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.\"
.IX Title "SSL_do_handshake 3"
.TH SSL_do_handshake 3 "0.9.7a" "2003-02-19" "OpenSSL"
.UC
.SH "NAME"
SSL_do_handshake \- perform a \s-1TLS/SSL\s0 handshake
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/ssl.h>
.Ve
.Vb 1
\& int SSL_do_handshake(SSL *ssl);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fISSL_do_handshake()\fR will wait for a \s-1SSL/TLS\s0 handshake to take place. If the
connection is in client mode, the handshake will be started. The handshake
routines may have to be explicitly set in advance using either
SSL_set_connect_state(3) or
SSL_set_accept_state(3).
.SH "NOTES"
.IX Header "NOTES"
The behaviour of \fISSL_do_handshake()\fR depends on the underlying \s-1BIO\s0.
.PP
If the underlying \s-1BIO\s0 is \fBblocking\fR, \fISSL_do_handshake()\fR will only return
once the handshake has been finished or an error occurred, except for \s-1SGC\s0
(Server Gated Cryptography). For \s-1SGC\s0, \fISSL_do_handshake()\fR may return with \-1,
but \fISSL_get_error()\fR will yield \fB\s-1SSL_ERROR_WANT_READ/WRITE\s0\fR and
\&\fISSL_do_handshake()\fR should be called again.
.PP
If the underlying \s-1BIO\s0 is \fBnon-blocking\fR, \fISSL_do_handshake()\fR will also return
when the underlying \s-1BIO\s0 could not satisfy the needs of \fISSL_do_handshake()\fR
to continue the handshake. In this case a call to \fISSL_get_error()\fR with the
return value of \fISSL_do_handshake()\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_do_handshake()\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.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
The following return values can occur:
.Ip "1" 4
.IX Item "1"
The \s-1TLS/SSL\s0 handshake was successfully completed, a \s-1TLS/SSL\s0 connection has been
established.
.Ip "0" 4
The \s-1TLS/SSL\s0 handshake was not successful but was shut down controlled and
by the specifications of the \s-1TLS/SSL\s0 protocol. Call \fISSL_get_error()\fR with the
return value \fBret\fR to find out the reason.
.Ip "<0" 4
.IX Item "<0"
The \s-1TLS/SSL\s0 handshake was not successful because a fatal error occurred either
at the protocol level or a connection failure occurred. The shutdown was
not clean. It can also occur of action is need to continue the operation
for non-blocking BIOs. Call \fISSL_get_error()\fR with the return value \fBret\fR
to find out the reason.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
SSL_get_error(3), SSL_connect(3),
SSL_accept(3), ssl(3), bio(3),
SSL_set_connect_state(3)