Clivern/main.go

## main.go
package main

import (
	"encoding/json"
	"fmt"
	"net/http"
	"os"
)

func main() {
	// reCAPTCHA v2 "I'm not a robot" keys from https://www.google.com/recaptcha/admin
	siteKey := "~~~~~~~~~~~"
	secretKey := "~~~~~~~~~~~"

	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Content-Type", "text/html; charset=utf-8")
		fmt.Fprintf(w, pageHTML, siteKey)
	})

	http.HandleFunc("/verify", func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Content-Type", "application/json")

		token := r.Header.Get("X-Recaptcha-Token")
		ok, err := VerifyRecaptchaV2(secretKey, token, r.RemoteAddr)
		if !ok {
			writeJSON(w, map[string]any{"success": false, "error": err})
			return
		}
		writeJSON(w, map[string]any{"success": ok})
	})

	addr := ":8080"
	if p := os.Getenv("PORT"); p != "" {
		addr = ":" + p
	}
	fmt.Println("Listening on http://localhost" + addr)
	if err := http.ListenAndServe(addr, nil); err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}
}

func writeJSON(w http.ResponseWriter, v any) {
	enc := json.NewEncoder(w)
	_ = enc.Encode(v)
}

const pageHTML = `<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>reCAPTCHA v2 demo</title>
  <style>
    body { font-family: system-ui, sans-serif; max-width: 32rem; margin: 2rem auto; padding: 0 1rem; }
  </style>
  <script src="https://www.google.com/recaptcha/api.js" async defer></script>
</head>
<body>
  <h1>reCAPTCHA v2 demo</h1>
  <p>Check "I'm not a robot", complete the challenge if shown, then click Submit.</p>
  <form id="form">
    <div class="g-recaptcha" data-sitekey="%s"></div>
    <br>
    <button type="submit" id="submit-btn">Submit</button>
  </form>
  <div id="result"></div>
  <script>
    document.getElementById('form').onsubmit = function(e) {
      e.preventDefault();
      var btn = document.getElementById('submit-btn');
      btn.disabled = true;
      document.getElementById('result').textContent = 'Verifying...';
      var token = document.querySelector('[name="g-recaptcha-response"]').value;
      if (!token) { document.getElementById('result').textContent = 'Error: complete the reCAPTCHA first'; btn.disabled = false; return; }
      fetch('/verify', {
        method: 'POST',
        headers: { 'X-Recaptcha-Token': token },
        body: new FormData(e.target)
      })
        .then(function(r) { return r.json(); })
        .then(function(data) {
          if (data.success) {
            document.getElementById('result').textContent = 'Verification passed!';
          } else {
            document.getElementById('result').textContent = 'Error: ' + (data.error || 'verification failed');
          }
        })
        .catch(function(err) {
          document.getElementById('result').textContent = 'Error: ' + err.message;
        })
        .finally(function() { btn.disabled = false; });
    };
  </script>
</body>
</html>
`

## recaptcha.go
package main

import (
	"encoding/json"
	"io"
	"net/http"
	"net/url"
)

const (
	verifyURL = "https://www.google.com/recaptcha/api/siteverify"
)

type VerifyResponse struct {
	Success     bool     `json:"success"`
	ChallengeTS string   `json:"challenge_ts,omitempty"`
	Hostname    string   `json:"hostname,omitempty"`
	ErrorCodes  []string `json:"error-codes,omitempty"`
}

func VerifyRecaptchaV2(secret, response, remoteIP string) (ok bool, errMsg string) {
	resp, err := http.PostForm(verifyURL, url.Values{
		"secret":   {secret},
		"response": {response},
		"remoteip": {remoteIP},
	})
	if err != nil {
		return false, err.Error()
	}

	defer resp.Body.Close()
	body, err := io.ReadAll(resp.Body)

	if err != nil {
		return false, err.Error()
	}

	var v VerifyResponse
	if err := json.Unmarshal(body, &v); err != nil {
		return false, err.Error()
	}
	if !v.Success {
		if len(v.ErrorCodes) > 0 {
			return false, v.ErrorCodes[0]
		}
		return false, "verification failed"
	}
	return true, ""
}
	package main

	import (
	"encoding/json"
	"fmt"
	"net/http"
	"os"
	)

	func main() {
	// reCAPTCHA v2 "I'm not a robot" keys from https://www.google.com/recaptcha/admin
	siteKey := "~~~~~~~~~~~"
	secretKey := "~~~~~~~~~~~"

	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	fmt.Fprintf(w, pageHTML, siteKey)
	})

	http.HandleFunc("/verify", func(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "application/json")

	token := r.Header.Get("X-Recaptcha-Token")
	ok, err := VerifyRecaptchaV2(secretKey, token, r.RemoteAddr)
	if !ok {
	writeJSON(w, map[string]any{"success": false, "error": err})
	return
	}
	writeJSON(w, map[string]any{"success": ok})
	})

	addr := ":8080"
	if p := os.Getenv("PORT"); p != "" {
	addr = ":" + p
	}
	fmt.Println("Listening on http://localhost" + addr)
	if err := http.ListenAndServe(addr, nil); err != nil {
	fmt.Fprintln(os.Stderr, err)
	os.Exit(1)
	}
	}

	func writeJSON(w http.ResponseWriter, v any) {
	enc := json.NewEncoder(w)
	_ = enc.Encode(v)
	}

	const pageHTML = `<!DOCTYPE html>
	<html>
	<head>
	<meta charset="utf-8">
	<title>reCAPTCHA v2 demo</title>
	<style>
	body { font-family: system-ui, sans-serif; max-width: 32rem; margin: 2rem auto; padding: 0 1rem; }
	</style>
	<script src="https://www.google.com/recaptcha/api.js" async defer></script>
	</head>
	<body>
	<h1>reCAPTCHA v2 demo</h1>
	<p>Check "I'm not a robot", complete the challenge if shown, then click Submit.</p>
	<form id="form">
	<div class="g-recaptcha" data-sitekey="%s"></div>
	<br>
	<button type="submit" id="submit-btn">Submit</button>
	</form>
	<div id="result"></div>
	<script>
	document.getElementById('form').onsubmit = function(e) {
	e.preventDefault();
	var btn = document.getElementById('submit-btn');
	btn.disabled = true;
	document.getElementById('result').textContent = 'Verifying...';
	var token = document.querySelector('[name="g-recaptcha-response"]').value;
	if (!token) { document.getElementById('result').textContent = 'Error: complete the reCAPTCHA first'; btn.disabled = false; return; }
	fetch('/verify', {
	method: 'POST',
	headers: { 'X-Recaptcha-Token': token },
	body: new FormData(e.target)
	})
	.then(function(r) { return r.json(); })
	.then(function(data) {
	if (data.success) {
	document.getElementById('result').textContent = 'Verification passed!';
	} else {
	document.getElementById('result').textContent = 'Error: ' + (data.error \|\| 'verification failed');
	}
	})
	.catch(function(err) {
	document.getElementById('result').textContent = 'Error: ' + err.message;
	})
	.finally(function() { btn.disabled = false; });
	};
	</script>
	</body>
	</html>
	`
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