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.\"
.\" Copyright (c) 2004-2005
.\"	Hartmut Brandt.
.\"	All rights reserved.
.\" Copyright (c) 2001-2003
.\"	Fraunhofer Institute for Open Communication Systems (FhG Fokus).
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.\" Author: Harti Brandt <harti@FreeBSD.org>
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.\" $Begemot: bsnmp/lib/asn1.3,v 1.9 2005/10/04 08:46:49 brandt_h Exp $
.\"
.Dd October 4, 2005
.Dt ASN1 3
.Os
.Sh NAME
.Nm asn_get_header ,
.Nm asn_put_header ,
.Nm asn_put_temp_header ,
.Nm asn_commit_header ,
.Nm asn_get_integer_raw ,
.Nm asn_get_integer ,
.Nm asn_put_integer ,
.Nm asn_get_octetstring_raw ,
.Nm asn_get_octetstring ,
.Nm asn_put_octetstring ,
.Nm asn_get_null_raw ,
.Nm asn_get_null ,
.Nm asn_put_null ,
.Nm asn_put_exception ,
.Nm asn_get_objid_raw ,
.Nm asn_get_objid ,
.Nm asn_put_objid ,
.Nm asn_get_sequence ,
.Nm asn_get_ipaddress_raw ,
.Nm asn_get_ipaddress ,
.Nm asn_put_ipaddress ,
.Nm asn_get_uint32_raw ,
.Nm asn_put_uint32 ,
.Nm asn_get_counter64_raw ,
.Nm asn_put_counter64 ,
.Nm asn_get_timeticks ,
.Nm asn_put_timeticks ,
.Nm asn_skip ,
.Nm asn_slice_oid ,
.Nm asn_append_oid ,
.Nm asn_compare_oid ,
.Nm asn_is_suboid ,
.Nm asn_oid2str_r ,
.Nm asn_oid2str
.Nd "ASN.1 library for SNMP"
.Sh LIBRARY
Begemot SNMP library
.Pq libbsnmp, -lbsnmp
.Sh SYNOPSIS
.In bsnmp/asn1.h
.Ft enum asn_err
.Fn asn_get_header "struct asn_buf *buf" "u_char *type" "asn_len_t *lenp"
.Ft enum asn_err
.Fn asn_put_header "struct asn_buf *buf" "u_char type" "asn_len_t len"
.Ft enum asn_err
.Fn asn_put_temp_header "struct asn_buf *buf" "u_char type" "u_char **ptr"
.Ft enum asn_err
.Fn asn_commit_header "struct asn_buf *buf" "u_char *ptr"
.Ft enum asn_err
.Fn asn_get_integer_raw "struct asn_buf *buf" "asn_len_t len" "int32_t *res"
.Ft enum asn_err
.Fn asn_get_integer "struct asn_buf *buf" "int32_t *res"
.Ft enum asn_err
.Fn asn_put_integer "struct asn_buf *buf" "int32_t arg"
.Ft enum asn_err
.Fn asn_get_octetstring_raw "struct asn_buf *buf" "asn_len_t len" "u_char *out" "u_int *outsize"
.Ft enum asn_err
.Fn asn_get_octetstring "struct asn_buf *buf" "u_char *out" "u_int *outsize"
.Ft enum asn_err
.Fn asn_put_octetstring "struct asn_buf *buf" "const u_char *str" "u_int strsize"
.Ft enum asn_err
.Fn asn_get_null_raw "struct asn_buf *buf" "asn_len_t len"
.Ft enum asn_err
.Fn asn_get_null "struct asn_buf *buf"
.Ft enum asn_err
.Fn asn_put_null "struct asn_buf *buf"
.Ft enum asn_err
.Fn asn_put_exception "struct asn_buf *buf" "u_int type"
.Ft enum asn_err
.Fn asn_get_objid_raw "struct asn_buf *buf" "asn_len_t len" "struct asn_oid *oid"
.Ft enum asn_err
.Fn asn_get_objid "struct asn_buf *buf" "struct asn_oid *oid"
.Ft enum asn_err
.Fn asn_put_objid "struct asn_buf *buf" "const struct asn_oid *oid"
.Ft enum asn_err
.Fn asn_get_sequence "struct asn_buf *buf" "asn_len_t *lenp"
.Ft enum asn_err
.Fn asn_get_ipaddress_raw "struct asn_buf *buf" "asn_len_t len" "u_char *ipa"
.Ft enum asn_err
.Fn asn_get_ipaddress "struct asn_buf *buf" "u_char *ipa"
.Ft enum asn_err
.Fn asn_put_ipaddress "struct asn_buf *buf" "const u_char *ipa"
.Ft enum asn_err
.Fn asn_get_uint32_raw "struct asn_buf *buf" "asn_len_t len" "u_int32_t *res"
.Ft enum asn_err
.Fn asn_put_uint32 "struct asn_buf *buf" "u_char type" "u_int32_t val"
.Ft enum asn_err
.Fn asn_get_counter64_raw "struct asn_buf *buf" "asn_len_t len" "u_int64_t *res"
.Ft enum asn_err
.Fn asn_put_counter64 "struct asn_buf *buf" "u_int64_t val"
.Ft enum asn_err
.Fn asn_get_timeticks "struct asn_buf *buf" "u_int32_t *valp"
.Ft enum asn_err
.Fn asn_put_timeticks "struct asn_buf *buf" "u_int32_t val"
.Ft enum asn_err
.Fn asn_skip "struct asn_buf *buf" "asn_len_t len"
.Ft void
.Fn asn_slice_oid "struct asn_oid *dest" "const struct asn_oid *src" "u_int from" "u_int to"
.Ft void
.Fn asn_append_oid "struct asn_oid *to" "const struct asn_oid *from"
.Ft int
.Fn asn_compare_oid "const struct asn_oid *oid1" "const struct asn_oid *oid2"
.Ft int
.Fn asn_is_suboid "const struct asn_oid *oid1" "const struct asn_oid *oid2"
.Ft char *
.Fn asn_oid2str_r "const struct asn_oid *oid" "char *buf"
.Ft char *
.Fn asn_oid2str "const struct asn_oid *oid"
.Sh DESCRIPTION
The ASN.1 library contains routines to handle ASN.1 encoding for SNMP.
