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Diffstat (limited to 'secure/lib/libssl/man/SSL_shutdown.3')
| -rw-r--r-- | secure/lib/libssl/man/SSL_shutdown.3 | 234 |
1 files changed, 234 insertions, 0 deletions
diff --git a/secure/lib/libssl/man/SSL_shutdown.3 b/secure/lib/libssl/man/SSL_shutdown.3 new file mode 100644 index 0000000..8b68da2 --- /dev/null +++ b/secure/lib/libssl/man/SSL_shutdown.3 @@ -0,0 +1,234 @@ +.\" Automatically generated by Pod::Man 2.28 (Pod::Simple 3.30) +.\" +.\" Standard preamble: +.\" ======================================================================== +.de Sp \" Vertical space (when we can't use .PP) +.if t .sp .5v +.if n .sp +.. +.de Vb \" Begin verbatim text +.ft CW +.nf +.ne \\$1 +.. +.de Ve \" End verbatim text +.ft R +.fi +.. +.\" Set up some character translations and predefined strings. \*(-- will +.\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left +.\" double quote, and \*(R" will give a right double quote. \*(C+ will +.\" give a nicer C++. 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Always turn off hyphenation; it makes +.\" way too many mistakes in technical documents. +.if n .ad l +.nh +.SH "NAME" +SSL_shutdown \- shut down a TLS/SSL connection +.SH "SYNOPSIS" +.IX Header "SYNOPSIS" +.Vb 1 +\& #include <openssl/ssl.h> +\& +\& int SSL_shutdown(SSL *ssl); +.Ve +.SH "DESCRIPTION" +.IX Header "DESCRIPTION" +\&\fISSL_shutdown()\fR shuts down an active \s-1TLS/SSL\s0 connection. It sends the +\&\*(L"close notify\*(R" shutdown alert to the peer. +.SH "NOTES" +.IX Header "NOTES" +\&\fISSL_shutdown()\fR tries to send the \*(L"close notify\*(R" shutdown alert to the peer. +Whether the operation succeeds or not, the \s-1SSL_SENT_SHUTDOWN\s0 flag is set and +a currently open session is considered closed and good and will be kept in the +session cache for further reuse. +.PP +The shutdown procedure consists of 2 steps: the sending of the \*(L"close notify\*(R" +shutdown alert and the reception of the peer's \*(L"close notify\*(R" shutdown +alert. According to the \s-1TLS\s0 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 \*(L"close notify\*(R" alerts) must be +performed, so that the peers stay synchronized. +.PP +\&\fISSL_shutdown()\fR supports both uni\- and bidirectional shutdown by its 2 step +behaviour. +.ie n .IP "When the application is the first party to send the ""close notify"" alert, \fISSL_shutdown()\fR will only send the alert and then set the \s-1SSL_SENT_SHUTDOWN\s0 flag (so that the session is considered good and will be kept in cache). \fISSL_shutdown()\fR will then return with 0. If a unidirectional shutdown is enough (the underlying connection shall be closed anyway), this first call to \fISSL_shutdown()\fR is sufficient. In order to complete the bidirectional shutdown handshake, \fISSL_shutdown()\fR must be called again. The second call will make \fISSL_shutdown()\fR wait for the peer's ""close notify"" shutdown alert. On success, the second call to \fISSL_shutdown()\fR will return with 1." 4 +.el .IP "When the application is the first party to send the ``close notify'' alert, \fISSL_shutdown()\fR will only send the alert and then set the \s-1SSL_SENT_SHUTDOWN\s0 flag (so that the session is considered good and will be kept in cache). \fISSL_shutdown()\fR will then return with 0. If a unidirectional shutdown is enough (the underlying connection shall be closed anyway), this first call to \fISSL_shutdown()\fR is sufficient. In order to complete the bidirectional shutdown handshake, \fISSL_shutdown()\fR must be called again. The second call will make \fISSL_shutdown()\fR wait for the peer's ``close notify'' shutdown alert. On success, the second call to \fISSL_shutdown()\fR will return with 1." 