// Parses a given field, return the ASN.1 BER Type, its header length and the data
func parseField(data []byte) (*RawBER, error) {
log := l.GetDefaultLogger()
var err error
if len(data) == 0 {
return nil, fmt.Errorf("Unable to parse BER: Data length 0")
}
ber := new(RawBER)
ber.Type = Asn1BER(data[0])
// Parse Length
length := data[1]
// Check if this is padded or not
if length > 0x80 {
length = length - 0x80
log.Debug("Field length is padded to %d bytes\n", length)
ber.DataLength = Uvarint(data[2 : 2+length])
log.Debug("Decoded final length: %d\n", ber.DataLength)
ber.HeaderLength = 2 + uint64(length)
} else {
ber.HeaderLength = 2
ber.DataLength = uint64(length)
}
// Do sanity checks
if ber.DataLength > uint64(len(data)) {
return nil, fmt.Errorf("Unable to parse BER: provided data length is longer than actual data (%d vs %d)", ber.DataLength, len(data))
}
ber.Data = data[ber.HeaderLength : ber.HeaderLength+ber.DataLength]
ber.BERVariable, err = decodeValue(ber.Type, ber.Data)
if err != nil {
return nil, fmt.Errorf("Unable to decode value: %s\n", err.Error())
}
return ber, nil
}
func Unmarshal(packet []byte) (*SnmpPacket, error) {
log := l.GetDefaultLogger()
//var err error
response := new(SnmpPacket)
response.Variables = make([]SnmpPDU, 0, 5)
// Start parsing the packet
cursor := 0
// First bytes should be 0x30
if MessageType(packet[0]) == Sequence {
// Parse packet length
var length int
// length of structure is spread over two bytes
if packet[1] == 0x82 {
length = int(packet[2])<<8 | int(packet[3])
length += 4 // account for header + length
cursor += 4
} else {
length = int(packet[1])
length += 2 // account for header + length
cursor += 2
}
if len(packet) == length {
log.Debug("Packet sanity verified, we got all the bytes (%d)\n", length)
// Parse SNMP Version
rawVersion, count, err := parseRawField(packet[cursor:])
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)
}
// Parse community
rawCommunity, count, err := parseRawField(packet[cursor:])
cursor += count
if community, ok := rawCommunity.(string); ok {
response.Community = community
log.Debug("Parsed community %s\n", community)
}
// Parse SNMP packet type
switch MessageType(packet[cursor]) {
case GetResponse:
log.Debug("SNMP Packet is get response\n")
response.RequestType = GetResponse
// Response length (dont really care what the length is)
if packet[cursor+1] == 0x82 {
cursor += 4
} else {
cursor += 2
}
log.Debug("Response length: %d\n", length)
// Parse Request ID
rawRequestId, count, err := parseRawField(packet[cursor:])
if err != nil {
return nil, fmt.Errorf("Error parsing SNMP packet request ID: %s", err.Error())
}
cursor += count
if requestid, ok := rawRequestId.(int); ok {
response.RequestID = uint8(requestid)
}
// Parse Error
rawError, count, err := parseRawField(packet[cursor:])
if err != nil {
return nil, fmt.Errorf("Error parsing SNMP packet error: %s", err.Error())
}
cursor += count
if errorNo, ok := rawError.(int); ok {
response.Error = uint8(errorNo)
}
// Parse Error Index
rawErrorIndex, count, err := parseRawField(packet[cursor:])
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)
}
log.Debug("Request ID: %d Error: %d Error Index: %d\n", response.RequestID, response.Error, response.ErrorIndex)
// Varbind list
if packet[cursor] == 0x30 && packet[cursor+1] == 0x82 {
cursor += 4
} else {
cursor += 2
}
// Loop & parse Varbinds
for cursor < length {
log.Debug("Parsing var bind response (Cursor at %d/%d)", cursor, length)
if packet[cursor] == 0x30 && packet[cursor+1] == 0x82 {
cursor += 4
log.Debug("Padded Varbind length\n")
} else {
cursor += 2
}
// Parse OID
rawOid, count, err := parseRawField(packet[cursor:])
cursor += count
log.Debug("OID (%v) Field was %d bytes\n", rawOid, count)
var pduLength int
var paddedLength int = 0
if packet[cursor+1] == 0x81 {
pduLength = int(packet[cursor+2])
paddedLength = 1
log.Debug("Padded Variable length\n")
} else {
pduLength = int(packet[cursor+1])
}
log.Debug("PDU Value length: %d\n", pduLength)
v, err := decodeValue(packet[cursor : cursor+pduLength])
if err != nil {
return nil, fmt.Errorf("Error parsing PDU Value: %s", err.Error())
}
if oid, ok := rawOid.([]int); ok {
response.Variables = append(response.Variables, SnmpPDU{oidToString(oid), v.Type, v.Value})
