=pod

=head1 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

=head1 SYNOPSIS

=for comment multiple includes

 #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);

=head1 DESCRIPTION

BIO_f_ssl() returns the SSL BIO method. This is a filter BIO which

is a wrapper round the OpenSSL SSL routines adding a BIO "flavour" to

SSL I/O.

I/O performed on an SSL BIO communicates using the SSL protocol with

the SSLs read and write BIOs. If an SSL connection is not established

then an attempt is made to establish one on the first I/O call.

If a BIO is appended to an SSL BIO using BIO_push() it is automatically

used as the SSL BIOs read and write BIOs.

Calling BIO_reset() on an SSL BIO closes down any current SSL connection

by calling SSL_shutdown(). BIO_reset() is then sent to the next BIO in

the chain: this will typically disconnect the underlying transport.

The SSL BIO is then reset to the initial accept or connect state.

If the close flag is set when an SSL BIO is freed then the internal

SSL structure is also freed using SSL_free().

BIO_set_ssl() sets the internal SSL pointer of BIO B to B<ssl> using

the close flag B<c>.

BIO_get_ssl() retrieves the SSL pointer of BIO B, it can then be

manipulated using the standard SSL library functions.

BIO_set_ssl_mode() sets the SSL BIO mode to B<client>. If B<client>

is 1 client mode is set. If B<client> is 0 server mode is set.

BIO_set_ssl_renegotiate_bytes() sets the renegotiate byte count

to B<num>. When set after every B<num> bytes of I/O (read and write)

the SSL session is automatically renegotiated. B<num> must be at

least 512 bytes.

BIO_set_ssl_renegotiate_timeout() sets the renegotiate timeout to

B<seconds>. When the renegotiate timeout elapses the session is

automatically renegotiated.

BIO_get_num_renegotiates() returns the total number of session

renegotiations due to I/O or timeout.

BIO_new_ssl() allocates an SSL BIO using SSL_CTX B<ctx> and using

client mode if B<client> is non zero.

BIO_new_ssl_connect() creates a new BIO chain consisting of an

SSL BIO (using B<ctx>) followed by a connect BIO.

BIO_new_buffer_ssl_connect() creates a new BIO chain consisting

of a buffering BIO, an SSL BIO (using B<ctx>) and a connect

BIO.

BIO_ssl_copy_session_id() copies an SSL session id between

BIO chains B<from> and B<to>. It does this by locating the

SSL BIOs in each chain and calling SSL_copy_session_id() on

the internal SSL pointer.

BIO_ssl_shutdown() closes down an SSL connection on BIO

chain B<bio>. It does this by locating the SSL BIO in the

chain and calling SSL_shutdown() on its internal SSL

pointer.

BIO_do_handshake() attempts to complete an SSL handshake on the

supplied BIO and establish the SSL connection. It returns 1

if the connection was established successfully. A zero or negative

value is returned if the connection could not be established, the

call BIO_should_retry() should be used for non blocking connect BIOs

to determine if the call should be retried. If an SSL connection has

already been established this call has no effect.

=head1 NOTES

SSL 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 BIO_read_ex() operation, one

case where this happens is when step up occurs.

The SSL flag SSL_AUTO_RETRY can be

set to disable this behaviour. That is when this flag is set

an SSL BIO using a blocking transport will never request a

retry.

Since unknown BIO_ctrl() operations are sent through filter

BIOs the servers name and port can be set using BIO_set_host()

on the BIO returned by BIO_new_ssl_connect() without having

to locate the connect BIO first.

Applications do not have to call BIO_do_handshake() but may wish

to do so to separate the handshake process from other I/O

processing.

BIO_set_ssl(), BIO_get_ssl(), BIO_set_ssl_mode(),

BIO_set_ssl_renegotiate_bytes(), BIO_set_ssl_renegotiate_timeout(),

BIO_get_num_renegotiates(), and BIO_do_handshake() are implemented as macros.

=head1 RETURN VALUES

BIO_f_ssl() returns the SSL B<BIO_METHOD> structure.

BIO_set_ssl(), BIO_get_ssl(), BIO_set_ssl_mode(), BIO_set_ssl_renegotiate_bytes(),

BIO_set_ssl_renegotiate_timeout() and BIO_get_num_renegotiates() return 1 on

success or a value which is less than or equal to 0 if an error occurred.

BIO_new_ssl(), BIO_new_ssl_connect() and BIO_new_buffer_ssl_connect() return

a valid B<BIO> structure on success or B<NULL> if an error occurred.

BIO_ssl_copy_session_id() returns 1 on success or 0 on error.

BIO_do_handshake() returns 1 if the connection was established successfully.

A zero or negative value is returned if the connection could not be established.

=head1 EXAMPLES

This SSL/TLS client example attempts to retrieve a page from an

SSL/TLS web server. The I/O routines are identical to those of the

unencrypted example in L<BIO_s_connect(3)>.

 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't locate SSL pointer\n");

     ERR_print_errors_fp(stderr);

     exit(1);

 }

 /* Don't want any retries */

 SSL_set_mode(ssl, SSL_MODE_AUTO_RETRY);

 /* 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\n");

     ERR_print_errors_fp(stderr);

     exit(1);

 }

 if (BIO_do_handshake(sbio) <= 0) {

     fprintf(stderr, "Error establishing SSL connection\n");

     ERR_print_errors_fp(stderr);

     exit(1);

 }

 /* XXX Could examine ssl here to get connection info */

 BIO_puts(sbio, "GET / HTTP/1.0\n\n");

 for (;;) {

     len = BIO_read(sbio, tmpbuf, 1024);

     if (len <= 0)

         break;

     BIO_write(out, tmpbuf, len);

 }

 BIO_free_all(sbio);

 BIO_free(out);

Here is a simple server example. It makes use of a buffering

BIO to allow lines to be read from the SSL BIO using BIO_gets.

It creates a pseudo web page containing the actual request from

a client and also echoes the request to standard output.

 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\n");

     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't locate SSL pointer\n");

     ERR_print_errors_fp(stderr);

     exit(1);

 }

 SSL_set_mode(ssl, SSL_MODE_AUTO_RETRY);

 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 'swallowed' 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);

 /* Setup accept BIO */

 if (BIO_do_accept(acpt) <= 0) {

     fprintf(stderr, "Error setting up accept BIO\n");

     ERR_print_errors_fp(stderr);

     exit(1);

 }

 /* 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\n");

     ERR_print_errors_fp(stderr);

     exit(1);

 }

 BIO_puts(sbio, "HTTP/1.0 200 OK\r\nContent-type: text/plain\r\n\r\n");

 BIO_puts(sbio, "\r\nConnection Established\r\nRequest headers:\r\n");

 BIO_puts(sbio, "--------------------------------------------------\r\n");

 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] == '\r' || tmpbuf[0] == '\n')

         break;

 }

 BIO_puts(sbio, "--------------------------------------------------\r\n");

 BIO_puts(sbio, "\r\n");

 BIO_flush(sbio);

 BIO_free_all(sbio);

=head1 HISTORY

In OpenSSL before 1.0.0 the BIO_pop() call was handled incorrectly,

the I/O BIO reference count was incorrectly incremented (instead of

decremented) and dissociated with the SSL BIO even if the SSL BIO 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 BIO.

=head1 COPYRIGHT

Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (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