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SNMP_API

Section: C Library Functions (3)
Updated: 1 June, 1992
Index

NAME

snmp_open, snmp_close, snmp_send, snmp_read, snmp_free_pdu, snmp_select_info, snmp_timeout - send and receive SNMP messages

SYNOPSIS

#include <sys/types>
#include <netinet/in.h>
#include <sys/time.h>
#include <netdb.h>
#include <ucd-snmp/asn1.h>
#include <ucd-snmp/snmp.h>
#include <ucd-snmp/snmp_api.h>

struct snmp_session *snmp_open(session)
struct snmp_session *session;

int snmp_close(session)
struct snmp_session *session;

int snmp_send(session, pdu)
struct snmp_session *session;
struct snmp_pdu *pdu;

void snmp_read(fdset)
fd_set *fdset;

int snmp_select_info(numfds, fdset, timeout, block)
int *numfds;
fd_set *fdset;
struct timeval *timeout;
int *block;

void snmp_timeout()

void snmp_free_pdu(pdu)
struct snmp_pdu *pdu;

int snmp_get_errno()

char *snmp_api_errstring(snmp_errno)
int snmp_errno;

void snmp_perror(msg)
char *msg;

DESCRIPTION

Snmp_open, snmp_close,andsnmp_sendeach take as input a pointer to an object with thefollowing structure. In addition,snmp_openalso returns a pointer to an object with this structure.This structure contains information for a set of transactions thatwill share similar transport characteristics.

typedef struct sockaddr_in  ipaddr;struct snmp_session {    u_char  *community; /* community for outgoing requests. */    int     community_len;  /* Length of community name. */    int     retries;    /* Number of retries before timeout. */    long    timeout;    /* Number of uS until first timeout, then exponential backoff */    char    *peername;  /* Domain name or dotted IP address of default peer */    u_short remote_port;/* UDP port number of peer. */    u_short local_port; /* My UDP port number, 0 for default, picked randomly */    /* Authentication function or NULL if null authentication is used */    u_char  *(*authenticator)();    int     (*callback)();  /* Function to interpret incoming data */    /* Pointer to data that the callback function may consider important */    void    *callback_magic;    int     version;    /* 0 for SNMP, 1 for secure SNMP */    oid     *srcParty;  /* partyID of source party */    int     srcPartyLen; /* length in subIDs of srcParty */    oid     *dstParty;  /* partyID of destination party */    int     dstPartyLen; /* length in subIDs of dstParty */};/* * Set fields in session and pdu to the following to get a default or unconfigured value. */#define SNMP_DEFAULT_COMMUNITY_LEN  0/* for default community name */#define SNMP_DEFAULT_RETRIES        -1#define SNMP_DEFAULT_TIMEOUT        -1#define SNMP_DEFAULT_REMPORT        0#define SNMP_DEFAULT_REQID          0#define SNMP_DEFAULT_ERRSTAT        -1#define SNMP_DEFAULT_ERRINDEX       -1#define SNMP_DEFAULT_ADDRESS        0#define SNMP_DEFAULT_PEERNAME       NULL#define SNMP_DEFAULT_ENTERPRISE_LENGTH  0#define SNMP_DEFAULT_TIME           0/* * This routine must be supplied by the application: * * u_char *authenticator(pdu, length, community, community_len) * u_char *pdu;         The rest of the PDU to be authenticated * int *length;         The length of the PDU (updated by the authenticator) * u_char *community;   The community name to authenticate under. * int  community_len   The length of the community name. * * Returns the authenticated pdu, or NULL if authentication failed. * If null authentication is used, the authenticator in snmp_session can be * set to NULL(0). *//* * This routine must be supplied by the application: * * int callback(operation, session, reqid, pdu, magic) * int operation; * struct snmp_session *session;    The session authenticated under. * int reqid;                       The request id of this pdu (0 for TRAP) * struct snmp_pdu *pdu;            The pdu information. * void *magic                      A link to the data for this routine. * * Returns 1 if request was successful, 0 if it should be kept pending. * Any data in the pdu must be copied because it will be freed elsewhere. * Operations are defined below: */#define RECEIVED_MESSAGE   1#define TIMED_OUT          2

