1. 1
2. 2
3. 3
4. 4
5. 5
6. 6
7. 7
8. 8
9. 9
10. 10
11. 11
12. 12
13. 13
14. 14
15. 15
16. 16
17. 17
18. 18
19. 19
20. 20
21. 21
22. 22
23. 23
24. 24
25. 25
26. 26
27. 27
28. 28
29. 29
30. 30
31. 31
32. 32
33. 33
34. 34
35. 35
36. 36
37. 37
38. 38
39. 39
40. 40
41. 41
42. 42
43. 43
44. 44
45. 45
46. 46
47. 47
48. 48
49. 49
50. 50
51. 51
52. 52
53. 53
54. 54
55. 55
56. 56
57. 57
58. 58
59. 59
60. 60
61. 61
62. 62
63. 63
64. 64
65. 65
66. 66
67. 67
68. 68
69. 69
70. 70
71. 71
72. 72
73. 73
74. 74
75. 75
76. 76
77. 77
78. 78
79. 79
80. 80
81. 81
82. 82
83. 83
84. 84
85. 85
86. 86
87. 87
88. 88
89. 89
90. 90
91. 91
92. 92
93. 93
94. 94
95. 95
96. 96
97. 97
98. 98
99. 99
100. 100
101. 101
102. 102
103. 103
104. 104
105. 105
106. 106
107. 107
108. 108
109. 109
110. 110
111. 111

package main

import (
	"crypto/ed25519"
	"encoding/base64"
	"encoding/gob"
	"errors"
	"log"
	"net/http"
	"os"
	"strings"
)

type user struct {
	dhtVal    []byte
	phase     int64
	servers   []string
	log       []string
	nextIndex map[string]int
}

var users map[string]*user

// Verify that a body was signed by this ID
func verify(id string, body []byte) error {
	b, err := base64.RawURLEncoding.DecodeString(id)
	if err != nil {
		return err
	}
	if len(body) < ed25519.SignatureSize {
		return errors.New("body too short")
	}
	message := body[:len(body)-ed25519.SignatureSize]
	sig := body[len(body)-ed25519.SignatureSize:]
	if !ed25519.Verify(ed25519.PublicKey(b), message, sig) {
		return errors.New("signature verification failed")
	}
	return nil
}

// Persist a user's data to disk
func persist(id string) {
	writer, err := os.OpenFile(dataDir+"/"+id+"/gob", os.O_CREATE|os.O_WRONLY, 0644)
	if err != nil {
		return
	}
	enc := gob.NewEncoder(writer)
	enc.Encode(users[id])
}

// Reconfigure a user based on a DHT get
func reconfigure(id string, dhtVal []byte) {
	mu.Lock()
	defer mu.Unlock()

	user := users[id]
	if timestamp(dhtVal) < timestamp(user.dhtVal) {
		return
	}

	user.dhtVal = dhtVal
	servers := strings.Split(string(dhtVal[8:len(dhtVal)-ed25519.SignatureSize]), "\n")
	log.Printf("Reconfiguring %s %s", id, servers)
	user.servers = servers
	if servers[0] == me {
		if user.nextIndex == nil {
			user.nextIndex = make(map[string]int)
		}
		for i, server := range servers {
			if _, ok := user.nextIndex[server]; !ok && i > 0 {
				user.nextIndex[server] = len(user.log)
				go replicate(id, server)
			}
		}
	}

	inServers := false
	for _, server := range servers {
		if server == me {
			inServers = true
		}
	}
	persist(id)
	if !inServers {
		delete(users, id)
		_ = os.RemoveAll(dataDir + "/" + id)
	}
}

// Handle user configuration changes
func userHandler(w http.ResponseWriter, r *http.Request) {
	id := r.URL.Path[6:]
	// Resolve ID to server list
	val := dhtGet(id, false)
	if verify(id, val) != nil {
		w.WriteHeader(http.StatusNotFound)
		return
	}
	mu.Lock()
	if _, ok := users[id]; !ok {
		// Add user
		users[id] = &user{dhtVal: val, phase: 0}
		os.Mkdir(dataDir+"/"+id, 0755)
		persist(id)
	}
	mu.Unlock()

	reconfigure(id, val)

	w.WriteHeader(http.StatusOK)
}