.\" Automatically generated by Pod::Man 4.11 (Pod::Simple 3.35)
.\"
.\" Standard preamble:
.\" ========================================================================
.de Sp \" Vertical space (when we can't use .PP)
.if t .sp .5v
.if n .sp
..
.de Vb \" Begin verbatim text
.ft CW
.nf
.ne \\$1
..
.de Ve \" End verbatim text
.ft R
.fi
..
.\" Set up some character translations and predefined strings.  \*(-- will
.\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left
.\" double quote, and \*(R" will give a right double quote.  \*(C+ will
.\" give a nicer C++.  Capital omega is used to do unbreakable dashes and
.\" therefore won't be available.  \*(C` and \*(C' expand to `' in nroff,
.\" nothing in troff, for use with C<>.
.tr \(*W-
.ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p'
.ie n \{\
.    ds -- \(*W-
.    ds PI pi
.    if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
.    if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\"  diablo 12 pitch
.    ds L" ""
.    ds R" ""
.    ds C` ""
.    ds C' ""
'br\}
.el\{\
.    ds -- \|\(em\|
.    ds PI \(*p
.    ds L" ``
.    ds R" ''
.    ds C`
.    ds C'
'br\}
.\"
.\" Escape single quotes in literal strings from groff's Unicode transform.
.ie \n(.g .ds Aq \(aq
.el       .ds Aq '
.\"
.\" If the F register is >0, we'll generate index entries on stderr for
.\" titles (.TH), headers (.SH), subsections (.SS), items (.Ip), and index
.\" entries marked with X<> in POD.  Of course, you'll have to process the
.\" output yourself in some meaningful fashion.
.\"
.\" Avoid warning from groff about undefined register 'F'.
.de IX
..
.nr rF 0
.if \n(.g .if rF .nr rF 1
.if (\n(rF:(\n(.g==0)) \{\
.    if \nF \{\
.        de IX
.        tm Index:\\$1\t\\n%\t"\\$2"
..
.        if !\nF==2 \{\
.            nr % 0
.            nr F 2
.        \}
.    \}
.\}
.rr rF
.\"
.\" Accent mark definitions (@(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2).
.\" Fear.  Run.  Save yourself.  No user-serviceable parts.
.    \" fudge factors for nroff and troff
.if n \{\
.    ds #H 0
.    ds #V .8m
.    ds #F .3m
.    ds #[ \f1
.    ds #] \fP
.\}
.if t \{\
.    ds #H ((1u-(\\\\n(.fu%2u))*.13m)
.    ds #V .6m
.    ds #F 0
.    ds #[ \&
.    ds #] \&
.\}
.    \" simple accents for nroff and troff
.if n \{\
.    ds ' \&
.    ds ` \&
.    ds ^ \&
.    ds , \&
.    ds ~ ~
.    ds /
.\}
.if t \{\
.    ds ' \\k:\h'-(\\n(.wu*8/10-\*(#H)'\'\h"|\\n:u"
.    ds ` \\k:\h'-(\\n(.wu*8/10-\*(#H)'\`\h'|\\n:u'
.    ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'^\h'|\\n:u'
.    ds , \\k:\h'-(\\n(.wu*8/10)',\h'|\\n:u'
.    ds ~ \\k:\h'-(\\n(.wu-\*(#H-.1m)'~\h'|\\n:u'
.    ds / \\k:\h'-(\\n(.wu*8/10-\*(#H)'\z\(sl\h'|\\n:u'
.\}
.    \" troff and (daisy-wheel) nroff accents
.ds : \\k:\h'-(\\n(.wu*8/10-\*(#H+.1m+\*(#F)'\v'-\*(#V'\z.\h'.2m+\*(#F'.\h'|\\n:u'\v'\*(#V'
.ds 8 \h'\*(#H'\(*b\h'-\*(#H'
.ds o \\k:\h'-(\\n(.wu+\w'\(de'u-\*(#H)/2u'\v'-.3n'\*(#[\z\(de\v'.3n'\h'|\\n:u'\*(#]
.ds d- \h'\*(#H'\(pd\h'-\w'~'u'\v'-.25m'\f2\(hy\fP\v'.25m'\h'-\*(#H'
.ds D- D\\k:\h'-\w'D'u'\v'-.11m'\z\(hy\v'.11m'\h'|\\n:u'
.ds th \*(#[\v'.3m'\s+1I\s-1\v'-.3m'\h'-(\w'I'u*2/3)'\s-1o\s+1\*(#]
