marshal.go

// Copyright 2012-2018 The GoSNMP Authors. All rights reserved.  Use of this
// source code is governed by a BSD-style license that can be found in the
// LICENSE file.

package gosnmp

import (
	"bytes"
	"encoding/asn1"
	"encoding/binary"
	"fmt"
	"net"
	"sync/atomic"
	"time"
)

//
// Remaining globals and definitions located here.
// See http://www.rane.com/note161.html for a succint description of the SNMP
// protocol.
//

// SnmpVersion 1, 2c and 3 implemented
type SnmpVersion uint8

// SnmpVersion 1, 2c and 3 implemented
const (
	Version1  SnmpVersion = 0x0
	Version2c SnmpVersion = 0x1
	Version3  SnmpVersion = 0x3
)

// SnmpPacket struct represents the entire SNMP Message or Sequence at the
// application layer.
type SnmpPacket struct {
	Version            SnmpVersion
	MsgFlags           SnmpV3MsgFlags
	SecurityModel      SnmpV3SecurityModel
	SecurityParameters SnmpV3SecurityParameters
	ContextEngineID    string
	ContextName        string
	Community          string
	PDUType            PDUType
	MsgID              uint32
	RequestID          uint32
	MsgMaxSize         uint32
	Error              SNMPError
	ErrorIndex         uint8
	NonRepeaters       uint8
	MaxRepetitions     uint8
	Variables          []SnmpPDU
	Logger             Logger

	// v1 traps have a very different format from v2c and v3 traps.
	//
	// These fields are set via the SnmpTrap parameter to SendTrap().
	SnmpTrap
}

// SnmpTrap is used to define a SNMP trap, and is passed into SendTrap
type SnmpTrap struct {
	Variables []SnmpPDU

	// These fields are required for SNMPV1 Trap Headers
	Enterprise   string
	AgentAddress string
	GenericTrap  int
	SpecificTrap int
	Timestamp    uint
}

// VarBind struct represents an SNMP Varbind.
type VarBind struct {
	Name  asn1.ObjectIdentifier
	Value asn1.RawValue
}

// PDUType describes which SNMP Protocol Data Unit is being sent.
type PDUType byte

// The currently supported PDUType's
const (
	Sequence       PDUType = 0x30
	GetRequest     PDUType = 0xa0
	GetNextRequest PDUType = 0xa1
	GetResponse    PDUType = 0xa2
	SetRequest     PDUType = 0xa3
	Trap           PDUType = 0xa4 // v1
	GetBulkRequest PDUType = 0xa5
	InformRequest  PDUType = 0xa6
	SNMPv2Trap     PDUType = 0xa7 // v2c, v3
	Report         PDUType = 0xa8
)

const rxBufSize = 65535 // max size of IPv4 & IPv6 packet

// Logger is an interface used for debugging. Both Print and
// Printf have the same interfaces as Package Log in the std library. The
// Logger interface is small to give you flexibility in how you do
// your debugging.
//
// For verbose logging to stdout:
//
//     gosnmp_logger = log.New(os.Stdout, "", 0)
type Logger interface {
	Print(v ...interface{})
	Printf(format string, v ...interface{})
}

func (x *GoSNMP) logPrint(v ...interface{}) {
	if x.loggingEnabled {
		x.Logger.Print(v...)
	}
}

func (x *GoSNMP) logPrintf(format string, v ...interface{}) {
	if x.loggingEnabled {
		x.Logger.Printf(format, v...)
	}
}

// send/receive one snmp request
func (x *GoSNMP) sendOneRequest(packetOut *SnmpPacket,
	wait bool) (result *SnmpPacket, err error) {
	finalDeadline := time.Now().Add(x.Timeout)

	allReqIDs := make([]uint32, 0, x.Retries+1)
	allMsgIDs := make([]uint32, 0, x.Retries+1)
	for retries := 0; ; retries++ {
		if retries > 0 {
			x.logPrintf("Retry number %d. Last error was: %v", retries, err)
			if time.Now().After(finalDeadline) {
				err = fmt.Errorf("Request timeout (after %d retries)", retries-1)
				break
			}
			if retries > x.Retries {
				// Report last error
				break
			}
		}
		err = nil

		reqDeadline := time.Now().Add(x.Timeout / time.Duration(x.Retries+1))
		x.Conn.SetDeadline(reqDeadline)

