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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_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 \fBnonblocking\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 nonblocking 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 if action is needed to continue the operation for nonblocking 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\|(7), \fBbio\fR\|(7), \&\fBSSL_set_connect_state\fR\|(3) .SH "COPYRIGHT" .IX Header "COPYRIGHT" Copyright 2002\-2020 The OpenSSL Project Authors. All Rights Reserved. .PP Licensed under the OpenSSL license (the \*(L"License\*(R"). You may not use this file except in compliance with the License. You can obtain a copy in the file \s-1LICENSE\s0 in the source distribution or at <https://www.openssl.org/source/license.html>.