C#调用微博api发送带图片微博,模拟http请求

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net;
using System.Text;
using System.Web;


namespace WebWeiboTest
{
    public class Weibo
    {
        /// <summary> 
        /// 上传图片文件 
        /// </summary> 
        /// <param name="url">提交的地址</param> 
        /// <param name="poststr">发送的文本串   比如：user=eking&pass=123456  </param> 
        /// <param name="fileformname">文本域的名称  比如：name="file"，那么fileformname=file  </param> 
        /// <param name="filepath">上传的文件路径  比如： c:\12.jpg </param> 
        /// <param name="filename">图片名字</param>  
        /// <returns></returns> 
        public string HttpUploadFile(string url, string poststr, string fileformname, string filepath, string filename)
        {
            try
            {

                // 这个可以是改变的，也可以是下面这个固定的字符串 
                string boundary = "---------------------------7803363818269";

                // 创建request对象 
                HttpWebRequest webrequest = (HttpWebRequest)WebRequest.Create(url);
                webrequest.ContentType = "multipart/form-data; boundary=" + boundary;
                webrequest.Method = "POST";

                // 构造发送数据 
                StringBuilder sb = new StringBuilder();

                // 文本域的数据，将user=eking&pass=123456  格式的文本域拆分 ，然后构造 
                foreach (string c in poststr.Split(‘&‘))
                {
                    string[] item = c.Split(‘=‘);
                    if (item.Length != 2)
                    {
                        break;
                    }
                    string name = item[0];
                    string value = item[1];
                    sb.Append("--" + boundary);
                    sb.Append("\r\n");
                    sb.Append("Content-Disposition: form-data; name=\"" + name + "\"");
                    sb.Append("\r\n\r\n");
                    sb.Append(value);
                    sb.Append("\r\n");
                }

                // 文件域的数据 
                sb.Append("--" + boundary);
                sb.Append("\r\n");
                sb.Append("Content-Disposition: form-data; name=\"pic\";filename="+filename);
                sb.Append("\r\n");

                sb.Append("Content-Type: image/png");
                sb.Append("\r\n\r\n");

                string postHeader = sb.ToString();
                byte[] postHeaderBytes = Encoding.UTF8.GetBytes(postHeader);

                //构造尾部数据 
                byte[] boundaryBytes = Encoding.UTF8.GetBytes("\r\n--" + boundary + "--\r\n");

                FileStream fileStream = new FileStream(filepath, FileMode.Open, FileAccess.Read);

                long length = postHeaderBytes.Length + fileStream.Length + boundaryBytes.Length;
                webrequest.ContentLength = length;

                Stream requestStream = webrequest.GetRequestStream();

                // 输入头部数据 
                requestStream.Write(postHeaderBytes, 0, postHeaderBytes.Length);

                // 输入文件流数据 
                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);

                // 输入尾部数据 
                requestStream.Write(boundaryBytes, 0, boundaryBytes.Length);
                WebResponse responce = webrequest.GetResponse();
                Stream s = responce.GetResponseStream();
                StreamReader sr = new StreamReader(s);
                return sr.ReadToEnd();

            }
            catch (Exception ex)
            {
                return "";
            }
            // 返回数据流(源码) 

        }
    }
}