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：
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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。
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