go captcha

🧩 go captcha is a simple, lightweight library for generating and verifying image-based CAPTCHA codes written in Go.

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✨ Features

• 🖼️ Generate CAPTCHA images with customizable size and font
• 🔐 Built-in encryption for secure token handling
• 🧠 Optional cache drivers: in-memory or Redis
• ⚙️ Flexible configuration using options pattern
• 💨 Zero external dependencies (except freetype and go-redis/v9)

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🚀 Installation

go get github.com/kal72/go-captcha@latest

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🧱 Usage Example

Basic Example

package main

import (
    "fmt"
    "github.com/kal72/go-captcha"
)

func main() {
    cap := captcha.New("secret-key")

    base64Image, text, token, err := cap.Generate()
	if err != nil {
		panic(err)
	}

	fmt.Println("text: " + text)
	fmt.Println("token: " + token)
	fmt.Println("image: " + base64Image)

    // Verify
    _, err = cap.Verify(text, token)
	if err != nil {
		panic("verify failed: " + err.Error())
	} else {
        fmt.Println("verify success ")
    }
}

Using Redis Driver

import (
    "github.com/kal72/go-captcha"
    "github.com/kal72/go-captcha/driver/redisstore"
)

cap := captcha.New("secret-key",
    captcha.WithStore(redisstore.New(redisstore.Config{
        Addr: "localhost:6379",
        Password: "pass",
        DB: 0,
        Prefix: "captcha",
    })),
)

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📸 Example CAPTCHA Image

Example output image generated:

CAPTCHA Example

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⚙️ Configuration Options

Option	Description
WithLength(n int)	Number of characters in the CAPTCHA code
WithSize(width, height int)	CAPTCHA image size in pixels
WithFontSize(size int)	Font size in pixels
WithExpire(seconds int)	Expiration time in seconds
WithStore(store Store)	Use custom store driver (memory, Redis, or your own)

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🧩 Custom Driver

To create a custom driver, implement the Store interface:

type Store interface {
    Set(key, value string, ttl time.Duration) error
    Get(key string) (string, error)
    Delete(key string) error
}

Then register it via:

captcha.WithStore(myCustomDriver)

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🖋️ Example Directory

See full runnable examples in the examples/ folder:

examples/
 ├── basic/
 ├── redis/

Run an example:

go run ./examples/basic/main.go

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📦 Project Structure

gocaptcha/
├── captcha.go
├── config.go
├── store.go
├── driver/
│   ├── memorystore/
│   └── redisstore/
├── internal/
│   ├── image/
│   ├── random/
│   └── assets/
│       └── fonts/
│           └── DejaVuSans-Bold.ttf
└── examples/