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.IX Title "SSL_CTX_SET_TLSEXT_SERVERNAME_CALLBACK 3SSL"
.TH SSL_CTX_SET_TLSEXT_SERVERNAME_CALLBACK 3SSL "2021-03-22" "1.1.1d" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.nh
.SH "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)
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #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);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The functionality provided by the servername callback is superseded by the
ClientHello callback, which can be set using \fBSSL_CTX_set_client_hello_cb()\fR.
The servername callback is retained for historical compatibility.
.PP
\&\fBSSL_CTX_set_tlsext_servername_callback()\fR sets the application callback \fBcb\fR
used by a server to perform any actions or configuration required based on
the servername extension received in the incoming connection. When \fBcb\fR
is \s-1NULL, SNI\s0 is not used. The \fBarg\fR value is a pointer which is passed to
the application callback.
.PP
\&\fBSSL_CTX_set_tlsext_servername_arg()\fR sets a context-specific argument to be
passed into the callback for this \fB\s-1SSL_CTX\s0\fR.
.PP
\&\fBSSL_get_servername()\fR returns a servername extension value of the specified
type if provided in the Client Hello or \s-1NULL.\s0
.PP
\&\fBSSL_get_servername_type()\fR returns the servername type or \-1 if no servername
is present. Currently the only supported type (defined in \s-1RFC3546\s0) is
\&\fBTLSEXT_NAMETYPE_host_name\fR.
.PP
\&\fBSSL_set_tlsext_host_name()\fR sets the server name indication ClientHello extension
to contain the value \fBname\fR. The type of server name indication extension is set
to \fBTLSEXT_NAMETYPE_host_name\fR (defined in \s-1RFC3546\s0).
.SH "NOTES"
.IX Header "NOTES"
Several callbacks are executed during ClientHello processing, including
the ClientHello, \s-1ALPN,\s0 and servername callbacks.  The ClientHello callback is
executed first, then the servername callback, followed by the \s-1ALPN\s0 callback.
.PP
The \fBSSL_set_tlsext_host_name()\fR function should only be called on \s-1SSL\s0 objects
that will act as clients; otherwise the configured \fBname\fR will be ignored.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBSSL_CTX_set_tlsext_servername_callback()\fR and
\&\fBSSL_CTX_set_tlsext_servername_arg()\fR both always return 1 indicating success.
\&\fBSSL_set_tlsext_host_name()\fR returns 1 on success, 0 in case of error.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBssl\fR\|(7), \fBSSL_CTX_set_alpn_select_cb\fR\|(3),
\&\fBSSL_get0_alpn_selected\fR\|(3), \fBSSL_CTX_set_client_hello_cb\fR\|(3)
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2017 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the OpenSSL license (the \*(L"License\*(R").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file \s-1LICENSE\s0 in the source distribution or at
<https://www.openssl.org/source/license.html>.