SSL_DO_HANDSHAKE(3SSL) OpenSSL SSL_DO_HANDSHAKE(3SSL)
NAME
SSL_do_handshake - perform a TLS/SSL handshake
SYNOPSIS
#include <openssl/ssl.h>
int SSL_do_handshake(SSL *ssl);
DESCRIPTION
SSL_do_handshake() will wait for an 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
SSL_set_connect_state(3) or SSL_set_accept_state(3).
NOTES
The behaviour of SSL_do_handshake() depends on the underlying BIO.
If the underlying BIO is blocking, SSL_do_handshake() will only return
once the handshake has been finished or an error occurred.
If the underlying BIO is nonblocking, 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
SSL_ERROR_WANT_READ or 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 nonblocking 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.
RETURN VALUES
The following return values can occur:
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 ret to find out the reason.
1 The TLS/SSL handshake was successfully completed, a TLS/SSL
connection has been established.
<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 if action is
needed to continue the operation for nonblocking BIOs. Call
SSL_get_error() with the return value ret to find out the reason.
SEE ALSO
SSL_get_error(3), SSL_connect(3), SSL_accept(3), ssl(7), bio(7),
SSL_set_connect_state(3)
COPYRIGHT
Copyright 2002-2020 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (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
<https://www.openssl.org/source/license.html>.
3.5.7 2026-06-09 SSL_DO_HANDSHAKE(3SSL)
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