+ int (*bwrite)(BIO *, const char *, int);
+ int (*bread)(BIO *, char *, int);
+ int (*bputs)(BIO *, const char *);
+ int (*bgets)(BIO *, char *, int);
+ long (*ctrl)(BIO *, int, long, void *);
+ int (*create)(BIO *);
+ int (*destroy)(BIO *);
+ long (*callback_ctrl)(BIO *, int, void (*)(struct bio_st *, int, const char *, int, long, long));