.\" $OpenBSD: i2a_ASN1_STRING.3,v 1.2 2021/11/23 13:52:27 schwarze Exp $
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.\" Copyright (c) 2019, 2021 Ingo Schwarze <schwarze@openbsd.org>
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.Dd $Mdocdate: November 23 2021 $
.Dt I2A_ASN1_STRING 3
.Os
.Sh NAME
.Nm i2a_ASN1_STRING ,
.Nm i2a_ASN1_INTEGER ,
.Nm i2a_ASN1_ENUMERATED ,
.Nm a2i_ASN1_STRING ,
.Nm a2i_ASN1_INTEGER ,
.Nm a2i_ASN1_ENUMERATED
.Nd hexadecimal dump of an ASN.1 string
.Sh SYNOPSIS
.In openssl/asn1.h
.Ft int
.Fo i2a_ASN1_STRING
.Fa "BIO *out_bio"
.Fa "const ASN1_STRING *a"
.Fa "int type"
.Fc
.Ft int
.Fo i2a_ASN1_INTEGER
.Fa "BIO *out_bio"
.Fa "const ASN1_INTEGER *a"
.Fc
.Ft int
.Fo i2a_ASN1_ENUMERATED
.Fa "BIO *out_bio"
.Fa "const i2a_ASN1_ENUMERATED *a"
.Fc
.Ft int
.Fo a2i_ASN1_STRING
.Fa "BIO *in_bio"
.Fa "ASN1_STRING *out_string"
.Fa "char *buffer"
.Fa "int size"
.Fc
.Ft int
.Fo a2i_ASN1_INTEGER
.Fa "BIO *in_bio"
.Fa "ASN1_INTEGER *out_string"
.Fa "char *buffer"
.Fa "int size"
.Fc
.Ft int
.Fo a2i_ASN1_ENUMERATED
.Fa "BIO *in_bio"
.Fa "ASN1_ENUMERATED *out_string"
.Fa "char *buffer"
.Fa "int size"
.Fc
.Sh DESCRIPTION
The functions
.Fn i2a_ASN1_STRING ,
.Fn i2a_ASN1_INTEGER ,
and
.Fn i2a_ASN1_ENUMERATED
write a hexadecimal representation of
.Fa a
to
.Fa out_bio .
The
.Fa type
argument is ignored.
.Pp
Each byte of
.Xr ASN1_STRING_get0_data 3
is written as a number consisting of two upper-case hexadecimal digits.
After each group of 70 digits, a backslash and a linefeed
are inserted before the next digit.
.Pp
If the
.Xr ASN1_STRING_length 3
of
.Fa a
is 0, instead a pair of zero digits
.Pq Qq 00
is written by
.Fn i2a_ASN1_INTEGER
and
.Fn i2a_ASN1_ENUMERATED
and a single zero digit
.Pq Qq 0
by
.Fn i2a_ASN1_STRING .
If
.Fa a
is a
.Dv NULL
pointer, nothing is written.
.Pp
If
.Fa a
represents a negative integer,
.Fn i2a_ASN1_INTEGER
prepends a minus sign to the output.
.Pp
The functions
.Fn a2i_ASN1_STRING ,
.Fn a2i_ASN1_INTEGER ,
and
.Fn a2i_ASN1_ENUMERATED
parse a hexadecimal representation of an ASN.1 string into
.Fa out_string .
Both lower-case and upper-case hexadecimal digits are accepted.
Every pair of input digits is converted into one output byte.
.Pp
On every input line, the trailing newline character and an optional
carrier return character character preceding it are ignored.
The trailing newline need not be present on the last line.
If there is a backslash character before the newline character,
parsing is continued on the next input line.
.Pp
At least one pair of input digits is required by
.Fn a2i_ASN1_INTEGER
and
.Fn a2i_ASN1_ENUMERATED ,
whereas
.Fn a2i_ASN1_STRING
converts empty input to an empty string.
.Pp
These functions are able to parse the output of
.Fn i2a_ASN1_ENUMERATED .
They can parse the output of
.Fn i2a_ASN1_INTEGER
unless
.Fa a
was negative, and they can parse the output of
.Fn i2a_ASN1_STRING
unless the
.Xr ASN1_STRING_length 3
of
.Fa a
was 0.
.Pp
Parsing fails if an input line contains an odd number of input
digits or if memory allocation fails.
.Pp
These functions use the
.Fa buffer
provided by the caller and assume it is at least
.Fa size
bytes long.
It is unspecified what the buffer contains after the functions return.
.Sh RETURN VALUES
The functions
.Fn i2a_ASN1_STRING ,
.Fn i2a_ASN1_INTEGER ,
and
.Fn i2a_ASN1_ENUMERATED
return the number of bytes written or \-1 if
.Xr BIO_write 3
fails.
In particular, they all return 0 when
.Fa a
is a
.Dv NULL
pointer.
.Fn i2a_ASN1_STRING
returns 1 for an empty string or an even number greater than 1
for a string that is not empty.
.Fn i2a_ASN1_INTEGER
returns an even number greater than 1 for positive input
or an odd number greater than 2 for negative input.
.Fn i2a_ASN1_ENUMERATED
always returns a non-negative even number when successful.
.Pp
The functions
.Fn a2i_ASN1_STRING ,
.Fn a2i_ASN1_INTEGER ,
and
.Fn a2i_ASN1_ENUMERATED
are intended to return 1 for success or 0 for failure, but see the
.Sx BUGS
section for a number of traps.
.Sh SEE ALSO
.Xr ASN1_STRING_length 3 ,
.Xr ASN1_STRING_new 3 ,
.Xr ASN1_STRING_print_ex 3 ,
.Xr i2a_ASN1_OBJECT 3
.Sh HISTORY
.Fn i2a_ASN1_INTEGER
and
.Fn a2i_ASN1_INTEGER
first appeared in SSLeay 0.6.0.
.Fn i2a_ASN1_STRING
and
.Fn a2i_ASN1_STRING
first appeared in SSLeay 0.6.5.
.Fn a2i_ASN1_STRING
has been part of the public API since SSLeay 0.6.5 and
.Fn i2a_ASN1_STRING
since SSLeay 0.8.0.
These functions have been available since
.Ox 2.4 .
.Pp
.Fn i2a_ASN1_ENUMERATED
and
.Fn a2i_ASN1_ENUMERATED
first appeared in OpenSSL 0.9.2 and have been available since
.Ox 2.6 .
.Sh BUGS
If the first call to
.Xr BIO_gets 3
does not return any data, even if that is caused by a fatal I/O error,
if the BIO type does not support the
.Dq gets
operation, or if it is caused by the BIO being non-blocking,
.Fn a2i_ASN1_STRING
immediately succeeds and returns an empty
.Fa out_string .
.Pp
If
.Fn BIO_gets 3
returns a partial line, for example because the given
.Fa size
is insufficient to contain one of the input lines
or for reasons specific to the BIO type,
.Fn a2i_ASN1_STRING ,
.Fn a2i_ASN1_INTEGER ,
and
.Fn a2i_ASN1_ENUMERATED
may fail or silently return a truncated result.
The caller is responsible for providing a
.Fa buffer
of sufficient size to contain the longest possible input line
and for choosing a BIO of a type that only returns complete
input lines and does not perform partial reads.
.Pp
The functions
.Fn a2i_ASN1_STRING ,
.Fn a2i_ASN1_INTEGER ,
and
.Fn a2i_ASN1_ENUMERATED
do not support non-blocking BIOs.
Reading is terminated as soon as
.Xr BIO_gets 3
returns a value less than 1.