forked from noelbenz/goseq
/
packetstream.go
227 lines (187 loc) · 5 KB
/
packetstream.go
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
package goseq
import (
"bytes"
"compress/bzip2"
"encoding/binary"
"errors"
"hash/crc32"
"io"
)
const (
pkt_NOT_SPLIT uint32 = 0xFFFFFFFF
pkt_SPLIT uint32 = 0xFFFFFFFE
)
const (
// PayloadSize is the official packet-payload size
// of UDP headers.
PayloadSize int = 1400
)
var (
PacketHeaderErr error = errors.New("Packet does not have expected header identifier byte.")
PacketMalformed error = errors.New("Packet appears malformed.")
PayloadSizeMismatch error = errors.New("Decompressed payload is not expected size.")
PayloadCRC32Fail error = errors.New("CRC validation failed on decompressed payload. Possible corruption?")
)
type pkt_header struct {
Std struct {
HeaderCode uint32
}
Extended struct { // if HeaderCode == pkt_SPLIT
Std struct {
ID uint32
Total byte
Number byte
Size int16
}
ComprInf struct { // if ID & (1 << 31)
Size uint32
CRC32 uint32
}
}
}
type packet struct {
Header pkt_header
Payload []byte
}
func newPacket() packet {
header := pkt_header{}
header.Extended.Std.Number = 0
header.Extended.Std.Total = 1
return packet{
Payload: make([]byte, 0, PayloadSize),
Header: header,
}
}
// Reads the packets coming from the wire
// and turns them into a single payload.
// Strips all Source Packet specific headers.
type packetStream struct {
expected int
packets []packet
}
func newPacketStream() packetStream {
return packetStream{
expected: 1,
packets: make([]packet, 1),
}
}
func pk_signals_compression(header *pkt_header) bool {
return (header.Extended.Std.ID & (1 << 31)) > 0
}
// Take a byte buffer and assume it's a fuill UDP packet,
// construct Source packet from it. AKA interpret source
// headers and find where the payload starts.
func contructPacket(full []byte) (packet, error) {
pk := newPacket()
buf := bytes.NewBuffer(full)
var err error
if err = binary.Read(buf, byteOrder, &pk.Header.Std.HeaderCode); err != nil {
return pk, err
}
if pk.Header.Std.HeaderCode == pkt_NOT_SPLIT {
pk.Payload = buf.Bytes()
return pk, nil
}
// weed out any funny packets that
// aren't correct
if pk.Header.Std.HeaderCode != pkt_SPLIT {
return pk, PacketMalformed
}
// The packet is not assumed to be split.
// Read split headers.
if err = binary.Read(buf, byteOrder, &pk.Header.Extended.Std); err != nil {
return pk, err
}
// test for compression
if pk_signals_compression(&pk.Header) {
// decode compression information
if err = binary.Read(buf, byteOrder, &pk.Header.Extended.ComprInf); err != nil {
return pk, err
}
// note that the payload is actually compressed and should
// be decompressed during read.
}
// Payload is the rest!
pk.Payload = buf.Bytes()
return pk, nil
}
// Gobble packets from the connection.
// Number of packets are determined by the format of
// the packet.
func (st *packetStream) Gobble(reader io.Reader) error {
for got := 0; got < st.expected; got++ {
var buffer [PayloadSize]byte
var n int
var err error
var pk packet
if n, err = reader.Read(buffer[0:]); err != nil {
return err
}
if pk, err = contructPacket(buffer[0:n]); err != nil {
return err
}
// resize packet buffer to fit new expected total
if st.expected != int(pk.Header.Extended.Std.Total) {
st.expected = int(pk.Header.Extended.Std.Total)
st.packets = make([]packet, st.expected)
}
// noone like buffer overflows.
if int(pk.Header.Extended.Std.Number) >= len(st.packets) {
// a naughty server is trying to crash us.
return PacketMalformed
}
st.packets[pk.Header.Extended.Std.Number] = pk
}
return nil
}
// Returns the conitguous payload, decompressing if necessary.
func (st *packetStream) GetFullPayload() ([]byte, error) {
payload := st.contiguous_payload()
// token packet header to decide if to decompress
pkh := &st.packets[0].Header
if !pk_signals_compression(pkh) {
// no need to decompress, just return the payload
return payload, nil
}
// Decompressed buffer
decompressed := bytes.NewBuffer(make([]byte, 0, pkh.Extended.ComprInf.Size))
// Decompress data
copied, err := io.Copy(decompressed, bzip2.NewReader(bytes.NewBuffer(payload)))
if err != nil {
return nil, err
}
if copied != int64(pkh.Extended.ComprInf.Size) {
return nil, PayloadSizeMismatch
}
decompressed_buf := decompressed.Bytes()
// time to checksum dis place up
checksum := crc32.ChecksumIEEE(decompressed_buf)
if checksum != pkh.Extended.ComprInf.CRC32 {
// all that work for nothing :(
return nil, PayloadCRC32Fail
}
return decompressed_buf, nil
}
func (st *packetStream) contiguous_payload() []byte {
sum := 0
for _, pk := range st.packets {
sum += len(pk.Payload)
}
contiguous := make([]byte, sum)
sum = 0
for _, pk := range st.packets {
copy(contiguous[sum:], pk.Payload)
sum += len(pk.Payload)
}
return contiguous
}
// Read a c string from the buffer
// and return a go-string without the NULL
// terminator
func rcstr(buf *bytes.Buffer) (string, error) {
str, err := buf.ReadString(0x0)
if err != nil {
return str, err
}
return str[:len(str)-1], nil
}