Stanislav N. aka pztrn
850fbb55ab
Added captcha generation. As we're working without JS - there is no possibility to reload image, only if user will reload whole web page. Some design works - set monospace font for paste textarea (will use system-defined default monospace font) and lowered font size in paste views.
276 lines
8.4 KiB
Markdown
276 lines
8.4 KiB
Markdown
Package captcha
|
|
=====================
|
|
|
|
import "github.com/dchest/captcha"
|
|
|
|
Package captcha implements generation and verification of image and audio
|
|
CAPTCHAs.
|
|
|
|
A captcha solution is the sequence of digits 0-9 with the defined length.
|
|
There are two captcha representations: image and audio.
|
|
|
|
An image representation is a PNG-encoded image with the solution printed on
|
|
it in such a way that makes it hard for computers to solve it using OCR.
|
|
|
|
An audio representation is a WAVE-encoded (8 kHz unsigned 8-bit) sound with the
|
|
spoken solution (currently in English, Russian, Chinese, and Japanese). To make
|
|
it hard for computers to solve audio captcha, the voice that pronounces numbers
|
|
has random speed and pitch, and there is a randomly generated background noise
|
|
mixed into the sound.
|
|
|
|
This package doesn't require external files or libraries to generate captcha
|
|
representations; it is self-contained.
|
|
|
|
To make captchas one-time, the package includes a memory storage that stores
|
|
captcha ids, their solutions, and expiration time. Used captchas are removed
|
|
from the store immediately after calling Verify or VerifyString, while
|
|
unused captchas (user loaded a page with captcha, but didn't submit the
|
|
form) are collected automatically after the predefined expiration time.
|
|
Developers can also provide custom store (for example, which saves captcha
|
|
ids and solutions in database) by implementing Store interface and
|
|
registering the object with SetCustomStore.
|
|
|
|
Captchas are created by calling New, which returns the captcha id. Their
|
|
representations, though, are created on-the-fly by calling WriteImage or
|
|
WriteAudio functions. Created representations are not stored anywhere, but
|
|
subsequent calls to these functions with the same id will write the same
|
|
captcha solution. Reload function will create a new different solution for the
|
|
provided captcha, allowing users to "reload" captcha if they can't solve the
|
|
displayed one without reloading the whole page. Verify and VerifyString are
|
|
used to verify that the given solution is the right one for the given captcha
|
|
id.
|
|
|
|
Server provides an http.Handler which can serve image and audio
|
|
representations of captchas automatically from the URL. It can also be used
|
|
to reload captchas. Refer to Server function documentation for details, or
|
|
take a look at the example in "capexample" subdirectory.
|
|
|
|
|
|
Examples
|
|
--------
|
|
|
|
|
|
|
|
[Audio](https://github.com/dchest/captcha/raw/master/capgen/example.wav)
|
|
|
|
|
|
Constants
|
|
---------
|
|
|
|
``` go
|
|
const (
|
|
// Default number of digits in captcha solution.
|
|
DefaultLen = 6
|
|
// The number of captchas created that triggers garbage collection used
|
|
// by default store.
|
|
CollectNum = 100
|
|
// Expiration time of captchas used by default store.
|
|
Expiration = 10 * time.Minute
|
|
)
|
|
```
|
|
|
|
``` go
|
|
const (
|
|
// Standard width and height of a captcha image.
|
|
StdWidth = 240
|
|
StdHeight = 80
|
|
)
|
|
```
|
|
|
|
|
|
Variables
|
|
---------
|
|
|
|
``` go
|
|
var (
|
|
ErrNotFound = errors.New("captcha: id not found")
|
|
)
|
|
```
|
|
|
|
|
|
|
|
Functions
|
|
---------
|
|
|
|
### func New
|
|
|
|
func New() string
|
|
|
|
New creates a new captcha with the standard length, saves it in the internal
|
|
storage and returns its id.
|
|
|
|
### func NewLen
|
|
|
|
func NewLen(length int) (id string)
|
|
|
|
NewLen is just like New, but accepts length of a captcha solution as the
|
|
argument.
|
|
|
|
### func RandomDigits
|
|
|
|
func RandomDigits(length int) (b []byte)
|
|
|
|
RandomDigits returns a byte slice of the given length containing
|
|
pseudorandom numbers in range 0-9. The slice can be used as a captcha
|
|
solution.
|
|
|
|
### func Reload
|
|
|
|
func Reload(id string) bool
|
|
|
|
Reload generates and remembers new digits for the given captcha id. This
|
|
function returns false if there is no captcha with the given id.
|
|
|
|
After calling this function, the image or audio presented to a user must be
|
|
refreshed to show the new captcha representation (WriteImage and WriteAudio
|
|
will write the new one).
|
|
|
|
### func Server
|
|
|
|
func Server(imgWidth, imgHeight int) http.Handler
|
|
|
|
Server returns a handler that serves HTTP requests with image or
|
|
audio representations of captchas. Image dimensions are accepted as
|
|
arguments. The server decides which captcha to serve based on the last URL
|
|
path component: file name part must contain a captcha id, file extension —
|
|
its format (PNG or WAV).
