C# The remote server returned an error: (500) Internal Server Error. GetRequest()

Http请求中的multipart/form-data,它会将表单的数据处理为一条消息，以标签为单元，用分隔符分开。既可以上传键值对，也可以上传文件。当上传的字段是文件时，会有Content-Type来表名文件类型；content-disposition用来说明字段的一些信息；由于有boundary隔离，所以multipart/form-data既可以上传文件，也可以上传键值对，它采用了键值对的方式，所以可以上传多个文件。

C#使用HttpRequest进行Post表单传送的时候爆 (500) Internal Server Error.
原因为ContentType设置为multipart/form-data;需要改为

string boundary = "----------------------------" + DateTime.Now.Ticks.ToString("x");
request.ContentType = "multipart/form-data; boundary="+boundary;

附C# multipart/form-data类型上传文件、表单代码:

//上传文件所需要的参数
public class UpLoadFile
{
    //上传名字
    public string Name { get; set; }
    //文件名
    public string FileName { get; set; }
    //文件全名 包含路径
    public string FileFullName { get; set; }
    //文件路径
    public string FilePath { get; set; }
    //文件Post上传路径
    public string FileContentType { get; set; }
}

/// <summary>
/// 发起httpPost 请求，可以上传文件
/// </summary>
/// <param name="url">请求的地址</param>
/// <param name="upLoadFiles">上传的文件参数</param>
/// <param name="formdatastrdict">表单数据</param>
/// <param name="headersdict">头文件</param>
/// <param name="endoding">编码类型</param>
/// <returns></returns>
public static string PostResponse(string url, List<UpLoadFile> upLoadFiles, Dictionary<string, string> formdatastrdict, Dictionary<string, string> headersdict, Encoding endoding)
{
    string boundary = "----------------------------" + DateTime.Now.Ticks.ToString("x");
    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
    //添加头文件
    if (headersdict != null)
    {
        foreach (var key in headersdict.Keys)
        {
            request.Headers.Add(key, headersdict[key]);
        }
    }
    request.ContentType = "multipart/form-data; boundary=" + boundary;
    request.Method = "POST";
    request.KeepAlive = true;
    //request.Credentials = CredentialCache.DefaultCredentials;
    request.Expect = "";
    MemoryStream stream = new MemoryStream();
    byte[] line = Encoding.ASCII.GetBytes("--" + boundary + "\r\n");
    byte[] enterER = Encoding.ASCII.GetBytes("\r\n");

    //提交文本字段
    if (formdatastrdict != null)
    {
        string format = "--" + boundary + "\r\nContent-Disposition:form-data;name=\"{0}\"\r\n\r\n{1}\r\n";    //自带项目分隔符
        foreach (string key in formdatastrdict.Keys)
        {
            string s = string.Format(format, key, formdatastrdict[key]);
            byte[] data = Encoding.UTF8.GetBytes(s);
            stream.Write(data, 0, data.Length);
        }
    }

    //提交文件 应放在文本后面
    if (upLoadFiles != null)
    {
        string fformat = "Content-Disposition:form-data; name=\"{0}\";filename=\"{1}\"\r\nContent-Type:{2}\r\n\r\n";
        foreach (var file in upLoadFiles)
        {
            stream.Write(line, 0, line.Length);        //项目分隔符
            //application/octet-stream
            string s = string.Format(fformat, file.Name, file.FileName, file.FileContentType);
            byte[] data = Encoding.UTF8.GetBytes(s);
            stream.Write(data, 0, data.Length);
            int bytesRead;
            byte[] buffer = new byte[1024];
            FileStream fileStream = new FileStream(file.FileFullName, FileMode.Open, FileAccess.Read);
            while ((bytesRead = fileStream.Read(buffer, 0, buffer.Length)) != 0)
            {
                //将文件流写入FormData项中
                stream.Write(buffer, 0, bytesRead);                             
            }
            //添加\r\n
            stream.Write(enterER, 0, enterER.Length); 
        }
    }
    //项目最后的分隔符字符串需要带上--  
    byte[] foot_data = Encoding.UTF8.GetBytes("--" + boundary + "--\r\n");      
    stream.Write(foot_data, 0, foot_data.Length);
    request.ContentLength = stream.Length;
    //写入请求数据
    Stream requestStream = request.GetRequestStream(); 
    stream.Position = 0L;
    stream.CopyTo(requestStream); 
    stream.Close();
    requestStream.Close();
    try
    {
        HttpWebResponse response;
        try
        {
            response = (HttpWebResponse)request.GetResponse();
            try
            {
                using (var responseStream = response.GetResponseStream())
                using (var mstream = new MemoryStream())
                {
                    responseStream.CopyTo(mstream);
                    string message = endoding.GetString(mstream.ToArray());
                    return message;
                }
            }
            catch (Exception ex)
            {
                throw ex;
            }
            finally
            {
                if (response != null)
                {
                    response.Close();
                }
                if (request != null)
                {
                    request.Abort();
                }
            }
        }
        catch (WebException ex)
        {
            //response = (HttpWebResponse)ex.Response;
            //if (response.StatusCode == HttpStatusCode.BadRequest)
            //{
            //    using (Stream data = response.GetResponseStream())
            //    {
            //        using (StreamReader reader = new StreamReader(data))
            //        {
            //            string text = reader.ReadToEnd();
            //            Console.WriteLine(text);
            //        }
            //    }
            //}
            throw ex;
        }
    }
    catch (Exception ex)
    {
        throw ex;
    }
}