL_ERROR_SYSCALL may be flagged even though no error occurred. |
| 55 56=item -1 57 58The shutdown was not successful because a fatal error occurred either | 106 107=item -1 108 109The shutdown was not successful because a fatal error occurred either |
| 59at the protocol level or a connection failure occurred. It can also occur of | 110at the protocol level or a connection failure occurred. It can also occur if |
| 60action is need to continue the operation for non-blocking BIOs. | 111action is need to continue the operation for non-blocking BIOs. |
| 61Call SSL_get_error() with the return value B<ret> to find out the reason. | 112Call L<SSL_get_error(3)|SSL_get_error(3)> with the return value B<ret> 113to find out the reason. |
| 62 63=back 64 65=head1 SEE ALSO 66 67L<SSL_get_error(3)|SSL_get_error(3)>, L<SSL_connect(3)|SSL_connect(3)>, 68L<SSL_accept(3)|SSL_accept(3)>, L<SSL_set_shutdown(3)|SSL_set_shutdown(3)>, | 114 115=back 116 117=head1 SEE ALSO 118 119L<SSL_get_error(3)|SSL_get_error(3)>, L<SSL_connect(3)|SSL_connect(3)>, 120L<SSL_accept(3)|SSL_accept(3)>, L<SSL_set_shutdown(3)|SSL_set_shutdown(3)>, |
| 121L<SSL_CTX_set_quiet_shutdown(3)|SSL_CTX_set_quiet_shutdown(3)>, |
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| 69L<SSL_clear(3)|SSL_clear(3)>, L<SSL_free(3)|SSL_free(3)>, 70L<ssl(3)|ssl(3)>, L<bio(3)|bio(3)> 71 72=cut | 122L<SSL_clear(3)|SSL_clear(3)>, L<SSL_free(3)|SSL_free(3)>, 123L<ssl(3)|ssl(3)>, L<bio(3)|bio(3)> 124 125=cut |