Question

I am creating an application for a company that will fill form in windows application and a post request will be sent to the server to sign up the user.

In order to send a POST request i used curl

    private void post_data(string url, string data)
    {
        Curl.GlobalInit((int)CURLinitFlag.CURL_GLOBAL_ALL);

        Easy e = new Easy();
        Easy.WriteFunction wf = MyWriteFunction;

        e.SetOpt(CURLoption.CURLOPT_URL, url);
        e.SetOpt(CURLoption.CURLOPT_POSTFIELDS, data);
        e.SetOpt(CURLoption.CURLOPT_WRITEFUNCTION, wf);
        e.Perform();
        e.Cleanup();
    }

    private int MyWriteFunction(byte[] buf, int size, int nmemb, Object extraData)
    {
        StreamWriter sw = new StreamWriter(@"curl.txt");

        foreach (byte b in buf)
        {
            sw.Write(((char)b));
        }
        sw.Flush();
        sw.Close();

        return buf.Length;
    }

And in order to extract the Captcha image path from source code and let the user type the text

    private void Get_Captcha_Image(string url)
    {
        Curl.GlobalInit((int)CURLinitFlag.CURL_GLOBAL_ALL);

        Easy e = new Easy();
        Easy.WriteFunction wf = MyWriteFunction;
        e.SetOpt(CURLoption.CURLOPT_URL, url);
        e.SetOpt(CURLoption.CURLOPT_WRITEFUNCTION, wf);
        e.Perform();
        e.Cleanup();

        get_ca_2();
    }

    private void get_ca_2()
    {
        Regex r = new Regex(@"(?<=src=('|""))https?://.*?(?=\1)");

        foreach (string line in File.ReadAllLines("curl.txt"))
        {
            Match m = r.Match(line);

            if (m.Success)
            {
                if (m.Value.Contains("http://www.google.com/recaptcha/api/image?c="))
                {
                    pictureBox1.ImageLocation = m.Value;
                }
            }
        }
    }

But what i noticed is that

<img width="300" height="57" src="http://www.google.com/recaptcha/api/image?c=03AHJ_VuvnenuZSRbfL_JTQLTYKFYzEFTkYrDgedu0SLyYvTDhsr2hHjQPwYlGJiP3dJRewkIhhdeILAd1_61_aFfU2dclbf8uovme-0gF3nm8Y7-LQVfaDQoI35bo3c35pOnF-xSY3Qfy_lh8TzhSWlMemEnkYnDpZw" alt="reCAPTCHA challenge image" style="display:block;">

For example is not present on the extracted webpage source code using curl

I tired a webbrowser and hide it and i was able to find the captcha image and i was successful on posting data , but i need to figure it on curl

Answer 1

I would investigate whether the website content changes based on your headers. Obviously the headers from curl are going to look very different from those from, say, IE. Try using a browser that lets you fake different user-agent and so on, see if that changes it. It might be as easy as using curl’s –user-agent flag.