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Diffstat (limited to 'deps/openssl/openssl/doc/man3/SSL_shutdown.pod')
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1 files changed, 163 insertions, 0 deletions
diff --git a/deps/openssl/openssl/doc/man3/SSL_shutdown.pod b/deps/openssl/openssl/doc/man3/SSL_shutdown.pod new file mode 100644 index 0000000000..0a3d6d370d --- /dev/null +++ b/deps/openssl/openssl/doc/man3/SSL_shutdown.pod @@ -0,0 +1,163 @@ +=pod + +=head1 NAME + +SSL_shutdown - shut down a TLS/SSL connection + +=head1 SYNOPSIS + + #include <openssl/ssl.h> + + int SSL_shutdown(SSL *ssl); + +=head1 DESCRIPTION + +SSL_shutdown() shuts down an active TLS/SSL connection. It sends the +close_notify shutdown alert to the peer. + +=head1 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 two steps: sending of the close_notify +shutdown alert, and reception of the peer's close_notify shutdown alert. +The order of those two steps depends on the application. + +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. +This should only be done when it is known that the other side will not send more +data, otherwise there is a risk of a truncation attack. + +When a client only writes and never reads from the connection, and the server +has sent a session ticket to establish a session, the client might not be able +to resume the session because it did not received and process the session ticket +from the server. +In case the application wants to be able to resume the session, it is recommended to +do a complete shutdown procedure (bidirectional close_notify alerts). + +When the underlying connection shall be used for more communications, the +complete shutdown procedure must be performed, so that the peers stay +synchronized. + +SSL_shutdown() only closes the write direction. +It is not possible to call SSL_write() after calling SSL_shutdown(). +The read direction is closed by the peer. + +=head2 First to close the connection + +When the application is the first party to send the close_notify +alert, SSL_shutdown() will only send the alert and then set the +SSL_SENT_SHUTDOWN flag (so that the session is considered good and will +be kept in the cache). +If successful, SSL_shutdown() will return 0. + +If a unidirectional shutdown is enough (the underlying connection shall be +closed anyway), this first successful call to SSL_shutdown() is sufficient. + +In order to complete the bidirectional shutdown handshake, the peer needs +to send back a close_notify alert. +The SSL_RECEIVED_SHUTDOWN flag will be set after receiving and processing +it. + +The peer is still allowed to send data after receiving the close_notify +event. +When it is done sending data, it will send the close_notify alert. +SSL_read() should be called until all data is received. +SSL_read() will indicate the end of the peer data by returning <= 0 +and SSL_get_error() returning SSL_ERROR_ZERO_RETURN. + +=head2 Peer closes the connection + +If the peer already sent the close_notify alert B<and> it was +already processed implicitly inside another function +(L<SSL_read(3)>), the SSL_RECEIVED_SHUTDOWN flag is set. +SSL_read() will return <= 0 in that case, and SSL_get_error() will return +SSL_ERROR_ZERO_RETURN. +SSL_shutdown() will send the close_notify alert, set the SSL_SENT_SHUTDOWN +flag. +If successful, SSL_shutdown() will return 1. + +Whether SSL_RECEIVED_SHUTDOWN is already set can be checked using the +SSL_get_shutdown() (see also L<SSL_set_shutdown(3)> call. + +=head1 NOTES + +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 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() +to continue the handshake. In this case a call to SSL_get_error() with the +return value of SSL_shutdown() will yield B<SSL_ERROR_WANT_READ> or +B<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. + +After SSL_shutdown() returned 0, it is possible to call SSL_shutdown() again +to wait for the peer's close_notify alert. +SSL_shutdown() will return 1 in that case. +However, it is recommended to wait for it using SSL_read() instead. + +SSL_shutdown() can be modified to only set the connection to "shutdown" +state but not actually send the close_notify alert messages, +see L<SSL_CTX_set_quiet_shutdown(3)>. +When "quiet shutdown" is enabled, SSL_shutdown() will always succeed +and return 1. + +=head1 RETURN VALUES + +The following return values can occur: + +=over 4 + +=item Z<>0 + +The shutdown is not yet finished: the close_notify was sent but the peer +did not send it back yet. +Call SSL_read() to do a bidirectional shutdown. +The output of L<SSL_get_error(3)> may be misleading, as an +erroneous SSL_ERROR_SYSCALL may be flagged even though no error occurred. + +=item Z<>1 + +The shutdown was successfully completed. The close_notify alert was sent +and the peer's close_notify alert was received. + +=item E<lt>0 + +The shutdown was not successful. +Call L<SSL_get_error(3)> with the return value B<ret> to find out the reason. +It can occur if an action is needed to continue the operation for non-blocking +BIOs. + +It can also occur when not all data was read using SSL_read(). + +=back + +=head1 SEE ALSO + +L<SSL_get_error(3)>, L<SSL_connect(3)>, +L<SSL_accept(3)>, L<SSL_set_shutdown(3)>, +L<SSL_CTX_set_quiet_shutdown(3)>, +L<SSL_clear(3)>, L<SSL_free(3)>, +L<ssl(7)>, L<bio(7)> + +=head1 COPYRIGHT + +Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved. + +Licensed under the OpenSSL license (the "License"). You may not use +this file except in compliance with the License. You can obtain a copy +in the file LICENSE in the source distribution or at +L<https://www.openssl.org/source/license.html>. + +=cut |