從 URL 下載將圖像轉換為 Base64 字符串

Question

我有問題，我想將圖像從 url 轉換為 base64，但出現錯誤

這是 url： https://www.jotform.com/widget-uploads/imagePreview/92613577901663/2922362Principios%20-%20Resultados.png

    public String ConvertImageURLToBase64(String url)
    {
        StringBuilder sb = new StringBuilder();

        Byte[] vbyte = this.GetImage(url);

        sb.Append(Convert.ToBase64String(vbyte, 0, vbyte.Length));

        return sb.ToString();
    }

    private byte[] GetImage(string url)
    {
        Stream stream = null;
        byte[] buf;

        try
        {
            WebProxy myProxy = new WebProxy();
            HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);

            HttpWebResponse response = (HttpWebResponse)req.GetResponse();
            stream = response.GetResponseStream();

            using (BinaryReader br = new BinaryReader(stream))
            {
                int len = (int)(response.ContentLength);
                buf = br.ReadBytes(len);
                br.Close();
            }

            stream.Close();
            response.Close();
        }
        catch (Exception exp)
        {
            buf = null;
        }

        return (buf);
    }

Answer 1

這是執行中出現的錯誤：

Answer 2

您似乎正在使用來自沒有響應的服務器的Content-Length響應，因此您使用默認值 -1 來創建一個數組。 這是失敗的，但有以下例外：

 Exception thrown: 'System.ArgumentOutOfRangeException' in mscorlib.dll An unhandled exception of type 'System.ArgumentOutOfRangeException' occurred in mscorlib.dll Non-negative number required.

您可以通過忽略從服務器返回的內容長度來解決此問題，並將所有數據讀入 memory 直到響應完成：

byte[] GetImage(string url)
{
    Stream stream = null;
    byte[] buf;

    try
    {
        WebProxy myProxy = new WebProxy();
        HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);

        HttpWebResponse response = (HttpWebResponse)req.GetResponse();
        stream = response.GetResponseStream();

        using (MemoryStream ms = new MemoryStream())
        {
            stream.CopyTo(ms);
            buf = ms.ToArray();
        }

        stream.Close();
        response.Close();
    }
    catch (Exception exp)
    {
        buf = null;
    }

    return (buf);
}

並且供將來參考：如果您顯示在try / catch塊中看到的異常，則調試這些類型的錯誤會容易得多，因此您對錯誤是什么有所了解。