| 1 | =pod
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| 2 |
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| 3 | =head1 NAME
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| 4 |
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| 5 | SSL_do_handshake - perform a TLS/SSL handshake
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| 6 |
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| 7 | =head1 SYNOPSIS
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| 8 |
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| 9 | #include <openssl/ssl.h>
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| 10 |
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| 11 | int SSL_do_handshake(SSL *ssl);
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| 12 |
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| 13 | =head1 DESCRIPTION
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| 14 |
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| 15 | SSL_do_handshake() will wait for a SSL/TLS handshake to take place. If the
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| 16 | connection is in client mode, the handshake will be started. The handshake
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| 17 | routines may have to be explicitly set in advance using either
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| 18 | L<SSL_set_connect_state(3)> or
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| 19 | L<SSL_set_accept_state(3)>.
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| 20 |
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| 21 | =head1 NOTES
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| 22 |
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| 23 | The behaviour of SSL_do_handshake() depends on the underlying BIO.
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| 24 |
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| 25 | If the underlying BIO is B<blocking>, SSL_do_handshake() will only return
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| 26 | once the handshake has been finished or an error occurred.
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| 27 |
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| 28 | If the underlying BIO is B<nonblocking>, SSL_do_handshake() will also return
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| 29 | when the underlying BIO could not satisfy the needs of SSL_do_handshake()
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| 30 | to continue the handshake. In this case a call to SSL_get_error() with the
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| 31 | return value of SSL_do_handshake() will yield B<SSL_ERROR_WANT_READ> or
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| 32 | B<SSL_ERROR_WANT_WRITE>. The calling process then must repeat the call after
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| 33 | taking appropriate action to satisfy the needs of SSL_do_handshake().
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| 34 | The action depends on the underlying BIO. When using a nonblocking socket,
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| 35 | nothing is to be done, but select() can be used to check for the required
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| 36 | condition. When using a buffering BIO, like a BIO pair, data must be written
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| 37 | into or retrieved out of the BIO before being able to continue.
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| 38 |
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| 39 | =head1 RETURN VALUES
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| 40 |
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| 41 | The following return values can occur:
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| 42 |
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| 43 | =over 4
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| 44 |
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| 45 | =item Z<>0
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| 46 |
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| 47 | The TLS/SSL handshake was not successful but was shut down controlled and
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| 48 | by the specifications of the TLS/SSL protocol. Call SSL_get_error() with the
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| 49 | return value B<ret> to find out the reason.
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| 50 |
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| 51 | =item Z<>1
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| 52 |
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| 53 | The TLS/SSL handshake was successfully completed, a TLS/SSL connection has been
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| 54 | established.
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| 55 |
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| 56 | =item E<lt>0
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| 57 |
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| 58 | The TLS/SSL handshake was not successful because a fatal error occurred either
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| 59 | at the protocol level or a connection failure occurred. The shutdown was
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| 60 | not clean. It can also occur if action is needed to continue the operation
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| 61 | for nonblocking BIOs. Call SSL_get_error() with the return value B<ret>
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| 62 | to find out the reason.
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| 63 |
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| 64 | =back
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| 65 |
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| 66 | =head1 SEE ALSO
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| 67 |
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| 68 | L<SSL_get_error(3)>, L<SSL_connect(3)>,
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| 69 | L<SSL_accept(3)>, L<ssl(7)>, L<bio(7)>,
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| 70 | L<SSL_set_connect_state(3)>
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| 71 |
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| 72 | =head1 COPYRIGHT
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| 73 |
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| 74 | Copyright 2002-2020 The OpenSSL Project Authors. All Rights Reserved.
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| 75 |
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| 76 | Licensed under the OpenSSL license (the "License"). You may not use
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| 77 | this file except in compliance with the License. You can obtain a copy
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| 78 | in the file LICENSE in the source distribution or at
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| 79 | L<https://www.openssl.org/source/license.html>.
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| 80 |
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| 81 | =cut
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