gosnmp

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// Copyright 2012 The GoSNMP Authors. All rights reserved.  Use of this
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// source code is governed by a BSD-style license that can be found in the
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// LICENSE file.
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//go:build netsnmp
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package netsnmp
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/*
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#cgo LDFLAGS: -lnetsnmp
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#include <stdint.h>
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#include <stdlib.h>
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#include <net-snmp/net-snmp-config.h>
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#include <net-snmp/output_api.h>
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#include <net-snmp/config_api.h>
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u_char* getPktStart(u_char* pkt, ulong len, ulong off){
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	return pkt+len-off;
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}
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*/
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import "C"
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import (
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	"errors"
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	"fmt"
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	"strconv"
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	"strings"
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	"unsafe"
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	"github.com/gosnmp/gosnmp"
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)
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func isPlayback() bool {
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	return false
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}
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type netSnmpValType int
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/*
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case TYPE_INTEGER:
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	case TYPE_INTEGER32:
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	    type = 'i';
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	    break;
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	case TYPE_GAUGE:
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	case TYPE_UNSIGNED32:
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	    type = 'u';
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	    break;
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	case TYPE_UINTEGER:
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	    type = '3';
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	    break;
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	case TYPE_COUNTER:
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	    type = 'c';
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	    break;
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	case TYPE_COUNTER64:
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	    type = 'C';
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	    break;
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	case TYPE_TIMETICKS:
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	    type = 't';
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	    break;
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	case TYPE_OCTETSTR:
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	    type = 's';
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	    break;
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	case TYPE_BITSTRING:
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	    type = 'b';
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	    break;
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	case TYPE_IPADDR:
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	    type = 'a';
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	    break;
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	case TYPE_OBJID:
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	    type = 'o';
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	    break;
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*/
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func berToSnmpValType(in gosnmp.Asn1BER) (C.char, error) {
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	switch in {
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	case gosnmp.Gauge32:
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		return 'u', nil
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	case gosnmp.Integer:
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		return 'i', nil
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	case gosnmp.OctetString:
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		return 's', nil
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	case gosnmp.IPAddress:
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		return 'a', nil
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	case gosnmp.ObjectIdentifier:
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		return 'o', nil
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	case gosnmp.Counter32:
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		return 'c', nil
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	case gosnmp.Counter64:
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		return 'C', nil
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	case gosnmp.OpaqueFloat:
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		return 'F', nil
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	case gosnmp.OpaqueDouble:
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		return 'D', nil
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	case gosnmp.TimeTicks:
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		return 't', nil
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	case gosnmp.Uinteger32:
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		return '3', nil
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	default:
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		return 0, errors.New("unhandled asn1 ber type" + in.String())
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	}
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}
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func verToSnmpVer(in gosnmp.SnmpVersion) (C.int, error) {
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	switch in {
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	case gosnmp.Version1:
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		return C.SNMP_VERSION_1, nil
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	case gosnmp.Version2c:
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		return C.SNMP_VERSION_2c, nil
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	case gosnmp.Version3:
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		return C.SNMP_VERSION_3, nil
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	default:
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		return 0, errors.New("handled snmp version " + in.String())
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	}
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}
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func netSnmpPduPkt(fname string, gopdu gosnmp.SnmpPDU, gosess *gosnmp.GoSNMP, reqid uint32, verbose bool) ([]byte, error) {
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	var errout *C.char
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	var err error
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	oid := oidStringToInts(gopdu.Name)
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	if verbose {
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		netSnmpEnableLogging()
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	}
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	//enable reverse encode
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	C.netsnmp_ds_set_boolean(C.NETSNMP_DS_LIBRARY_ID,
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		C.NETSNMP_DS_LIB_REVERSE_ENCODE,
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		C.NETSNMP_DEFAULT_ASNENCODING_DIRECTION)
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	//create session
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	sess := &C.struct_snmp_session{
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		version:       C.SNMP_DEFAULT_VERSION,
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		community:     (*C.uchar)((unsafe.Pointer)(C.CString(gosess.Community))),
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		community_len: C.size_t(len(gosess.Community)),
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	}
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	defer C.free(unsafe.Pointer(sess.community))
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	//create pdu
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	pdu := C.snmp_pdu_create(C.SNMP_MSG_SET)
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	defer C.free(unsafe.Pointer(pdu))
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	tmp, err := verToSnmpVer(gosess.Version)
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	if err != nil {
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		return nil, err
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	}
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	pdu.version = C.long(tmp)
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	pdu.reqid = C.long(reqid)
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	tstoid := [1024]C.oid{}
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	tstoidcnt := C.size_t(0)
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	for i := range oid {
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		tstoid[i] = C.oid(oid[i])
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		tstoidcnt++
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	}
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	cval := C.CString(valToString(gopdu))
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	defer C.free(unsafe.Pointer(cval))
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	ctype, err := berToSnmpValType(gopdu.Type)
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	if err != nil {
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		return nil, err
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	}
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	rv := C.snmp_add_var(pdu, (*C.oid)(unsafe.Pointer(&tstoid)), tstoidcnt, ctype, cval)
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	if rv < 0 {
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		C.snmp_perror(errout)
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		err = fmt.Errorf("net-snmp error: snmp_add_var: %s", C.GoString(errout))
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		return nil, err
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	}
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	//render packet
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	sz := 2048
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	pktout := (*C.uchar)(C.malloc(C.size_t(sz)))
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	pktoutlen := C.size_t(sz)
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	var pktoutoffset C.size_t
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	rv = C.snmp_build(&pktout, &pktoutlen, &pktoutoffset, sess, pdu)
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	if rv < C.int(0) {
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		C.snmp_error(sess, nil, nil, &errout)
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		err = fmt.Errorf("net-snmp error: snmp_build: %s", C.GoString(errout))
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		return nil, err
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	}
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	defer C.free(unsafe.Pointer(pktout))
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	return C.GoBytes(unsafe.Pointer(C.getPktStart(pktout, pktoutlen, pktoutoffset)), C.int(pktoutoffset)), nil
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}
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func netSnmpEnableLogging() {
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	C.snmp_enable_stderrlog()
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	C.snmp_set_do_debugging(1)
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	C.snmp_set_dump_packet(1)
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	tmp := C.CString("")
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	C.debug_register_tokens(tmp)
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	C.free(unsafe.Pointer(tmp))
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}
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func oidStringToInts(in string) []int {
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	out := make([]int, 0, len(in))
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	for _, oi := range strings.Split(in, ".") {
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		tmp, err := strconv.Atoi(oi)
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		if err == nil {
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			out = append(out, tmp)
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		}
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	}
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	return out
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}
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func valToString(gopdu gosnmp.SnmpPDU) string {
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	var val any
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	switch gopdu.Type {
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	case gosnmp.OctetString:
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		b, ok := gopdu.Value.([]byte)
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		if ok {
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			val = string(b)
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		} else {
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			val = gopdu.Value
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		}
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	default:
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		val = gopdu.Value
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	}
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	return fmt.Sprintf("%v", val)
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}
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