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_synch_response,
       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_synch_response ( void *handle,
              netsnmp_pdu *pdu,
              netsnmp_pdu **response);

       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 versions 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  characteristics.   snmp_sess_session()  takes  the  opaque
       session handle and returns a pointer to its associated 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.

       With  the  snmp_sess_async_send()  call, snmp_sess_read will invoke the specified callback
       when the response is received.

       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.

       snmp_sess_synch_response is a convenience routine that will send the request, wait for the
       response  and  process  it  before  returning.   See  the descriptions of snmp_sess_send ,
       snmp_sess_read etc for details.

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 variable, 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),     netsnmp_session_api(3),     netsnmp_pdu_api(3),     netsnmp_varbind_api(3),
       netsnmp_mib_api(3), snmp_api.h