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donkahlero
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gconnell
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Add Support for LCM Defragmentation
This patch includes support for defragmentation of LCM packages, as specified in the LCM protocol description (https://lcm-proj.github.io/udp_multicast_protocol.html). This patch code should also be used in combination with an upcoming PR towards the GitHub LCM repository that adds golang + gopacket support.
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‎.travis.golint.sh

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@@ -3,7 +3,7 @@
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cd "$(dirname $0)"
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go get github.com/golang/lint/golint
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DIRS=". tcpassembly tcpassembly/tcpreader ip4defrag reassembly macs pcapgo pcap afpacket pfring routing"
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DIRS=". tcpassembly tcpassembly/tcpreader ip4defrag reassembly macs pcapgo pcap afpacket pfring routing defrag"
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# Add subdirectories here as we clean up golint on each.
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for subdir in $DIRS; do
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pushd $subdir

‎.travis.govet.sh

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@@ -1,7 +1,7 @@
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#!/bin/bash
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cd "$(dirname $0)"
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DIRS=". layers pcap pcapgo pfring tcpassembly tcpassembly/tcpreader routing ip4defrag bytediff macs"
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DIRS=". layers pcap pcapgo pfring tcpassembly tcpassembly/tcpreader routing ip4defrag bytediff macs defrag"
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set -e
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for subdir in $DIRS; do
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pushd $subdir

‎defrag/lcmdefrag.go

Lines changed: 143 additions & 0 deletions
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// Copyright 2018 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 defrag
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import (
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"fmt"
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"time"
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"github.com/google/gopacket"
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"github.com/google/gopacket/layers"
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)
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const (
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// Packages are cleaned up/removed after no input was received for this
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// amount of seconds.
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timeout time.Duration = 3 * time.Second
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)
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type lcmPacket struct {
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lastPacket time.Time
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done bool
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recFrags uint16
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totalFrags uint16
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frags map[uint16]*layers.LCM
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}
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// LCMDefragmenter supports defragmentation of LCM messages.
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//
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// References
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// https://lcm-proj.github.io/
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// https://github.com/lcm-proj/lcm
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type LCMDefragmenter struct {
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packets map[uint32]*lcmPacket
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}
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func newLCMPacket(totalFrags uint16) *lcmPacket {
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return &lcmPacket{
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done: false,
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recFrags: 0,
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totalFrags: totalFrags,
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frags: make(map[uint16]*layers.LCM),
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}
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}
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// NewLCMDefragmenter returns a new LCMDefragmenter.
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func NewLCMDefragmenter() *LCMDefragmenter {
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return &LCMDefragmenter{
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packets: make(map[uint32]*lcmPacket),
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}
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}
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func (lp *lcmPacket) append(in *layers.LCM) {
57+
lp.frags[in.FragmentNumber] = in
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lp.recFrags++
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lp.lastPacket = time.Now()
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}
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func (lp *lcmPacket) assemble() (out *layers.LCM, err error) {
63+
var blob []byte
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//Extract packets
66+
for i := uint16(0); i < lp.totalFrags; i++ {
67+
fragment, ok := lp.frags[i]
68+
if !ok {
69+
err = fmt.Errorf("Tried to defragment incomplete packet. Waiting "+
70+
"for more potential (unordered) packets... %d", i)
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return
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}
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// For the very first packet, we also want the header.
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if i == 0 {
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blob = append(blob, fragment.LayerContents()...)
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}
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// Append the data for each packet.
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blob = append(blob, fragment.Payload()...)
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}
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packet := gopacket.NewPacket(blob, layers.LayerTypeLCM, gopacket.NoCopy)
84+
lcmHdrLayer := packet.Layer(layers.LayerTypeLCM)
85+
out, ok := lcmHdrLayer.(*layers.LCM)
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if !ok {
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err = fmt.Errorf("Error while decoding the defragmented packet. " +
88+
"Erasing/dropping packet.")
89+
}
90+
91+
lp.done = true
92+
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return
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}
95+
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func (ld *LCMDefragmenter) cleanUp() {
97+
for key, packet := range ld.packets {
98+
if packet.done || time.Now().Sub(packet.lastPacket) > timeout {
99+
delete(ld.packets, key)
100+
}
101+
}
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}
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// Defrag takes a reference to an LCM packet and processes it.
105+
// In case the packet does not need to be defragmented, it immediately returns
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// the as in passed reference. In case in was the last missing fragment, out
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// will be the defragmented packet. If in was a fragment, but we are awaiting
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// more, out will be set to nil.
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// In the case that in was nil, we will just run the internal cleanup of the
110+
// defragmenter that times out packages.
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// If an error was encountered during defragmentation, out will also be nil,
112+
// while err will contain further information on the failure.
113+
func (ld *LCMDefragmenter) Defrag(in *layers.LCM) (out *layers.LCM, err error) {
114+
// Timeout old packages and erase error prone ones.
115+
ld.cleanUp()
116+
117+
// For running cleanup only
118+
if in == nil {
119+
return
120+
}
121+
122+
// Quick check if this is acutally a single packet. In that case, just
123+
// return it quickly.
124+
if !in.Fragmented {
125+
out = in
126+
return
127+
}
128+
129+
// Do we need to start a new fragments obj?
130+
if _, ok := ld.packets[in.SequenceNumber]; !ok {
131+
ld.packets[in.SequenceNumber] = newLCMPacket(in.TotalFragments)
132+
}
133+
134+
// Append the packet
135+
ld.packets[in.SequenceNumber].append(in)
136+
137+
// Check if this is the last package of that series
138+
if ld.packets[in.SequenceNumber].recFrags == in.TotalFragments {
139+
out, err = ld.packets[in.SequenceNumber].assemble()
140+
}
141+
142+
return
143+
}

