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NETSNMP_SESS_API(3)                               Net-SNMP                               NETSNMP_SESS_API(3)



NAME
       snmp_sess_init,     snmp_sess_open,    snmp_sess_session,    snmp_sess_send,    snmp_sess_async_send,
       snmp_sess_select_info, snmp_sess_read, snmp_sess_timeout, snmp_sess_close, snmp_sess_error -  session
       functions

SYNOPSIS
       #include <net-snmp/session_api.h>

       void snmp_sess_init(struct snmp_session *session);

       void *snmp_sess_open(struct snmp_session *session);

       struct snmp_session *snmp_sess_session(void *handle);

       int snmp_sess_send(void *handle, struct snmp_pdu *pdu);

       int snmp_sess_async_send(void *handle,
                                struct snmp_pdu *pdu,
                                snmp_callback callback,
                                void *callbackData);

       int snmp_sess_select_info(void *handle,
                                 int *numfds, fd_set *fdset,
                                 struct timeval *timeout,
                                 int *block);

       int snmp_sess_read(void *handle, fd_set *fdset);

       void snmp_sess_timeout(void *handle);

       int snmp_sess_close(void *handle);

       void snmp_sess_error(void *handle, int *pcliberr,
                           int *psnmperr, char **pperrstring);

DESCRIPTION
       These  functions  define  a  subset  of  the API that can be used to manage single SNMP sessions in a
       multi-threaded application.  Except for snmp_sess_session(), these functions are single session  ver-sions versions
       sions of the traditional SNMP library API.

       Note that these functions use an opaque pointer (handle in the above prototypes) to identify a single
       session in lieu of a session pointer (as in the traditional API).

       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_sess_open() to create an SNMP session, the structure is no  longer  used.   Instead  the  opaque
       pointer returned by snmp_sess_open() is used to refer to that session henceforth.

       SNMP  sessions  that  are  created  with snmp_sess_open() are not affected by, and SHOULD NOT BE USED
       WITH, snmp_select_info(), snmp_read(), snmp_timeout() nor snmp_close().  Rather the equivalent single
       session functions described here should be used.

       snmp_sess_init()  and  snmp_sess_open() each take as input a pointer to a struct snmp_session object.
       This structure contains information for a set of transactions that will share similar transport char-acteristics. characteristics.
       acteristics.   snmp_sess_session() takes the opaque session handle and returns a pointer to its asso-ciated associated
       ciated struct snmp_session.

       snmp_sess_send() and snmp_sess_async_send() each take a pdu  parameter,  which  points  to  a  struct
       snmp_pdu  object  containing  information that describes a transaction that will be performed over an
       open session.

       Consult snmp_api.h for the definitions of these structures.

       snmp_sess_select_info(), snmp_sess_read() and snmp_sess_timeout() provide an interface for the use of
       the select(2) system call so that SNMP transactions for a single session can occur asynchronously.

       snmp_sess_select_info()  is  passed  the  information that would have been passed to select(2) in the
       absence of SNMP.  For example, this might include file descriptors associated with the main loop of a
       graphical  application.  This  information  is modified so that SNMP will get the service it requires
       from the call to select(2).  In this case, numfds, fdset and timeout correspond to the nfds,  readfds
       and  timeout  arguments  to  select(2)  respectively.  The only exception is that timeout must ALWAYS
       point to an allocated  (but  perhaps  uninitialized)  struct  timeval  (it  cannot  be  NULL  as  for
       select(2)).   If timeout would have been passed as NULL, block is instead set to true, and timeout is
       treated as undefined.  This same rule applies upon return from snmp_select_info().

       After calling snmp_sess_select_info() , select(2) should be called with the returned data.   When  it
       returns,  snmp_sess_read()  should then be called with the fd_set returned from select(2).  This will
       read any input from this session's SNMP socket.  If select(2) times out (that is, it  returns  zero),
       snmp_sess_timeout() should be called to see if a timeout has occurred on the SNMP session.

DIAGNOSTICS
       Error  return  status  from  snmp_sess_open() is indicated by return of a NULL pointer.  Error return
       status from snmp_sess_close() and snmp_sess_send() is indicated by a return value of 0.  A successful
       status will return 1.

       Further  information  can  be  obtained  by  using  snmp_sess_error()  to  see what type of error has
       occurred.  This function returns the SNMP snmp_errno variable, the value of the  system  errno  vari-able, variable,
       able,  and  a  string  interpretation  of  both variables.  The string must be freed after use by the
       caller.

       For errors returned by snmp_sess_open(), use  the  corresponding  function  snmp_error()  instead  of
       snmp_sess_error().

       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.

         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_RCVFROM

         SNMPERR_BAD_PARSE

         SNMPERR_BAD_VERSION

         SNMPERR_BAD_COMMUNITY

         SNMPERR_NOAUTH_DESPRIV

         SNMPERR_ABORT

         SNMPERR_UNKNOWN_PDU

         SNMPERR_TIMEOUT


SEE ALSO
       select(2), snmp_api(3), snmp_api.h



V5.6                                             13 Aug 2010                             NETSNMP_SESS_API(3)