path: root/lib/libcrypto/man/BIO_new.3

.\" $OpenBSD: BIO_new.3,v 1.28 2023/07/26 20:01:04 tb Exp $
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.Dd $Mdocdate: July 26 2023 $
.Dt BIO_NEW 3
.Os
.Sh NAME
.Nm BIO_new ,
.Nm BIO_up_ref ,
.Nm BIO_set ,
.Nm BIO_free ,
.Nm BIO_vfree ,
.Nm BIO_free_all
.Nd construct and destruct I/O abstraction objects
.Sh SYNOPSIS
.In openssl/bio.h
.Ft BIO *
.Fo BIO_new
.Fa "const BIO_METHOD *type"
.Fc
.Ft int
.Fo BIO_up_ref
.Fa "BIO *a"
.Fc
.Ft int
.Fo BIO_set
.Fa "BIO *a"
.Fa "const BIO_METHOD *type"
.Fc
.Ft int
.Fo BIO_free
.Fa "BIO *a"
.Fc
.Ft void
.Fo BIO_vfree
.Fa "BIO *a"
.Fc
.Ft void
.Fo BIO_free_all
.Fa "BIO *a"
.Fc
.Sh DESCRIPTION
A
.Vt 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.
.Pp
The
.Fn BIO_new
function constructs a new
.Vt BIO
using the method
.Fa type
and sets its reference count to 1.
There are two groups of BIO types, source/sink BIOs and filter BIOs.
.Pp
Source/sink BIOs provide input or consume output.
Examples include socket BIOs and file BIOs.
.Pp
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.
.Pp
Some BIOs (such as memory BIOs) can be used immediately after calling
.Fn BIO_new .
Others (such as file BIOs) need some additional initialization, and
utility functions exists to construct and initialize such BIOs.
.Pp
Normally the
.Fa type
argument is supplied by a function which returns a pointer to a
.Vt BIO_METHOD .
There is a naming convention for such functions:
the methods for source/sink BIOs are called
.Fn BIO_s_*
and those for filter BIOs
.Fn BIO_f_* .
.Pp
.Fn BIO_up_ref
increments the reference count of
.Fa a
by 1.
.Pp
.Fn BIO_set
is a deprecated function to initialize an unused
.Vt BIO
structure located in static memory or on the stack,
to set its method to
.Fa type ,
and to set its reference count to 1.
It must not be called on
.Vt BIO
objects created with
.Fn BIO_new ,
nor on objects that were already used.
.Pp
.Fn BIO_free
and
.Fn BIO_vfree
decrement the reference count of
.Fa a
by 1, and if the reference count reaches 0, they destruct the single
.Vt BIO
.Fa 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
.Fa a
is a
.Dv NULL
pointer, no action occurs.
If
.Fn BIO_free
is called on a BIO chain, it destructs at most one BIO,
resulting in a memory leak.
.Pp
.Fn BIO_free_all
calls
.Fn BIO_free
on
.Fa a
and on all following
.Vt BIO
objects in the chain.
As soon as the reference count of a
.Vt BIO
is still non-zero after calling
.Fn BIO_free
on it, the function
.Fn BIO_free_all
returns right away and refrains from freeing the remaining
.Vt BIO
objects in the chain.
It does not halt if an error occurs
destructing an individual BIO in the chain.
If
.Fa a
is a
.Dv NULL
pointer, no action occurs.
Calling
.Fn BIO_free_all
on a single BIO has the same effect as
.Fn BIO_vfree .
.Pp
Common I/O functions are documented in
.Xr BIO_read 3 .
Forming chains is explained in
.Xr BIO_push 3 ;
inspecting them is explained in
.Xr BIO_find_type 3 .
For more details about the different kinds of BIOs, see the individual
.Vt BIO_METHOD
manual pages.
.Sh RETURN VALUES
.Fn BIO_new
returns a newly constructed
.Vt BIO
object or
.Dv NULL
on failure.
.Pp
.Fn BIO_up_ref ,
.Fn BIO_set ,
and
.Fn BIO_free
return 1 for success or 0 for failure.
.Sh EXAMPLES
Create a memory BIO:
.Pp
.Dl BIO *mem = BIO_new(BIO_s_mem());
.Sh SEE ALSO
.Xr BIO_accept 3 ,
.Xr BIO_ctrl 3 ,
.Xr BIO_dump 3 ,
.Xr BIO_dup_chain 3 ,
.Xr BIO_f_base64 3 ,
.Xr BIO_f_buffer 3 ,
.Xr BIO_f_cipher 3 ,
.Xr BIO_f_md 3 ,
.Xr BIO_f_null 3 ,
.Xr BIO_f_ssl 3 ,
.Xr BIO_find_type 3 ,
.Xr BIO_get_ex_new_index 3 ,
.Xr BIO_meth_new 3 ,
.Xr BIO_new_CMS 3 ,
.Xr BIO_printf 3 ,
.Xr BIO_push 3 ,
.Xr BIO_read 3 ,
.Xr BIO_s_accept 3 ,
.Xr BIO_s_bio 3 ,
.Xr BIO_s_connect 3 ,
.Xr BIO_s_datagram 3 ,
.Xr BIO_s_fd 3 ,
.Xr BIO_s_file 3 ,
.Xr BIO_s_mem 3 ,
.Xr BIO_s_null 3 ,
.Xr BIO_s_socket 3 ,
.Xr BIO_set_callback 3 ,
.Xr BIO_set_data 3 ,
.Xr BIO_should_retry 3 ,
.Xr BUF_MEM_new 3 ,
.Xr crypto 3
.Sh HISTORY
.Fn BIO_new ,
.Fn BIO_set ,
and
.Fn BIO_free
first appeared in SSLeay 0.6.0.
.Fn BIO_free_all
first appeared in SSLeay 0.6.6.
All these functions have been available since
.Ox 2.4 .
.Pp
.Fn BIO_vfree
first appeared in OpenSSL 0.9.6 and has been available since
.Ox 2.9 .
.Pp
.Fn BIO_up_ref
first appeared in OpenSSL 1.1.0 and has been available since
.Ox 6.3 .