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.TH NETSNMP_SESSION_API 3 "19 May 2011" VVERSIONINFO "Net-SNMP"
.SH NAME
snmp_sess_init,
snmp_open,
snmp_send,
snmp_select_info,
snmp_read,
snmp_timeout,
snmp_close,
snmp_perror,
snmp_sess_perror,
snmp_error,
snmp_api_errstring \- netsnmp_session_api functions
.SH SYNOPSIS
.B #include <net-snmp/session_api.h>
.PP
.BI "void snmp_sess_init ( netsnmp_session*" "sess" );
.PP
.BI "netsnmp_session* snmp_open ( netsnmp_session *" "sess");
.RS
.I /* Input parameter not used in active sessions */
.RE
.PP
.BI "int snmp_send ( netsnmp_session *" "session,"
.RS
.BI "netsnmp_pdu *" "pdu" );
.RE
.PP
.BI "int snmp_select_info ( int * " numfds, "fd_set *" fdset,
.RS
.BI "struct timeval *" timeout, "int *" block );
.RE
.PP
.BI "void snmp_read ( fd_set *" fdset );
.PP
.B  void snmp_timeout ( void );
.PP
.BI "int snmp_close ( netsnmp_session *" session );
.br
.B  "int snmp_close_sessions ( void );
.PP
.SS Error Reporting
.I (Move to output_api(3))
.br
.BI "void snmp_error ( netsnmp_session *session,
.RS
.BI "int *" pcliberr, "int *" psnmperr, "char **" pperrstring );
.RE
.PP
.BI "char *snmp_api_errstring ( int" snmperr );
.PP
.BI "void snmp_perror ( char *" msg );
.RS
.I /* for parsing errors only */
.RE
.PP
.BI "void snmp_sess_perror (char *" msg, "netsnmp_session *" sess );
.RS
.I /* all other SNMP library errors */
.RE
.PP
.SH DESCRIPTION
.I Snmp_sess_init
prepares a netsnmp_session that sources transport characteristics
and common information that will be used for a set of SNMP transactions.
After this structure is passed to
.I snmp_open
to create an SNMP session, the structure is not used.
.PP
.I Snmp_open
returns a pointer to a newly-formed
.I netsnmp_session
object, which the application must use to reference the
active SNMP session.
.PP
.I Snmp_send
takes as input a pointer to a
.I netsnmp_pdu
object.
This structure contains information that describes a transaction
that will be performed over an open session.
.PP
Consult snmp_api.h for the definitions of these structures.
.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
should be called with the
.I fd_set
returned from
.I select
to read each SNMP socket that has input.
If
.I select
times out,
.I snmp_timeout
should be called to see if the timeout was intended for SNMP.
.SH DIAGNOSTICS
.PP
Previous versions of the library used
.IR snmp_get_errno
to read the global variable
.I snmp_errno
which may have held the error status within the SNMP library.
The existing method
.I snmp_perror
should be used to log ASN.1 coding errors only.
.PP
The new method
.I snmp_sess_perror
is provided to capture errors that occur during the processing
of a particular SNMP session.
.I Snmp_sess_perror
calls
.IR snmp_error
function to obtain the "C" library error
.I errno
, the SNMP library error
.I snmperr
, and the SNMP library detailed error message
that is associated with an error that occurred during a given session.
.PP
Note that in all cases except one,
.IR snmp_sess_perror
should be handed the
.I netsnmp_session *
pointer returned from
.IR snmp_open.
If
.IR snmp_open
returns a null pointer, pass the INPUT
.I netsnmp_session *
pointer used to call
.IR snmp_open.
.PP
Error return status from 
.I snmp_close
and
.I snmp_send
is indicated by return of 0.  A successful status will return a 1 for
.I snmp_close
and the request id of the packet for
.I snmp_send.
Upon successful return from
.I snmp_send
the pdu will be freed by the library.
.PP
Consult snmp_api.h for the complete set of SNMP library
error values.
The SNMP library error value
.IR snmperr
can be one of the following values:
.RS 2n
.IP SNMPERR_GENERR \w'SNMPERR_BAD_REPETITIONS'u+2n
A generic error occurred.
.IP SNMPERR_BAD_LOCPORT \w'SNMPERR_BAD_REPETITIONS'u+2n
The local port was bad because it had already been
allocated or permission was denied.
.IP SNMPERR_BAD_ADDRESS \w'SNMPERR_BAD_REPETITIONS'u+2n
The host name or address given was not useable.
.IP SNMPERR_BAD_SESSION \w'SNMPERR_BAD_REPETITIONS'u+2n
The specified session was not open.
.IP SNMPERR_TOO_LONG \w'SNMPERR_BAD_REPETITIONS'u+2n
.IP SNMPERR_NO_SOCKET \w'SNMPERR_BAD_REPETITIONS'u+2n
.IP SNMPERR_V2_IN_V1 \w'SNMPERR_BAD_REPETITIONS'u+2n
.IP SNMPERR_V1_IN_V2 \w'SNMPERR_BAD_REPETITIONS'u+2n
.IP SNMPERR_BAD_REPEATERS \w'SNMPERR_BAD_REPETITIONS'u+2n
.IP SNMPERR_BAD_REPETITIONS \w'SNMPERR_BAD_REPETITIONS'u+2n
.IP SNMPERR_BAD_ASN1_BUILD \w'SNMPERR_BAD_REPETITIONS'u+2n
.IP SNMPERR_BAD_SENDTO \w'SNMPERR_BAD_REPETITIONS'u+2n
.IP SNMPERR_BAD_PARSE \w'SNMPERR_BAD_REPETITIONS'u+2n
.IP SNMPERR_BAD_VERSION \w'SNMPERR_BAD_REPETITIONS'u+2n
.IP SNMPERR_NOAUTH_DESPRIV \w'SNMPERR_BAD_REPETITIONS'u+2n
.IP SNMPERR_ABORT \w'SNMPERR_BAD_REPETITIONS'u+2n
.IP SNMPERR_UNKNOWN_PDU \w'SNMPERR_BAD_REPETITIONS'u+2n
.IP SNMPERR_TIMEOUT \w'SNMPERR_BAD_REPETITIONS'u+2n
.RE
.PP
A string representation of the error code can be obtained with
.IR snmp_api_errstring ,
and a standard error message may be printed using
.I snmp_perror
that functions like the
.I perror
standard routine.
.SH "SEE ALSO"
select(2), netsnmp_sess_api(3), netsnmp_mib_api(3), netsnmp_pdu_api(3),
netsnmp_varbind_api(3), snmp_api.h