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.\" ========================================================================
.\"
.IX Title "SSL_do_handshake 3"
.TH SSL_do_handshake 3 "2019-12-20" "1.0.2u" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
SSL_do_handshake \- perform a TLS/SSL handshake
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/ssl.h>
\&
\& int SSL_do_handshake(SSL *ssl);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fBSSL_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
\&\fBSSL_set_connect_state\fR\|(3) or
\&\fBSSL_set_accept_state\fR\|(3).
.SH "NOTES"
.IX Header "NOTES"
The behaviour of \fBSSL_do_handshake()\fR depends on the underlying \s-1BIO.\s0
.PP
If the underlying \s-1BIO\s0 is \fBblocking\fR, \fBSSL_do_handshake()\fR will only return
once the handshake has been finished or an error occurred.
.PP
If the underlying \s-1BIO\s0 is \fBnon-blocking\fR, \fBSSL_do_handshake()\fR will also return
when the underlying \s-1BIO\s0 could not satisfy the needs of \fBSSL_do_handshake()\fR
to continue the handshake. In this case a call to \fBSSL_get_error()\fR with the
return value of \fBSSL_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 \fBSSL_do_handshake()\fR.
The action depends on the underlying \s-1BIO.\s0 When using a non-blocking socket,
nothing is to be done, but \fBselect()\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 "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 \fBSSL_get_error()\fR with the
return value \fBret\fR to find out the reason.
.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
.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 \fBSSL_get_error()\fR with the return value \fBret\fR
to find out the reason.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBSSL_get_error\fR\|(3), \fBSSL_connect\fR\|(3),
\&\fBSSL_accept\fR\|(3), \fBssl\fR\|(3), \fBbio\fR\|(3),
\&\fBSSL_set_connect_state\fR\|(3)