C#采用HttpWebRequest实现保持会话上传文件到HTTP的方法

本文实例讲述了c#采用httpwebrequest实现保持会话上传文件到http的方法，在项目开发中有一定的实用价值，具体方法如下：

一、前言：

这篇文章翻译来自madmik3 写在 codeproject 上的文章，原标题为: c#'s webclient.uploadfile with more functionality.

二、正文：

我们使用 webrequest 来获取网页内容是非常简单的，可是用他来上传文件就没有那么简单了。

如果我们在网页中上传文件，加入下面代码即可：

html 文件上传代码实例：

<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> 

但，如果在c#中使用 webrequest 上传，必须对本地文件进行相应的处理才能提交到指定的http地址，下面这个函数哦就帮我们做了这烦恼的操作

uploadfileex 上传文件函数：

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();  
}

调用代码如下：

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); 

至此，所有主要功能代码都已经介绍完毕，至于美化你的程序就要读者根据自己的喜好完成了。

作者还提供了接收文件的php代码，，个人觉得既然能写上传的程序，接收文件的server page应该不在话下的，况且又不是php才能接收提交的文件，asp，asp.net,jsp都可以，这里就不再啰嗦了。