4 +.IX 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." +.PD 0 +.ie n .IP "If the peer already sent the ""close notify"" alert \fBand\fR it was already processed implicitly inside another function (\fISSL_read\fR\|(3)), the \s-1SSL_RECEIVED_SHUTDOWN\s0 flag is set. \fISSL_shutdown()\fR will send the ""close notify"" alert, set the \s-1SSL_SENT_SHUTDOWN\s0 flag and will immediately return with 1. Whether \s-1SSL_RECEIVED_SHUTDOWN\s0 is already set can be checked using the \fISSL_get_shutdown()\fR (see also \fISSL_set_shutdown\fR\|(3) call." 4 +.el .IP "If the peer already sent the ``close notify'' alert \fBand\fR it was already processed implicitly inside another function (\fISSL_read\fR\|(3)), the \s-1SSL_RECEIVED_SHUTDOWN\s0 flag is set. \fISSL_shutdown()\fR will send the ``close notify'' alert, set the \s-1SSL_SENT_SHUTDOWN\s0 flag and will immediately return with 1. Whether \s-1SSL_RECEIVED_SHUTDOWN\s0 is already set can be checked using the \fISSL_get_shutdown()\fR (see also \fISSL_set_shutdown\fR\|(3) call." 4 +.IX Item "If the peer already sent the close notify alert and it was already processed implicitly inside another function (SSL_read), 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 call." +.PD +.PP +It is therefore recommended, to check the return value of \fISSL_shutdown()\fR +and call \fISSL_shutdown()\fR 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, \fISSL_shutdown()\fR will succeed on +the first call. +.PP +The behaviour of \fISSL_shutdown()\fR additionally depends on the underlying \s-1BIO. \s0 +.PP +If the underlying \s-1BIO\s0 is \fBblocking\fR, \fISSL_shutdown()\fR will only return once the +handshake step has been finished or an error occurred. +.PP +If the underlying \s-1BIO\s0 is \fBnon-blocking\fR, \fISSL_shutdown()\fR will also return +when the underlying \s-1BIO\s0 could not satisfy the needs of \fISSL_shutdown()\fR +to continue the handshake. In this case a call to \fISSL_get_error()\fR with the +return value of \fISSL_shutdown()\fR will yield \fB\s-1SSL_ERROR_WANT_READ\s0\fR or +\&\fB\s-1SSL_ERROR_WANT_WRITE\s0\fR. The calling process then must repeat the call after +taking appropriate action to satisfy the needs of \fISSL_shutdown()\fR. +The action depends on the underlying \s-1BIO.\s0 When using a non-blocking socket, +nothing is to be done, but \fIselect()\fR can be used to check for the required +condition. When using a buffering \s-1BIO,\s0 like a \s-1BIO\s0 pair, data must be written +into or retrieved out of the \s-1BIO\s0 before being able to continue. +.PP +\&\fISSL_shutdown()\fR can be modified to only set the connection to \*(L"shutdown\*(R" +state but not actually send the \*(L"close notify\*(R" alert messages, +see \fISSL_CTX_set_quiet_shutdown\fR\|(3). +When \*(L"quiet shutdown\*(R" is enabled, \fISSL_shutdown()\fR will always succeed +and return 1. +.SH "RETURN VALUES" +.IX Header "RETURN VALUES" +The following return values can occur: +.IP "0" 4 +The shutdown is not yet finished. Call \fISSL_shutdown()\fR for a second time, +if a bidirectional shutdown shall be performed. +The output of \fISSL_get_error\fR\|(3) may be misleading, as an +erroneous \s-1SSL_ERROR_SYSCALL\s0 may be flagged even though no error occurred. +.IP "1" 4 +.IX Item "1" +The shutdown was successfully completed. The \*(L"close notify\*(R" alert was sent +and the peer's \*(L"close notify\*(R" alert was received. +.IP "<0" 4 +.IX Item "<0" +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 \fISSL_get_error\fR\|(3) with the return value \fBret\fR +to find out the reason. +.SH "SEE ALSO" +.IX Header "SEE ALSO" +\&\fISSL_get_error\fR\|(3), \fISSL_connect\fR\|(3), +\&\fISSL_accept\fR\|(3), \fISSL_set_shutdown\fR\|(3), +\&\fISSL_CTX_set_quiet_shutdown\fR\|(3), +\&\fISSL_clear\fR\|(3), \fISSL_free\fR\|(3), +\&\fIssl\fR\|(3), \fIbio\fR\|(3) |
