freebsd/contrib/bsnmp/lib/bsnmplib.3

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.\"	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/bsnmplib.3,v 1.5 2004/08/06 08:46:52 brandt Exp $
.\"
.Dd August 15, 2002
.Dt bsnmplib 3
.Os
.Sh NAME
.Nm snmp_value_free ,
.Nm snmp_value_parse ,
.Nm snmp_value_copy ,
.Nm snmp_pdu_free ,
.Nm snmp_code snmp_pdu_decode ,
.Nm snmp_code snmp_pdu_encode ,
.Nm snmp_pdu_dump ,
.Nm TRUTH_MK ,
.Nm TRUTH_GET ,
.Nm TRUTH_OK
.Nd "SNMP decoding and encoding library"
.Sh LIBRARY
Begemot SNMP library
.Pq libbsnmp, -lbsnmp
.Sh SYNOPSIS
.In bsnmp/asn1.h
.In bsnmp/snmp.h
.Ft void
.Fn snmp_value_free "struct snmp_value *value"
.Ft int
.Fn snmp_value_parse "const char *buf" "enum snmp_syntax" "union snmp_values *value"
.Ft int
.Fn snmp_value_copy "struct snmp_value *to" "const struct snmp_value *from"
.Ft void
.Fn snmp_pdu_free "struct snmp_pdu *value"
.Ft enum snmp_code
.Fn snmp_pdu_decode "struct asn_buf *buf" "struct snmp_pdu *pdu" "int32_t *ip"
.Ft enum snmp_code
.Fn snmp_pdu_encode "struct snmp_pdu *pdu" "struct asn_buf *buf"
.Ft void
.Fn snmp_pdu_dump "const struct snmp_pdu *pdu"
.Ft int
.Fn TRUTH_MK "F"
.Ft int
.Fn TRUTH_GET "T"
.Ft int
.Fn TRUTH_OK "T"
.Sh DESCRIPTION
The SNMP library contains routines to handle SNMP version 1 and 2 PDUs.
There are two basic structures used throughout the library:
.Bd -literal -offset indent
struct snmp_value {
	struct asn_oid		var;
	enum snmp_syntax	syntax;
	union snmp_values {
	  int32_t		integer;/* also integer32 */
	  struct {
	    u_int		len;
	    u_char		*octets;
	  }			octetstring;
	  struct asn_oid	oid;
	  u_char		ipaddress[4];
	  u_int32_t		uint32;	/* also gauge32, counter32,
					   unsigned32, timeticks */
	  u_int64_t		counter64;
	}			v;
};
.Ed
.Pp
This structure represents one variable binding from an SNMP PDU. The
field
.Fa var
is the ASN.1 of the variable that is bound.
.Fa syntax
contains either the syntax code of the value or an exception code for SNMPv2
and may be one of:
.Bd -literal -offset indent
enum snmp_syntax {
	SNMP_SYNTAX_NULL	= 0,
	SNMP_SYNTAX_INTEGER,	/* == INTEGER32 */
	SNMP_SYNTAX_OCTETSTRING,
	SNMP_SYNTAX_OID,
	SNMP_SYNTAX_IPADDRESS,
	SNMP_SYNTAX_COUNTER,
	SNMP_SYNTAX_GAUGE,	/* == UNSIGNED32 */
	SNMP_SYNTAX_TIMETICKS,

	/* v2 additions */
	SNMP_SYNTAX_COUNTER64,
	/* exceptions */
	SNMP_SYNTAX_NOSUCHOBJECT,
	SNMP_SYNTAX_NOSUCHINSTANCE,
	SNMP_SYNTAX_ENDOFMIBVIEW,
};
.Ed
The field
.Fa v
holds the actual value depending on
.Fa syntax .
Note, that if
.Fa syntax
is
.Li SNMP_SYNTAX_OCTETSTRING
and
.Fa v.octetstring.len
is not zero,
.Fa v.octetstring.octets
points to a string allocated by
.Xr malloc 3 .
.Pp
.Bd -literal -offset indent
#define SNMP_COMMUNITY_MAXLEN	128
#define SNMP_MAX_BINDINGS	100

struct snmp_pdu {
	char		community[SNMP_COMMUNITY_MAXLEN + 1];
	enum snmp_version version;
	u_int		type;