}
cursor += pduLength + paddedLength + 2
}
}
} else {
return nil, fmt.Errorf("Error verifying packet sanity: Got %d Expected: %d\n", len(packet), length)
}
} else {
return nil, fmt.Errorf("Invalid packet header\n")
}
return response, nil
}
func Unmarshal(packet []byte) (*SnmpPacket, error) {
log := l.GetDefaultLogger()
log.Debug("Begin SNMP Packet unmarshal\n")
//var err error
response := new(SnmpPacket)
response.Variables = make([]SnmpPDU, 0, 5)
// Start parsing the packet
var cursor uint64 = 0
// First bytes should be 0x30
if Asn1BER(packet[0]) == Sequence {
// Parse packet length
ber, err := parseField(packet)
if err != nil {
log.Error("Unable to parse packet header: %s\n", err.Error())
return nil, err
}
log.Debug("Packet sanity verified, we got all the bytes (%d)\n", ber.DataLength)
cursor += ber.HeaderLength
// Parse SNMP Version
rawVersion, err := parseField(packet[cursor:])
if err != nil {
return nil, fmt.Errorf("Error parsing SNMP packet version: %s", err.Error())
}
cursor += rawVersion.DataLength + rawVersion.HeaderLength
if version, ok := rawVersion.BERVariable.Value.(int); ok {
response.Version = SnmpVersion(version)
log.Debug("Parsed Version %d\n", version)
}
// Parse community
rawCommunity, err := parseField(packet[cursor:])
if err != nil {
log.Debug("Unable to parse Community Field: %s\n", err)
}
cursor += rawCommunity.DataLength + rawCommunity.HeaderLength
if community, ok := rawCommunity.BERVariable.Value.(string); ok {
response.Community = community
log.Debug("Parsed community %s\n", community)
}
rawPDU, err := parseField(packet[cursor:])
if err != nil {
log.Debug("Unable to parse SNMP PDU: %s\n", err.Error())
}
response.RequestType = rawPDU.Type
switch rawPDU.Type {
default:
log.Debug("Unsupported SNMP Packet Type %s\n", rawPDU.Type.String())
log.Debug("PDU Size is %d\n", rawPDU.DataLength)
case GetRequest, GetResponse, GetBulkRequest:
log.Debug("SNMP Packet is %s\n", rawPDU.Type.String())
log.Debug("PDU Size is %d\n", rawPDU.DataLength)
cursor += rawPDU.HeaderLength
// Parse Request ID
rawRequestId, err := parseField(packet[cursor:])
if err != nil {
return nil, err
}
cursor += rawRequestId.DataLength + rawRequestId.HeaderLength
if requestid, ok := rawRequestId.BERVariable.Value.(int); ok {
response.RequestID = uint8(requestid)
log.Debug("Parsed Request ID: %d\n", requestid)
}
// Parse Error
rawError, err := parseField(packet[cursor:])
if err != nil {
return nil, err
}
cursor += rawError.DataLength + rawError.HeaderLength
if errorNo, ok := rawError.BERVariable.Value.(int); ok {
response.Error = uint8(errorNo)
}
// Parse Error Index
rawErrorIndex, err := parseField(packet[cursor:])
if err != nil {
return nil, err
}
cursor += rawErrorIndex.DataLength + rawErrorIndex.HeaderLength
if errorindex, ok := rawErrorIndex.BERVariable.Value.(int); ok {
response.ErrorIndex = uint8(errorindex)
}
log.Debug("Request ID: %d Error: %d Error Index: %d\n", response.RequestID, response.Error, response.ErrorIndex)
rawResp, err := parseField(packet[cursor:])
if err != nil {
return nil, err
}
cursor += rawResp.HeaderLength
// Loop & parse Varbinds
for cursor < uint64(len(packet)) {
log.Debug("Parsing var bind response (Cursor at %d/%d)", cursor, len(packet))
rawVarbind, err := parseField(packet[cursor:])
if err != nil {
return nil, err
}
cursor += rawVarbind.HeaderLength
log.Debug("Varbind length: %d/%d\n", rawVarbind.HeaderLength, rawVarbind.DataLength)
log.Debug("Parsing OID (Cursor at %d)\n", cursor)
// Parse OID
rawOid, err := parseField(packet[cursor:])
if err != nil {
return nil, err
}
cursor += rawOid.HeaderLength + rawOid.DataLength
log.Debug("OID (%v) Field was %d bytes\n", rawOid, rawOid.DataLength)
rawValue, err := parseField(packet[cursor:])
if err != nil {
return nil, err
}
cursor += rawValue.HeaderLength + rawValue.DataLength
log.Debug("Value field was %d bytes\n", rawValue.DataLength)
if oid, ok := rawOid.BERVariable.Value.([]int); ok {
log.Debug("Varbind decoding success\n")
response.Variables = append(response.Variables, SnmpPDU{oidToString(oid), rawValue.Type, rawValue.BERVariable.Value})
}
}
}
} else {
return nil, fmt.Errorf("Invalid packet header\n")
}
return response, nil
}
