.\" $OpenBSD: BIO_f_asn1.3,v 1.2 2021/12/12 17:31:18 schwarze Exp $
.\"
.\" Copyright (c) 2021 Ingo Schwarze <schwarze@openbsd.org>
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.Dd $Mdocdate: December 12 2021 $
.Dt BIO_F_ASN1 3
.Os
.Sh NAME
.Nm BIO_f_asn1 ,
.Nm asn1_ps_func ,
.Nm BIO_asn1_set_prefix ,
.Nm BIO_asn1_get_prefix ,
.Nm BIO_asn1_set_suffix ,
.Nm BIO_asn1_get_suffix
.Nd BER-encoding filter BIO
.Sh SYNOPSIS
.In openssl/asn1.h
.Ft const BIO_METHOD *
.Fn BIO_f_asn1 void
.In openssl/bio.h
.Ft typedef int
.Fo asn1_ps_func
.Fa "BIO *bio"
.Fa "unsigned char **pbuf"
.Fa "int *plen"
.Fa "void *parg"
.Fc
.Ft int
.Fo BIO_asn1_set_prefix
.Fa "BIO *chain"
.Fa "asn1_ps_func *prefix"
.Fa "asn1_ps_func *prefix_free"
.Fc
.Ft int
.Fo BIO_asn1_get_prefix
.Fa "BIO *chain"
.Fa "asn1_ps_func **pprefix"
.Fa "asn1_ps_func **pprefix_free"
.Fc
.Ft int
.Fo BIO_asn1_set_suffix
.Fa "BIO *chain"
.Fa "asn1_ps_func *suffix"
.Fa "asn1_ps_func *suffix_free"
.Fc
.Ft int
.Fo BIO_asn1_get_suffix
.Fa "BIO *chain"
.Fa "asn1_ps_func **psuffix"
.Fa "asn1_ps_func **psuffix_free"
.Fc
.Sh DESCRIPTION
.Fn BIO_f_asn1
returns the
.Qq asn1
BIO method.
BIOs created from it with
.Xr BIO_new 3
are filter BIOs intended to BER-encode data written to them
and pass the encoded data on to the next BIO in the chain.
Such BIOs operate as follows:
.Bl -hang -width 1n
.It Xr BIO_method_type 3
returns
.Dv BIO_TYPE_ASN1 .
.It Xr BIO_method_name 3
returns a pointer to the static string
.Qq asn1 .
.It Xr BIO_write 3
writes the DER encoding of an ASN.1 OCTET STRING with the
.Fa len
content octets in
.Fa buf
to the next BIO in the chain.
.Pp
If a
.Fa prefix
function was installed with
.Fn BIO_asn1_set_prefix ,
that function is called before writing the object.
It may for example produce additional output.
If it fails, writing fails.
.Pp
If a
.Fa prefix_free
function was installed as well, that function is called
after writing any output produced by
.Fa prefix
but before writing the object.
Failure of
.Fa prefix_free
is silently ignored.
.It Xr BIO_puts 3
operates like
.Xr BIO_write 3
but uses the
.Xr strlen 3
of
.Fa buf
instead of a
.Fa len
argument.
.It Xr BIO_flush 3
calls the
.Fa suffix
callback function, if any.
If that produces any output, it calls the
.Fa suffix_free
callback function, if any, silently ignoring failure.
Finally, it calls
.Xr BIO_flush 3
on the next BIO in the chain.
It fails if no data was previously written or if the
.Fa suffix
callback, writing, or
.Xr BIO_flush 3
on the next BIO fail.
.It Xr BIO_ctrl 3
with a
.Fa cmd
of
.Dv BIO_C_SET_EX_ARG
stores the pointer
.Fa parg
internally such that it will be passed to the
.Fn asn1_ps_func
callback functions.
With a
.Fa cmd
of
.Dv BIO_C_GET_EX_ARG ,
it retrieves that pointer, storing it in
.Pf * Fa parg .
The commands
.Dv BIO_C_SET_PREFIX ,
.Dv BIO_C_GET_PREFIX ,
.Dv BIO_C_SET_SUFFIX ,
.Dv BIO_C_GET_SUFFIX ,
and
.Dv BIO_CTRL_FLUSH
are used internally to implement
.Fn BIO_asn1_set_prefix ,
.Fn BIO_asn1_get_prefix ,
.Fn BIO_asn1_set_suffix ,
.Fn BIO_asn1_get_suffix
and
.Xr BIO_flush 3
and are not intended for use by application programs.
Other commands are merely forwarded to the next BIO in the chain.
.It Xo
.Xr BIO_read 3 ,
.Xr BIO_gets 3 ,
and
.Xr BIO_callback_ctrl 3
.Xc
merely call the same function on the next BIO in the chain.
.El
.Pp
If the above description of a function mentions the next BIO in the
chain, that function fails if the asn1 BIO is the last BIO in the chain.
.Pp
.Fn BIO_asn1_set_prefix
and
.Fn BIO_asn1_get_prefix
install and retrieve the
.Fa prefix
and
.Fa prefix_free
callback functions in and from the first asn1 BIO in the given
.Fa chain .
Similarly,
.Fn BIO_asn1_set_suffix
and
.Fn BIO_asn1_get_suffix
install and retrieve the
.Fa suffix
and
.Fa suffix_free
callback functions.
Passing a
.Dv NULL
pointer for any of the
.Fn asn1_ps_func
arguments disables that particular callback.
.Sh RETURN VALUES
.Fn BIO_f_asn1
always returns a pointer to a static built-in object.
.Pp
Functions of the type
.Fn asn1_ps_func
are supposed to return 1 on success or 0 on failure.
.Pp
.Fn BIO_asn1_set_prefix ,
.Fn BIO_asn1_get_prefix ,
.Fn BIO_asn1_set_suffix ,
and
.Fn BIO_asn1_get_suffix
return 1 on success or 0 if
.Fa chain
is a
.Dv NULL
pointer or does not contain any asn1 BIO.
They may return \-2 if a BIO is encountered in the
.Fa chain
that is not properly initialized.
.Sh SEE ALSO
.Xr ASN1_put_object 3 ,
.Xr BIO_ctrl 3 ,
.Xr BIO_new 3 ,
.Xr BIO_new_NDEF 3 ,
.Xr BIO_next 3 ,
.Xr BIO_write 3 ,
.Xr i2d_ASN1_OCTET_STRING 3
.Sh HISTORY
These functions first appeared in OpenSSL 1.0.0
and have been available since
.Ox 4.9 .