openssl/doc/ssl/SSL_connect.pod

=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.

=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(3)>, L<bio(3)>,
L<SSL_set_connect_state(3)>,
L<SSL_do_handshake(3)>,
L<SSL_CTX_new(3)>

=cut