.\" Automatically generated by Pod::Man 4.14 (Pod::Simple 3.42)
.\"
.\" 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 "BIO_F_SSL 3ossl"
.TH BIO_F_SSL 3ossl "2026-01-27" "3.5.5" "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"
BIO_do_handshake,
BIO_f_ssl, BIO_set_ssl, BIO_get_ssl, BIO_set_ssl_mode,
BIO_set_ssl_renegotiate_bytes,
BIO_get_num_renegotiates, BIO_set_ssl_renegotiate_timeout, BIO_new_ssl,
BIO_new_ssl_connect, BIO_new_buffer_ssl_connect, BIO_ssl_copy_session_id,
BIO_ssl_shutdown \- SSL BIO
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\& #include <openssl/bio.h>
\& #include <openssl/ssl.h>
\&
\& const BIO_METHOD *BIO_f_ssl(void);
\&
\& long BIO_set_ssl(BIO *b, SSL *ssl, long c);
\& long BIO_get_ssl(BIO *b, SSL **sslp);
\& long BIO_set_ssl_mode(BIO *b, long client);
\& long BIO_set_ssl_renegotiate_bytes(BIO *b, long num);
\& long BIO_set_ssl_renegotiate_timeout(BIO *b, long seconds);
\& long BIO_get_num_renegotiates(BIO *b);
\&
\& BIO *BIO_new_ssl(SSL_CTX *ctx, int client);
\& BIO *BIO_new_ssl_connect(SSL_CTX *ctx);
\& BIO *BIO_new_buffer_ssl_connect(SSL_CTX *ctx);
\& int BIO_ssl_copy_session_id(BIO *to, BIO *from);
\& void BIO_ssl_shutdown(BIO *bio);
\&
\& long BIO_do_handshake(BIO *b);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fBBIO_f_ssl()\fR returns the \s-1SSL BIO\s0 method. This is a filter \s-1BIO\s0 which
is a wrapper round the OpenSSL \s-1SSL\s0 routines adding a \s-1BIO\s0 \*(L"flavour\*(R" to
\&\s-1SSL I/O.\s0
.PP
I/O performed on an \s-1SSL BIO\s0 communicates using the \s-1SSL\s0 protocol with
the SSLs read and write BIOs. If an \s-1SSL\s0 connection is not established
then an attempt is made to establish one on the first I/O call.
.PP
If a \s-1BIO\s0 is appended to an \s-1SSL BIO\s0 using \fBBIO_push()\fR it is automatically
used as the \s-1SSL\s0 BIOs read and write BIOs.
.PP
Calling \fBBIO_reset()\fR on an \s-1SSL BIO\s0 closes down any current \s-1SSL\s0 connection
by calling \fBSSL_shutdown()\fR. \fBBIO_reset()\fR is then sent to the next \s-1BIO\s0 in
the chain: this will typically disconnect the underlying transport.
The \s-1SSL BIO\s0 is then reset to the initial accept or connect state.
.PP
If the close flag is set when an \s-1SSL BIO\s0 is freed then the internal
\&\s-1SSL\s0 structure is also freed using \fBSSL_free()\fR.
.PP
\&\fBBIO_set_ssl()\fR sets the internal \s-1SSL\s0 pointer of \s-1SSL BIO\s0 \fBb\fR to \fBssl\fR using
the close flag \fBc\fR.
.PP
\&\fBBIO_get_ssl()\fR retrieves the \s-1SSL\s0 pointer of \s-1SSL BIO\s0 \fBb\fR, it can then be
manipulated using the standard \s-1SSL\s0 library functions.
.PP
\&\fBBIO_set_ssl_mode()\fR sets the \s-1SSL BIO\s0 mode to \fBclient\fR. If \fBclient\fR
is 1 client mode is set. If \fBclient\fR is 0 server mode is set.
