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marshal.go
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marshal.go
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// Copyright 2012 Andreas Louca, 2013 Sonia Hamilton. 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"
"io/ioutil"
"log"
"time"
)
//
// Remaining globals and definitions located here.
//
type SnmpVersion uint8
const (
Version1 SnmpVersion = 0x0
Version2c SnmpVersion = 0x1
)
type SnmpPacket struct {
Version SnmpVersion
Community string
PDUType PDUType
RequestID uint32
Error uint8
ErrorIndex uint8
NonRepeaters uint8
MaxRepetitions uint8
Variables []SnmpPDU
}
type Variable struct {
Name []int
Type Asn1BER
Value interface{}
}
type VarBind struct {
Name asn1.ObjectIdentifier
Value asn1.RawValue
}
type PDUType byte
const (
Sequence PDUType = 0x30
GetRequest PDUType = 0xa0
GetNextRequest = 0xa1
GetResponse = 0xa2
SetRequest = 0xa3
Trap = 0xa4
GetBulkRequest = 0xa5
)
// 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{})
}
// slog is a global variable that is used for debug logging
var slog Logger
// generic "sender"
func (x *GoSNMP) send(pdus []SnmpPDU, packet_out *SnmpPacket) (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()")
}
x.Conn.SetDeadline(time.Now().Add(x.Timeout))
if x.Logger == nil {
x.Logger = log.New(ioutil.Discard, "", 0)
}
slog = x.Logger // global variable for debug logging
// RequestID is only used during tests, therefore use an arbitrary uint32 ie 1
fBuf, err := packet_out.marshalMsg(pdus, packet_out.PDUType, 1)
if err != nil {
return nil, fmt.Errorf("marshal: %v", err)
}
_, err = x.Conn.Write(fBuf)
if err != nil {
return nil, fmt.Errorf("Error writing to socket: %s", err.Error())
}
// Read and unmarshal the response
resp := make([]byte, 4096, 4096)
n, err := x.Conn.Read(resp)
if err != nil {
return nil, fmt.Errorf("Error reading from UDP: %s", err.Error())
}
packet_in, err := unmarshal(resp[:n])
if err != nil {
return nil, fmt.Errorf("Unable to decode packet: %s", err.Error())
}
if packet_in == nil {
return nil, fmt.Errorf("Unable to decode packet: nil")
}
if len(packet_in.Variables) < 1 {
return nil, fmt.Errorf("No response received.")
}
return packet_in, nil
}
// -- Marshalling Logic --------------------------------------------------------
// marshal an SNMP message
func (packet *SnmpPacket) marshalMsg(pdus []SnmpPDU,
pdutype PDUType, requestid uint32) ([]byte, error) {
buf := new(bytes.Buffer)
// version
buf.Write([]byte{2, 1, byte(packet.Version)})
// community
buf.Write([]byte{4, uint8(len(packet.Community))})
buf.WriteString(packet.Community)
// pdu
pdu, err := packet.marshalPDU(pdus, requestid)
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))
buf_length_bytes, err2 := marshalLength(buf.Len())
if err2 != nil {
return nil, err2
}
msg.Write(buf_length_bytes)
buf.WriteTo(msg) // reverse logic - want to do msg.Write(buf)
return msg.Bytes(), nil
}
// marshal a PDU
func (packet *SnmpPacket) marshalPDU(pdus []SnmpPDU, requestid uint32) ([]byte, error) {
buf := new(bytes.Buffer)
// requestid
buf.Write([]byte{2, 4})
err := binary.Write(buf, binary.BigEndian, requestid)
if err != nil {
return nil, err
}
if packet.PDUType == GetBulkRequest {
// non repeaters
buf.Write([]byte{2, 1, packet.NonRepeaters})
// max repetitions
buf.Write([]byte{2, 1, packet.MaxRepetitions})
} else { // get and getnext have same packet format
// error
buf.Write([]byte{2, 1, 0})
// error index
buf.Write([]byte{2, 1, 0})
}
// varbind list
vbl, err := packet.marshalVBL(pdus)
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))
buf_length_bytes, err2 := marshalLength(buf.Len())
if err2 != nil {
return nil, err2
}
pdu.Write(buf_length_bytes)
buf.WriteTo(pdu) // reverse logic - want to do pdu.Write(buf)
return pdu.Bytes(), nil
}
// marshal a varbind list
func (packet *SnmpPacket) marshalVBL(pdus []SnmpPDU) ([]byte, error) {
vbl_buf := new(bytes.Buffer)
for _, pdu := range pdus {
vb, err := marshalVarbind(&pdu)
if err != nil {
return nil, err
}
vbl_buf.Write(vb)
}
vbl_bytes := vbl_buf.Bytes()
vbl_length_bytes, err := marshalLength(len(vbl_bytes))
if err != nil {
return nil, err
}
// FIX does bytes.Buffer give better performance than byte slices?