It supports only the restricted form of ASN.1 as required by SNMP.
There are two basic structures used throughout the library:
.Bd -literal -offset indent
/* these restrictions are in the SMI */
#define ASN_MAXID	0xffffffff
#define ASN_MAXOIDLEN	128

/* type of subidentifiers */
typedef u_int32_t asn_subid_t;

struct asn_oid {
	u_int	len;
	asn_subid_t subs[ASN_MAXOIDLEN];
};
.Ed
.Pp
This structure represents an OID with the restrictions defined in the SNMP
SMI.
.Fa len
holds the current length of the OID and
.Fa subs
holds the elements of the OID.
.Bd -literal -offset indent
struct asn_buf {
	union {
		u_char	*ptr;
		const u_char *cptr;
	}	asn_u;
	size_t	asn_len;
};
#define asn_cptr	asn_u.cptr
#define asn_ptr	asn_u.ptr
.Ed
.Pp
This structure is used to encode and decode ASN.1.
It describes the output
buffer for encoding routines and the input buffer for decoding routines.
For encoding
.Fa asn_len
holds the number of remaining free octets in the buffer.
The first free byte is pointed to by
.Fa asn_ptr .
For decoding
.Fa asn_len
holds the number of remaining bytes to decode.
The next byte to decode is pointed to by
.Fa asn_cptr .
.Pp
Most of the functions return an error code
.Fa "enum asn_error" :
.Bd -literal -offset indent
enum asn_err {
	/* conversion was ok */
	ASN_ERR_OK	= 0,
	/* conversion failed and stopped */
	ASN_ERR_FAILED	= 1 | 0x1000,
	/* length field bad, value skipped */
	ASN_ERR_BADLEN	= 2,
	/* out of buffer, stopped */
	ASN_ERR_EOBUF	= 3 | 0x1000,
	/* length ok, but value is out of range */
	ASN_ERR_RANGE	= 4,
	/* not the expected tag, stopped */
	ASN_ERR_TAG	= 5 | 0x1000,
};
#define ASN_ERR_STOPPED(E) (((E) & 0x1000) != 0)
.Ed
.Pp
If
.Fn ASN_ERR_STOPPED
returns true, the error was fatal and processing has stopped at the point
of error.
.Pp
The function
.Fn asn_get_header
reads the next header from the input octet stream.
It returns the tag in the variable pointed to by
.Fa type
(note that only single byte tags are supported) and the decoded length field
in the value pointed to by
.Fa lenp
(this is restricted to a unsigned 32-bit value).
All errors in this function are fatal and stop processing.
.Pp
The function
.Fn asn_put_header
writes an ASN.1 header.
.Fa type
is the tag to write and is restricted to one byte tags (i.e., tags
lesser or equal than 0x30).
.Fa len
is the length of the value and is restricted to 16-bit.
.Pp
The functions
.Fn asn_put_temp_header
and
.Fn asn_commit_header
are used to write a header when the length of the value is not known in
advance, for example, for sequences.
.Fn asn_put_temp_header
writes a header with the given tag
.Fa type
and space for the maximum supported length field and sets the pointer pointed
to by
.Fa ptr
to the begin of this length field.
This pointer must then be fed into
.Fn asn_commit_header
directly after writing the value to the buffer.
The function will compute the
length, insert it into the right place and shift the value if the resulting
length field is shorter than the estimated one.
.Pp
The function
.Fn asn_get_integer_raw
is used to decode a signed integer value (32-bit).
It assumes, that the
header of the integer has been decoded already.
.Fa len
is the length obtained from the ASN.1 header and the integer will be returned
in the value pointed to by
.Fa res .
.Pp
The function
.Fn asn_get_integer
decodes a complete 32-bit signed integer including the header.
If the tag is wrong
.Li ASN_ERR_TAG
is returned.
The function
.Fn asn_put_integer
encodes a 32-bit signed integer.
.Pp
The function
.Fn asn_get_octetstring_raw
decodes the value field of an ASN.1 octet string.