Snmp_sendandsnmp_free_pdueach take as input a pointer to an object with thefollowing structure.This structure contains information that describes a transactionthat will be performed over an open session.

struct snmp_pdu {    ipaddr  address;    /* Address of peer */    int     command;    /* Type of this PDU */    u_long  reqid;      /* Request id */    u_long  errstat;    /* Error status */    u_long  errindex;   /* Error index */    /* Trap information */    oid     *enterprise;/* System OID */    int     enterprise_length;    ipaddr  agent_addr; /* address of object generating trap */    int     trap_type;  /* trap type */    int     specific_type;  /* specific type */    u_long  time;       /* Uptime */    struct variable_list *variables;};struct variable_list {    struct variable_list *next_variable;    /* NULL for last variable */    oid     *name;  /* Object identifier of variable */    int     name_length;    /* number of subid's in name */    u_char  type;   /* ASN type of variable */    union { /* value of variable */        long    *integer;        u_char  *string;        oid     *objid;    } val;    int     val_len;};

Snmp_read, snmp_select_info,andsnmp_timeoutprovide an interface for the use of theselect(2)system call so that SNMP transactions can occur asynchronously.

Snmp_select_infois given the information that would have been passed toselectin the absence of SNMP. For example, this might include window update information.This information is modified so that SNMP will get the service it requires from thecall toselect.In this case,numfds, fdset,andtimeoutcorrespond to thenfds, readfds,andtimeoutarguments toselect,respectively. The only exception is that timeout must always point to an allocated (but perhaps uninitialized)struct timeval.Iftimeoutwould have been passed as NULL,blockis set to true, andtimeoutis treated as undefined. This same rule applies upon return fromsnmp_select_info.

After callingsnmp_select_info, selectis called with the returned data. When select returns,snmp_readis called with thefd_setreturned fromselect.This will read all SNMP sockets with input.Ifselecttimes out,snmp_timeoutshould be called to see if the timeout was intended for SNMP.

DIAGNOSTICS

Error return status from snmp_openis indicated by return of a null pointer.Error return status from snmp_closeandsnmp_sendis indicated by return of 0. A successful status will return a 1.The integersnmp_errnomay then be retrieved usingsnmp_get_errnoto see what type of error has occurred

snmp_errnocan have the following values:

SNMPERR_GENERR: A generic error occurred.
SNMPERR_BAD_LOCPORT: The local port was bad because it had already beenallocated or permission was denied.
SNMPERR_BAD_ADDRESS: The host name or address given was not useable.
SNMPERR_BAD_SESSION: The specified session was not open.
SNMPERR_TOO_LONG
SNMPERR_NO_SOCKET
SNMPERR_V2_IN_V1
SNMPERR_V1_IN_V2
SNMPERR_BAD_REPEATERS
SNMPERR_BAD_REPETITIONS
SNMPERR_BAD_ASN1_BUILD
SNMPERR_BAD_SENDTO
SNMPERR_BAD_PARSE
SNMPERR_BAD_VERSION
SNMPERR_BAD_SRC_PARTY
SNMPERR_BAD_DST_PARTY
SNMPERR_BAD_CONTEXT
SNMPERR_BAD_COMMUNITY
SNMPERR_NOAUTH_DESPRIV
SNMPERR_BAD_ACL
SNMPERR_BAD_PARTY
SNMPERR_ABORT
SNMPERR_UNKNOWN_PDU
SNMPERR_TIMEOUT

A string representation of the error code can be obtained withsnmp_api_errstring,and a standard error message may be printed usingsnmp_perrorthat functions like theperrorstandard routine.

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