1 package mailmux
2 
3 import (
4 	"bufio"
5 	"errors"
6 	"fmt"
7 	"io"
8 	"math/rand"
9 	"os"
10 	"strings"
11 )
12 
13 func randomLine(f *os.File) (string, error) {
14 	fi, err := f.Stat()
15 	if err != nil {
16 		return "", err
17 	}
18 	offset := rand.Int63n(fi.Size())
19 	offset, err = f.Seek(offset, io.SeekStart)
20 	if err != nil {
21 		return "", err
22 	}
23 
24 	br := bufio.NewReader(f)
25 	for {
26 		b, err := br.ReadByte()
27 		if b == '\n' {
28 			break
29 		}
30 		if err != nil {
31 			return "", err
32 		}
33 	}
34 	line, err := br.ReadString('\n')
35 	if errors.Is(err, io.EOF) {
36 		// the file ends without a newline - no problem
37 	} else if err != nil {
38 		return "", err
39 	}
40 
41 	line = strings.TrimSpace(line)
42 	if line == "" {
43 		// empty line. we're either at the end or hit a blank line. try again
44 		return randomLine(f)
45 	}
46 	return line, nil
47 }
48 
49 // RandomUsername generates a random username from the dictionary file at dictpath.
50 // The dictionary file should be a newline delimited text file, one word per line.
51 // On Unix systems, the file /usr/share/dic/words is a suitable file.
52 func RandomUsername(dictpath string) (string, error) {
53 	f, err := os.Open(dictpath)
54 	if err != nil {
55 		return "", fmt.Errorf("open dictionary: %w", err)
56 	}
57 	defer f.Close()
58 
59 	first, err := randomLine(f)
60 	if err != nil {
61 		return "", fmt.Errorf("first random word: %w", err)
62 	}
63 	first = strings.ToLower(first)
64 	second, err := randomLine(f)
65 	if err != nil {
66 		return "", fmt.Errorf("second random word: %w", err)
67 	}
68 	second = strings.ToLower(second)
69 
70 	return fmt.Sprintf("%s_%s%02d", first, second, rand.Intn(99)), nil
71 }