.ds Th \*(#[\s+2I\s-2\h'-\w'I'u*3/5'\v'-.3m'o\v'.3m'\*(#]
.ds ae a\h'-(\w'a'u*4/10)'e
.ds Ae A\h'-(\w'A'u*4/10)'E
.    \" corrections for vroff
.if v .ds ~ \\k:\h'-(\\n(.wu*9/10-\*(#H)'\s-2\u~\d\s+2\h'|\\n:u'
.if v .ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'\v'-.4m'^\v'.4m'\h'|\\n:u'
.    \" for low resolution devices (crt and lpr)
.if \n(.H>23 .if \n(.V>19 \
\{\
.    ds : e
.    ds 8 ss
.    ds o a
.    ds d- d\h'-1'\(ga
.    ds D- D\h'-1'\(hy
.    ds th \o'bp'
.    ds Th \o'LP'
.    ds ae ae
.    ds Ae AE
.\}
.rm #[ #] #H #V #F C
.\" ========================================================================
.\"
.IX Title "SSL_CTX_set_alpn_select_cb 3"
.TH SSL_CTX_set_alpn_select_cb 3 "2019-12-20" "1.0.2u" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
SSL_CTX_set_alpn_protos, SSL_set_alpn_protos, SSL_CTX_set_alpn_select_cb,
SSL_select_next_proto, SSL_get0_alpn_selected \- handle application layer
protocol negotiation (ALPN)
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/ssl.h>
\&
\& int SSL_CTX_set_alpn_protos(SSL_CTX *ctx, const unsigned char *protos,
\&                             unsigned protos_len);
\& int SSL_set_alpn_protos(SSL *ssl, const unsigned char *protos,
\&                         unsigned protos_len);
\& void SSL_CTX_set_alpn_select_cb(SSL_CTX *ctx,
\&                                 int (*cb) (SSL *ssl,
\&                                            const unsigned char **out,
\&                                            unsigned char *outlen,
\&                                            const unsigned char *in,
\&                                            unsigned int inlen,
\&                                            void *arg), void *arg);
\& int SSL_select_next_proto(unsigned char **out, unsigned char *outlen,
\&                           const unsigned char *server,
\&                           unsigned int server_len,
\&                           const unsigned char *client,
\&                           unsigned int client_len)
\& void SSL_get0_alpn_selected(const SSL *ssl, const unsigned char **data,
\&                             unsigned int *len);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fBSSL_CTX_set_alpn_protos()\fR and \fBSSL_set_alpn_protos()\fR are used by the client to
set the list of protocols available to be negotiated. The \fBprotos\fR must be in
protocol-list format, described below. The length of \fBprotos\fR is specified in
\&\fBprotos_len\fR.
.PP
\&\fBSSL_CTX_set_alpn_select_cb()\fR sets the application callback \fBcb\fR used by a
server to select which protocol to use for the incoming connection. When \fBcb\fR
is \s-1NULL, ALPN\s0 is not used. The \fBarg\fR value is a pointer which is passed to
the application callback.
.PP
\&\fBcb\fR is the application defined callback. The \fBin\fR, \fBinlen\fR parameters are a
vector in protocol-list format. The value of the \fBout\fR, \fBoutlen\fR vector
should be set to the value of a single protocol selected from the \fBin\fR,
\&\fBinlen\fR vector. The \fBarg\fR parameter is the pointer set via
\&\fBSSL_CTX_set_alpn_select_cb()\fR.