result := []byte{byte(Sequence)}
result = append(result, vbl_length_bytes...)
result = append(result, vbl_bytes...)
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:
pduBuf.Write([]byte{byte(Sequence), byte(len(oid) + 4)})
pduBuf.Write([]byte{byte(ObjectIdentifier), byte(len(oid))})
pduBuf.Write(oid)
pduBuf.Write([]byte{Null, 0x00})
case Integer:
// Oid
tmpBuf.Write([]byte{byte(ObjectIdentifier), byte(len(oid))})
tmpBuf.Write(oid)
// Integer
int_bytes := []byte{byte(pdu.Value.(int))}
tmpBuf.Write([]byte{byte(Integer), byte(len(int_bytes))})
tmpBuf.Write(int_bytes)
// Sequence, length of oid + integer, then oid/integer data
pduBuf.WriteByte(byte(Sequence))
pduBuf.WriteByte(byte(len(oid) + len(int_bytes) + 4))
pduBuf.Write(tmpBuf.Bytes())
default:
return nil, fmt.Errorf("Unable to marshal PDU: unknown BER type %d", pdu.Type)
}
return pduBuf.Bytes(), nil
}
// -- Unmarshalling Logic ------------------------------------------------------
func unmarshal(packet []byte) (*SnmpPacket, error) {
response := new(SnmpPacket)
response.Variables = make([]SnmpPDU, 0, 5)
// Start parsing the packet
cursor := 0
// First bytes should be 0x30
if PDUType(packet[0]) != Sequence {
return nil, fmt.Errorf("Invalid packet header\n")
}
length, cursor := parseLength(packet)
if len(packet) != length {
return nil, fmt.Errorf("Error verifying packet sanity: Got %d Expected: %d\n", len(packet), length)
}
slog.Printf("Packet sanity verified, we got all the bytes (%d)", length)
// Parse SNMP Version
rawVersion, count, err := parseRawField(packet[cursor:], "version")
if err != nil {
return nil, fmt.Errorf("Error parsing SNMP packet version: %s", err.Error())
}
cursor += count
if version, ok := rawVersion.(int); ok {
response.Version = SnmpVersion(version)
slog.Printf("Parsed version %d", version)
}
// Parse community
rawCommunity, count, err := parseRawField(packet[cursor:], "community")
cursor += count
if community, ok := rawCommunity.(string); ok {
response.Community = community
slog.Printf("Parsed community %s", community)
}
// Parse SNMP packet type
request_type := PDUType(packet[cursor])
switch request_type {
// known, supported types
case GetResponse, GetNextRequest, GetBulkRequest:
response, err = unmarshalResponse(packet[cursor:], response, length, request_type)
if err != nil {
return nil, fmt.Errorf("Error in unmarshalResponse: %s", err.Error())
}
default:
return nil, fmt.Errorf("Unknown PDUType %#x")
}
return response, nil
}
func unmarshalResponse(packet []byte, response *SnmpPacket, length int, request_type PDUType) (*SnmpPacket, error) {
cursor := 0
dumpBytes1(packet, "SNMP Packet is GET RESPONSE", 16)
response.PDUType = request_type
getresponse_length, cursor := parseLength(packet)
if len(packet) != getresponse_length {
return nil, fmt.Errorf("Error verifying Response sanity: Got %d Expected: %d\n", len(packet), getresponse_length)
}
slog.Printf("getresponse_length: %d", getresponse_length)
// Parse Request-ID
rawRequestId, count, err := parseRawField(packet[cursor:], "request id")
if err != nil {
return nil, fmt.Errorf("Error parsing SNMP packet request ID: %s", err.Error())
