1package captcha
 2
 3import (
 4	"bytes"
 5	"crypto/rand"
 6	"github.com/dchest/uniuri"
 7	"io"
 8	"os"
 9)
10
11// Standard number of numbers in captcha
12const StdLength = 6
13
14var globalStore = newStore()
15
16// randomNumbers return a byte slice of the given length containing random
17// numbers in range 0-9.
18func randomNumbers(length int) []byte {
19	n := make([]byte, length)
20	if _, err := io.ReadFull(rand.Reader, n); err != nil {
21		panic(err)
22	}
23	for i := range n {
24		n[i] %= 10
25	}
26	return n
27}
28
29// New creates a new captcha of the given length, saves it in the internal
30// storage, and returns its id.
31func New(length int) (id string) {
32	id = uniuri.New()
33	globalStore.saveCaptcha(id, randomNumbers(length))
34	return
35}
36
37// Reload generates new numbers for the given captcha id.  This function does
38// nothing if there is no captcha with the given id.
39//
40// After calling this function, the image presented to a user must be refreshed
41// to show the new captcha (WriteImage will write the new one).
42func Reload(id string) {
43	oldns := globalStore.getNumbers(id)
44	if oldns == nil {
45		return
46	}
47	globalStore.saveCaptcha(id, randomNumbers(len(oldns)))
48}
49
50// WriteImage writes PNG-encoded captcha image of the given width and height
51// with the given captcha id into the io.Writer.
52func WriteImage(w io.Writer, id string, width, height int) os.Error {
53	ns := globalStore.getNumbers(id)
54	if ns == nil {
55		return os.NewError("captcha id not found")
56	}
57	return NewImage(ns, width, height).PNGEncode(w)
58}
59
60// Verify returns true if the given numbers are the numbers that were used to
61// create the given captcha id.
62// 
63// The function deletes the captcha with the given id from the internal
64// storage, so that the same captcha can't be verified anymore.
65func Verify(id string, numbers []byte) bool {
66	realns := globalStore.getNumbersClear(id)
67	if realns == nil {
68		return false
69	}
70	return bytes.Equal(numbers, realns)
71}
72
73// Collect deletes expired and used captchas from the internal
74// storage. It is called automatically by New function every CollectNum
75// generated captchas, but still exported to enable freeing memory manually if
76// needed.
77//
78// Collection is launched in a new goroutine, so this function returns
79// immediately.
80func Collect() {
81	go globalStore.collect()
82}