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SNMP_API(3)				     Net-SNMP				      SNMP_API(3)

       snmp_sess_init,	 snmp_open,   snmp_send,   snmp_free_pdu,   snmp_select_info,  snmp_read,
       snmp_timeout, snmp_close, snmp_perror, snmp_sess_perror, snmp_error, snmp_api_errstring	-
       send and receive SNMP messages

       #include <net-snmp/session_api.h>

       void snmp_sess_init ( struct snmp_session * );

       struct snmp_session * snmp_open ( struct snmp_session *);
	      /* Input parameter not used in active sessions */

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

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

       void snmp_read ( fd_set *fdset );

       void snmp_timeout ( void );

       int snmp_close ( struct snmp_session *session );

       void snmp_free_pdu ( struct snmp_pdu *pdu );

       void snmp_error ( struct snmp_session *session,
	      int *pcliberr, int *psnmperr, char **pperrstring );

       char *snmp_api_errstring ( int snmperr );

       void snmp_perror ( char * msg );
	      /* for parsing errors only */

       void snmp_sess_perror (char * msg, struct snmp_session *);
	      /* all other SNMP library errors */

       Snmp_sess_init  prepares  a struct snmp_session that sources transport characteristics and
       common information that will be used for a set of SNMP transactions.  After this structure
       is passed to snmp_open to create an SNMP session, the structure is not used.

       Snmp_open returns a pointer to a newly-formed struct snmp_session object, which the appli-
       cation must use to reference the active SNMP session.

       Snmp_send and snmp_free_pdu each take as input a pointer  to  a	struct	snmp_pdu  object.
       This  structure	contains  information that describes a transaction that will be performed
       over an open session.

       Consult snmp_api.h for the definitions of these structures.

       Snmp_read, snmp_select_info, and snmp_timeout provide an interface  for	the  use  of  the
       select(2) system call so that SNMP transactions can occur asynchronously.

       Snmp_select_info  is  given  the  information that would have been passed to select in the
       absence of SNMP.  For example, this might include window update information.  This  infor-
       mation  is modified so that SNMP will get the service it requires from the call to select.
       In this case, numfds, fdset, and timeout correspond to  the  nfds,  readfds,  and  timeout
       arguments  to  select, respectively.  The only exception is that timeout must always point
       to an allocated (but perhaps uninitialized) struct timeval.  If timeout	would  have  been
       passed as NULL, block is set to true, and timeout is treated as undefined.  This same rule
       applies upon return from snmp_select_info.

       After calling snmp_select_info, select is called with  the  returned  data.   When  select
       returns, snmp_read should be called with the fd_set returned from select to read each SNMP
       socket that has input.  If select times out, snmp_timeout should be called to see  if  the
       timeout was intended for SNMP.

       Previous  versions  of  the  library  used  snmp_get_errno  to  read  the  global variable
       snmp_errno which may have held the error status within the  SNMP  library.   The  existing
       method snmp_perror should be used to log ASN.1 coding errors only.

       The  new  method snmp_sess_perror is provided to capture errors that occur during the pro-
       cessing of a particular SNMP  session.	Snmp_sess_perror  calls  snmp_error  function  to
       obtain the "C" library error errno , the SNMP library error snmperr , and the SNMP library
       detailed error message that is associated with an error that occurred during a given  ses-

       Note  that in all cases except one, snmp_sess_perror should be handed the struct snmp_ses-
       sion * pointer returned from snmp_open.	If snmp_open returns a	null  pointer,	pass  the
       INPUT struct snmp_session * pointer used to call snmp_open.

       Error return status from snmp_close and snmp_send is indicated by return of 0.  A success-
       ful status will return a 1 for snmp_close and then request id of the packet for snmp_send.
       Upon successful return from snmp_send the pdu will be freed by the library.

       Consult	snmp_api.h  for  the complete set of SNMP library error values.  The SNMP library
       error value snmperr can be one of the following values:

	 SNMPERR_GENERR 	  A generic error occurred.

	 SNMPERR_BAD_LOCPORT	  The local port was bad because it had already been allocated 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.















       A  string  representation of the error code can be obtained with snmp_api_errstring, and a
       standard error message may be printed using snmp_perror that  functions	like  the  perror
       standard routine.

       select(2), snmp_api.h

4.2 Berkeley Distribution		   21 Oct 1999				      SNMP_API(3)
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