/contrib/bsnmp/lib/asn1.3

  1.\"
  2.\" Copyright (c) 2004-2005
  3.\"	Hartmut Brandt.
  4.\"	All rights reserved.
  5.\" Copyright (c) 2001-2003
  6.\"	Fraunhofer Institute for Open Communication Systems (FhG Fokus).
  7.\"	All rights reserved.
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  9.\" Author: Harti Brandt <harti@FreeBSD.org>
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 32.\" $Begemot: bsnmp/lib/asn1.3,v 1.9 2005/10/04 08:46:49 brandt_h Exp $
 33.\"
 34.Dd October 4, 2005
 35.Dt ASN1 3
 36.Os
 37.Sh NAME
 38.Nm asn_get_header ,
 39.Nm asn_put_header ,
 40.Nm asn_put_temp_header ,
 41.Nm asn_commit_header ,
 42.Nm asn_get_integer_raw ,
 43.Nm asn_get_integer ,
 44.Nm asn_put_integer ,
 45.Nm asn_get_octetstring_raw ,
 46.Nm asn_get_octetstring ,
 47.Nm asn_put_octetstring ,
 48.Nm asn_get_null_raw ,
 49.Nm asn_get_null ,
 50.Nm asn_put_null ,
 51.Nm asn_put_exception ,
 52.Nm asn_get_objid_raw ,
 53.Nm asn_get_objid ,
 54.Nm asn_put_objid ,
 55.Nm asn_get_sequence ,
 56.Nm asn_get_ipaddress_raw ,
 57.Nm asn_get_ipaddress ,
 58.Nm asn_put_ipaddress ,
 59.Nm asn_get_uint32_raw ,
 60.Nm asn_put_uint32 ,
 61.Nm asn_get_counter64_raw ,
 62.Nm asn_put_counter64 ,
 63.Nm asn_get_timeticks ,
 64.Nm asn_put_timeticks ,
 65.Nm asn_skip ,
 66.Nm asn_slice_oid ,
 67.Nm asn_append_oid ,
 68.Nm asn_compare_oid ,
 69.Nm asn_is_suboid ,
 70.Nm asn_oid2str_r ,
 71.Nm asn_oid2str
 72.Nd "ASN.1 library for SNMP"
 73.Sh LIBRARY
 74Begemot SNMP library
 75.Pq libbsnmp, -lbsnmp
 76.Sh SYNOPSIS
 77.In bsnmp/asn1.h
 78.Ft enum asn_err
 79.Fn asn_get_header "struct asn_buf *buf" "u_char *type" "asn_len_t *lenp"
 80.Ft enum asn_err
 81.Fn asn_put_header "struct asn_buf *buf" "u_char type" "asn_len_t len"
 82.Ft enum asn_err
 83.Fn asn_put_temp_header "struct asn_buf *buf" "u_char type" "u_char **ptr"
 84.Ft enum asn_err
 85.Fn asn_commit_header "struct asn_buf *buf" "u_char *ptr"
 86.Ft enum asn_err
 87.Fn asn_get_integer_raw "struct asn_buf *buf" "asn_len_t len" "int32_t *res"
 88.Ft enum asn_err
 89.Fn asn_get_integer "struct asn_buf *buf" "int32_t *res"
 90.Ft enum asn_err
 91.Fn asn_put_integer "struct asn_buf *buf" "int32_t arg"
 92.Ft enum asn_err
 93.Fn asn_get_octetstring_raw "struct asn_buf *buf" "asn_len_t len" "u_char *out" "u_int *outsize"
 94.Ft enum asn_err
 95.Fn asn_get_octetstring "struct asn_buf *buf" "u_char *out" "u_int *outsize"
 96.Ft enum asn_err
 97.Fn asn_put_octetstring "struct asn_buf *buf" "const u_char *str" "u_int strsize"
 98.Ft enum asn_err
 99.Fn asn_get_null_raw "struct asn_buf *buf" "asn_len_t len"
100.Ft enum asn_err
101.Fn asn_get_null "struct asn_buf *buf"
102.Ft enum asn_err
103.Fn asn_put_null "struct asn_buf *buf"
104.Ft enum asn_err
105.Fn asn_put_exception "struct asn_buf *buf" "u_int type"
106.Ft enum asn_err
107.Fn asn_get_objid_raw "struct asn_buf *buf" "asn_len_t len" "struct asn_oid *oid"
108.Ft enum asn_err
109.Fn asn_get_objid "struct asn_buf *buf" "struct asn_oid *oid"
