.\"/***********************************************************
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.\" 
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.TH SNMP_API 3 "June, 1996"
.UC 5
.SH NAME
snmp_open, snmp_close, snmp_send, snmp_read, snmp_free_pdu, snmp_select_info, snmp_timeout \- send and receive SNMP messages
.SH SYNOPSIS
.B "#include <sys/types>
.br
.B "#include <netinet/in.h>
.br
.B "#include <sys/time.h>
.br
.B #include <snmp/snmp.h>
.br
.B #include <snmp/snmp_impl.h>
.br
.B #include <snmp/asn1.h>
.br
.B #include <snmp/snmp_api.h>
.PP
.B "extern int snmp_errno;
.PP
.B "extern int snmp_dump_packet;
.PP
.B "struct snmp_session *snmp_open(session)
.br
.B "struct snmp_session *session;
.PP
.B "int snmp_close(session)
.br
.B "struct snmp_session *session;
.PP
.B "int snmp_send(session, pdu)
.br
.B "struct snmp_session *session;
.br
.B "struct snmp_pdu *pdu;
.PP
.B "void snmp_read(fdset)
.br
.B "fd_set *fdset;
.PP
.B "int snmp_select_info(numfds, fdset, timeout, block)
.br
.B "int *numfds;
.br
.B "fd_set *fdset;
.br
.B "struct timeval *timeout;
.br
.B "int *block;
.PP
.B "void snmp_timeout()
.PP
.B "void snmp_pdu_create(tag)
.br
.B "int tag;
.PP
.B "void snmp_free_pdu(pdu)
.br
.B "struct snmp_pdu *pdu;
.PP
.SH DESCRIPTION
.I Snmp_open, snmp_close,
and
.I snmp_send
each take as input a pointer to an object with the
following structure.  In addition,
.I snmp_open
also returns a pointer to an object with this structure.
This structure contains information for a set of transactions that
will share similar transport characteristics.
.\" .RS
.\" .PP

.nf
typedef struct sockaddr_in  ipaddr;

struct snmp_session {
    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 or IPX 
				   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 */
#ifdef HAVE_IPX
    u_short remote_port_ipx;	/* IPX port number of peer. */
    u_short local_port_ipx;	/* My IPX port number, 0 for default, 
				   picked randomly */
#endif
    /* Authentication function or NULL if null authentication is used */
    int    (*authenticator)();
#if 1
  /* Function to interpret incoming data */
  int	    (*callback)  _ANSI_ARGS_(( int operation,
			 struct snmp_session *session,
			 int reqid,
			 struct snmp_pdu *response,
			 void *magic,
			 ... ));
#else
    int (*callback)();
#endif

    /* Pointer to data that the callback function may consider important */
    void    *callback_magic;

    int		version; 	/* SNMP version number */

    /* fields to support SNMPv1 community model */
    int	        community_len;
    u_char      *community;

    /* the private keys to use for user-based security */
    u_char   	authKey[16];
    u_char   	privKey[16];

    /* fields to support user-based security model in SNMPv2 */
    Parameters	params;

    u_char	qoS;
    u_char	agentID[16];
    u_long	agentBoots;
    int		agentTime;		/* the agentTime value */
    int		agentClock;		/* the running agentClock */
    int	     	userLen;
    u_char   	userName[32];
    int		MMS;
    int		contextLen;
    u_char	contextSelector[64];

    /* misc stuff */
    int		readView;
    int		writeView;
};

/*
 * 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 /* , ... request */ )
 * 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.
 *
 * struct request_list *request;    The original request -- Note: this 
 *				    parameter was added to cmu-snmp-linux-3.5
 *				    and is only avail starting with this 
 *				    release; if the request is not known a
 *				    NULL pointer is passed.
 *
 * 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
.ft R
.ad
.fi
.RE
.PP
.I Snmp_send
and
.I snmp_free_pdu
each take as input a pointer to an object with the
following structure.
This structure contains information that describes a transaction
that will be performed over an open session.
.RS
.PP
.nf
struct snmp_pdu {
#ifdef HAVE_IPX
    struct sockaddr address;	/* Address of peer (ip or ipx addr) */
#else
    ipaddr address;		/* Address of peer (ip addr) */
#endif
    int	    command;		/* Type of this PDU */

    Parameters params;

    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;
};
.ft R
.ad
.fi
.RE
.PP
.I Snmp_read, snmp_select_info,
and
.I snmp_timeout
provide an interface for the use of the
.IR select (2)
system call so that SNMP transactions can occur asynchronously.
.PP
.I Snmp_select_info
is given the information that would have been passed to
.I select
in 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 the
call to
.I select.
In this case,
.I numfds, fdset,
and
.I timeout
correspond to the
.I nfds, readfds,
and
.I timeout
arguments to
.I select,
respectively.  The only exception is that timeout must always point to an allocated (but perhaps uninitialized)
.I struct timeval.
If
.I timeout
would have been passed as NULL,
.I block
is set to true, and
.I timeout
is treated as undefined.  This same rule applies upon return from
.I snmp_select_info.
.PP
After calling
.I snmp_select_info, select
is called with the returned data.  When select returns,
.I snmp_read
is called with the
.I fd_set
returned from
.I select.
This will read all SNMP sockets with input.
If
.I select
times out,
.I snmp_timeout
should be called to see if the timeout was intended for SNMP.
.SH DIAGNOSTICS
.PP
Error return status from 
.I snmp_open
is indicated by return of a null pointer.
Error return status from 
.I snmp_close
and
.I snmp_send
is indicated by return of 0.  A successful status will return a 1.
The external integer
.IR snmp_errno
may then be checked to see what type of error has occurred
.PP
.IR snmp_errno
can have the following values:
.RS
.IP SNMPERR_GENERR \w'SNMPERR_BAD_LOCPORT'u+2n
A generic error occurred.
.IP SNMPERR_BAD_LOCPORT \w'SNMPERR_BAD_LOCPORT'u+2n
The local port was bad because it had already been
allocated or permission was denied.
.IP SNMPERR_BAD_ADDRESS \w'SNMPERR_BAD_LOCPORT'u+2n
The host name or address given was not useable.
.IP SNMPERR_BAD_SESSION \w'SNMPERR_BAD_SESSION'u+2n
The specified session was not open.
.RE
.PP
The variable
.I snmp_dump_packet
can be set to a value != 0 to force hex dumps of packets sent/read.
.br
Please Note: In the linux port this variable is part of the library 
and should not be declared by the application.
.SH NOTE
Since cmu-snmp-linux v3.6 there is optional IPX support included.
It is currently only avail if compiled in.
.SH "SEE ALSO"
select(2), snmp_api.h