=pod =head1 NAME SSL_do_handshake - perform a TLS/SSL handshake =head1 SYNOPSIS #include <openssl/ssl.h> int SSL_do_handshake(SSL *ssl); =head1 DESCRIPTION SSL_do_handshake() will wait for a SSL/TLS 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 L<SSL_set_connect_state(3)> or L<SSL_set_accept_state(3)>. =head1 NOTES The behaviour of SSL_do_handshake() depends on the underlying BIO. If the underlying BIO is B<blocking>, SSL_do_handshake() will only return once the handshake has been finished or an error occurred. If the underlying BIO is B<non-blocking>, SSL_do_handshake() will also return when the underlying BIO could not satisfy the needs of SSL_do_handshake() to continue the handshake. In this case a call to SSL_get_error() with the return value of SSL_do_handshake() will yield B<SSL_ERROR_WANT_READ> or B<SSL_ERROR_WANT_WRITE>. The calling process then must repeat the call after taking appropriate action to satisfy the needs of SSL_do_handshake(). 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. =head1 RETURN VALUES The following return values can occur: =over 4 =item Z<>0 The TLS/SSL handshake was not successful but was shut down controlled and by the specifications of the TLS/SSL protocol. Call SSL_get_error() with the return value B<ret> to find out the reason. =item Z<>1 The TLS/SSL handshake was successfully completed, a TLS/SSL connection has been established. =item E<lt>0 The TLS/SSL 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 SSL_get_error() with the return value B<ret> to find out the reason. =back =head1 SEE ALSO L<SSL_get_error(3)>, L<SSL_connect(3)>, L<SSL_accept(3)>, L<ssl(7)>, L<bio(7)>, L<SSL_set_connect_state(3)> =head1 COPYRIGHT Copyright 2002-2016 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<https://www.openssl.org/source/license.html>. =cut