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.\" $OpenBSD: PEM_ASN1_read.3,v 1.2 2020/07/23 17:34:53 schwarze Exp $
.\"
.\" Copyright (c) 2020 Ingo Schwarze <schwarze@openbsd.org>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd $Mdocdate: July 23 2020 $
.Dt PEM_ASN1_READ 3
.Os
.Sh NAME
.Nm d2i_of_void ,
.Nm PEM_ASN1_read ,
.Nm PEM_ASN1_read_bio
.Nd PEM and DER decode an arbitrary ASN.1 value
.Sh SYNOPSIS
.In openssl/pem.h
.Ft typedef void *
.Fo d2i_of_void
.Fa "void **val_out"
.Fa "const unsigned char **der_in"
.Fa "long length"
.Fc
.Ft void *
.Fo PEM_ASN1_read
.Fa "d2i_of_void *d2i"
.Fa "const char *name"
.Fa "FILE *in_fp"
.Fa "void **val_out"
.Fa "pem_password_cb *cb"
.Fa "void *u"
.Fc
.Ft void *
.Fo PEM_ASN1_read_bio
.Fa "d2i_of_void *d2i"
.Fa "const char *name"
.Fa "BIO *in_bp"
.Fa "void **val_out"
.Fa "pem_password_cb *cb"
.Fa "void *u"
.Fc
.Sh DESCRIPTION
These functions read one object from
.Fa in_fp
or
.Fa in_bp
and perform both PEM and DER decoding.
They are needed when more specific decoding functions
like those documented in
.Xr PEM_read_bio_PrivateKey 3
and
.Xr PEM_read_SSL_SESSION 3
are inadequate for the type
.Fa name .
.Pp
For PEM decoding,
.Xr PEM_bytes_read_bio 3
is called internally.
Consequently, the first object of type
.Fa name
is returned and preceding objects of other types are discarded.
If necessary, data is decrypted, using
.Fa cb
and/or
.Fa u
if they are not
.Dv NULL ,
as described in the
.Xr pem_password_cb 3
manual page.
.Pp
For subsequent DER decoding, pass a
.Fa d2i
callback function that is adequate for the type
.Fa name ,
typically returning a pointer of a type more specific than
.Ft void * .
For example,
.Xr d2i_ASN1_TYPE 3
can always be used and its manual page describes the required
behaviour of the callback function to be passed.
Normally, passing a more specific function is more useful;
candidate functions can be found with
.Ql man -k Nm~^d2i_ .
.Pp
For the
.Fa name
argument, the
.Dv PEM_STRING_*
string constants defined in
.In openssl/pem.h
can be used.
.Pp
The
.Fa val_out
argument is useless and its many dangers are described in detail in the
.Xr d2i_ASN1_TYPE 3
manual page.
To reduce the risk of bugs, always passing
.Dv NULL
is recommended.
.Sh RETURN VALUES
These functions return a pointer to the decoded object or
.Dv NULL
if an error occurs.
They fail if
.Xr PEM_bytes_read_bio 3
fails, for example because of invalid syntax in the input, an unknown
encryption, or an invalid passphrase entered by the user.
They also fail if
.Fa d2i
returns
.Dv NULL ,
for example due to DER decoding errors.
.Pp
.Fn PEM_ASN1_read
may also fail if memory is exhausted.
.Sh EXAMPLES
Typical usage of
.Fn PEM_ASN1_read
is demonstrated by the implementation of the more specific function
to PEM and DER decode an X.509 certificate:
.Bd -literal -offset 2n
X509 *
PEM_read_X509(FILE *fp, X509 **val_out, pem_password_cb *cb, void *u)
{
return PEM_ASN1_read((d2i_of_void *)d2i_X509, PEM_STRING_X509,
fp, (void **)val_out, cb, u);
}
.Ed
.Sh ERRORS
Diagnostics that can be retrieved with
.Xr ERR_get_error 3 ,
.Xr ERR_GET_REASON 3 ,
and
.Xr ERR_reason_error_string 3
include:
.Bl -tag -width Ds
.It Dv ERR_R_BUF_LIB Qq "BUF lib"
.Fn PEM_ASN1_read
failed to set up a temporary BIO,
for example because memory was exhausted.
.It Dv ERR_R_ASN1_LIB Qq "ASN1 lib"
.Fa d2i
returned
.Dv NULL ,
for example due to a DER syntax error.
.El
.Pp
Additional types of errors can result from
.Xr PEM_bytes_read_bio 3 .
.Sh SEE ALSO
.Xr BIO_new 3 ,
.Xr d2i_ASN1_TYPE 3 ,
.Xr PEM_bytes_read_bio 3 ,
.Xr PEM_read 3 ,
.Xr PEM_read_bio_PrivateKey 3 ,
.Xr PEM_read_SSL_SESSION 3 ,
.Xr PEM_X509_INFO_read 3
.Sh HISTORY
These functions first appeared in SSLeay 0.5.1
and have been available since
.Ox 2.4 .
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