.PP
\&\fBSSL_select_next_proto()\fR is a helper function used to select protocols. It
implements the standard protocol selection. It is expected that this function
is called from the application callback \fBcb\fR. The protocol data in \fBserver\fR,
\&\fBserver_len\fR and \fBclient\fR, \fBclient_len\fR must be in the protocol-list format
described below. The first item in the \fBserver\fR, \fBserver_len\fR list that
matches an item in the \fBclient\fR, \fBclient_len\fR list is selected, and returned
in \fBout\fR, \fBoutlen\fR. The \fBout\fR value will point into either \fBserver\fR or
\&\fBclient\fR, so it should be copied immediately. If no match is found, the first
item in \fBclient\fR, \fBclient_len\fR is returned in \fBout\fR, \fBoutlen\fR. This
function can also be used in the \s-1NPN\s0 callback.
.PP
\&\fBSSL_get0_alpn_selected()\fR returns a pointer to the selected protocol in \fBdata\fR
with length \fBlen\fR. It is not NUL-terminated. \fBdata\fR is set to \s-1NULL\s0 and \fBlen\fR
is set to 0 if no protocol has been selected. \fBdata\fR must not be freed.
.SH "NOTES"
.IX Header "NOTES"
The protocol-lists must be in wire-format, which is defined as a vector of
non-empty, 8\-bit length-prefixed, byte strings. The length-prefix byte is not
included in the length. Each string is limited to 255 bytes. A byte-string
length of 0 is invalid. A truncated byte-string is invalid. The length of the
vector is not in the vector itself, but in a separate variable.
.PP
Example:
.PP
.Vb 5
\& unsigned char vector[] = {
\&     6, \*(Aqs\*(Aq, \*(Aqp\*(Aq, \*(Aqd\*(Aq, \*(Aqy\*(Aq, \*(Aq/\*(Aq, \*(Aq1\*(Aq,
\&     8, \*(Aqh\*(Aq, \*(Aqt\*(Aq, \*(Aqt\*(Aq, \*(Aqp\*(Aq, \*(Aq/\*(Aq, \*(Aq1\*(Aq, \*(Aq.\*(Aq, \*(Aq1\*(Aq
\& };
\& unsigned int length = sizeof(vector);
.Ve
.PP
The \s-1ALPN\s0 callback is executed after the servername callback; as that servername
callback may update the \s-1SSL_CTX,\s0 and subsequently, the \s-1ALPN\s0 callback.
.PP
If there is no \s-1ALPN\s0 proposed in the ClientHello, the \s-1ALPN\s0 callback is not
invoked.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBSSL_CTX_set_alpn_protos()\fR and \fBSSL_set_alpn_protos()\fR return 0 on success, and
non\-0 on failure. \s-1WARNING:\s0 these functions reverse the return value convention.
.PP
\&\fBSSL_select_next_proto()\fR returns one of the following:
.IP "\s-1OPENSSL_NPN_NEGOTIATED\s0" 4
.IX Item "OPENSSL_NPN_NEGOTIATED"
A match was found and is returned in \fBout\fR, \fBoutlen\fR.
.IP "\s-1OPENSSL_NPN_NO_OVERLAP\s0" 4
.IX Item "OPENSSL_NPN_NO_OVERLAP"
No match was found. The first item in \fBclient\fR, \fBclient_len\fR is returned in
\&\fBout\fR, \fBoutlen\fR.
.PP
The \s-1ALPN\s0 select callback \fBcb\fR, must return one of the following:
.IP "\s-1SSL_TLSEXT_ERR_OK\s0" 4
.IX Item "SSL_TLSEXT_ERR_OK"
\&\s-1ALPN\s0 protocol selected.
.IP "\s-1SSL_TLSEXT_ERR_NOACK\s0" 4
.IX Item "SSL_TLSEXT_ERR_NOACK"
\&\s-1ALPN\s0 protocol not selected.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBssl\fR\|(3), \fBSSL_CTX_set_tlsext_servername_callback\fR\|(3),
\&\fBSSL_CTX_set_tlsext_servername_arg\fR\|(3)