分享一个模拟提交带文件的表单的方法

public string PostFormData(List<FormItem> list, string uri)        {            string boundary = "---------------------------" + DateTime.Now.Ticks.ToString("x");            //请求             WebRequest req = WebRequest.Create(uri);            req.Method = "POST";            req.ContentType = "multipart/form-data; boundary=" + boundary;            //���织表单数据             StringBuilder sb = new StringBuilder();            foreach (FormItem item in list)            {                switch (item.ParamType)                {                    case ParamType.Text:                        sb.Append("--" + boundary);                        sb.Append("\r\n");                        sb.Append("Content-Disposition: form-data; name=\"" + item.Name + "\"");                        sb.Append("\r\n\r\n");                        sb.Append(item.Value);                        sb.Append("\r\n");                        break;                    case ParamType.File:                        sb.Append("--" + boundary);                        sb.Append("\r\n");                        sb.Append("Content-Disposition: form-data; name=\"" + item.Name + "\"; filename=\"" + item.Value + "\"");                        sb.Append("\r\n");                        sb.Append("Content-Type: application/octet-stream");                        sb.Append("\r\n\r\n");                        break;                }            }            string head = sb.ToString();            //post字节总长度            long length = 0;            byte[] form_data = Encoding.UTF8.GetBytes(head);            //结尾             byte[] foot_data = Encoding.UTF8.GetBytes("\r\n--" + boundary + "--\r\n");            List<FormItem> fileList = list.Where(f => f.ParamType == ParamType.File).ToList();            length = form_data.Length + foot_data.Length;            foreach (FormItem fi in fileList)            {                FileStream fileStream = new FileStream(fi.Value, FileMode.Open, FileAccess.Read);                length += fileStream.Length;                fileStream.Close();            }            req.ContentLength = length;            Stream requestStream = req.GetRequestStream();            //发送表单参数             requestStream.Write(form_data, 0, form_data.Length);            foreach (FormItem fd in fileList)            {                FileStream fileStream = new FileStream(fd.Value, FileMode.Open, FileAccess.Read);                //文件内容                 byte[] buffer = new Byte[checked((uint)Math.Min(4096, (int)fileStream.Length))];                int bytesRead = 0;                while ((bytesRead = fileStream.Read(buffer, 0, buffer.Length)) != 0)                    requestStream.Write(buffer, 0, bytesRead);                //结尾                 requestStream.Write(foot_data, 0, foot_data.Length);            }            requestStream.Close();            //响应             WebResponse pos = req.GetResponse();            StreamReader sr = new StreamReader(pos.GetResponseStream(), Encoding.UTF8);            string html = sr.ReadToEnd().Trim();            sr.Close();            if (pos != null)            {                pos.Close();                pos = null;            }            if (req != null)            {                req = null;            }            return html;        }        public string SaveFileFromUrl(string fileName, string url)        {            WebResponse response = null;            Stream stream = null;            try            {                HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);                response = request.GetResponse();                stream = response.GetResponseStream();                if (!response.ContentType.ToLower().StartsWith("text/"))                {                    SaveBinaryFile(response, fileName);                }                else                {                    StreamReader sr = new StreamReader(stream, System.Text.Encoding.UTF8);                    return sr.ReadToEnd();                }            }            catch (Exception err)            {                return err.ToString();            }            return "complete";        }        public bool SaveBinaryFile(WebResponse response, string fileName)        {            bool value = true;            byte[] buffer = new byte[1024];            try            {                if (System.IO.File.Exists(fileName))                    System.IO.File.Delete(fileName);                Stream outStream = System.IO.File.Create(fileName);                Stream inStream = response.GetResponseStream();                int l;                do                {                    l = inStream.Read(buffer, 0, buffer.Length);                    if (l > 0)                        outStream.Write(buffer, 0, l);                }                while (l > 0);                outStream.Close();                inStream.Close();            }            catch            {                value = false;            }            return value;        }        public class FormItem        {            public string Name { get; set; }            public ParamType ParamType { get; set; }            public string Value { get; set; }        }        public enum ParamType        {            Text,            File        }