.PP
\&\fBBIO_set_ssl_renegotiate_bytes()\fR sets the renegotiate byte count of \s-1SSL BIO\s0 \fBb\fR
to \fBnum\fR. When set after every \fBnum\fR bytes of I/O (read and write)
the \s-1SSL\s0 session is automatically renegotiated. \fBnum\fR must be at
least 512 bytes.
.PP
\&\fBBIO_set_ssl_renegotiate_timeout()\fR sets the renegotiate timeout of \s-1SSL BIO\s0 \fBb\fR
to \fBseconds\fR.
When the renegotiate timeout elapses the session is automatically renegotiated.
.PP
\&\fBBIO_get_num_renegotiates()\fR returns the total number of session
renegotiations due to I/O or timeout of \s-1SSL BIO\s0 \fBb\fR.
.PP
\&\fBBIO_new_ssl()\fR allocates an \s-1SSL BIO\s0 using \s-1SSL_CTX\s0 \fBctx\fR and using
client mode if \fBclient\fR is non zero.
.PP
\&\fBBIO_new_ssl_connect()\fR creates a new \s-1BIO\s0 chain consisting of an
\&\s-1SSL BIO\s0 (using \fBctx\fR) followed by a connect \s-1BIO.\s0
.PP
\&\fBBIO_new_buffer_ssl_connect()\fR creates a new \s-1BIO\s0 chain consisting
of a buffering \s-1BIO,\s0 an \s-1SSL BIO\s0 (using \fBctx\fR), and a connect \s-1BIO.\s0
.PP
\&\fBBIO_ssl_copy_session_id()\fR copies an \s-1SSL\s0 session id between
\&\s-1BIO\s0 chains \fBfrom\fR and \fBto\fR. It does this by locating the
\&\s-1SSL\s0 BIOs in each chain and calling \fBSSL_copy_session_id()\fR on
the internal \s-1SSL\s0 pointer.
.PP
\&\fBBIO_ssl_shutdown()\fR closes down an \s-1SSL\s0 connection on \s-1BIO\s0
chain \fBbio\fR. It does this by locating the \s-1SSL BIO\s0 in the
chain and calling \fBSSL_shutdown()\fR on its internal \s-1SSL\s0
pointer.
.PP
\&\fBBIO_do_handshake()\fR attempts to complete an \s-1SSL\s0 handshake on the
supplied \s-1BIO\s0 and establish the \s-1SSL\s0 connection.
For non-SSL BIOs the connection is done typically at \s-1TCP\s0 level.
If domain name resolution yields multiple \s-1IP\s0 addresses all of them are tried
after \fBconnect()\fR failures.
The function returns 1 if the connection was established successfully.
A zero or negative value is returned if the connection could not be established.
The call \fBBIO_should_retry()\fR should be used for nonblocking connect BIOs
to determine if the call should be retried.
If a connection has already been established this call has no effect.
.SH "NOTES"
.IX Header "NOTES"
\&\s-1SSL\s0 BIOs are exceptional in that if the underlying transport
is non blocking they can still request a retry in exceptional
circumstances. Specifically this will happen if a session
renegotiation takes place during a \fBBIO_read_ex()\fR operation, one
case where this happens is when step up occurs.
.PP
The \s-1SSL\s0 flag \s-1SSL_AUTO_RETRY\s0 can be
set to disable this behaviour. That is when this flag is set
an \s-1SSL BIO\s0 using a blocking transport will never request a
retry.
.PP
Since unknown \fBBIO_ctrl()\fR operations are sent through filter
BIOs the servers name and port can be set using \fBBIO_set_host()\fR
on the \s-1BIO\s0 returned by \fBBIO_new_ssl_connect()\fR without having
to locate the connect \s-1BIO\s0 first.
.PP
Applications do not have to call \fBBIO_do_handshake()\fR but may wish
to do so to separate the handshake process from other I/O
processing.
.PP
\&\fBBIO_set_ssl()\fR, \fBBIO_get_ssl()\fR, \fBBIO_set_ssl_mode()\fR,
\&\fBBIO_set_ssl_renegotiate_bytes()\fR, \fBBIO_set_ssl_renegotiate_timeout()\fR,
\&\fBBIO_get_num_renegotiates()\fR, and \fBBIO_do_handshake()\fR are implemented as macros.
