.\" $OpenBSD: ASN1_put_object.3,v 1.1 2019/08/26 11:41:31 schwarze Exp $
.\"
.\" Copyright (c) 2019 Ingo Schwarze <schwarze@openbsd.org>
.\"
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.Dd $Mdocdate: August 26 2019 $
.Dt ASN1_PUT_OBJECT 3
.Os
.Sh NAME
.Nm ASN1_put_object ,
.Nm ASN1_put_eoc
.Nd start and end the BER encoding of an arbitrary ASN.1 data element
.Sh SYNOPSIS
.In openssl/asn1.h
.Ft void
.Fo ASN1_put_object
.Fa "unsigned char **ber_out"
.Fa "int constructed"
.Fa "int length"
.Fa "int tag"
.Fa "int class"
.Fc
.Ft int
.Fo ASN1_put_eoc
.Fa "unsigned char **ber_out"
.Fc
.Sh DESCRIPTION
.Fn ASN1_put_object
begins writing the BER encoding of an arbitrary ASN.1 data element
to the buffer
.Pf * ber_out
by writing the identifier and the length bytes.
Making sure that there is sufficient space in the buffer
is the responsibility of the caller.
This function does not write any content bytes
nor any end-of-content bytes.
.Pp
The tag
.Fa class
can be
.Dv V_ASN1_UNIVERSAL ,
.Dv V_ASN1_APPLICATION ,
.Dv V_ASN1_CONTEXT_SPECIFIC ,
or
.Dv V_ASN1_PRIVATE
and is written to the two most significant bits of the first byte written.
.Pp
The
.Fa constructed
argument can have the following values:
.Bl -tag -width 1n -offset 2n -compact
.It 0
Start a primitive value by setting the third most significant bit
of the first byte written to 0.
Always use the definite form.
.It 1
Start a constructed value by setting the third most significant bit
of the first byte written to 1, and use the definite form.
.It 2
Start a constructed value and use the indefinite form,
.El
.Pp
If the
.Fa tag
is less than 0x1f, it is written to the five least significant bits
of the only identifier byte written.
Otherwise, these five bits are all set to 1, and the
.Fa tag
is encoded in one or more following identifier bytes as needed.
.Pp
After completing the identifier byte(s),
when using the definite form, the given
.Fa length
is encoded in one or more bytes as needed.
Otherwise, the special byte 0x80 is written instead and the
.Ar length
argument is ignored.
.Pp
At the end,
.Pf * Fa ber_out
is set to the byte following the last byte written.
The calling code can then start writing content bytes.
.Pp
If the indefinite form was selected,
the calling code is also responsible for calling
.Fn ASN1_put_eoc
which writes an end-of-content marker to
.Pf * Fa ber_out ,
consisting of two NUL bytes, and advances
.Pf * Fa ber_out
by two bytes.
.Sh RETURN VALUES
.Fn ASN1_put_eoc
returns the number of bytes written, which is always 2.
.Sh SEE ALSO
.Xr ASN1_item_i2d 3 ,
.Xr ASN1_TYPE_get 3 ,
.Xr i2d_ASN1_NULL 3 ,
.Xr i2d_ASN1_OBJECT 3 ,
.Xr i2d_ASN1_OCTET_STRING 3 ,
.Xr i2d_ASN1_SEQUENCE_ANY 3
.Sh HISTORY
.Fn ASN1_put_object
first appeared in SSLeay 0.5.1 and has been available since
.Ox 2.4 .
.Pp
.Fn ASN1_put_eoc
first appeared in OpenSSL 0.9.8 and has been available since
.Ox 4.5 .
.Sh CAVEATS
Neither
.Fn ASN1_put_object
nor
.Fn ASN1_put_eoc
do any sanity checking.
When called in inconsistent ways, invalid content may result in
.Pf * Fa ber_out ,
for example
.Bl -dash -compact
.It
a
.Fa tag
number less than 0x1f with a non-universal
.Fa class
.It
a
.Fa tag
number equal to 0x00 or 0x1f
.It
a
.Vt BOOLEAN ,
.Vt INTEGER ,
.Vt NULL
etc. with the
.Fa constructed
bit set
.It
a
.Vt SEQUENCE
or
.Vt SET
etc. without the
.Fa constructed
bit set
.It
a
.Fa length
that makes no sense for the given
.Fa tag
.It
a
.Fa length
that disagrees with the following data
.It
a
.Vt BOOLEAN ,
.Vt INTEGER ,
.Vt NULL
etc. in indefinite form
.It
an end-of-content marker even though no indefinite form was started
.It
\&...
.El
.Pp
If the calling code wants to find out how many bytes were written,
it needs to save a copy of the pointer
.Pf * Fa ber_out
before calling
.Fn ASN1_put_object .