		// Request ID is an atomic counter (started at a random value)
		reqID := atomic.AddUint32(&(x.requestID), 1) // TODO: fix overflows
		allReqIDs = append(allReqIDs, reqID)

		packetOut.RequestID = reqID

		if x.Version == Version3 {
			msgID := atomic.AddUint32(&(x.msgID), 1) // TODO: fix overflows
			allMsgIDs = append(allMsgIDs, msgID)

			packetOut.MsgID = msgID

			err = x.initPacket(packetOut)
			if err != nil {
				break
			}

		}
		if x.loggingEnabled && x.Version == Version3 {
			packetOut.SecurityParameters.Log()
		}

		var outBuf []byte
		outBuf, err = packetOut.marshalMsg()
		if err != nil {
			// Don't retry - not going to get any better!
			err = fmt.Errorf("marshal: %v", err)
			break
		}

		x.logPrintf("SENDING PACKET: %#+v", *packetOut)
		_, err = x.Conn.Write(outBuf)
		if err != nil {
			continue
		}

		// all sends wait for the return packet, except for SNMPv2Trap
		if wait == false {
			return &SnmpPacket{}, nil
		}

	waitingResponse:
		for {
			x.logPrint("WAITING RESPONSE...")
			// Receive response and try receiving again on any decoding error.
			// Let the deadline abort us if we don't receive a valid response.

			var resp []byte
			resp, err = x.receive()
			if err != nil {
				// receive error. retrying won't help. abort
				break
			}
			x.logPrint("GET RESPONSE OK : %+v", resp)
			result = new(SnmpPacket)
			result.Logger = x.Logger

			result.MsgFlags = packetOut.MsgFlags
			if packetOut.SecurityParameters != nil {
				result.SecurityParameters = packetOut.SecurityParameters.Copy()
			}

			var cursor int
			cursor, err = x.unmarshalHeader(resp, result)
			if err != nil {
				x.logPrintf("ERROR on unmarshall header: %s", err)
				err = fmt.Errorf("Unable to decode packet: %s", err.Error())
				continue
			}

			if x.Version == Version3 {
				err = x.testAuthentication(resp, result)
				if err != nil {
					x.logPrintf("ERROR on Test Authentication on v3: %s", err)
					break
				}
				resp, cursor, err = x.decryptPacket(resp, cursor, result)
			}

			err = x.unmarshalPayload(resp, cursor, result)
			if err != nil {
				x.logPrintf("ERROR on UnmarshalPayload on v3: %s", err)
				err = fmt.Errorf("Unable to decode packet: %s", err.Error())
				continue
			}
			if result == nil || len(result.Variables) < 1 {
				x.logPrintf("ERROR on UnmarshalPayload on v3: %s", err)
				err = fmt.Errorf("Unable to decode packet: nil")
				continue
			}

			// Detect usmStats report PDUs and go out of this function with all data
			// (usmStatsNotInTimeWindows [1.3.6.1.6.3.15.1.1.2.0] will be handled by the calling
			// function, and retransmitted.  All others need to be handled by user code)
			if result.Version == Version3 && len(result.Variables) == 1 && result.PDUType == Report {
				switch result.Variables[0].Name {
				case ".1.3.6.1.6.3.15.1.1.1.0", ".1.3.6.1.6.3.15.1.1.2.0",
					".1.3.6.1.6.3.15.1.1.3.0", ".1.3.6.1.6.3.15.1.1.4.0",
					".1.3.6.1.6.3.15.1.1.5.0", ".1.3.6.1.6.3.15.1.1.6.0":
					break waitingResponse
				}
			}

			validID := false
			for _, id := range allReqIDs {
				if id == result.RequestID {
					validID = true
				}
			}
			if result.RequestID == 0 {
				validID = true
			}
			if !validID {
				x.logPrint("ERROR  out of order ")
				err = fmt.Errorf("Out of order response")
				continue
			}

