From aa4d426b4d3527d7e166df1a05058c9a4a0f6683 Mon Sep 17 00:00:00 2001 From: Wojtek Kosior Date: Fri, 30 Apr 2021 00:33:56 +0200 Subject: initial/final commit --- openssl-1.1.0h/doc/ssl/SSL_shutdown.pod | 132 ++++++++++++++++++++++++++++++++ 1 file changed, 132 insertions(+) create mode 100644 openssl-1.1.0h/doc/ssl/SSL_shutdown.pod (limited to 'openssl-1.1.0h/doc/ssl/SSL_shutdown.pod') diff --git a/openssl-1.1.0h/doc/ssl/SSL_shutdown.pod b/openssl-1.1.0h/doc/ssl/SSL_shutdown.pod new file mode 100644 index 0000000..e8ec454 --- /dev/null +++ b/openssl-1.1.0h/doc/ssl/SSL_shutdown.pod @@ -0,0 +1,132 @@ +=pod + +=head1 NAME + +SSL_shutdown - shut down a TLS/SSL connection + +=head1 SYNOPSIS + + #include + + 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 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. + +=over 4 + +=item 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 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. + +=item If the peer already sent the "close notify" alert B it was +already processed implicitly inside another function +(L), 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 L call. + +=back + +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). + +The behaviour of SSL_shutdown() additionally depends on the underlying BIO. + +If the underlying BIO is B, SSL_shutdown() will only return once the +handshake step has been finished or an error occurred. + +If the underlying BIO is B, 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 or +B. 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 L. +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. Call SSL_shutdown() for a second time, +if a bidirectional shutdown shall be performed. +The output of L 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 E0 + +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 L with the return value B +to find out the reason. + +=back + +=head1 SEE ALSO + +L, L, +L, L, +L, +L, L, +L, L + +=head1 COPYRIGHT + +Copyright 2000-2016 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. + +=cut -- cgit v1.2.3