BIO_METH_NEW(3) | Library Functions Manual | BIO_METH_NEW(3)

# NAME

`BIO_get_new_index`, `BIO_meth_new`, `BIO_meth_free`, `BIO_meth_get_write`, `BIO_meth_set_write`, `BIO_meth_get_read`, `BIO_meth_set_read`, `BIO_meth_get_puts`, `BIO_meth_set_puts`, `BIO_meth_get_gets`, `BIO_meth_set_gets`, `BIO_meth_get_ctrl`, `BIO_meth_set_ctrl`, `BIO_meth_get_create`, `BIO_meth_set_create`, `BIO_meth_get_destroy`, `BIO_meth_set_destroy`, `BIO_meth_get_callback_ctrl`, `BIO_meth_set_callback_ctrl` — manipulate BIO_METHOD structures

# SYNOPSIS

library “libcrypto”
`#include <openssl/bio.h>`

int
`BIO_get_new_index`(void);

BIO_METHOD *
`BIO_meth_new`(int type, const char *name);

void
`BIO_meth_free`(BIO_METHOD *biom);

int
(*BIO_meth_get_write(const BIO_METHOD `*biom))`(BIO *, const char *, int);

int
`BIO_meth_set_write`(BIO_METHOD *biom, int (*write)(BIO *, const char *, int));

int
(*BIO_meth_get_read(const BIO_METHOD `*biom))`(BIO *, char *, int);

int
`BIO_meth_set_read`(BIO_METHOD *biom, int (*read)(BIO *, char *, int));

int
(*BIO_meth_get_puts(const BIO_METHOD `*biom))`(BIO *, const char *);

int
`BIO_meth_set_puts`(BIO_METHOD *biom, int (*puts)(BIO *, const char *));

int
(*BIO_meth_get_gets(const BIO_METHOD `*biom))`(BIO *, char *, int);

int
`BIO_meth_set_gets`(BIO_METHOD *biom, int (*gets)(BIO *, char *, int));

long
(*BIO_meth_get_ctrl(const BIO_METHOD `*biom))`(BIO *, int, long, void *);

int
`BIO_meth_set_ctrl`(BIO_METHOD *biom, long (*ctrl)(BIO *, int, long, void *));

int
(*BIO_meth_get_create(const BIO_METHOD `*biom))`(BIO *);

int
`BIO_meth_set_create`(BIO_METHOD *biom, int (*create)(BIO *));

int
(*BIO_meth_get_destroy(const BIO_METHOD `*biom))`(BIO *);

int
`BIO_meth_set_destroy`(BIO_METHOD *biom, int (*destroy)(BIO *));

long
`(*BIO_meth_get_callback_ctrl(const BIO_METHOD *biom))`(BIO *, int, BIO_info_cb *);

int
`BIO_meth_set_callback_ctrl`(BIO_METHOD *biom, long (*callback_ctrl)(BIO *, int, BIO_info_cb *));

# DESCRIPTION

The BIO_METHOD structure stores function pointers implementing a BIO type. See BIO_new(3) for more information about BIO objects.

`BIO_meth_new`() creates a new BIO_METHOD structure. It requires a unique integer type; use `BIO_get_new_index`() to get the value for type. Currently, the user can only create up to 127 different BIO types, and type is limited to the range 129–255. The name pointer is stored in the structure and will not be freed by `BIO_meth_free`().

The standard BIO types are listed in `<openssl/bio.h>`. Some examples include `BIO_TYPE_BUFFER` and `BIO_TYPE_CIPHER`. The type of filter BIOs should have the `BIO_TYPE_FILTER` bit set. Source/sink BIOs should have the `BIO_TYPE_SOURCE_SINK` bit set. File descriptor based BIOs (e.g. socket, fd, connect, accept etc.) should additionally have the `BIO_TYPE_DESCRIPTOR` bit set. See BIO_find_type(3) for more information.

`BIO_meth_free`() is an alias for free(3).

`BIO_meth_get_write`(), `BIO_meth_set_write`(), `BIO_meth_get_read`(), and `BIO_meth_set_read`() get and set the functions write and read used for writing and reading arbitrary length data to and from the BIO. These functions are called from BIO_write(3) and BIO_read(3), respectively. The parameters and return values of write and read have the same meaning as for BIO_write(3) and BIO_read(3).

`BIO_meth_get_puts`() and `BIO_meth_set_puts`() get and set the function puts used for writing a NUL-terminated string to the BIO. This function is called from BIO_puts(3). The parameters and the return value of puts have the same meaning as for BIO_puts(3).

`BIO_meth_get_gets`() and `BIO_meth_set_gets`() get and set the function gets used for reading a line of data from the BIO. This function is called from BIO_gets(3). The parameters and the return value of gets have the same meaning as for BIO_gets(3).

`BIO_meth_get_ctrl`() and `BIO_meth_set_ctrl`() get and set the function ctrl used for processing control messages in the BIO. This function is called from BIO_ctrl(3). The parameters and return value of ctrl have the same meaning as for BIO_ctrl(3).

`BIO_meth_get_create`() and `BIO_meth_set_create`() get and set a function create used while initializing a new instance of the BIO. This function is called from BIO_new(3). The BIO_new(3) function allocates the memory for the new BIO, and a pointer to this newly allocated structure is passed as the parameter to create.

`BIO_meth_get_destroy`() and `BIO_meth_set_destroy`() get and set a function destroy used while destroying an instance of a BIO. This function is called from BIO_free(3). A pointer to the BIO to be destroyed is passed as the parameter. The destroy function is intended to perform clean-up specific to the BIO type. The memory for the BIO itself must not be freed by this function.

`BIO_meth_get_callback_ctrl`() and `BIO_meth_set_callback_ctrl`() get and set the function callback_ctrl used for processing callback control messages in the BIO. This function is called from BIO_callback_ctrl(3). The parameters and return value of callback_ctrl have the same meaning as for BIO_callback_ctrl(3).

# RETURN VALUES

`BIO_get_new_index`() returns the new BIO type value or -1 if an error occurs.

`BIO_meth_new`() returns the new BIO_METHOD structure or `NULL` if an error occurs.

The `BIO_meth_set_*`() functions return 1 on success or 0 on error. Currently, they cannot fail.

The `BIO_meth_get_*`() functions return function pointers.

# SEE ALSO

BIO_ctrl(3), BIO_find_type(3), BIO_new(3), BIO_read(3)

# HISTORY

These functions first appeared in OpenSSL 1.1.0 and have been available since OpenBSD 6.3.

June 8, 2025 | Debian