	/* trap only */
	struct asn_oid	enterprise;
	u_char		agent_addr[4];
	int32_t		generic_trap;
	int32_t		specific_trap;
	u_int32_t	time_stamp;

	/* others */
	int32_t		request_id;
	int32_t		error_status;
	int32_t		error_index;

	/* fixes for encoding */
	u_char		*outer_ptr;
	u_char		*pdu_ptr;
	u_char		*vars_ptr;

	struct snmp_value bindings[SNMP_MAX_BINDINGS];
	u_int		nbindings;
};
.Ed
This structure contains a decoded SNMP PDU.
.Fa version
is one of
.Bd -literal -offset indent
enum snmp_version {
	SNMP_Verr = 0,
	SNMP_V1 = 1,
	SNMP_V2c,
};
.Ed
and
.Fa type
is the type of the PDU.
.Pp
The function
.Fn snmp_value_free
is used to free all the dynamic allocated contents of an SNMP value. It does
not free the structure pointed to by
.Fa value
itself.
.Pp
The function
.Fn snmp_value_parse
parses the ASCII representation of an SNMP value into its binary form.
This function is mainly used by the configuration file reader of
.Xr snmpd 1 .
.Pp
The function
.Fn snmp_value_copy
makes a deep copy of the value pointed to by
.Fa from
to the structure pointed to by
.Fa to .
It assumes that
.Fa to
is uninitialized and will overwrite its previous contents. It does not itself
allocate the structure pointed to by
.Fa to .
.Pp
The function
.Fn snmp_pdu_free
frees all the dynamically allocated components of the PDU. It does not itself
free the structure pointed to by
.Fa pdu .
.Pp
The function
.Fn snmp_pdu_decode
decodes the PDU pointed to by
.Fa buf
and stores the result into
.Fa pdu .
If an error occurs in a variable binding the (1 based) index of this binding
is stored in the variable pointed to by
.Fa ip .
.Pp
The function
.Fn snmp_pdu_encode
encodes the PDU
.Fa pdu
into the an octetstring in buffer
.Fa buf .
.Pp
The function
.Fn snmp_pdu_dump
dumps the PDU in a human readable form by calling
.Fn snmp_printf .
.Pp
The function
.Fn TRUTH_MK
takes a C truth value (zero or non-zero) and makes an SNMP truth value (2 or 1).
The function
.Fn TRUTH_GET
takes an SNMP truth value and makes a C truth value (0 or 1).
The function
.Fn TRUTH_OK
checks, whether its argument is a legal SNMP truth value.
.Sh DIAGNOSTICS
When an error occures in any of the function the function pointed to
by the global pointer
.Bd -literal -offset indent
extern void (*snmp_error)(const char *, ...);
.Ed
.Pp
with a
.Xr printf 3
style format string.
There is a default error handler in the library that prints a message
starting with
.Sq SNMP:
followed by the error message to standard error.
.Pp
The function pointed to by
.Bd -literal -offset indent
extern void (*snmp_printf)(const char *, ...);
.Ed
.Pp
is called by the
.Fn snmp_pdu_dump
function.
The default handler is
.Xr printf 3 .
.Sh ERRORS
.Fn snmp_pdu_decode
will return one of the following return codes:
.Bl -tag -width Er
.It Bq Er SNMP_CODE_OK
Success.
.It Bq Er SNMP_CODE_FAILED
The ASN.1 coding was wrong.
.It Bq Er SNMP_CODE_BADLEN
A variable binding value had a wrong length field.
.It Bq Er SNMP_CODE_OORANGE
A variable binding value was out of the allowed range.
.It Bq Er SNMP_CODE_BADVERS
The PDU is of an unsupported version.
.It Bq Er SNMP_CODE_BADENQ
There was an ASN.1 value with an unsupported tag.
.El
.Pp
.Fn snmp_pdu_encode
will return one of the following return codes:
.Bl -tag -width Er
.It Bq Er SNMP_CODE_OK
Success.
.It Bq Er SNMP_CODE_FAILED
Encoding failed.
.El
.Sh SEE ALSO
.Xr snmpd 1 ,
.Xr gensnmptree 1 ,
.Xr bsnmplib 3
.Xr bsnmpclient 3 ,
.Xr bsnmpagent 3
.Sh STANDARDS
This implementation conforms to the applicable IETF RFCs and ITU-T
recommendations.
.Sh AUTHORS
.An Hartmut Brandt Aq harti@freebsd.org