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       SSL_connect - initiate the TLS/SSL handshake with an TLS/SSL server

	#include <openssl/ssl.h>

	int SSL_connect(SSL *ssl);

       SSL_connect() initiates the TLS/SSL handshake with a server. The
       communication channel must already have been set	and assigned to	the
       ssl by setting an underlying BIO.

       The behaviour of	SSL_connect() depends on the underlying	BIO.

       If the underlying BIO is	blocking, SSL_connect()	will only return once
       the handshake has been finished or an error occurred.

       If the underlying BIO is	nonblocking, 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	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_connect().  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.

       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 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 TCP_NODELAY option.

       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.

       SSL_get_error(3), SSL_accept(3),	SSL_shutdown(3), ssl(7), bio(7),
       SSL_set_connect_state(3), SSL_do_handshake(3), SSL_CTX_new(3)

       Copyright 2000-2020 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

1.1.1k				  2021-03-25			SSL_CONNECT(3)


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