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