construct and destruct I/O abstraction
const BIO_METHOD *type);
A BIO is an I/O abstraction object, hiding many of the underlying I/O details from an application. If an application uses BIOs for its I/O, it can transparently handle SSL connections, unencrypted network connections, and file I/O.
function constructs a new BIO using the method
type and sets its reference count to 1. There are two
groups of BIO types, source/sink BIOs and filter BIOs.
Source/sink BIOs provide input or consume output. Examples include socket BIOs and file BIOs.
Filter BIOs take data from one BIO and pass it through to another, or to the application, forming a chain of BIOs. The data may be left unmodified (for example by a message digest BIO) or translated (for example by an encryption BIO). The effect of a filter BIO may change according to the I/O operation it is performing: for example an encryption BIO encrypts data if it is written to and decrypts data if it is read from.
Some BIOs (such as memory BIOs) can be used
immediately after calling
Others (such as file BIOs) need some additional initialization, and utility
functions exists to construct and initialize such BIOs.
Normally the type argument is
supplied by a function which returns a pointer to a
BIO_METHOD. There is a naming convention for such
functions: the methods for source/sink BIOs are called
and those for filter BIOs
increments the reference count of a by 1.
is a deprecated function to initialize an unused BIO
structure located in static memory or on the stack, to set its method to
type, and to set its reference count to 1. It must not
be called on BIO objects created with
BIO_new(), nor on objects that were already
decrement the reference count of a by 1, and if the
reference count reaches 0, they destruct the single
BIO a, which may also have some
effect on the underlying I/O structure, for example it may close the file
being referred to under certain circumstances. If a is
NULL pointer, no action occurs. If
BIO_free() is called on a BIO chain, it destructs at
most one BIO, resulting in a memory leak.
BIO_free() on a and on
all following BIO objects in the chain. As soon as the
reference count of a BIO is still non-zero after
BIO_free() on it, the function
BIO_free_all() returns right away and refrains from
freeing the remaining BIO objects in the chain. It
does not halt if an error occurs destructing an individual BIO in the chain.
If a is a
NULL pointer, no
action occurs. Calling
BIO_free_all() on a single
BIO has the same effect as
Common I/O functions are documented in BIO_read(3). Forming chains is explained in BIO_push(3); inspecting them is explained in BIO_find_type(3). For more details about the different kinds of BIOs, see the individual BIO_METHOD manual pages.
BIO_new() returns a newly constructed
BIO object or
return 1 for success or 0 for failure.
Create a memory BIO:
BIO *mem = BIO_new(BIO_s_mem());
BIO_ctrl(3), BIO_dump(3), BIO_f_asn1(3), BIO_f_base64(3), BIO_f_buffer(3), BIO_f_cipher(3), BIO_f_md(3), BIO_f_null(3), BIO_f_ssl(3), BIO_find_type(3), BIO_get_ex_new_index(3), BIO_meth_new(3), BIO_new_CMS(3), BIO_printf(3), BIO_push(3), BIO_read(3), BIO_s_accept(3), BIO_s_bio(3), BIO_s_connect(3), BIO_s_fd(3), BIO_s_file(3), BIO_s_mem(3), BIO_s_null(3), BIO_s_socket(3), BIO_set_callback(3), BIO_set_data(3), BIO_should_retry(3), BUF_MEM_new(3), crypto(3)
first appeared in SSLeay 0.6.0.
appeared in SSLeay 0.6.6. All these functions have been available since
BIO_vfree() first appeared in OpenSSL
0.9.6 and has been available since OpenBSD 2.9.
BIO_up_ref() first appeared in OpenSSL
1.1.0 and has been available since OpenBSD 6.3.