The length obtained from the header must be fed into the
.Fa len
argument and
.Fa out
must point to a buffer to receive the octet string.
On entry to the function
.Fa outsize
must point to the size of the buffer.
On exit
.Fa outsize
will point to the number of octets decoded (if no error occurs this will be
equal to
.Fa len ).
The function
.Fn asn_get_octetstring
decodes an octetstring including the header.
.Fa out
must point to a buffer to receive the string,
.Fa outsize
must point to the size of the buffer.
On exit of the function
.Fa outsize
will point to the number of octets decoded.
The function
.Fn asn_put_octetstring
encodes an octetstring (including the header).
.Fa str
points to the string to encode and
.Fa strsize
is the length of the string (the string may contain embedded
.Li NUL Ns s).
.Pp
The function
.Fn asn_get_null_raw
decodes a null value.
.Fa len
is the length obtained from the header and must be 0.
The function
.Fn asn_get_null
decodes a null including the header and the function
.Fn asn_put_null
encodes a null.
.Pp
The function
.Fn asn_put_exception
is used to encode an SNMPv2 exception.
The exception type is
.Fa type .
.Pp
The function
.Fn asn_get_objid_raw
is used to decode an OID value.
.Fa len
must be the value length obtained from the header and
.Fa oid
will receive the decoded OID.
The function
.Fn asn_get_objid
decodes a complete OID (including the header) and the function
.Fn asn_put_objid
encodes a complete OID.
.Pp
The function
.Fn asn_get_sequence
decodes a sequence header.
The length of the sequence value will be stored in the value pointed to by
.Fa lenp .
.Pp
The function
.Fn asn_get_ipaddress_raw
decodes an IP address value.
.Fa len
is the length from the header and must be 4.
.Fa ipa
will receive the decoded IP address and must point to a buffer of at least
four bytes.
The function
.Fn asn_get_ipaddress
decodes a complete IP address (including the header) and
.Fn asn_put_ipaddress
encodes an IP address.
.Pp
The function
.Fn asn_get_uint32_raw
decodes an unsigned 32-bit integer value.
.Fa len
is the length from the header and
.Fa res
will get the decoded value.
The function
.Fn asn_put_uint32
encodes an unsigned 32-bit integer value and inserts the tag given in
.Fa type
into the header.
.Pp
The function
.Fn asn_get_counter64_raw
decodes an unsigned 64-bit integer value.
.Fa len
must be the value length from the header.
The resulting value is stored into the variable pointed to by
.Fa res .
The function
.Fn asn_put_counter64
encodes a complete unsigned 64-bit value.
.Pp
The function
.Fn asn_get_timeticks
decodes an ASN.1 object of type
.Li TIMETICKS
and the function
.Fn asn_put_timeticks
encodes such an object.
.Pp
The function
.Fn asn_skip
can be used to skip
.Fa len
bytes in the input buffer.
.Pp
The function
.Fn asn_slice_oid
splits a part out from an OID.
It takes all the subids from the OID pointed to by
.Fa src
starting with the subid at position
.Fa from
(the first subid being subid 0) up to, but not including, subid
.Fa to
and generates a new OID in
.Fa dest .
If
.Fa to
is less or equal to
.Fa from
the resulting OID will have a length of zero.
.Pp
The function
.Fn asn_append_oid
appends the OID
.Fa from
to the OID
.Fa to
given that the resulting OID is not too long.
If the maximum length is exceeded the result is undefined.
.Pp
The function
.Fn asn_compare_oid
compares two oids and returns the values
.Li -1 ,
.Li 0 or
.Li +1
when
.Fa oid1
is lesser than, equal, or larger than
.Fa oid2
resp.
.Pp
The function
.Fn asn_is_suboid
returns 1 if
.Fa oid1
is equal to the leading part of
.Fa oid2 .
It returns 0 otherwise.
.Pp
The function
.Fn asn_oid2str_r
makes a printable string from
.Fa oid .
The buffer pointed to by
.Fa str
must be large enough to hold the result.
The constant
.Li ASN_OIDSTRLEN
is defined to be the length of the maximum string generated by this function
(including the trailing NUL).
The function
.Fn asn_oid2str
makes a printable string from
.Fa oid
into a private buffer that is overwritten by each call.
.Sh DIAGNOSTICS
When an error occurs in any of the function the function pointed to
by the global pointer
.Bd -literal -offset indent
extern void (*asn_error)(const struct asn_buf *, const char *, ...);
.Ed
.Pp
is called with the current buffer (this may be
.Li NULL )
and a
.Xr printf 3
style format string.
There is a default error handler in the library that prints a message
starting with
.Sq ASN.1:
followed by the error message and an optional dump of the buffer.
.Sh SEE ALSO
.Xr gensnmptree 1 ,
.Xr bsnmpd 1 ,
.Xr bsnmpagent 3 ,
.Xr bsnmpclient 3 ,
.Xr bsnmplib 3
.Sh STANDARDS
This implementation conforms to the applicable IETF RFCs and ITU-T
recommendations.
.Sh AUTHORS
.An Hartmut Brandt Aq harti@FreeBSD.org