BIO_find_type, BIO_next — BIO chain traversal


#include  <openssl/bio.h>
BIO *  BIO_find_type(BIO *b,int bio_type);
BIO *  BIO_next(BIO *b);
#define BIO_method_type(b)     ((b)->method->type)
#define BIO_TYPE_NONE          0
#define BIO_TYPE_MEM           (1|0x0400)
#define BIO_TYPE_FILE          (2|0x0400)
#define BIO_TYPE_FD            (4|0x0400|0x0100)
#define BIO_TYPE_SOCKET        (5|0x0400|0x0100)
#define BIO_TYPE_NULL          (6|0x0400)
#define BIO_TYPE_SSL           (7|0x0200)
#define BIO_TYPE_MD            (8|0x0200)
#define BIO_TYPE_BUFFER        (9|0x0200)
#define BIO_TYPE_CIPHER        (10|0x0200)
#define BIO_TYPE_BASE64        (11|0x0200)
#define BIO_TYPE_CONNECT       (12|0x0400|0x0100)
#define BIO_TYPE_ACCEPT        (13|0x0400|0x0100)
#define BIO_TYPE_PROXY_CLIENT  (14|0x0200)
#define BIO_TYPE_PROXY_SERVER  (15|0x0200)
#define BIO_TYPE_NBIO_TEST     (16|0x0200)
#define BIO_TYPE_NULL_FILTER   (17|0x0200)
#define BIO_TYPE_BER           (18|0x0200)
#define BIO_TYPE_BIO           (19|0x0400)
#define BIO_TYPE_DESCRIPTOR    0x0100
#define BIO_TYPE_FILTER        0x0200
#define BIO_TYPE_SOURCE_SINK   0x0400


The BIO_find_type() searches for a BIO of a given type in a chain, starting at BIO b. If type is a specific type (such as BIO_TYPE_MEM) then a search is made for a BIO of that type. If type is a general type (such as BIO_TYPE_SOURCE_SINK) then the next matching BIO of the given general type is searched for. BIO_find_type() returns the next matching BIO or NULL if none is found.

Note: not all the BIO_TYPE_* types above have corresponding BIO implementations.

BIO_next() returns the next BIO in a chain. It can be used to traverse all BIOs in a chain or used in conjunction with BIO_find_type() to find all BIOs of a certain type.

BIO_method_type() returns the type of a BIO.


BIO_find_type() returns a matching BIO or NULL for no match.

BIO_next() returns the next BIO in a chain.

BIO_method_type() returns the type of the BIO b.


BIO_next() was added to OpenSSL 0.9.6 to provide a 'clean' way to traverse a BIO chain or find multiple matches using BIO_find_type(). Previous versions had to use:

next = bio->next_bio;


BIO_find_type() in OpenSSL 0.9.5a and earlier could not be safely passed a NULL pointer for the b argument.


Traverse a chain looking for digest BIOs:

BIO *btmp;
btmp = in_bio; /* in_bio is chain to search through */

do {
       btmp = BIO_find_type(btmp, BIO_TYPE_MD);
       if(btmp == NULL) break; /* Not found */
       /* btmp is a digest BIO, do something with it …*/

       btmp = BIO_next(btmp);
} while(btmp);