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decoder.go
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decoder.go
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package decoder
import (
"fmt"
"github.com/elastic/libbeat/logp"
"github.com/elastic/packetbeat/protos"
"github.com/elastic/packetbeat/protos/tcp"
"github.com/elastic/packetbeat/protos/udp"
"github.com/tsg/gopacket"
"github.com/tsg/gopacket/layers"
)
type DecoderStruct struct {
Parser *gopacket.DecodingLayerParser
sll layers.LinuxSLL
d1q layers.Dot1Q
lo layers.Loopback
eth layers.Ethernet
ip4 layers.IPv4
ip6 layers.IPv6
tcp layers.TCP
udp layers.UDP
payload gopacket.Payload
decoded []gopacket.LayerType
tcpProc tcp.Processor
udpProc udp.Processor
}
// Creates and returns a new DecoderStruct.
func NewDecoder(datalink layers.LinkType, tcp tcp.Processor, udp udp.Processor) (*DecoderStruct, error) {
d := DecoderStruct{tcpProc: tcp, udpProc: udp}
logp.Debug("pcapread", "Layer type: %s", datalink.String())
switch datalink {
case layers.LinkTypeLinuxSLL:
d.Parser = gopacket.NewDecodingLayerParser(
layers.LayerTypeLinuxSLL,
&d.sll, &d.d1q, &d.ip4, &d.ip6, &d.tcp, &d.udp, &d.payload)
case layers.LinkTypeEthernet:
d.Parser = gopacket.NewDecodingLayerParser(
layers.LayerTypeEthernet,
&d.eth, &d.d1q, &d.ip4, &d.ip6, &d.tcp, &d.udp, &d.payload)
case layers.LinkTypeNull: // loopback on OSx
d.Parser = gopacket.NewDecodingLayerParser(
layers.LayerTypeLoopback,
&d.lo, &d.d1q, &d.ip4, &d.ip6, &d.tcp, &d.udp, &d.payload)
default:
return nil, fmt.Errorf("Unsupported link type: %s", datalink.String())
}
d.decoded = []gopacket.LayerType{}
return &d, nil
}
func (decoder *DecoderStruct) DecodePacketData(data []byte, ci *gopacket.CaptureInfo) {
var err error
var packet protos.Packet
err = decoder.Parser.DecodeLayers(data, &decoder.decoded)
if err != nil {
// Ignore UnsupportedLayerType errors that can occur while parsing
// UDP packets.
lastLayer := decoder.decoded[len(decoder.decoded)-1]
_, unsupported := err.(gopacket.UnsupportedLayerType)
if !(unsupported && lastLayer == layers.LayerTypeUDP) {
logp.Debug("pcapread", "Decoding error: %s", err)
return
}
}
has_tcp := false
has_udp := false
for _, layerType := range decoder.decoded {
switch layerType {
case layers.LayerTypeIPv4:
logp.Debug("ip", "IPv4 packet")
packet.Tuple.Src_ip = decoder.ip4.SrcIP
packet.Tuple.Dst_ip = decoder.ip4.DstIP
packet.Tuple.Ip_length = 4
case layers.LayerTypeIPv6:
logp.Debug("ip", "IPv6 packet")
packet.Tuple.Src_ip = decoder.ip6.SrcIP
packet.Tuple.Dst_ip = decoder.ip6.DstIP
packet.Tuple.Ip_length = 16
case layers.LayerTypeTCP:
logp.Debug("ip", "TCP packet")
packet.Tuple.Src_port = uint16(decoder.tcp.SrcPort)
packet.Tuple.Dst_port = uint16(decoder.tcp.DstPort)
has_tcp = true
case layers.LayerTypeUDP:
logp.Debug("ip", "UDP packet")
packet.Tuple.Src_port = uint16(decoder.udp.SrcPort)
packet.Tuple.Dst_port = uint16(decoder.udp.DstPort)
packet.Payload = decoder.udp.Payload
has_udp = true
case gopacket.LayerTypePayload:
packet.Payload = decoder.payload
}
}
packet.Ts = ci.Timestamp
packet.Tuple.ComputeHashebles()
if has_udp {
decoder.udpProc.Process(&packet)
} else if has_tcp {
if len(packet.Payload) == 0 && !decoder.tcp.FIN {
// We have no use for this atm.
logp.Debug("pcapread", "Ignore empty non-FIN packet")
return
}
decoder.tcpProc.Process(&decoder.tcp, &packet)
}
}