|
1 | 1 | package main |
2 | 2 |
|
3 | | -import "fmt" |
| 3 | +import ( |
| 4 | + "encoding/base64" |
| 5 | + "flag" |
| 6 | + "fmt" |
| 7 | + "io/ioutil" |
| 8 | + "log" |
| 9 | + "net" |
| 10 | + "os" |
| 11 | + "path" |
| 12 | + "strconv" |
| 13 | + "strings" |
| 14 | + |
| 15 | + "golang.org/x/net/dns/dnsmessage" |
| 16 | +) |
| 17 | + |
| 18 | +var ( |
| 19 | + port = flag.Int("port", 53, "Port for listening") |
| 20 | + verbose = flag.Bool("v", false, "Enable verbose logging") |
| 21 | + dataDirF = flag.String("data", "", "Data directory, default is temp dir") |
| 22 | +) |
| 23 | + |
| 24 | +type entry struct { |
| 25 | + token string |
| 26 | + count int |
| 27 | + data []byte |
| 28 | +} |
| 29 | + |
| 30 | +func (e entry) save(dir string) error { |
| 31 | + dirPath := path.Join(dir, e.token) |
| 32 | + if err := os.MkdirAll(dirPath, 0744); err != nil { |
| 33 | + return fmt.Errorf("failed creating dir %s, %w", dirPath, err) |
| 34 | + } |
| 35 | + |
| 36 | + filename := path.Join(dir, e.token, fmt.Sprintf("%08d.out", e.count)) |
| 37 | + if err := ioutil.WriteFile(filename, e.data, 0644); err != nil { |
| 38 | + return fmt.Errorf("failed writing file %s, %w", filename, err) |
| 39 | + } |
| 40 | + |
| 41 | + return nil |
| 42 | +} |
4 | 43 |
|
5 | 44 | func main() { |
6 | | - fmt.Println("Hello, World!") |
| 45 | + flag.Parse() |
| 46 | + |
| 47 | + dataDir := path.Join(os.TempDir(), "exodus") |
| 48 | + if *dataDirF != "" { |
| 49 | + dataDir = *dataDirF |
| 50 | + } |
| 51 | + |
| 52 | + conn, err := net.ListenUDP("udp4", &net.UDPAddr{Port: *port}) |
| 53 | + if err != nil { |
| 54 | + log.Fatalf("failed network listen, %s", err.Error()) |
| 55 | + } |
| 56 | + defer conn.Close() |
| 57 | + |
| 58 | + if *verbose { |
| 59 | + log.Println("started") |
| 60 | + log.Println("data dir:", dataDir) |
| 61 | + } |
| 62 | + |
| 63 | + start(conn, dataDir) |
| 64 | +} |
| 65 | + |
| 66 | +func extractData(msg dnsmessage.Message) (e entry, err error) { |
| 67 | + if len(msg.Questions) != 1 { |
| 68 | + return e, fmt.Errorf("dns query has no questions") |
| 69 | + } |
| 70 | + |
| 71 | + domains := strings.Split(msg.Questions[0].Name.String(), ".") |
| 72 | + if len(domains) < 5 { |
| 73 | + return e, fmt.Errorf("dns question is missing requiered information") |
| 74 | + } |
| 75 | + |
| 76 | + e.data, err = base64.RawStdEncoding.DecodeString(domains[0]) |
| 77 | + if err != nil { |
| 78 | + return e, fmt.Errorf("failed decoding data, %w", err) |
| 79 | + } |
| 80 | + |
| 81 | + e.count, _ = strconv.Atoi(domains[1]) |
| 82 | + e.token = domains[2] |
| 83 | + |
| 84 | + return |
| 85 | +} |
| 86 | + |
| 87 | +func start(conn *net.UDPConn, dataDir string) { |
| 88 | + for { |
| 89 | + var ( |
| 90 | + buffer [512]byte |
| 91 | + msg dnsmessage.Message |
| 92 | + ) |
| 93 | + |
| 94 | + read, addr, err := conn.ReadFromUDP(buffer[:]) |
| 95 | + if err != nil { |
| 96 | + log.Printf("failed network read, %s\n", err.Error()) |
| 97 | + continue |
| 98 | + } |
| 99 | + |
| 100 | + if err := msg.Unpack(buffer[:read]); err != nil { |
| 101 | + log.Printf("failed message unpacking, %s\n", err.Error()) |
| 102 | + continue |
| 103 | + } |
| 104 | + |
| 105 | + e, err := extractData(msg) |
| 106 | + if err != nil { |
| 107 | + log.Println(err) |
| 108 | + continue |
| 109 | + } |
| 110 | + |
| 111 | + if *verbose { |
| 112 | + log.Printf("received [token: %16s] [count: %8d]\n", e.token, e.count) |
| 113 | + } |
| 114 | + |
| 115 | + if err := e.save(dataDir); err != nil { |
| 116 | + log.Println(err) |
| 117 | + continue |
| 118 | + } |
| 119 | + |
| 120 | + msg.Header.Response = true |
| 121 | + |
| 122 | + packed, err := msg.Pack() |
| 123 | + if err != nil { |
| 124 | + log.Printf("failed packing dns msg, %s\n", err.Error()) |
| 125 | + } |
| 126 | + |
| 127 | + if _, err := conn.WriteToUDP(packed, addr); err != nil { |
| 128 | + log.Printf("failed network write, %s\n", err.Error()) |
| 129 | + } |
| 130 | + } |
7 | 131 | } |
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