C#采用HttpWebRequest实现保持会话上传文件到HTTP的方法

<form action ="http://localhost/test.php" method = POST>  <input type = text name = uname>  <input type = password name =passwd>  <input type = FILE name = uploadfile>  <input type=submit> </form> 

public static string UploadFileEx( string uploadfile, string url,    string fileFormName, string contenttype,NameValueCollection querystring,    CookieContainer cookies)  {    if( (fileFormName== null) ||      (fileFormName.Length ==0))    {      fileFormName = "file";    }     if( (contenttype== null) ||      (contenttype.Length ==0))    {      contenttype = "application/octet-stream";    }     string postdata;    postdata = "?";    if (querystring!=null)    {      foreach(string key in querystring.Keys)      {        postdata+= key +"=" + querystring.Get(key)+"&";      }    }    Uri uri = new Uri(url+postdata);    string boundary = "----------" + DateTime.Now.Ticks.ToString("x");    HttpWebRequest webrequest = (HttpWebRequest)WebRequest.Create(uri);    webrequest.CookieContainer = cookies;    webrequest.ContentType = "multipart/form-data; boundary=" + boundary;    webrequest.Method = "POST";    // Build up the post message header    StringBuilder sb = new StringBuilder();    sb.Append("--");    sb.Append(boundary);    sb.Append("");    sb.Append("Content-Disposition: form-data; name=/"");    sb.Append(fileFormName);    sb.Append("/"; filename=/"");    sb.Append(Path.GetFileName(uploadfile));    sb.Append("/"");    sb.Append("");    sb.Append("Content-Type: ");    sb.Append(contenttype);    sb.Append("");    sb.Append("");           string postHeader = sb.ToString();    byte[] postHeaderBytes = Encoding.UTF8.GetBytes(postHeader);     // Build the trailing boundary string as a byte array    // ensuring the boundary appears on a line by itself    byte[] boundaryBytes =        Encoding.ASCII.GetBytes("--" + boundary + "");     FileStream fileStream = new FileStream(uploadfile,                  FileMode.Open, FileAccess.Read);    long length = postHeaderBytes.Length + fileStream.Length +                        boundaryBytes.Length;    webrequest.ContentLength = length;     Stream requestStream = webrequest.GetRequestStream();     // Write out our post header    requestStream.Write(postHeaderBytes, 0, postHeaderBytes.Length);     // Write out the file contents    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);     // Write out the trailing boundary    requestStream.Write(boundaryBytes, 0, boundaryBytes.Length);    WebResponse responce = webrequest.GetResponse();    Stream s = responce.GetResponseStream();    StreamReader sr = new StreamReader(s);     return sr.ReadToEnd();  }

CookieContainer cookies = new CookieContainer();  //add or use cookies  NameValueCollection querystring = new NameValueCollection();  querystring["uname"]="uname";  querystring["passwd"]="snake3";  string uploadfile;// set to file to upload  uploadfile = "c://test.jpg";   //everything except upload file and url can be left blank if needed  string outdata = UploadFileEx(uploadfile,     "http://localhost/test.php","uploadfile", "image/pjpeg",     querystring,cookies);