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captcha/captcha.go

290 lines
7.1 KiB
Go

// Package captcha provides an easy to use, unopinionated API for captcha generation
package captcha
import (
"bytes"
"github.com/golang/freetype"
"github.com/golang/freetype/truetype"
"golang.org/x/image/font"
"image"
"image/color"
"image/draw"
"image/png"
"io"
"math"
"math/rand"
"strconv"
"time"
)
const charPreset = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"
var rng = rand.New(rand.NewSource(time.Now().UnixNano()))
var ttfFont *truetype.Font
// Options manage captcha generation details.
type Options struct {
// BackgroundColor is captcha image's background color.
// It defaults to color.Transparent.
BackgroundColor color.Color
// CharPreset decides what text will be on captcha image.
// It defaults to digit 0-9 and all English alphabet.
// ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789
CharPreset string
// TextLength is the length of captcha text.
// It defaults to 4.
TextLength int
// CurveNumber is the number of curves to draw on captcha image.
// It defaults to 2.
CurveNumber int
// FontDPI controls DPI (dots per inch) of font.
// The default is 72.0.
FontDPI float64
// FontScale controls the scale of font.
// The default is 1.0.
FontScale float64
width int
height int
}
func newDefaultOption(width, height int) *Options {
return &Options{
BackgroundColor: color.Transparent,
CharPreset: charPreset,
TextLength: 4,
CurveNumber: 2,
FontDPI: 72.0,
FontScale: 1.0,
width: width,
height: height,
}
}
// SetOption is a function that can be used to modify default options.
type SetOption func(*Options)
// Data is the result of captcha generation.
// It has a `Text` field and a private `img` field that will
// be used in `WriteImage` receiver
type Data struct {
// Text is captcha solution
Text string
img *image.NRGBA
}
// WriteImage encodes image data and writes to an io.Writer.
// It returns possible error from PNG encoding
func (data *Data) WriteImage(w io.Writer) error {
return png.Encode(w, data.img)
}
func init() {
ttfFont, _ = freetype.ParseFont(ttf)
}
// LoadFont let you load an external font.
func LoadFont(fontData []byte) error {
var err error
ttfFont, err = freetype.ParseFont(fontData)
return err
}
// LoadFontFromReader load an external font from an io.Reader interface.
func LoadFontFromReader(reader io.Reader) error {
var buf bytes.Buffer
if _, err := io.Copy(&buf, reader); err != nil {
return err
}
return LoadFont(buf.Bytes())
}
// New creates a new captcha.
// It returns captcha data and any freetype drawing error encountered
func New(width int, height int, option ...SetOption) (*Data, error) {
options := newDefaultOption(width, height)
for _, setOption := range option {
setOption(options)
}
text := randomText(options)
img := image.NewNRGBA(image.Rect(0, 0, width, height))
draw.Draw(img, img.Bounds(), &image.Uniform{options.BackgroundColor}, image.ZP, draw.Src)
drawNoise(img, options)
drawCurves(img, options)
err := drawText(text, img, options)
if err != nil {
return nil, err
}
return &Data{Text: text, img: img}, nil
}
// NewMathExpr creates a new captcha.
