以multipart/form-datafa方式向flickr发送照片

     flickr要求的POST格式是 multipart/form-datafa （格式范例）,而.NET的HttpWebRequest类，只能POST标准的 application/x-www-form-urlencoded, 所以我们只能手工将数据打包成 multipart/form-datafa ,我参考了Python的例子，写了一版C#的，代码如下:

 1 public static string HttpPostByMultipartFormData(string url, List<FormField> fields,string filefieldname,string filename,Stream filestream)
 2         {
 3             HttpWebResponse response = null;
 4             Stream strm = null;
 5             StreamReader sr = null;
 6 
 7             try
 8             {
 9                 string Boundary = "--------------------------------ThIs_Is_tHe_bouNdaRY_$";
                 string CRLF = "\r\n";
 
                 string body = "";
 
                 foreach (FormField field in fields)
                 {
                     body += "--" + Boundary;
                     body += CRLF;
                     body += "Content-Disposition: form-data; name=\"" + field.Key + "\"";
                     body += CRLF+CRLF;
                     body += field.Value;
                     body += CRLF;
                 }
 
                 body += "--" + Boundary;
                 body += CRLF;
                 body += "Content-Disposition: form-data; name=\"" + filefieldname + "\"; filename=\"" + filename + "\"";
                 body += CRLF;
                 body += "Content-Type: " + GetContentType(filename);
                 body += CRLF+CRLF;
 
                 byte[] buf1 = System.Text.Encoding.UTF8.GetBytes(body);
                 byte[] buf2 = new byte[filestream.Length];
                 filestream.Read(buf2, 0, (int)filestream.Length);
                 filestream.Close();
 
                 byte[] buf3 = new byte[buf1.Length + buf2.Length];
                 Array.Copy(buf1,0,buf3,0,buf1.Length);
                 Array.Copy(buf2,0,buf3,buf1.Length,buf2.Length);
 
                 
                 string end = CRLF+"--" + Boundary + "--"+CRLF;
                 buf1 = System.Text.Encoding.UTF8.GetBytes(end);
                 buf2 = new byte[buf1.Length + buf3.Length];
                 Array.Copy(buf3, 0, buf2, 0, buf3.Length);
                 Array.Copy(buf1, 0, buf2, buf3.Length, buf1.Length);
 
                 
                 HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;
 
                 request.Method = "POST";
                 request.ContentLength = buf2.Length;
                 request.ContentType = "multipart/form-data; boundary=" + Boundary;//"application/x-www-form-urlencoded";
 
                 strm = request.GetRequestStream();
                 strm.Write(buf2, 0, buf2.Length);
                 strm.Close();
 
                 
 
                 response = request.GetResponse() as HttpWebResponse;
                 strm = response.GetResponseStream();
                 sr = new StreamReader(strm);
                 string strXML = sr.ReadToEnd();
                 sr.Close();
 
                 strm.Close();
                 response.Close();
 
                 return strXML;
 
             }
             catch
             {
 
                 if (sr != null)
                 {
                     sr.Close();
                 }
 
                 if (strm != null)
                 { strm.Close(); }
 
                 if (response != null)
                 { response.Close(); }
 
                 return null;
             }
         
         }