<form id="Form1" encType="multipart/form-data" runat="server">
   
 </form>

逻辑代码:

    Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        '在此处放置初始化页的用户代码
        Dim b() As Byte = Request.BinaryRead(Request.ContentLength)

        Dim fs As New System.IO.FileStream("c:\k.txt", IO.FileMode.Append) //把request 请求的数据dump 到一个文件中
        Dim sw As New System.IO.BinaryWriter(fs)
        sw.Write(b)
        sw.Close()
        fs.Close()

        Request.Files(0).SaveAs("C:\t\" & Request.Files(0).FileName) //另存客户端传上来的文件

    End Sub

运行这个程序. 你会发现客户端发过去的 请求,起始很有规则:

-----------------------8c64f47716481f0  //时间戳

Content-Disposition: form-data; name="file"; filename="a.txt"  //文件名

Content-Type: application/octet-stream

//文件的内容

-----------------------8c64f47716481f0

这个是.NET 测试的一些结果. 起始我们看一下 WebClient.UploadFile , 他起始内部就是整理形成一个 request 流.以下是对 webclient.uploadFile 反编译后看到的结果.

public byte[] UploadFile(string address, string method, string fileName)
{
      string text1;
      string text2;
      WebRequest request1;
      string text3;
      byte[] buffer1;
      byte[] buffer2;
      long num1;
      byte[] buffer3;
      int num2;
      WebResponse response1;
      byte[] buffer4;
      DateTime time1;
      long num3;
      string[] textArray1;
      FileStream stream1 = null;
      try
      {
            fileName = Path.GetFullPath(fileName);
            time1 = DateTime.Now;
            num3 = time1.Ticks;
            text1 = "---------------------" + num3.ToString("x");
            if (this.m_headers == null)
            {
                  this.m_headers = new WebHeaderCollection();
            }
            text2 = this.m_headers["Content-Type"];
            if (text2 != null)
            {
                  if (text2.ToLower(CultureInfo.InvariantCulture).StartsWith("multipart/"))
                  {
                        throw new WebException(SR.GetString("net_webclient_Multipart"));
                  }
            }
            else
            {
                  text2 = "application/octet-stream";
            }
            this.m_headers["Content-Type"] = "multipart/form-data; boundary=" + text1;
            this.m_responseHeaders = null;
            stream1 = new FileStream(fileName, FileMode.Open, FileAccess.Read);
            request1 = WebRequest.Create(this.GetUri(address));
            request1.Credentials = this.Credentials;
            this.CopyHeadersTo(request1);
            request1.Method = method;
            textArray1 = new string[7];
            textArray1[0] = "--";
            textArray1[1] = text1;
            textArray1[2] = "\r\nContent-Disposition: form-data; name=\"file\"; filename=\"";
            textArray1[3] = Path.GetFileName(fileName);
            textArray1[4] = "\"\r\nContent-Type: ";
            textArray1[5] = text2;
            textArray1[6] = "\r\n\r\n";
            text3 = string.Concat(textArray1);
            buffer1 = Encoding.UTF8.GetBytes(text3);
            buffer2 = Encoding.ASCII.GetBytes("\r\n--" + text1 + "\r\n");
            num1 = 9223372036854775807;
            try
            {
                  num1 = stream1.Length;
                  request1.ContentLength = ((num1 + ((long) buffer1.Length)) + ((long) buffer2.Length));
            }
            catch
            {
            }
            buffer3 = new byte[Math.Min(((int) 8192), ((int) num1))];
            using (Stream stream2 = request1.GetRequestStream())
            {
                  stream2.Write(buffer1, 0, buffer1.Length);
                  do
                  {
                        num2 = stream1.Read(buffer3, 0, buffer3.Length);
                        if (num2 != 0)
                        {
                              stream2.Write(buffer3, 0, num2);
                        }
                  }
                  while ((num2 != 0));
                  stream2.Write(buffer2, 0, buffer2.Length);
            }
            stream1.Close();
            stream1 = null;
            response1 = request1.GetResponse();
            this.m_responseHeaders = response1.Headers;
            return this.ResponseAsBytes(response1);
      }
      catch (Exception exception1)
      {
            if (stream1 != null)
            {
                  stream1.Close();
                  stream1 = null;
            }
            if ((exception1 is WebException) || (exception1 is SecurityException))
            {
                  throw;
            }
            throw new WebException(SR.GetString("net_webclient"), exception1);
      }
      return buffer4;
}

还是很容易看懂的.

如果写 Activex 的话, 在 VB 中可以调用 Internet Transfer 控件, 我们模拟发一个文件给服务端.

Private Sub Command1_Click()
    Dim s As String
    s = s & "-----------------------8c64f47716481f0" & vbCrLf
    s = s & "Content-Disposition: form-data; name=""file""; filename=""a.txt""" & vbCrLf
    s = s & "Content-Type: application/octet-stream" & vbCrLf & vbCrLf
   
    s = s & "Hello , World" & vbCrLf
    s = s & "-----------------------8c64f47716481f0"
    Inet1.Execute "http://localhost/aspnet/UPloadFile/WebForm1.aspx", "POST", s
End Sub

这时候服务端就会收到一个文件.

需要说明的是:

1. 仅仅为了说明 HTTP Post 的原理,没有考虑很多的代码细节.
2. 使用的时候请做适当的调整.