|
|
|
|
For example, for file name "LBm5vMjHDtdUfaWYXiQX.png" it serves an image captcha
|
|
with id "LBm5vMjHDtdUfaWYXiQX", and for "LBm5vMjHDtdUfaWYXiQX.wav" it serves the
|
|
same captcha in audio format.
|
|
|
|
To serve a captcha as a downloadable file, the URL must be constructed in
|
|
such a way as if the file to serve is in the "download" subdirectory:
|
|
"/download/LBm5vMjHDtdUfaWYXiQX.wav".
|
|
|
|
To reload captcha (get a different solution for the same captcha id), append
|
|
"?reload=x" to URL, where x may be anything (for example, current time or a
|
|
random number to make browsers refetch an image instead of loading it from
|
|
cache).
|
|
|
|
By default, the Server serves audio in English language. To serve audio
|
|
captcha in one of the other supported languages, append "lang" value, for
|
|
example, "?lang=ru".
|
|
|
|
### func SetCustomStore
|
|
|
|
func SetCustomStore(s Store)
|
|
|
|
SetCustomStore sets custom storage for captchas, replacing the default
|
|
memory store. This function must be called before generating any captchas.
|
|
|
|
### func Verify
|
|
|
|
func Verify(id string, digits []byte) bool
|
|
|
|
Verify returns true if the given digits are the ones that were used to
|
|
create the given captcha id.
|
|
|
|
The function deletes the captcha with the given id from the internal
|
|
storage, so that the same captcha can't be verified anymore.
|
|
|
|
### func VerifyString
|
|
|
|
func VerifyString(id string, digits string) bool
|
|
|
|
VerifyString is like Verify, but accepts a string of digits. It removes
|
|
spaces and commas from the string, but any other characters, apart from
|
|
digits and listed above, will cause the function to return false.
|
|
|
|
### func WriteAudio
|
|
|
|
func WriteAudio(w io.Writer, id string, lang string) error
|
|
|
|
WriteAudio writes WAV-encoded audio representation of the captcha with the
|
|
given id and the given language. If there are no sounds for the given
|
|
language, English is used.
|
|
|
|
### func WriteImage
|
|
|
|
func WriteImage(w io.Writer, id string, width, height int) error
|
|
|
|
WriteImage writes PNG-encoded image representation of the captcha with the
|
|
given id. The image will have the given width and height.
|
|
|
|
|
|
Types
|
|
-----
|
|
|
|
``` go
|
|
type Audio struct {
|
|
// contains unexported fields
|
|
}
|
|
```
|
|
|
|
|
|
### func NewAudio
|
|
|
|
func NewAudio(id string, digits []byte, lang string) *Audio
|
|
|
|
NewAudio returns a new audio captcha with the given digits, where each digit
|
|
must be in range 0-9. Digits are pronounced in the given language. If there
|
|
are no sounds for the given language, English is used.
|
|
|
|
Possible values for lang are "en", "ja", "ru", "zh".
|
|
|
|
### func (*Audio) EncodedLen
|
|
|
|
func (a *Audio) EncodedLen() int
|
|
|
|
EncodedLen returns the length of WAV-encoded audio captcha.
|
|
|
|
### func (*Audio) WriteTo
|
|
|
|
func (a *Audio) WriteTo(w io.Writer) (n int64, err error)
|
|
|
|
WriteTo writes captcha audio in WAVE format into the given io.Writer, and
|
|
returns the number of bytes written and an error if any.
|
|
|
|
``` go
|
|
type Image struct {
|
|
*image.Paletted
|
|
// contains unexported fields
|
|
}
|
|
```
|
|
|
|
|
|
### func NewImage
|
|
|
|
func NewImage(id string, digits []byte, width, height int) *Image
|
|
|
|
NewImage returns a new captcha image of the given width and height with the
|
|
given digits, where each digit must be in range 0-9.
|
|
|
|
### func (*Image) WriteTo
|
|
|
|
func (m *Image) WriteTo(w io.Writer) (int64, error)
|
|
|
|
WriteTo writes captcha image in PNG format into the given writer.
|
|
|
|
``` go
|
|
type Store interface {
|
|
// Set sets the digits for the captcha id.
|
|
Set(id string, digits []byte)
|
|
|
|
// Get returns stored digits for the captcha id. Clear indicates
|
|
// whether the captcha must be deleted from the store.
|
|
Get(id string, clear bool) (digits []byte)
|
|
}
|
|
```
|
|
|
|
An object implementing Store interface can be registered with SetCustomStore
|
|
function to handle storage and retrieval of captcha ids and solutions for
|
|
them, replacing the default memory store.
|
|
|
|
It is the responsibility of an object to delete expired and used captchas
|
|
when necessary (for example, the default memory store collects them in Set
|
|
method after the certain amount of captchas has been stored.)
|
|
|
|
### func NewMemoryStore
|
|
|
|
func NewMemoryStore(collectNum int, expiration time.Duration) Store
|
|
|
|
NewMemoryStore returns a new standard memory store for captchas with the
|
|
given collection threshold and expiration time in seconds. The returned
|
|
store must be registered with SetCustomStore to replace the default one.
|