			break
		}
		if err != nil {
			continue
		}

		// Success!
		return result, nil
	}

	// Return last error
	return nil, err
}

// generic "sender" that negotiate any version of snmp request
//
// all sends wait for the return packet, except for SNMPv2Trap
func (x *GoSNMP) send(packetOut *SnmpPacket, wait bool) (result *SnmpPacket, err error) {
	defer func() {
		if e := recover(); e != nil {
			err = fmt.Errorf("recover: %v", e)
		}
	}()

	if x.Conn == nil {
		return nil, fmt.Errorf("&GoSNMP.Conn is missing. Provide a connection or use Connect()")
	}

	if x.Retries < 0 {
		x.Retries = 0
	}
	x.logPrint("SEND INIT")
	if packetOut.Version == Version3 {
		x.logPrint("SEND INIT NEGOTIATE SECURITY PARAMS")
		if err = x.negotiateInitialSecurityParameters(packetOut, wait); err != nil {
			return &SnmpPacket{}, err
		}
		x.logPrint("SEND END NEGOTIATE SECURITY PARAMS")
	}

	// perform request
	result, err = x.sendOneRequest(packetOut, wait)
	if err != nil {
		x.logPrintf("SEND Error on the first Request Error: %s", err)
		return result, err
	}

	if result.Version == Version3 {
		x.logPrintf("SEND STORE SECURITY PARAMS from result: %+v", result)
		err = x.storeSecurityParameters(result)

		// detect out-of-time-window error and retransmit with updated auth engine parameters
		if len(result.Variables) == 1 && result.Variables[0].Name == ".1.3.6.1.6.3.15.1.1.2.0" {
			x.logPrintf("WARNING detected out-of-time-window ERROR")
			err = x.updatePktSecurityParameters(packetOut)
			if err != nil {
				x.logPrintf("ERROR  updatePktSecurityParameters error: %s", err)
				return nil, err
			}
			result, err = x.sendOneRequest(packetOut, wait)
		}
	}

	// detect unknown engine id error and retransmit with updated engine id
	if len(result.Variables) == 1 && result.Variables[0].Name == ".1.3.6.1.6.3.15.1.1.4.0" {
		x.logPrintf("WARNING detected unknown enginer id ERROR")
		err = x.updatePktSecurityParameters(packetOut)
		if err != nil {
			x.logPrintf("ERROR  updatePktSecurityParameters error: %s", err)
			return nil, err
		}
		result, err = x.sendOneRequest(packetOut, wait)
	}
	return result, err
}

// -- Marshalling Logic --------------------------------------------------------
func (packet *SnmpPacket) MarshalMsg() ([]byte, error) {
	return packet.marshalMsg()
}

// marshal an SNMP message
func (packet *SnmpPacket) marshalMsg() ([]byte, error) {
	var err error
	buf := new(bytes.Buffer)

	// version
	buf.Write([]byte{2, 1, byte(packet.Version)})

	if packet.Version == Version3 {
		buf, err = packet.marshalV3(buf)
		if err != nil {
			return nil, err
		}
	} else {
		// community
		buf.Write([]byte{4, uint8(len(packet.Community))})
		buf.WriteString(packet.Community)
		// pdu
		pdu, err := packet.marshalPDU()
		if err != nil {
			return nil, err
		}
		buf.Write(pdu)
	}

	// build up resulting msg - sequence, length then the tail (buf)
	msg := new(bytes.Buffer)
	msg.WriteByte(byte(Sequence))

	bufLengthBytes, err2 := marshalLength(buf.Len())
	if err2 != nil {
		return nil, err2
	}
	msg.Write(bufLengthBytes)
	buf.WriteTo(msg) // reverse logic - want to do msg.Write(buf)

	authenticatedMessage, err := packet.authenticate(msg.Bytes())
	if err != nil {
		return nil, err
	}

	return authenticatedMessage, nil
}

func (packet *SnmpPacket) marshalSNMPV1TrapHeader() ([]byte, error) {
	buf := new(bytes.Buffer)

	mOid, err := marshalOID(packet.Enterprise)
	if err != nil {
		return nil, fmt.Errorf("Unable to marshal OID: %s\n", err.Error())
	}

	buf.Write([]byte{ObjectIdentifier, byte(len(mOid))})
	buf.Write(mOid)