‎defrag/lcmdefrag_test.go

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,105 @@
1+
// Copyright 2018 Google, Inc. All rights reserved.
2+
//
3+
// Use of this source code is governed by a BSD-style license
4+
// that can be found in the LICENSE file in the root of the source
5+
// tree.
6+
7+
package defrag
8+
9+
import (
10+
"testing"
11+
12+
"github.com/google/gopacket"
13+
"github.com/google/gopacket/layers"
14+
)
15+
16+
var (
17+
fragmentOne = []byte{
18+
0x4c, 0x43, 0x30, 0x33, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x0d,
19+
0x00, 0x00, 0x00, 0x2d, 0x00, 0x00, 0x00, 0x02, 0x4c, 0x43, 0x4d, 0x5f,
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0x53, 0x45, 0x4c, 0x46, 0x5f, 0x54, 0x45, 0x53, 0x54, 0x00, 0x6c, 0x63,
21+
0x6d, 0x20, 0x73, 0x65, 0x6c, 0x66, 0x20, 0x74, 0x65, 0x73, 0x74,
22+
}
23+
24+
fragmentTwo = []byte{
25+
0x4c, 0x43, 0x30, 0x33, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x0d,
26+
0x00, 0x00, 0x00, 0x2d, 0x00, 0x01, 0x00, 0x02, 0x6c, 0x63, 0x6d, 0x20,
27+
0x73, 0x65, 0x6c, 0x66, 0x20, 0x74, 0x65, 0x73, 0x74,
28+
}
29+
30+
completePacket = []byte{
31+
0x4c, 0x43, 0x30, 0x32, 0x00, 0x00, 0x00, 0x00, 0x4c, 0x43, 0x4d, 0x5f,
32+
0x53, 0x45, 0x4c, 0x46, 0x5f, 0x54, 0x45, 0x53, 0x54, 0x00, 0x6c, 0x63,
33+
0x6d, 0x20, 0x73, 0x65, 0x6c, 0x66, 0x20, 0x74, 0x65, 0x73, 0x74,
34+
}
35+
)
36+
37+
func TestOrderedLCMDefrag(t *testing.T) {
38+
defragmenter := NewLCMDefragmenter()
39+
var err error
40+
41+
packet := gopacket.NewPacket(fragmentOne, layers.LayerTypeLCM, gopacket.NoCopy)
42+
lcm := packet.Layer(layers.LayerTypeLCM).(*layers.LCM)
43+
44+
lcm, err = defragmenter.Defrag(lcm)
45+
if lcm != nil {
46+
t.Fatal("Returned incomplete LCM message.")
47+
}
48+
if err != nil {
49+
t.Fatal(err)
50+
}
51+
52+
packet = gopacket.NewPacket(fragmentTwo, layers.LayerTypeLCM, gopacket.NoCopy)
53+
lcm = packet.Layer(layers.LayerTypeLCM).(*layers.LCM)
54+
55+
lcm, err = defragmenter.Defrag(lcm)
56+
if lcm == nil {
57+
t.Fatal("Did not receive defragmented LCM message.")
58+
}
59+
if err != nil {
60+
t.Fatal(err)
61+
}
62+
}
63+
64+
func TestUnorderedLCMDefrag(t *testing.T) {
65+
defragmenter := NewLCMDefragmenter()
66+
var err error
67+
68+
packet := gopacket.NewPacket(fragmentTwo, layers.LayerTypeLCM, gopacket.NoCopy)
69+
lcm := packet.Layer(layers.LayerTypeLCM).(*layers.LCM)
70+
71+
lcm, err = defragmenter.Defrag(lcm)
72+
if lcm != nil {
73+
t.Fatal("Returned incomplete LCM message.")
74+
}
75+
if err != nil {
76+
t.Fatal(err)
77+
}
78+
79+
packet = gopacket.NewPacket(fragmentOne, layers.LayerTypeLCM, gopacket.NoCopy)
80+
lcm = packet.Layer(layers.LayerTypeLCM).(*layers.LCM)
81+
82+
lcm, err = defragmenter.Defrag(lcm)
83+
if lcm == nil {
84+
t.Fatal("Did not receive defragmented LCM message.")
85+
}
86+
if err != nil {
87+
t.Fatal(err)
88+
}
89+
}
90+
91+
func TestNonLCMDefrag(t *testing.T) {
92+
defragmenter := NewLCMDefragmenter()
93+
var err error
94+
95+
packet := gopacket.NewPacket(completePacket, layers.LayerTypeLCM, gopacket.NoCopy)
96+
lcm := packet.Layer(layers.LayerTypeLCM).(*layers.LCM)
97+
98+
lcm, err = defragmenter.Defrag(lcm)
99+
if lcm == nil {
100+
t.Fatal("Did not receive complete LCM message.")
101+
}
102+
if err != nil {
103+
t.Fatal(err)
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}
105+
}

‎gc

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Original file line numberDiff line numberDiff line change
@@ -186,6 +186,12 @@ if [ -f /usr/include/pfring.h ]; then
186186
go build
187187
popd
188188
fi
189+
pushd ip4defrag
190+
go test ./...
191+
popd
192+
pushd defrag
193+
go test ./...
194+
popd
189195

190196
for travis_script in `ls .travis.*.sh`; do
191197
./$travis_script

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