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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"
"github.com/google/gopacket"
)
// PPP is the layer for PPP encapsulation headers.
type PPP struct {
BaseLayer
PPPType PPPType
HasPPTPHeader bool
}
// PPPEndpoint is a singleton endpoint for PPP. Since there is no actual
// addressing for the two ends of a PPP connection, we use a singleton value
// named 'point' for each endpoint.
var PPPEndpoint = gopacket.NewEndpoint(EndpointPPP, nil)
// PPPFlow is a singleton flow for PPP. Since there is no actual addressing for
// the two ends of a PPP connection, we use a singleton value to represent the
// flow for all PPP connections.
var PPPFlow = gopacket.NewFlow(EndpointPPP, nil, nil)
// LayerType returns LayerTypePPP
func (p *PPP) LayerType() gopacket.LayerType { return LayerTypePPP }
// LinkFlow returns PPPFlow.
func (p *PPP) LinkFlow() gopacket.Flow { return PPPFlow }
func decodePPP(data []byte, p gopacket.PacketBuilder) error {
ppp := &PPP{}
offset := 0
if data[0] == 0xff && data[1] == 0x03 {
offset = 2
ppp.HasPPTPHeader = true
}
if data[offset]&0x1 == 0 {
if data[offset+1]&0x1 == 0 {
return errors.New("PPP has invalid type")
}
ppp.PPPType = PPPType(binary.BigEndian.Uint16(data[offset : offset+2]))
ppp.Contents = data[offset : offset+2]
ppp.Payload = data[offset+2:]
} else {
ppp.PPPType = PPPType(data[offset])
ppp.Contents = data[offset : offset+1]
ppp.Payload = data[offset+1:]
}
p.AddLayer(ppp)
p.SetLinkLayer(ppp)
return p.NextDecoder(ppp.PPPType)
}
// SerializeTo writes the serialized form of this layer into the
// SerializationBuffer, implementing gopacket.SerializableLayer.
// See the docs for gopacket.SerializableLayer for more info.
func (p *PPP) SerializeTo(b gopacket.SerializeBuffer, opts gopacket.SerializeOptions) error {
if p.PPPType&0x100 == 0 {
bytes, err := b.PrependBytes(2)
if err != nil {
return err
}
binary.BigEndian.PutUint16(bytes, uint16(p.PPPType))
} else {
bytes, err := b.PrependBytes(1)
if err != nil {
return err
}
bytes[0] = uint8(p.PPPType)
}
if p.HasPPTPHeader {
bytes, err := b.PrependBytes(2)
if err != nil {
return err
}
bytes[0] = 0xff
bytes[1] = 0x03
}
return nil
}
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