SSL_connect

SSL_CONNECT(3)                       OpenSSL                      SSL_CONNECT(3)



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

SYNOPSIS
        #include <openssl/ssl.h>

        int SSL_connect(SSL *ssl);

DESCRIPTION
       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.

NOTES
       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.

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_accept(3), SSL_shutdown(3), ssl(7), bio(7),
       SSL_set_connect_state(3), SSL_do_handshake(3), SSL_CTX_new(3)

COPYRIGHT
       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
       <https://www.openssl.org/source/license.html>.



1.1.1j                             2021-02-16                     SSL_CONNECT(3)