	// write IPAddress type, length and ipAddress value
	ip := net.ParseIP(packet.AgentAddress)
	ipAddressBytes := ipv4toBytes(ip)
	buf.Write([]byte{IPAddress, byte(len(ipAddressBytes))})
	buf.Write(ipAddressBytes)

	buf.Write([]byte{Integer, 1})
	buf.WriteByte(byte(packet.GenericTrap))

	buf.Write([]byte{Integer, 1})
	buf.WriteByte(byte(packet.SpecificTrap))

	timeTicks, e := marshalUint32(uint32(packet.Timestamp))
	if e != nil {
		return nil, fmt.Errorf("Unable to Timestamp: %s\n", e.Error())
	}

	buf.Write([]byte{TimeTicks, byte(len(timeTicks))})
	buf.Write(timeTicks)

	return buf.Bytes(), nil
}

// marshal a PDU
func (packet *SnmpPacket) marshalPDU() ([]byte, error) {
	buf := new(bytes.Buffer)

	switch packet.PDUType {

	case GetBulkRequest:
		// requestid
		buf.Write([]byte{2, 4})
		err := binary.Write(buf, binary.BigEndian, packet.RequestID)
		if err != nil {
			return nil, err
		}

		// non repeaters
		buf.Write([]byte{2, 1, packet.NonRepeaters})

		// max repetitions
		buf.Write([]byte{2, 1, packet.MaxRepetitions})

	case Trap:
		// write SNMP V1 Trap Header fields
		snmpV1TrapHeader, err := packet.marshalSNMPV1TrapHeader()
		if err != nil {
			return nil, err
		}

		buf.Write(snmpV1TrapHeader)
	default:
		// requestid
		buf.Write([]byte{2, 4})
		err := binary.Write(buf, binary.BigEndian, packet.RequestID)

		if err != nil {
			return nil, fmt.Errorf("Unable to marshal OID: %s\n", err.Error())
		}

		// error
		buf.Write([]byte{2, 1, 0})

		// error index
		buf.Write([]byte{2, 1, 0})

	}

	// varbind list
	vbl, err := packet.marshalVBL()
	if err != nil {
		return nil, err
	}
	buf.Write(vbl)

	// build up resulting pdu - request type, length, then the tail (buf)
	pdu := new(bytes.Buffer)
	pdu.WriteByte(byte(packet.PDUType))

	bufLengthBytes, err2 := marshalLength(buf.Len())
	if err2 != nil {
		return nil, err2
	}
	pdu.Write(bufLengthBytes)

	buf.WriteTo(pdu) // reverse logic - want to do pdu.Write(buf)
	return pdu.Bytes(), nil
}

// marshal a varbind list
func (packet *SnmpPacket) marshalVBL() ([]byte, error) {

	vblBuf := new(bytes.Buffer)
	for _, pdu := range packet.Variables {
		vb, err := marshalVarbind(&pdu)
		if err != nil {
			return nil, err
		}
		vblBuf.Write(vb)
	}

	vblBytes := vblBuf.Bytes()
	vblLengthBytes, err := marshalLength(len(vblBytes))
	if err != nil {
		return nil, err
	}

	// FIX does bytes.Buffer give better performance than byte slices?
	result := []byte{byte(Sequence)}
	result = append(result, vblLengthBytes...)
	result = append(result, vblBytes...)
	return result, nil
}

// marshal a varbind
func marshalVarbind(pdu *SnmpPDU) ([]byte, error) {
	oid, err := marshalOID(pdu.Name)
	if err != nil {
		return nil, err
	}
	pduBuf := new(bytes.Buffer)
	tmpBuf := new(bytes.Buffer)