.PP
\&\fBBIO_ssl_copy_session_id()\fR is not currently supported on \s-1QUIC SSL\s0 objects and
fails if called on such an object.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBBIO_f_ssl()\fR returns the \s-1SSL\s0 \fB\s-1BIO_METHOD\s0\fR structure.
.PP
\&\fBBIO_set_ssl()\fR, \fBBIO_get_ssl()\fR, \fBBIO_set_ssl_mode()\fR, \fBBIO_set_ssl_renegotiate_bytes()\fR,
\&\fBBIO_set_ssl_renegotiate_timeout()\fR and \fBBIO_get_num_renegotiates()\fR return 1 on
success or a value which is less than or equal to 0 if an error occurred.
.PP
\&\fBBIO_new_ssl()\fR, \fBBIO_new_ssl_connect()\fR and \fBBIO_new_buffer_ssl_connect()\fR return
a valid \fB\s-1BIO\s0\fR structure on success or \fB\s-1NULL\s0\fR if an error occurred.
.PP
\&\fBBIO_ssl_copy_session_id()\fR returns 1 on success or 0 on error, or if called
on a \s-1QUIC SSL\s0 object.
.PP
\&\fBBIO_do_handshake()\fR returns 1 if the connection was established successfully.
A zero or negative value is returned if the connection could not be established.
.SH "EXAMPLES"
.IX Header "EXAMPLES"
This \s-1SSL/TLS\s0 client example attempts to retrieve a page from an
\&\s-1SSL/TLS\s0 web server. The I/O routines are identical to those of the
unencrypted example in \fBBIO_s_connect\fR\|(3).
.PP
.Vb 5
\& BIO *sbio, *out;
\& int len;
\& char tmpbuf[1024];
\& SSL_CTX *ctx;
\& SSL *ssl;
\&
\& /* XXX Seed the PRNG if needed. */
\&
\& ctx = SSL_CTX_new(TLS_client_method());
\&
\& /* XXX Set verify paths and mode here. */
\&
\& sbio = BIO_new_ssl_connect(ctx);
\& BIO_get_ssl(sbio, &ssl);
\& if (ssl == NULL) {
\&     fprintf(stderr, "Can\*(Aqt locate SSL pointer\en");
\&     ERR_print_errors_fp(stderr);
\&     exit(1);
\& }
\&
\& /* XXX We might want to do other things with ssl here */
\&
\& /* An empty host part means the loopback address */
\& BIO_set_conn_hostname(sbio, ":https");
\&
\& out = BIO_new_fp(stdout, BIO_NOCLOSE);
\& if (BIO_do_connect(sbio) <= 0) {
\&     fprintf(stderr, "Error connecting to server\en");
\&     ERR_print_errors_fp(stderr);
\&     exit(1);
\& }
\&
\& /* XXX Could examine ssl here to get connection info */
\&
\& BIO_puts(sbio, "GET / HTTP/1.0\en\en");
\& for (;;) {
\&     len = BIO_read(sbio, tmpbuf, 1024);
\&     if (len <= 0)
\&         break;
\&     BIO_write(out, tmpbuf, len);
\& }
\& BIO_free_all(sbio);
\& BIO_free(out);
.Ve
.PP
Here is a simple server example. It makes use of a buffering
\&\s-1BIO\s0 to allow lines to be read from the \s-1SSL BIO\s0 using BIO_gets.
It creates a pseudo web page containing the actual request from
a client and also echoes the request to standard output.
