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+=pod
+
+=head1 NAME
+
+SSL_connect - initiate the TLS/SSL handshake with an TLS/SSL server
+
+=head1 SYNOPSIS
+
+ #include <openssl/ssl.h>
+
+ int SSL_connect(SSL *ssl);
+
+=head1 DESCRIPTION
+
+SSL_connect() initiates the TLS/SSL handshake with a server. The communication
+channel must already have been set and assigned to the B<ssl> by setting an
+underlying B<BIO>.
+
+=head1 NOTES
+
+The behaviour of SSL_connect() depends on the underlying BIO.
+
+If the underlying BIO is B<blocking>, SSL_connect() will only return once the
+handshake has been finished or an error occurred.
+
+If the underlying BIO is B<non-blocking>, SSL_connect() will also return
+when the underlying BIO could not satisfy the needs of SSL_connect()
+to continue the handshake, indicating the problem by the return value -1.
+In this case a call to SSL_get_error() with the
+return value of SSL_connect() 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_connect().
+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.
+
+Many systems implement Nagle's algorithm by default which means that it will
+buffer outgoing TCP data if a TCP packet has already been sent for which no
+corresponding ACK has been received yet from the peer. This can have performance
+impacts after a successful TLSv1.3 handshake or a successful TLSv1.2 (or below)
+resumption handshake, because the last peer to communicate in the handshake is
+the client. If the client is also the first to send application data (as is
+typical for many protocols) then this data could be buffered until an ACK has
+been received for the final handshake message.
+
+The B<TCP_NODELAY> socket option is often available to disable Nagle's
+algorithm. If an application opts to disable Nagle's algorithm consideration
+should be given to turning it back on again later if appropriate. The helper
+function BIO_set_tcp_ndelay() can be used to turn on or off the B<TCP_NODELAY>
+option.
+
+=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_accept(3)>,
+L<SSL_shutdown(3)>, L<ssl(7)>, L<bio(7)>,
+L<SSL_set_connect_state(3)>,
+L<SSL_do_handshake(3)>,
+L<SSL_CTX_new(3)>
+
+=head1 COPYRIGHT
+
+Copyright 2000-2018 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