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。