	// Marshal the PDU type into the appropriate BER
	switch pdu.Type {

	case Null:
		ltmp, err := marshalLength(len(oid))
		if err != nil {
			return nil, err
		}
		tmpBuf.Write([]byte{byte(ObjectIdentifier)})
		tmpBuf.Write(ltmp)
		tmpBuf.Write(oid)
		tmpBuf.Write([]byte{Null, 0x00})

		ltmp, err = marshalLength(tmpBuf.Len())
		if err != nil {
			return nil, err
		}
		pduBuf.Write([]byte{byte(Sequence)})
		pduBuf.Write(ltmp)
		tmpBuf.WriteTo(pduBuf)

	/*
		snmp Integer32 and INTEGER:
		-2^31 and 2^31-1 inclusive (-2147483648 to 2147483647 decimal)
		(FYI https://groups.google.com/forum/#!topic/comp.protocols.snmp/1xaAMzCe_hE)

		snmp Counter32, Gauge32, TimeTicks, Unsigned32:
		non-negative integer, maximum value of 2^32-1 (4294967295 decimal)
	*/

	case Integer:
		// TODO tests currently only cover positive integers

		// Oid
		tmpBuf.Write([]byte{byte(ObjectIdentifier), byte(len(oid))})
		tmpBuf.Write(oid)

		// Number
		var intBytes []byte
		switch value := pdu.Value.(type) {
		case byte:
			intBytes = []byte{byte(pdu.Value.(int))}
		case int:
			intBytes, err = marshalInt16(value)
			pdu.Check(err)
		default:
			return nil, fmt.Errorf("Unable to marshal PDU Integer; not byte or int.")
		}
		tmpBuf.Write([]byte{byte(Integer), byte(len(intBytes))})
		tmpBuf.Write(intBytes)

		// Sequence, length of oid + integer, then oid/integer data
		pduBuf.WriteByte(byte(Sequence))
		pduBuf.WriteByte(byte(len(oid) + len(intBytes) + 4))
		pduBuf.Write(tmpBuf.Bytes())

	case Counter32, Gauge32, TimeTicks, Uinteger32:
		// Oid
		tmpBuf.Write([]byte{byte(ObjectIdentifier), byte(len(oid))})
		tmpBuf.Write(oid)

		// Number
		var intBytes []byte
		switch value := pdu.Value.(type) {
		case uint32:
			intBytes, err = marshalUint32(value)
			pdu.Check(err)
		default:
			return nil, fmt.Errorf("Unable to marshal pdu.Type %v; unknown pdu.Value %v", pdu.Type, pdu.Value)
		}
		tmpBuf.Write([]byte{byte(pdu.Type), byte(len(intBytes))})
		tmpBuf.Write(intBytes)

		// Sequence, length of oid + integer, then oid/integer data
		pduBuf.WriteByte(byte(Sequence))
		pduBuf.WriteByte(byte(len(oid) + len(intBytes) + 4))
		pduBuf.Write(tmpBuf.Bytes())

	case OctetString:

		//Oid
		tmpBuf.Write([]byte{byte(ObjectIdentifier), byte(len(oid))})
		tmpBuf.Write(oid)

		//OctetString
		var octetStringBytes []byte
		switch value := pdu.Value.(type) {
		case []byte:
			octetStringBytes = value
		case string:
			octetStringBytes = []byte(value)
		default:
			return nil, fmt.Errorf("Unable to marshal PDU OctetString; not []byte or String.")
		}

		var length []byte
		length, err = marshalLength(len(octetStringBytes))
		if err != nil {
			return nil, err
		}
		tmpBuf.WriteByte(byte(OctetString))
		tmpBuf.Write(length)
		tmpBuf.Write(octetStringBytes)

		tmpBytes := tmpBuf.Bytes()

		length, err = marshalLength(len(tmpBytes))
		if err != nil {
			return nil, err
		}
		// Sequence, length of oid + octetstring, then oid/octetstring data
		pduBuf.WriteByte(byte(Sequence))

		pduBuf.Write(length)
		pduBuf.Write(tmpBytes)

	case ObjectIdentifier:

		//Oid
		tmpBuf.Write([]byte{byte(ObjectIdentifier), byte(len(oid))})
		tmpBuf.Write(oid)
		value := pdu.Value.(string)
		oidBytes, err := marshalOID(value)
		pdu.Check(err)

