=pod

=head1 NAME

SSL_CTX_set_tlsext_servername_callback, SSL_CTX_set_tlsext_servername_arg,
SSL_get_servername_type, SSL_get_servername,
SSL_set_tlsext_host_name - handle server name indication (SNI)

=head1 SYNOPSIS

 #include <openssl/ssl.h>

 long SSL_CTX_set_tlsext_servername_callback(SSL_CTX *ctx,
                                   int (*cb)(SSL *, int *, void *));
 long SSL_CTX_set_tlsext_servername_arg(SSL_CTX *ctx, void *arg);

 const char *SSL_get_servername(const SSL *s, const int type);
 int SSL_get_servername_type(const SSL *s);

 int SSL_set_tlsext_host_name(const SSL *s, const char *name);

=head1 DESCRIPTION

The functionality provided by the servername callback is superseded by the
ClientHello callback, which can be set using SSL_CTX_set_client_hello_cb().
The servername callback is retained for historical compatibility.

SSL_CTX_set_tlsext_servername_callback() sets the application callback B<cb>
used by a server to perform any actions or configuration required based on
the servername extension received in the incoming connection. When B<cb>
is NULL, SNI is not used. The B<arg> value is a pointer which is passed to
the application callback.

SSL_CTX_set_tlsext_servername_arg() sets a context-specific argument to be
passed into the callback for this B<SSL_CTX>.

SSL_get_servername() returns a servername extension value of the specified
type if provided in the Client Hello or NULL.

SSL_get_servername_type() returns the servername type or -1 if no servername
is present. Currently the only supported type (defined in RFC3546) is
B<TLSEXT_NAMETYPE_host_name>.

SSL_set_tlsext_host_name() sets the server name indication ClientHello extension
to contain the value B<name>. The type of server name indication extension is set
to B<TLSEXT_NAMETYPE_host_name> (defined in RFC3546).

=head1 NOTES

Several callbacks are executed during ClientHello processing, including
the ClientHello, ALPN, and servername callbacks.  The ClientHello callback is
executed first, then the servername callback, followed by the ALPN callback.

The SSL_set_tlsext_host_name() function should only be called on SSL objects
that will act as clients; otherwise the configured B<name> will be ignored.

=head1 RETURN VALUES

SSL_CTX_set_tlsext_servername_callback() and
SSL_CTX_set_tlsext_servername_arg() both always return 1 indicating success.
SSL_set_tlsext_host_name() returns 1 on success, 0 in case of error.

=head1 SEE ALSO

L<ssl(7)>, L<SSL_CTX_set_alpn_select_cb(3)>,
L<SSL_get0_alpn_selected(3)>, L<SSL_CTX_set_client_hello_cb(3)>

=head1 COPYRIGHT

Copyright 2017 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
L<https://www.openssl.org/source/license.html>.

=cut
