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// Copyright 2012 Google, Inc. All rights reserved.
//
// Use of this source code is governed by a BSD-style license
// that can be found in the LICENSE file in the root of the source
// tree.
package layers
import (
"encoding/binary"
"errors"
"fmt"
"github.com/google/gopacket"
)
// Loopback contains the header for loopback encapsulation. This header is
// used by both BSD and OpenBSD style loopback decoding (pcap's DLT_NULL
// and DLT_LOOP, respectively).
type Loopback struct {
BaseLayer
Family ProtocolFamily
}
// LayerType returns LayerTypeLoopback.
func (l *Loopback) LayerType() gopacket.LayerType { return LayerTypeLoopback }
// DecodeFromBytes decodes the given bytes into this layer.
func (l *Loopback) DecodeFromBytes(data []byte, df gopacket.DecodeFeedback) error {
if len(data) < 4 {
return errors.New("Loopback packet too small")
}
// The protocol could be either big-endian or little-endian, we're
// not sure. But we're PRETTY sure that the value is less than
// 256, so we can check the first two bytes.
var prot uint32
if data[0] == 0 && data[1] == 0 {
prot = binary.BigEndian.Uint32(data[:4])
} else {
prot = binary.LittleEndian.Uint32(data[:4])
}
if prot > 0xFF {
return fmt.Errorf("Invalid loopback protocol %q", data[:4])
}
l.Family = ProtocolFamily(prot)
l.BaseLayer = BaseLayer{data[:4], data[4:]}
return nil
}
// CanDecode returns the set of layer types that this DecodingLayer can decode.
func (l *Loopback) CanDecode() gopacket.LayerClass {
return LayerTypeLoopback
}
// NextLayerType returns the layer type contained by this DecodingLayer.
func (l *Loopback) NextLayerType() gopacket.LayerType {
return l.Family.LayerType()
}
// SerializeTo writes the serialized form of this layer into the
// SerializationBuffer, implementing gopacket.SerializableLayer.
func (l *Loopback) SerializeTo(b gopacket.SerializeBuffer, opts gopacket.SerializeOptions) error {
bytes, err := b.PrependBytes(4)
if err != nil {
return err
}
binary.LittleEndian.PutUint32(bytes, uint32(l.Family))
return nil
}
func decodeLoopback(data []byte, p gopacket.PacketBuilder) error {
l := Loopback{}
if err := l.DecodeFromBytes(data, gopacket.NilDecodeFeedback); err != nil {
return err
}
p.AddLayer(&l)
return p.NextDecoder(l.Family)
}