		//Oid data
		var length []byte
		length, err = marshalLength(len(oidBytes))
		if err != nil {
			return nil, err
		}
		tmpBuf.WriteByte(byte(pdu.Type))
		tmpBuf.Write(length)
		tmpBuf.Write(oidBytes)

		tmpBytes := tmpBuf.Bytes()
		length, err = marshalLength(len(tmpBytes))
		if err != nil {
			return nil, err
		}
		// Sequence, length of oid + oid, then oid/oid data
		pduBuf.WriteByte(byte(Sequence))
		pduBuf.Write(length)
		pduBuf.Write(tmpBytes)

	// TODO no tests
	case IPAddress:
		//Oid
		tmpBuf.Write([]byte{byte(ObjectIdentifier), byte(len(oid))})
		tmpBuf.Write(oid)
		//OctetString
		var ipAddressBytes []byte
		switch value := pdu.Value.(type) {
		case []byte:
			ipAddressBytes = value
		case string:
			ip := net.ParseIP(value)
			ipAddressBytes = ipv4toBytes(ip)
		default:
			return nil, fmt.Errorf("Unable to marshal PDU IPAddress; not []byte or String.")
		}
		tmpBuf.Write([]byte{byte(IPAddress), byte(len(ipAddressBytes))})
		tmpBuf.Write(ipAddressBytes)
		// Sequence, length of oid + octetstring, then oid/octetstring data
		pduBuf.WriteByte(byte(Sequence))
		pduBuf.WriteByte(byte(len(oid) + len(ipAddressBytes) + 4))
		pduBuf.Write(tmpBuf.Bytes())

	default:
		return nil, fmt.Errorf("Unable to marshal PDU: unknown BER type %q", pdu.Type)
	}

	return pduBuf.Bytes(), nil
}

// -- Unmarshalling Logic ------------------------------------------------------

func (x *GoSNMP) unmarshalHeader(packet []byte, response *SnmpPacket) (int, error) {
	if len(packet) < 2 {
		return 0, fmt.Errorf("Cannot unmarshal empty packet")
	}
	if response == nil {
		return 0, fmt.Errorf("Cannot unmarshal response into nil packet reference")
	}

	response.Variables = make([]SnmpPDU, 0, 5)

	// Start parsing the packet
	cursor := 0

	// First bytes should be 0x30
	if PDUType(packet[0]) != Sequence {
		return 0, fmt.Errorf("Invalid packet header\n")
	}

	length, cursor := parseLength(packet)
	if len(packet) != length {
		return 0, fmt.Errorf("Error verifying packet sanity: Got %d Expected: %d\n", len(packet), length)
	}
	x.logPrintf("Packet sanity verified, we got all the bytes (%d)", length)

	// Parse SNMP Version
	rawVersion, count, err := parseRawField(packet[cursor:], "version")
	if err != nil {
		return 0, fmt.Errorf("Error parsing SNMP packet version: %s", err.Error())
	}

	cursor += count
	if version, ok := rawVersion.(int); ok {
		response.Version = SnmpVersion(version)
		x.logPrintf("Parsed version %d", version)
	}

	if response.Version == Version3 {
		cursor, err = x.unmarshalV3Header(packet, cursor, response)
		if err != nil {
			return 0, err
		}
	} else {
		// Parse community
		rawCommunity, count, err := parseRawField(packet[cursor:], "community")
		if err != nil {
			return 0, fmt.Errorf("Error parsing community string: %s", err.Error())
		}
		cursor += count
		if community, ok := rawCommunity.(string); ok {
			response.Community = community
			x.logPrintf("Parsed community %s", community)
		}
	}
	return cursor, nil
}