}
cursor += count
if requestid, ok := rawRequestId.(uint); ok {
response.RequestID = uint32(requestid)
slog.Printf("request-id: %d", response.RequestID)
}
if response.PDUType == GetBulkRequest {
// Parse Non Repeaters
rawNonRepeaters, count, err := parseRawField(packet[cursor:], "non repeaters")
if err != nil {
return nil, fmt.Errorf("Error parsing SNMP packet non repeaters: %s", err.Error())
}
cursor += count
if non_repeaters, ok := rawNonRepeaters.(int); ok {
response.NonRepeaters = uint8(non_repeaters)
}
// Parse Max Repetitions
rawMaxRepetitions, count, err := parseRawField(packet[cursor:], "max repetitions")
if err != nil {
return nil, fmt.Errorf("Error parsing SNMP packet max repetitions: %s", err.Error())
}
cursor += count
if max_repetitions, ok := rawMaxRepetitions.(int); ok {
response.MaxRepetitions = uint8(max_repetitions)
}
} else {
// Parse Error-Status
rawError, count, err := parseRawField(packet[cursor:], "error-status")
if err != nil {
return nil, fmt.Errorf("Error parsing SNMP packet error: %s", err.Error())
}
cursor += count
if error_status, ok := rawError.(int); ok {
response.Error = uint8(error_status)
slog.Printf("error-status: %d", uint8(error_status))
}
// Parse Error-Index
rawErrorIndex, count, err := parseRawField(packet[cursor:], "error index")
if err != nil {
return nil, fmt.Errorf("Error parsing SNMP packet error index: %s", err.Error())
}
cursor += count
if errorindex, ok := rawErrorIndex.(int); ok {
response.ErrorIndex = uint8(errorindex)
slog.Printf("error-index: %d", uint8(errorindex))
}
}
return unmarshalVBL(packet[cursor:], response, length)
}
// unmarshal a Varbind list
func unmarshalVBL(packet []byte, response *SnmpPacket,
length int) (*SnmpPacket, error) {
dumpBytes1(packet, "\n=== unmarshalVBL()", 32)
var cursor, cursor_inc int
var vbl_length int
if packet[cursor] != 0x30 {
return nil, fmt.Errorf("Expected a sequence when unmarshalling a VBL, got %x",
packet[cursor])
}
vbl_length, cursor = parseLength(packet)
if len(packet) != vbl_length {
return nil, fmt.Errorf("Error verifying: packet length %d vbl length %d\n",
len(packet), vbl_length)
}
slog.Printf("vbl_length: %d", vbl_length)
// Loop & parse Varbinds
for cursor < vbl_length {
dumpBytes1(packet[cursor:], fmt.Sprintf("\nSTARTING a varbind. Cursor %d", cursor), 32)
if packet[cursor] != 0x30 {
return nil, fmt.Errorf("Expected a sequence when unmarshalling a VB, got %x", packet[cursor])
}
_, cursor_inc = parseLength(packet[cursor:])
cursor += cursor_inc
// Parse OID
rawOid, oid_length, err := parseRawField(packet[cursor:], "OID")
if err != nil {
return nil, fmt.Errorf("Error parsing OID Value: %s", err.Error())
}
cursor += oid_length
var oid []int
var ok bool
if oid, ok = rawOid.([]int); !ok {
return nil, fmt.Errorf("unable to type assert rawOid |%v| to []int", rawOid)
}
slog.Printf("OID: %s", oidToString(oid))
// Parse Value
v, err := decodeValue(packet[cursor:], "value")
value_length, _ := parseLength(packet[cursor:])
cursor += value_length
response.Variables = append(response.Variables, SnmpPDU{oidToString(oid), v.Type, v.Value})
}
return response, nil
}