110.Ft enum asn_err
111.Fn asn_put_objid "struct asn_buf *buf" "const struct asn_oid *oid"
112.Ft enum asn_err
113.Fn asn_get_sequence "struct asn_buf *buf" "asn_len_t *lenp"
114.Ft enum asn_err
115.Fn asn_get_ipaddress_raw "struct asn_buf *buf" "asn_len_t len" "u_char *ipa"
116.Ft enum asn_err
117.Fn asn_get_ipaddress "struct asn_buf *buf" "u_char *ipa"
118.Ft enum asn_err
119.Fn asn_put_ipaddress "struct asn_buf *buf" "const u_char *ipa"
120.Ft enum asn_err
121.Fn asn_get_uint32_raw "struct asn_buf *buf" "asn_len_t len" "u_int32_t *res"
122.Ft enum asn_err
123.Fn asn_put_uint32 "struct asn_buf *buf" "u_char type" "u_int32_t val"
124.Ft enum asn_err
125.Fn asn_get_counter64_raw "struct asn_buf *buf" "asn_len_t len" "u_int64_t *res"
126.Ft enum asn_err
127.Fn asn_put_counter64 "struct asn_buf *buf" "u_int64_t val"
128.Ft enum asn_err
129.Fn asn_get_timeticks "struct asn_buf *buf" "u_int32_t *valp"
130.Ft enum asn_err
131.Fn asn_put_timeticks "struct asn_buf *buf" "u_int32_t val"
132.Ft enum asn_err
133.Fn asn_skip "struct asn_buf *buf" "asn_len_t len"
134.Ft void
135.Fn asn_slice_oid "struct asn_oid *dest" "const struct asn_oid *src" "u_int from" "u_int to"
136.Ft void
137.Fn asn_append_oid "struct asn_oid *to" "const struct asn_oid *from"
138.Ft int
139.Fn asn_compare_oid "const struct asn_oid *oid1" "const struct asn_oid *oid2"
140.Ft int
141.Fn asn_is_suboid "const struct asn_oid *oid1" "const struct asn_oid *oid2"
142.Ft char *
143.Fn asn_oid2str_r "const struct asn_oid *oid" "char *buf"
144.Ft char *
145.Fn asn_oid2str "const struct asn_oid *oid"
146.Sh DESCRIPTION
147The ASN.1 library contains routines to handle ASN.1 encoding for SNMP.
148It supports only the restricted form of ASN.1 as required by SNMP.
149There are two basic structures used throughout the library:
150.Bd -literal -offset indent
151/* these restrictions are in the SMI */
152#define ASN_MAXID	0xffffffff
153#define ASN_MAXOIDLEN	128
154
155/* type of subidentifiers */
156typedef u_int32_t asn_subid_t;
157
158struct asn_oid {
159	u_int	len;
160	asn_subid_t subs[ASN_MAXOIDLEN];
161};
162.Ed
163.Pp
164This structure represents an OID with the restrictions defined in the SNMP
165SMI.
166.Fa len
167holds the current length of the OID and
168.Fa subs
169holds the elements of the OID.
170.Bd -literal -offset indent
171struct asn_buf {
172	union {
173		u_char	*ptr;
174		const u_char *cptr;
175	}	asn_u;
176	size_t	asn_len;
177};
178#define asn_cptr	asn_u.cptr
179#define asn_ptr	asn_u.ptr
180.Ed
181.Pp
182This structure is used to encode and decode ASN.1.
183It describes the output
184buffer for encoding routines and the input buffer for decoding routines.
185For encoding
186.Fa asn_len
187holds the number of remaining free octets in the buffer.
188The first free byte is pointed to by
189.Fa asn_ptr .
190For decoding
191.Fa asn_len
192holds the number of remaining bytes to decode.
193The next byte to decode is pointed to by
194.Fa asn_cptr .
