C# 使用 HttpWebRequest 保持会话上传文件到 HTTP

转载自：http://www.codeproject.com/KB/cs/uploadfileex.aspx

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.

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：

调用代码

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，所有代码都已经奉献完毕，接下来就看你怎么去美化你的程序了。

作者还提供了接收文件的PHP代码，，我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，所以就不贴了。