.PP
.Vb 5
\& BIO *sbio, *bbio, *acpt, *out;
\& int len;
\& char tmpbuf[1024];
\& SSL_CTX *ctx;
\& SSL *ssl;
\&
\& /* XXX Seed the PRNG if needed. */
\&
\& ctx = SSL_CTX_new(TLS_server_method());
\& if (!SSL_CTX_use_certificate_file(ctx, "server.pem", SSL_FILETYPE_PEM)
\&         || !SSL_CTX_use_PrivateKey_file(ctx, "server.pem", SSL_FILETYPE_PEM)
\&         || !SSL_CTX_check_private_key(ctx)) {
\&     fprintf(stderr, "Error setting up SSL_CTX\en");
\&     ERR_print_errors_fp(stderr);
\&     exit(1);
\& }
\&
\& /* XXX Other things like set verify locations, EDH temp callbacks. */
\&
\& /* New SSL BIO setup as server */
\& sbio = BIO_new_ssl(ctx, 0);
\& BIO_get_ssl(sbio, &ssl);
\& if (ssl == NULL) {
\&     fprintf(stderr, "Can\*(Aqt locate SSL pointer\en");
\&     ERR_print_errors_fp(stderr);
\&     exit(1);
\& }
\&
\& bbio = BIO_new(BIO_f_buffer());
\& sbio = BIO_push(bbio, sbio);
\& acpt = BIO_new_accept("4433");
\&
\& /*
\&  * By doing this when a new connection is established
\&  * we automatically have sbio inserted into it. The
\&  * BIO chain is now \*(Aqswallowed\*(Aq by the accept BIO and
\&  * will be freed when the accept BIO is freed.
\&  */
\& BIO_set_accept_bios(acpt, sbio);
\& out = BIO_new_fp(stdout, BIO_NOCLOSE);
\&
\& /* First call to BIO_do_accept() sets up accept BIO */
\& if (BIO_do_accept(acpt) <= 0) {
\&     fprintf(stderr, "Error setting up accept BIO\en");
\&     ERR_print_errors_fp(stderr);
\&     exit(1);
\& }
.Ve
.PP
/* Second call to \fBBIO_do_accept()\fR waits for incoming connection */
 if (BIO_do_accept(acpt) <= 0) {
    fprintf(stderr, \*(L"Error accepting connection\en\*(R");
    ERR_print_errors_fp(stderr);
    \fBexit\fR\|(1);
 }
.PP
.Vb 3
\& /* We only want one connection so remove and free accept BIO */
\& sbio = BIO_pop(acpt);
\& BIO_free_all(acpt);
\&
\& if (BIO_do_handshake(sbio) <= 0) {
\&     fprintf(stderr, "Error in SSL handshake\en");
\&     ERR_print_errors_fp(stderr);
\&     exit(1);
\& }
\&
\& BIO_puts(sbio, "HTTP/1.0 200 OK\er\enContent\-type: text/plain\er\en\er\en");
\& BIO_puts(sbio, "\er\enConnection Established\er\enRequest headers:\er\en");
\& BIO_puts(sbio, "\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\er\en");
\&
\& for (;;) {
\&     len = BIO_gets(sbio, tmpbuf, 1024);
\&     if (len <= 0)
\&         break;
\&     BIO_write(sbio, tmpbuf, len);
\&     BIO_write(out, tmpbuf, len);
\&     /* Look for blank line signifying end of headers*/
\&     if (tmpbuf[0] == \*(Aq\er\*(Aq || tmpbuf[0] == \*(Aq\en\*(Aq)
\&         break;
\& }
\&
\& BIO_puts(sbio, "\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\er\en");
\& BIO_puts(sbio, "\er\en");
\& BIO_flush(sbio);
\& BIO_free_all(sbio);
.Ve
.SH "HISTORY"
.IX Header "HISTORY"
In OpenSSL before 1.0.0 the \fBBIO_pop()\fR call was handled incorrectly,
the I/O \s-1BIO\s0 reference count was incorrectly incremented (instead of
decremented) and dissociated with the \s-1SSL BIO\s0 even if the \s-1SSL BIO\s0 was not
explicitly being popped (e.g. a pop higher up the chain). Applications which
included workarounds for this bug (e.g. freeing BIOs more than once) should
be modified to handle this fix or they may free up an already freed \s-1BIO.\s0
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2000\-2023 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the Apache License 2.0 (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>.