195.Pp
196Most of the functions return an error code
197.Fa "enum asn_error" :
198.Bd -literal -offset indent
199enum asn_err {
200	/* conversion was ok */
201	ASN_ERR_OK	= 0,
202	/* conversion failed and stopped */
203	ASN_ERR_FAILED	= 1 | 0x1000,
204	/* length field bad, value skipped */
205	ASN_ERR_BADLEN	= 2,
206	/* out of buffer, stopped */
207	ASN_ERR_EOBUF	= 3 | 0x1000,
208	/* length ok, but value is out of range */
209	ASN_ERR_RANGE	= 4,
210	/* not the expected tag, stopped */
211	ASN_ERR_TAG	= 5 | 0x1000,
212};
213#define ASN_ERR_STOPPED(E) (((E) & 0x1000) != 0)
214.Ed
215.Pp
216If
217.Fn ASN_ERR_STOPPED
218returns true, the error was fatal and processing has stopped at the point
219of error.
220.Pp
221The function
222.Fn asn_get_header
223reads the next header from the input octet stream.
224It returns the tag in the variable pointed to by
225.Fa type
226(note that only single byte tags are supported) and the decoded length field
227in the value pointed to by
228.Fa lenp
229(this is restricted to a unsigned 32-bit value).
230All errors in this function are fatal and stop processing.
231.Pp
232The function
233.Fn asn_put_header
234writes an ASN.1 header.
235.Fa type
236is the tag to write and is restricted to one byte tags (i.e., tags
237lesser or equal than 0x30).
238.Fa len
239is the length of the value and is restricted to 16-bit.
240.Pp
241The functions
242.Fn asn_put_temp_header
243and
244.Fn asn_commit_header
245are used to write a header when the length of the value is not known in
246advance, for example, for sequences.
247.Fn asn_put_temp_header
248writes a header with the given tag
249.Fa type
250and space for the maximum supported length field and sets the pointer pointed
251to by
252.Fa ptr
253to the begin of this length field.
254This pointer must then be fed into
255.Fn asn_commit_header
256directly after writing the value to the buffer.
257The function will compute the
258length, insert it into the right place and shift the value if the resulting
259length field is shorter than the estimated one.
260.Pp
261The function
262.Fn asn_get_integer_raw
263is used to decode a signed integer value (32-bit).
264It assumes, that the
265header of the integer has been decoded already.
266.Fa len
267is the length obtained from the ASN.1 header and the integer will be returned
268in the value pointed to by
269.Fa res .
270.Pp
271The function
272.Fn asn_get_integer
273decodes a complete 32-bit signed integer including the header.
274If the tag is wrong
275.Li ASN_ERR_TAG
276is returned.
277The function
278.Fn asn_put_integer
279encodes a 32-bit signed integer.
280.Pp
281The function
282.Fn asn_get_octetstring_raw
283decodes the value field of an ASN.1 octet string.
284The length obtained from the header must be fed into the
285.Fa len
286argument and
287.Fa out
288must point to a buffer to receive the octet string.
289On entry to the function
290.Fa outsize
291must point to the size of the buffer.
292On exit
293.Fa outsize
294will point to the number of octets decoded (if no error occurs this will be
295equal to
296.Fa len ).
297The function
298.Fn asn_get_octetstring
299decodes an octetstring including the header.
300.Fa out
301must point to a buffer to receive the string,
302.Fa outsize
303must point to the size of the buffer.
304On exit of the function
305.Fa outsize
306will point to the number of octets decoded.
307The function
308.Fn asn_put_octetstring
309encodes an octetstring (including the header).
310.Fa str
311points to the string to encode and
312.Fa strsize
313is the length of the string (the string may contain embedded
314.Li NUL Ns s).
315.Pp
316The function
317.Fn asn_get_null_raw
318decodes a null value.
319.Fa len
320is the length obtained from the header and must be 0.
321The function
322.Fn asn_get_null
323decodes a null including the header and the function
324.Fn asn_put_null
325encodes a null.
326.Pp
327The function
328.Fn asn_put_exception
329is used to encode an SNMPv2 exception.
330The exception type is
331.Fa type .
332.Pp
333The function
334.Fn asn_get_objid_raw
335is used to decode an OID value.
336.Fa len
337must be the value length obtained from the header and
338.Fa oid
339will receive the decoded OID.