func (x *GoSNMP) unmarshalPayload(packet []byte, cursor int, response *SnmpPacket) error {
	var err error
	// Parse SNMP packet type
	requestType := PDUType(packet[cursor])
	switch requestType {
	// known, supported types
	case GetResponse, GetNextRequest, GetBulkRequest, Report, SNMPv2Trap:
		response.PDUType = requestType
		err = x.unmarshalResponse(packet[cursor:], response)
		if err != nil {
			return fmt.Errorf("Error in unmarshalResponse: %s", err.Error())
		}
	case Trap:
		response.PDUType = requestType
		err = x.unmarshalTrapV1(packet[cursor:], response)
		if err != nil {
			return fmt.Errorf("Error in unmarshalTrapV1: %s", err.Error())
		}
	default:
		return fmt.Errorf("Unknown PDUType %#x", requestType)
	}
	return nil
}

func (x *GoSNMP) unmarshalResponse(packet []byte, response *SnmpPacket) error {
	cursor := 0

	getResponseLength, cursor := parseLength(packet)
	if len(packet) != getResponseLength {
		return fmt.Errorf("Error verifying Response sanity: Got %d Expected: %d\n", len(packet), getResponseLength)
	}
	x.logPrintf("getResponseLength: %d", getResponseLength)

	// Parse Request-ID
	rawRequestID, count, err := parseRawField(packet[cursor:], "request id")
	if err != nil {
		return fmt.Errorf("Error parsing SNMP packet request ID: %s", err.Error())
	}
	cursor += count
	if requestid, ok := rawRequestID.(int); ok {
		response.RequestID = uint32(requestid)
		x.logPrintf("requestID: %d", response.RequestID)
	}

	if response.PDUType == GetBulkRequest {
		// Parse Non Repeaters
		rawNonRepeaters, count, err := parseRawField(packet[cursor:], "non repeaters")
		if err != nil {
			return fmt.Errorf("Error parsing SNMP packet non repeaters: %s", err.Error())
		}
		cursor += count
		if nonRepeaters, ok := rawNonRepeaters.(int); ok {
			response.NonRepeaters = uint8(nonRepeaters)
		}

		// Parse Max Repetitions
		rawMaxRepetitions, count, err := parseRawField(packet[cursor:], "max repetitions")
		if err != nil {
			return fmt.Errorf("Error parsing SNMP packet max repetitions: %s", err.Error())
		}
		cursor += count
		if maxRepetitions, ok := rawMaxRepetitions.(int); ok {
			response.MaxRepetitions = uint8(maxRepetitions)
		}
	} else {
		// Parse Error-Status
		rawError, count, err := parseRawField(packet[cursor:], "error-status")
		if err != nil {
			return fmt.Errorf("Error parsing SNMP packet error: %s", err.Error())
		}
		cursor += count
		if errorStatus, ok := rawError.(int); ok {
			response.Error = SNMPError(errorStatus)
			x.logPrintf("errorStatus: %d", uint8(errorStatus))
		}

		// Parse Error-Index
		rawErrorIndex, count, err := parseRawField(packet[cursor:], "error index")
		if err != nil {
			return fmt.Errorf("Error parsing SNMP packet error index: %s", err.Error())
		}
		cursor += count
		if errorindex, ok := rawErrorIndex.(int); ok {
			response.ErrorIndex = uint8(errorindex)
			x.logPrintf("error-index: %d", uint8(errorindex))
		}
	}

	return x.unmarshalVBL(packet[cursor:], response)
}

func (x *GoSNMP) unmarshalTrapV1(packet []byte, response *SnmpPacket) error {
	cursor := 0

	getResponseLength, cursor := parseLength(packet)
	if len(packet) != getResponseLength {
		return fmt.Errorf("Error verifying Response sanity: Got %d Expected: %d\n", len(packet), getResponseLength)
	}
	x.logPrintf("getResponseLength: %d", getResponseLength)

	// Parse Enterprise
	rawEnterprise, count, err := parseRawField(packet[cursor:], "enterprise")
	if err != nil {
		return fmt.Errorf("Error parsing SNMP packet error: %s", err.Error())
	}
	cursor += count
	if Enterprise, ok := rawEnterprise.([]int); ok {
		response.Enterprise = oidToString(Enterprise)
		x.logPrintf("Enterprise: %+v", Enterprise)
	}