// It will generate a image with a math expression like `1 + 2`
func NewMathExpr(width int, height int, option ...SetOption) (*Data, error) {
options := newDefaultOption(width, height)
for _, setOption := range option {
setOption(options)
}
text, equation := randomEquation()
img := image.NewNRGBA(image.Rect(0, 0, width, height))
draw.Draw(img, img.Bounds(), &image.Uniform{options.BackgroundColor}, image.ZP, draw.Src)
drawNoise(img, options)
drawCurves(img, options)
err := drawText(equation, img, options)
if err != nil {
return nil, err
}
return &Data{Text: text, img: img}, nil
}
func randomText(opts *Options) (text string) {
n := len(opts.CharPreset)
for i := 0; i < opts.TextLength; i++ {
text += string(opts.CharPreset[rng.Intn(n)])
}
return text
}
func drawNoise(img *image.NRGBA, opts *Options) {
noiseCount := (opts.width * opts.height) / 28
for i := 0; i < noiseCount; i++ {
x := rng.Intn(opts.width)
y := rng.Intn(opts.height)
img.Set(x, y, randomColor())
}
}
func randomColor() color.RGBA {
red := rng.Intn(255)
green := rng.Intn(255)
blue := rng.Intn(255)
return color.RGBA{R: uint8(red), G: uint8(green), B: uint8(blue), A: uint8(255)}
}
func drawCurves(img *image.NRGBA, opts *Options) {
for i := 0; i < opts.CurveNumber; i++ {
drawSineCurve(img, opts)
}
}
// Ideally we want to draw bezier curves
// For now sine curves will do the job
func drawSineCurve(img *image.NRGBA, opts *Options) {
var xStart, xEnd int
if opts.width <= 40 {
xStart, xEnd = 1, opts.width-1
} else {
xStart = rng.Intn(opts.width/10) + 1
xEnd = opts.width - rng.Intn(opts.width/10) - 1
}
curveHeight := float64(rng.Intn(opts.height/6) + opts.height/6)
yStart := rng.Intn(opts.height*2/3) + opts.height/6
angle := 1.0 + rng.Float64()
flip := rng.Intn(2) == 0
yFlip := 1.0
if flip {
yFlip = -1.0
}
curveColor := randomInvertColor(opts.BackgroundColor)
for x1 := xStart; x1 <= xEnd; x1++ {
y := math.Sin(math.Pi*angle*float64(x1)/float64(opts.width)) * curveHeight * yFlip
img.Set(x1, int(y)+yStart, curveColor)
}
}
func drawText(text string, img *image.NRGBA, opts *Options) error {
ctx := freetype.NewContext()
ctx.SetDPI(opts.FontDPI)
ctx.SetClip(img.Bounds())
ctx.SetDst(img)
ctx.SetHinting(font.HintingFull)
ctx.SetFont(ttfFont)
fontSpacing := opts.width / len(text)
fontOffset := rng.Intn(fontSpacing / 2)
for idx, char := range text {
fontScale := 0.8 + rng.Float64()*0.4
fontSize := float64(opts.height) / fontScale * opts.FontScale
ctx.SetFontSize(fontSize)
ctx.SetSrc(image.NewUniform(randomInvertColor(opts.BackgroundColor)))
x := fontSpacing*idx + fontOffset
y := opts.height/6 + rng.Intn(opts.height/3) + int(fontSize/2)
pt := freetype.Pt(x, y)
if _, err := ctx.DrawString(string(char), pt); err != nil {
return err
}
}
return nil
}
func randomInvertColor(base color.Color) color.Color {
baseLightness := getLightness(base)
var value float64
if baseLightness >= 0.5 {
value = baseLightness - 0.3 - rng.Float64()*0.2
} else {
value = baseLightness + 0.3 + rng.Float64()*0.2
}
hue := float64(rng.Intn(361)) / 360
saturation := 0.6 + rng.Float64()*0.2
return hsva{h: hue, s: saturation, v: value, a: uint8(255)}
}
func getLightness(colour color.Color) float64 {
r, g, b, a := colour.RGBA()
// transparent
if a == 0 {
return 1.0
}
max := maxColor(r, g, b)
min := minColor(r, g, b)
l := (float64(max) + float64(min)) / (2 * 255)
return l
}
func maxColor(numList ...uint32) (max uint32) {
for _, num := range numList {
colorVal := num & 255
if colorVal > max {
max = colorVal
}
}
return max
}
func minColor(numList ...uint32) (min uint32) {
min = 255
for _, num := range numList {
colorVal := num & 255
if colorVal < min {
min = colorVal
}
}
return min
}
func randomEquation() (text string, equation string) {
left := 1 + rng.Intn(9)
right := 1 + rng.Intn(9)
text = strconv.Itoa(left + right)
equation = strconv.Itoa(left) + "+" + strconv.Itoa(right)
return text, equation
}