go-tg-screenshot-bot

1
package xgb
2

3
/*
4
auth.go contains functions to facilitate the parsing of .Xauthority files.
5

6
It is largely unmodified from the original XGB package that I forked.
7
*/
8

9
import (
10
	"encoding/binary"
11
	"errors"
12
	"io"
13
	"os"
14
)
15

16
// readAuthority reads the X authority file for the DISPLAY.
17
// If hostname == "" or hostname == "localhost",
18
// then use the system's hostname (as returned by os.Hostname) instead.
19
func readAuthority(hostname, display string) (
20
	name string, data []byte, err error) {
21

22
	// b is a scratch buffer to use and should be at least 256 bytes long
23
	// (i.e. it should be able to hold a hostname).
24
	b := make([]byte, 256)
25

26
	// As per /usr/include/X11/Xauth.h.
27
	const familyLocal = 256
28
	const familyWild = 65535
29

30
	if len(hostname) == 0 || hostname == "localhost" {
31
		hostname, err = os.Hostname()
32
		if err != nil {
33
			return "", nil, err
34
		}
35
	}
36

37
	fname := os.Getenv("XAUTHORITY")
38
	if len(fname) == 0 {
39
		home := os.Getenv("HOME")
40
		if len(home) == 0 {
41
			err = errors.New("Xauthority not found: $XAUTHORITY, $HOME not set")
42
			return "", nil, err
43
		}
44
		fname = home + "/.Xauthority"
45
	}
46

47
	r, err := os.Open(fname)
48
	if err != nil {
49
		return "", nil, err
50
	}
51
	defer r.Close()
52

53
	for {
54
		var family uint16
55
		if err := binary.Read(r, binary.BigEndian, &family); err != nil {
56
			return "", nil, err
57
		}
58

59
		addr, err := getString(r, b)
60
		if err != nil {
61
			return "", nil, err
62
		}
63

64
		disp, err := getString(r, b)
65
		if err != nil {
66
			return "", nil, err
67
		}
68

69
		name0, err := getString(r, b)
70
		if err != nil {
71
			return "", nil, err
72
		}
73

74
		data0, err := getBytes(r, b)
75
		if err != nil {
76
			return "", nil, err
77
		}
78

79
		addrmatch := (family == familyWild) ||
80
			(family == familyLocal && addr == hostname)
81
		dispmatch := (disp == "") || (disp == display)
82

83
		if addrmatch && dispmatch {
84
			return name0, data0, nil
85
		}
86
	}
87
	panic("unreachable")
88
}
89

90
func getBytes(r io.Reader, b []byte) ([]byte, error) {
91
	var n uint16
92
	if err := binary.Read(r, binary.BigEndian, &n); err != nil {
93
		return nil, err
94
	} else if n > uint16(len(b)) {
95
		return nil, errors.New("bytes too long for buffer")
96
	}
97

98
	if _, err := io.ReadFull(r, b[0:n]); err != nil {
99
		return nil, err
100
	}
101
	return b[0:n], nil
102
}
103

104
func getString(r io.Reader, b []byte) (string, error) {
105
	b, err := getBytes(r, b)
106
	if err != nil {
107
		return "", err
108
	}
109
	return string(b), nil
110
}
111