BIO_f_ssl (3)

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========================================================================

(The comments found at the beginning of the groff file "man3/BIO_f_ssl.3ssl".)

NAME

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

SYNOPSIS

 #include <openssl/bio.h>
 #include <openssl/ssl.h>

 BIO_METHOD *BIO_f_ssl(void);

 #define BIO_set_ssl(b,ssl,c)   BIO_ctrl(b,BIO_C_SET_SSL,c,(char *)ssl)
 #define BIO_get_ssl(b,sslp)    BIO_ctrl(b,BIO_C_GET_SSL,0,(char *)sslp)
 #define BIO_set_ssl_mode(b,client)     BIO_ctrl(b,BIO_C_SSL_MODE,client,NULL)
 #define BIO_set_ssl_renegotiate_bytes(b,num) \
        BIO_ctrl(b,BIO_C_SET_SSL_RENEGOTIATE_BYTES,num,NULL);
 #define BIO_set_ssl_renegotiate_timeout(b,seconds) \
        BIO_ctrl(b,BIO_C_SET_SSL_RENEGOTIATE_TIMEOUT,seconds,NULL);
 #define BIO_get_num_renegotiates(b) \
        BIO_ctrl(b,BIO_C_SET_SSL_NUM_RENEGOTIATES,0,NULL);

 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);

 #define BIO_do_handshake(b)    BIO_ctrl(b,BIO_C_DO_STATE_MACHINE,0,NULL)

DESCRIPTION

BIO_f_ssl() returns the method. This is a filter which is a wrapper round the OpenSSL routines adding a ``flavour'' to

I/O performed on an

communicates using the protocol with the SSLs read and write BIOs. If an connection is not established then an attempt is made to establish one on the first I/O call.

If a

is appended to an using BIO_push() it is automatically used as the BIOs read and write BIOs.

Calling BIO_reset() on an

closes down any current connection by calling SSL_shutdown(). BIO_reset() is then sent to the next in the chain: this will typically disconnect the underlying transport. The is then reset to the initial accept or connect state.

If the close flag is set when an

is freed then the internal structure is also freed using SSL_free().

BIO_set_ssl() sets the internal

pointer of b to ssl using the close flag c.

BIO_get_ssl() retrieves the

pointer of b, it can then be manipulated using the standard library functions.

BIO_set_ssl_mode() sets the

mode to client. If client is 1 client mode is set. If client is 0 server mode is set.

BIO_set_ssl_renegotiate_bytes() sets the renegotiate byte count to num. When set after every num bytes of I/O (read and write) the

session is automatically renegotiated. num must be at least 512 bytes.

BIO_set_ssl_renegotiate_timeout() sets the renegotiate timeout to 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

using ctx and using client mode if client is non zero.

BIO_new_ssl_connect() creates a new

chain consisting of an (using ctx) followed by a connect

BIO_new_buffer_ssl_connect() creates a new

chain consisting of a buffering an (using ctx) and a connect

BIO_ssl_copy_session_id() copies an

session id between chains from and to. It does this by locating the BIOs in each chain and calling SSL_copy_session_id() on the internal pointer.

BIO_ssl_shutdown() closes down an

connection on chain bio. It does this by locating the in the chain and calling SSL_shutdown() on its internal pointer.

BIO_do_handshake() attempts to complete an

handshake on the supplied and establish the 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 connection has already been established this call has no effect.

NOTES

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() operation, one case where this happens is when step up occurs.

In OpenSSL 0.9.6 and later the

flag can be set to disable this behaviour. That is when this flag is set an 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

returned by BIO_new_ssl_connect() without having to locate the connect 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.

RETURN VALUES

EXAMPLE

This client example, attempts to retrieve a page from an web server. The I/O routines are identical to those of the unencrypted example in BIO_s_connect(3).

 BIO *sbio, *out;
 int len;
 char tmpbuf[1024];
 SSL_CTX *ctx;
 SSL *ssl;

 ERR_load_crypto_strings();
 ERR_load_SSL_strings();
 OpenSSL_add_all_algorithms();

 /* We would seed the PRNG here if the platform didn't
  * do it automatically
  */

 ctx = SSL_CTX_new(SSLv23_client_method());

 /* We'd normally set some stuff like the verify paths and
  * mode here because as things stand this will connect to
  * any server whose certificate is signed by any CA.
  */

 sbio = BIO_new_ssl_connect(ctx);

 BIO_get_ssl(sbio, &ssl);

 if(!ssl) {
   fprintf(stderr, "Can't locate SSL pointer\n");
   /* whatever ... */
 }

 /* Don't want any retries */
 SSL_set_mode(ssl, SSL_MODE_AUTO_RETRY);

 /* We might want to do other things with ssl here */

 BIO_set_conn_hostname(sbio, "localhost: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);
        /* whatever ... */
 }

 if(BIO_do_handshake(sbio) <= 0) {
        fprintf(stderr, "Error establishing SSL connection\n");
        ERR_print_errors_fp(stderr);
        /* whatever ... */
 }

 /* 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

to allow lines to be read from the 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;

 ERR_load_crypto_strings();
 ERR_load_SSL_strings();
 OpenSSL_add_all_algorithms();

 /* Might seed PRNG here */

 ctx = SSL_CTX_new(SSLv23_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);
        return 0;
 }

 /* Might do other things here like setting verify locations and
  * DH and/or RSA temporary key callbacks
  */

 /* New SSL BIO setup as server */
 sbio=BIO_new_ssl(ctx,0);

 BIO_get_ssl(sbio, &ssl);

 if(!ssl) {
   fprintf(stderr, "Can't locate SSL pointer\n");
   /* whatever ... */
 }

 /* Don't want any retries */
 SSL_set_mode(ssl, SSL_MODE_AUTO_RETRY);

 /* Create the buffering BIO */

 bbio = BIO_new(BIO_f_buffer());

 /* Add to chain */
 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);
        return 0;
 }

 /* Now wait for incoming connection */
 if(BIO_do_accept(acpt) <= 0) {
        fprintf(stderr, "Error in connection\n");
        ERR_print_errors_fp(stderr);
        return 0;
 }

 /* 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);
        return 0;
 }

 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");

 /* Since there is a buffering BIO present we had better flush it */
 BIO_flush(sbio);

 BIO_free_all(sbio);

BUGS

In OpenSSL versions before 1.0.0 the BIO_pop() call was handled incorrectly, the I/O reference count was incorrectly incremented (instead of decremented) and dissociated with the even if the 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

SEE ALSO