	// Parse AgentAddress
	rawAgentAddress, count, err := parseRawField(packet[cursor:], "agent-address")
	if err != nil {
		return fmt.Errorf("Error parsing SNMP packet error: %s", err.Error())
	}
	cursor += count
	if AgentAddress, ok := rawAgentAddress.(string); ok {
		response.AgentAddress = AgentAddress
		x.logPrintf("AgentAddress: %s", AgentAddress)
	}

	// Parse GenericTrap
	rawGenericTrap, count, err := parseRawField(packet[cursor:], "generic-trap")
	if err != nil {
		return fmt.Errorf("Error parsing SNMP packet error: %s", err.Error())
	}
	cursor += count
	if GenericTrap, ok := rawGenericTrap.(int); ok {
		response.GenericTrap = GenericTrap
		x.logPrintf("GenericTrap: %d", GenericTrap)
	}

	// Parse SpecificTrap
	rawSpecificTrap, count, err := parseRawField(packet[cursor:], "specific-trap")
	if err != nil {
		return fmt.Errorf("Error parsing SNMP packet error: %s", err.Error())
	}
	cursor += count
	if SpecificTrap, ok := rawSpecificTrap.(int); ok {
		response.SpecificTrap = SpecificTrap
		x.logPrintf("SpecificTrap: %d", SpecificTrap)
	}

	// Parse TimeStamp
	rawTimestamp, count, err := parseRawField(packet[cursor:], "time-stamp")
	if err != nil {
		return fmt.Errorf("Error parsing SNMP packet error: %s", err.Error())
	}
	cursor += count
	if Timestamp, ok := rawTimestamp.(uint); ok {
		response.Timestamp = Timestamp
		x.logPrintf("Timestamp: %d", Timestamp)
	}

	return x.unmarshalVBL(packet[cursor:], response)
}

// unmarshal a Varbind list
func (x *GoSNMP) unmarshalVBL(packet []byte, response *SnmpPacket) error {

	var cursor, cursorInc int
	var vblLength int
	if packet[cursor] != 0x30 {
		return fmt.Errorf("Expected a sequence when unmarshalling a VBL, got %x", packet[cursor])
	}

	vblLength, cursor = parseLength(packet)
	if len(packet) != vblLength {
		return fmt.Errorf("Error verifying: packet length %d vbl length %d\n", len(packet), vblLength)
	}
	x.logPrintf("vblLength: %d", vblLength)

	// check for an empty response
	if vblLength == 2 && packet[1] == 0x00 {
		return nil
	}

	// Loop & parse Varbinds
	for cursor < vblLength {
		if packet[cursor] != 0x30 {
			return fmt.Errorf("Expected a sequence when unmarshalling a VB, got %x", packet[cursor])
		}

		_, cursorInc = parseLength(packet[cursor:])
		cursor += cursorInc

		// Parse OID
		rawOid, oidLength, err := parseRawField(packet[cursor:], "OID")
		if err != nil {
			return fmt.Errorf("Error parsing OID Value: %s", err.Error())
		}
		cursor += oidLength

		var oid []int
		var ok bool
		if oid, ok = rawOid.([]int); !ok {
			return fmt.Errorf("unable to type assert rawOid |%v| to []int", rawOid)
		}
		oidStr := oidToString(oid)
		x.logPrintf("OID: %s", oidStr)

		// Parse Value
		v, err := x.decodeValue(packet[cursor:], "value")
		if err != nil {
			return fmt.Errorf("Error decoding value: %v", err)
		}
		valueLength, _ := parseLength(packet[cursor:])
		cursor += valueLength
		response.Variables = append(response.Variables, SnmpPDU{oidStr, v.Type, v.Value, x.Logger})
	}
	return nil
}

// receive response from network and read into a byte array
func (x *GoSNMP) receive() ([]byte, error) {
	n, err := x.Conn.Read(x.rxBuf[:])
	if err != nil {
		return nil, fmt.Errorf("Error reading from UDP: %s", err.Error())
	}

	if n == rxBufSize {
		// This should never happen unless we're using something like a unix domain socket.
		return nil, fmt.Errorf("response buffer too small")
	}

	resp := make([]byte, n)
	copy(resp, x.rxBuf[:n])
	return resp, nil
}