340The function
341.Fn asn_get_objid
342decodes a complete OID (including the header) and the function
343.Fn asn_put_objid
344encodes a complete OID.
345.Pp
346The function
347.Fn asn_get_sequence
348decodes a sequence header.
349The length of the sequence value will be stored in the value pointed to by
350.Fa lenp .
351.Pp
352The function
353.Fn asn_get_ipaddress_raw
354decodes an IP address value.
355.Fa len
356is the length from the header and must be 4.
357.Fa ipa
358will receive the decoded IP address and must point to a buffer of at least
359four bytes.
360The function
361.Fn asn_get_ipaddress
362decodes a complete IP address (including the header) and
363.Fn asn_put_ipaddress
364encodes an IP address.
365.Pp
366The function
367.Fn asn_get_uint32_raw
368decodes an unsigned 32-bit integer value.
369.Fa len
370is the length from the header and
371.Fa res
372will get the decoded value.
373The function
374.Fn asn_put_uint32
375encodes an unsigned 32-bit integer value and inserts the tag given in
376.Fa type
377into the header.
378.Pp
379The function
380.Fn asn_get_counter64_raw
381decodes an unsigned 64-bit integer value.
382.Fa len
383must be the value length from the header.
384The resulting value is stored into the variable pointed to by
385.Fa res .
386The function
387.Fn asn_put_counter64
388encodes a complete unsigned 64-bit value.
389.Pp
390The function
391.Fn asn_get_timeticks
392decodes an ASN.1 object of type
393.Li TIMETICKS
394and the function
395.Fn asn_put_timeticks
396encodes such an object.
397.Pp
398The function
399.Fn asn_skip
400can be used to skip
401.Fa len
402bytes in the input buffer.
403.Pp
404The function
405.Fn asn_slice_oid
406splits a part out from an OID.
407It takes all the subids from the OID pointed to by
408.Fa src
409starting with the subid at position
410.Fa from
411(the first subid being subid 0) up to, but not including, subid
412.Fa to
413and generates a new OID in
414.Fa dest .
415If
416.Fa to
417is less or equal to
418.Fa from
419the resulting OID will have a length of zero.
420.Pp
421The function
422.Fn asn_append_oid
423appends the OID
424.Fa from
425to the OID
426.Fa to
427given that the resulting OID is not too long.
428If the maximum length is exceeded the result is undefined.
429.Pp
430The function
431.Fn asn_compare_oid
432compares two oids and returns the values
433.Li -1 ,
434.Li 0 or
435.Li +1
436when
437.Fa oid1
438is lesser than, equal, or larger than
439.Fa oid2
440resp.
441.Pp
442The function
443.Fn asn_is_suboid
444returns 1 if
445.Fa oid1
446is equal to the leading part of
447.Fa oid2 .
448It returns 0 otherwise.
449.Pp
450The function
451.Fn asn_oid2str_r
452makes a printable string from
453.Fa oid .
454The buffer pointed to by
455.Fa str
456must be large enough to hold the result.
457The constant
458.Li ASN_OIDSTRLEN
459is defined to be the length of the maximum string generated by this function
460(including the trailing NUL).
461The function
462.Fn asn_oid2str
463makes a printable string from
464.Fa oid
465into a private buffer that is overwritten by each call.
466.Sh DIAGNOSTICS
467When an error occurs in any of the function the function pointed to
468by the global pointer
469.Bd -literal -offset indent
470extern void (*asn_error)(const struct asn_buf *, const char *, ...);
471.Ed
472.Pp
473is called with the current buffer (this may be
474.Li NULL )
475and a
476.Xr printf 3
477style format string.
478There is a default error handler in the library that prints a message
479starting with
480.Sq ASN.1:
481followed by the error message and an optional dump of the buffer.
482.Sh SEE ALSO
483.Xr gensnmptree 1 ,
484.Xr bsnmpd 1 ,
485.Xr bsnmpagent 3 ,
486.Xr bsnmpclient 3 ,
487.Xr bsnmplib 3
488.Sh STANDARDS
489This implementation conforms to the applicable IETF RFCs and ITU-T
490recommendations.
491.Sh AUTHORS
492.An Hartmut Brandt Aq harti@FreeBSD.org