Cryptography and SSL/TLS Toolkit



BIO_find_type, BIO_next, BIO_method_type - 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);